Professor Anthony J Sargeant, BEd, BSc, PhD - Vrije Universiteit Amsterdam - Emeritus Professor

Professor Anthony J Sargeant

BEd, BSc, PhD

Vrije Universiteit Amsterdam

Emeritus Professor

Amsterdam | The Netherlands

Main Specialties: Biology

Additional Specialties: Physiology

Professor Anthony J Sargeant, BEd, BSc, PhD - Vrije Universiteit Amsterdam - Emeritus Professor

Professor Anthony J Sargeant

BEd, BSc, PhD

Introduction

Primary Affiliation: Vrije Universiteit Amsterdam - Amsterdam , The Netherlands

Specialties:

Additional Specialties:


View Professor Anthony J Sargeant’s Resume / CV

Education

Aug 1976
University of London
PhD
Aug 1973
University of London
BSc (Physiology)
Aug 1970
Goldsmeiths College University of London
BEd

Experience

Jul 1977
Medical Research Council
Travelling Research Fellow
Spent at McMaster University Medical School with Professor Norman Jones

Publications

129Publications

46Reads

25Profile Views

2PubMed Central Citations

Age-dependency in bone mass and geometry: a pQCT study on male and female master sprinters, middle and long distance runners, race-walkers and sedentary people

J Musculoskelet Neuronal Interact. 2009 Oct-Dec;9(4):236-46

Journal of Musculoskeletal and Neuronal Interaction

Abstract OBJECTIVE: To investigate whether athletic participation allows master athletes to preserve their good bone health into old age. METHODS: Bone strength indicators of the tibia and the radius were obtained of master runners and race-walkers (n=300) competing at World and European Master Championships and of 75 sedentary controls, all aged 33-94 yrs. RESULTS: In the tibia, diaphyseal cortical area (Ar.Ct), polar moment of resistance (RPol) and trabecular bone mineral density (vBMD) were generally greater in athletes than controls at all ages. In the athletes, but not the controls, Ar.Ct, RPol (females) and trabecular vBMD were negatively correlated with age (p<0.01). Radius measures were comparable between athlete and control groups at all ages. The amalgamated data revealed negative correlations of age with Ar.Ct, RPol (females), cortical vBMD and trabecular vBMD (males; p<0.005) and positive correlations with endocortical circumference (p<0.001). CONCLUSION: This cross-sectional study found age-related differences in tibial bone strength indicators of master athletes, but not sedentary controls, thus, groups becoming more similar with advancing age. Age-related differences were noticeable in the radius too, without any obvious group difference. Results are compatible with the notion that bones adapt to exercise-specific forces throughout the human lifespan.

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October 2009
37 Reads

Variation in the determinants of power of chemically skinned human muscle fibres

Exp Physiol. 2009 Oct;94(10):1070-8.

Experimental Physiology

.We have explored the extent to which the maximal velocity of unloaded shortening (V(max)), the force generated per unit cross-sectional area (P(0)) and the curvature of the force-velocity relationship (a/P(0) in the Hill equation) contribute to differences in peak power of chemically skinned single fibres from the quadriceps muscle of healthy young male subjects. The analysis was restricted to type I and IIA fibres that contained a single type of myosin heavy chain on electrophoretic separation. Force-velocity relationships were determined from isotonic contractions of maximally activated fibres at 15 degrees C. Mean (+/- s.d.) peak powers were 1.99 +/- 0.72 watts per litre (W L(-1)) for type I fibres and 6.92 +/- 2.41 W L(-1), for type IIA fibres. The most notable feature, however, was the very large, sevenfold, range of power outputs within a single fibre type. This wide range was a consequence of variations in each of the three components determining power: P(0), V(max) and a/P(0). Within a single fibre type, P(0) varied threefold, and V(max) and a/P(0) two- to threefold. There were no obvious relationships between P(0) and V(max) or between P(0) and a/P(0). However, there was a suggestion of an inverse relationship between a/P(0) and V(max), the effect being to reduce, somewhat, the impact of differences in V(max) on peak power. In searching for the causes of variation in peak power of fibres of the same type, it appears likely that there are two factors, one that affects P(0) and another that leads to variation in both V(max) and a/P(0).

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October 2009
24 Reads

Bone mass and geometry of the tibia and the radius of master sprinters, middle and long distance runners, race-walkers and sedentary control participants: a pQCT study.

Bone. 2009 Jul;45(1):91-7

Bone

Mechanical loading is thought to be a determinant of bone mass and geometry. Both ground reaction forces and tibial strains increase with running speed. This study investigates the hypothesis that surrogates of bone strength in male and female master sprinters, middle and long distance runners and race-walkers vary according to discipline-specific mechanical loading from sedentary controls. Bone scans were obtained by peripheral Quantitative Computed Tomography (pQCT) from the tibia and from the radius in 106 sprinters, 52 middle distance runners, 93 long distance runners and 49 race-walkers who were competing at master championships, and who were aged between 35 and 94 years. Seventy-five age-matched, sedentary people served as control group. Most athletes of this study had started to practice their athletic discipline after the age of 20, but the current training regime had typically been maintained for more than a decade. As hypothesised, tibia diaphyseal bone mineral content (vBMC), cortical area and polar moment of resistance were largest in sprinters, followed in descending order by middle and long distance runners, race-walkers and controls. When compared to control people, the differences in these measures were always >13% in male and >23% in female sprinters (p<0.001). Similarly, the periosteal circumference in the tibia shaft was larger in male and female sprinters by 4% and 8%, respectively, compared to controls (p<0.001). Epiphyseal group differences were predominantly found for trabecular vBMC in both male and female sprinters, who had 15% and 18% larger values, respectively, than controls (p<0.001). In contrast, a reverse pattern was found for cortical vBMD in the tibia, and only few group differences of lower magnitude were found between athletes and control people for the radius. In conclusion, tibial bone strength indicators seemed to be related to exercise-specific peak forces, whilst cortical density was inversely related to running distance. These results may be explained in two, non-exclusive ways. Firstly, greater skeletal size may allow larger muscle forces and power to be exerted, and thus bias towards engagement in athletics. Secondly, musculoskeletal forces related to running can induce skeletal adaptation and thus enhance bone strength

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July 2009
19 Reads

The training stimulus experienced by the leg muscles during cycling in humans

Exp Physiol. 2009 Jun;94(6):684-94

Experimental Physiology

Considerable variability exists between people in their health- and performance-related adaptations to conventional endurance training. We hypothesized that some of this variability might be due to differences in the training stimulus received by the working muscles. In 71 young sedentary women we observed large variations in the ratio of one-leg cycling muscle aerobic capacity (V(O2peak)) to two-leg cycling whole-body maximal oxygen uptake (V(O2max); Ratio(1:2); range 0.58-0.96). The variability in Ratio(1:2) was primarily due to differences between people in one-leg V(O2peak) (r = 0.71, P < 0.0005) and was not related to two-leg V(O2max) (r = 0.15, P = 0.209). Magnetic resonance imaging (n = 30) and muscle biopsy sampling (n = 20) revealed that one-leg V(O2peak) was mainly determined by muscle volume (r = 0.73, P < 0.0005) rather than muscle fibre type or oxidative capacity. A high one-leg V(O2peak) was associated with favourable lipoprotein profiles (P = 0.033, n = 24) but this was not the case for two-leg V(O2max). Calculations based on these data suggest that conventional two-leg exercise at 70% V(O2max) requires subjects with the lowest Ratio(1:2) to work their legs at 60% of single-leg V(O2peak), whilst those with the highest Ratio(1:2) work their legs at only 36% of maximum. It was concluded that endurance training carried out according to current guidelines will result in highly variable training stimuli for the leg muscles and variable magnitudes of adaptation. These conclusions have implications for the prescription of exercise to improve health and for investigations into the genetic basis of muscle adaptations

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June 2009
18 Reads

The rate of muscle temperature increase during acute whole-body vibration exercise.

Eur J Appl Physiol. 2008 Jul;103(4):441-8

European Journal of Applied Physiology

This study compared the rate of muscle temperature (Tm) increase during acute whole-body vibration (WBV), to that of stationary cycling and passive warm-up. Additionally we wanted to determine if the purported increase in counter-movement jump and peak power cycling from acute WBV could be explained by changes in muscle temperature. Eight active participants volunteered for the study, which involved a rest period of 30 min to collect baseline measures of muscle, core, skin temperature, heart rate (HR), and thermal leg sensation (TLS), which was followed by three vertical jumps and 5 s maximal cycle performance test. A second rest period of 40 min was enforced followed by the intervention and performance tests. The change in Tm elicited during cycling was matched in the hot bath and WBV interventions. Therefore cycling was performed first, proceeded by, in a random order of hot bath and acute WBV. The rate of Tm was significantly greater (P < 0.001) during acute WBV (0.30 degree C min(-1)) compared to cycle (0.15 degree C min(-1)) and hot bath (0.09 degree C min(-1)) however there was no difference between the cycle and hot bath, and the metabolic rate was the same in cycling and WBV (19 mL kg(-1) min(-1)). All three interventions showed a significant (P < 0.001) increase in countermovement jump peak power and height. For the 5 s maximal cycle test (MIC) there were no significant differences in peak power between the three interventions. In conclusion, acute WBV elevates Tm more quickly than traditional forms of cycling and passive warm-up. Given that all three warm-up methods yielded the same increase in peak power output, we propose that the main effect is caused by the increase in Tm

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July 2008
27 Reads

Recruitment of single muscle fibers during submaximal cycling exercise

J Appl Physiol (1985). 2007 Nov;103(5)

Journal of Applied Physiology

In literature, an inconsistency exists in the submaximal exercise intensity at which type II fibers are activated. In the present study, the recruitment of type I and II fibers was investigated from the very beginning and throughout a 45-min cycle exercise at 75% of the maximal oxygen uptake, which corresponded to 38% of the maximal dynamic muscle force. Biopsies of the vastus lateralis muscle were taken from six subjects at rest and during the exercise, two at each time point. From the first biopsy single fibers were isolated and characterized as type I and II, and phosphocreatine-to-creatine (PCr/Cr) ratios and periodic acid-Schiff (PAS) stain intensities were measured. Cross sections were cut from the second biopsy, individual fibers were characterized as type I and II, and PAS stain intensities were measured. A decline in PCr/Cr ratio and in PAS stain intensity was used as indication of fiber recruitment. Within 1 min of exercise both type I and, although to a lesser extent, type II fibers were recruited. Furthermore, the PCr/Cr ratio revealed that the same proportion of fibers was recruited during the whole 45 min of exercise, indicating a rather constant recruitment. The PAS staining, however, proved inadequate to fully demonstrate fiber recruitment even after 45 min of exercise. We conclude that during cycling exercise a greater proportion of type II fibers is recruited than previously reported for isometric contractions, probably because of the dynamic character of the exercise. Furthermore, the PCr/Cr ratio method is more sensitive in determining fiber activation than the PAS stain intensity method.

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November 2007
24 Reads

Structural and functional determinants of human muscle power

Exp Physiol. 2007 Mar;92(2):323-31

Experimental Physiology

Measurements of human power need to be interpreted in relation to the movement frequency, since that will determine the velocity of contraction of the active muscle and hence the power available according to the power-velocity relationship. Techniques are described which enable movement frequency to be kept constant during human exercise under different conditions. Combined with microdissection and analysis of muscle fibre fragments from needle biopsies obtained pre- and postexercise we have been able 'to take the muscle apart', having measured the power output, including the effect of fatigue, under conditions of constant movement frequency. We have shown that fatigue may be the consequence of a metabolic challenge to a relatively small population of fast fatigue-sensitive fibres, as indicated by [ATP] depletion to approximately 30% of resting values in those fibres expressing myosin heavy chain isoform IIX after just 10 s of maximal dynamic exercise. Since these same fibres will have a high maximal velocity of contraction, they also make a disproportionate contribution to power output in relation to their number, especially at faster movement rates. The microdissection technique can also be used to measure phosphocreatine concentration ([PCr]), which is an exquisitely sensitive indicator of muscle fibre activity; thus, in just seven brief maximal contractions [PCr] is depleted to levels < 50% of rest in all muscle fibre types. The technique has been applied to study exercise at different intensities, and to compare recruitment in lengthening, shortening and isometric contractions, thus yielding new information on patterns of recruitment, energy turnover and efficiency.

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March 2007
48 Reads

Human muscle fatigue: the significance of muscle fibre type variability studied using a micro-dissection approach

J Physiol Pharmacol. 2006 Nov;57 Suppl 10:5-16

Journal of Physiology and Pharmacology

During human locomotion the ability to generate and sustain mechanical power output is dependent on the organised variability in contractile and metabolic properties of the muscle fibres that comprise the active muscles. In studies of human exercise we have used a micro-dissection technique to obtain fragments of single muscle fibres from needle biopsies before and after exercise. Each fibre fragment is divided into two parts. One part is used to characterize the fibre type in respect of the heavy chain myosin isoform expressed. The other part of the fragment is analysed for high energy phosphate concentrations. Fibres are classified on the basis of expressing either type I, type IIA, or type IIX myosin heavy chain isoforms. It should be noted however that in the type II population many fibres co-express both IIA and the IIX isoforms and we therefore characterize these fibres on the basis of the degree of co-expression. We have used this technique to examine the time course of high energy phosphate concentration and fatigue in different fibre populations during exercise. The progressive reduction of power during maximal sprint efforts may be interpreted as the cumulative effect of metabolic depletion in successive fibre type populations from IIX to IIXa to IIAx to IIA to I. One important application of the micro-dissection technique is that PCr content may also be used as a very sensitive metabolic marker for fibre type recruitment during very short duration concentric, isometric and eccentric exercise

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November 2006
21 Reads

Human calf muscle responses during repeated isometric plantarflexions

J Biomech. 2006;39(7):1249-55

Journal of Biomechanics

In the present study, we measured the contraction-induced shortening (dL) of individual synergistic human muscles in a repeated motor task to assess their contractile behaviour. Ultrasonography was used to obtain dL measurements in the gastrocnemius (GS) and soleus (SOL) muscles of six men performing 11 consecutive isometric plantarflexions. Contractions 1 and 11 were performed with maximal effort, and contractions 2-4, 5-7 and 8-10 were performed with efforts generating 50, 70 and 90%, respectively, of the plantarflexion moment produced in contraction 1. In contractions 5-10, the SOL muscle dL was similar (p > 0.05) to that produced in contraction 1 (approximately 6 mm), indicating that the SOL muscle became fully activated at 70% of the maximum plantarflexion moment. The GS muscle dL in contractions 10 and 11 exceeded by approximately 0.5 mm (p < 0.05) and 1.3 mm (p < 0.01), respectively, that generated in contraction 1 (approximately 10 mm), despite evidence obtained by superimposed stimulation that contraction 1 was produced with full motor unit activation. The consequent paradox that the GS muscle would produce in contractions 10 and 11 a greater activation and therefore more force than its actual potential is resolved when considering the interaction between the time-dependent tensile response of tendon and the performance of muscle as dictated by the sliding filament mechanism of contraction

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July 2006
14 Reads

Adaptive response of human tendon to paralysis

Muscle Nerve. 2006 Jan;33(1):85-92

Muscle and Nerve

To gain insight into the adaptive response of human tendon to paralysis, we compared the mechanical properties of the in vivo patellar tendon in six men who were spinal cord-injured (SCI) and eight age-matched, able-bodied men. Measurements were taken by combining dynamometry, electrical stimulation, and ultrasonography. Tendon stiffness and Young's modulus, calculated from force-elongation and stress-strain curves, respectively, were lower by 77% (P < 0.01) and 59% (P < 0.05) in the SCI than able-bodied subjects. The cross-sectional area (CSA) of the tendon was 17% smaller (P < 0.05) in the SCI subjects, but there was no difference in tendon length between the two groups. Our results indicate that paralysis causes substantial deterioration of the structural and material properties of tendon. This needs to be taken into consideration in the design of electrical stimulation protocols for rehabilitation and experimental purposes, and when interpreting changes in the contractile speed of paralyzed muscle.

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January 2006
40 Reads

Influence of knee joint angle on muscle properties of paralyzed and nonparalyzed human knee extensors.

Muscle Nerve 2005 Jul;32(1):73-80

Institute for Fundamental and Clinical Human Movement Sciences, Vrije University, van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands.

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http://dx.doi.org/10.1002/mus.20328DOI Listing
July 2005
36 Reads
2 Citations
2.283 Impact Factor

Skeletal muscle morphology and capillarization of renal failure patients receiving different dialysis therapies

Clin Sci (Lond). 2004 Dec;107(6):617-23

Clinical Science

The morphology of gastrocnemius muscles was examined in RFPs (renal failure patients) being treated using HD (haemodialysis) and CAPD (continuous ambulatory peritoneal dialysis). RFPs (n=24) volunteered to participate in the present study. Twelve RFPs (five women and seven men; mean age, 55 years) were undergoing CAPD treatment and 12 RFPs (two women and ten men; mean age, 62 years) were undergoing HD treatment. Muscle biopsies from gastrocnemius muscles were found not to differ (P>0.05) in fibre type distribution, MyHC (myosin heavy chain) expression or fibre CSA (cross-sectional area) between the two groups. There were, however, significant differences (P<0.05) in CC/F (capillary contact/fibre), C/F (capillary to fibre ratio) and cytochrome c oxidase activity. The HD group had 33% more CC/F, with a 19% higher C/F and 33% greater cytochrome c activity in glycolytic fibres (II) than the CAPD group. There were no apparent differences in age, gender, co-morbidity, self-reported physical activity or physical functioning between the two groups, which could account for the difference in muscle capillarity between the groups. The HD patients were, however, administered heparin as a routine part of the dialysis therapy. The possibility is discussed that heparin in combination with mild anaemia and acidosis may have augmented angiogenesis in the HD patients

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December 2004
21 Reads

Metabolic cost of lengthening, isometric and shortening contractions in maximally stimulated rat skeletal muscle

Acta Physiol Scand. 2004 Oct;182(2):179-87

Acta Physiologica Scandanavica

Abstract AIM: The present study investigated the energy cost of lengthening, isometric and shortening contractions in rat muscle (n = 19). METHODS: With electrical stimulation the rat medial gastrocnemius muscle was maximally stimulated to perform 10 lengthening, isometric and shortening contractions (velocity 25 mm s(-1)) under experimental conditions (e.g. temperature, movement velocity) that resemble conditions in human movement. RESULTS: Mean +/- SD force-time-integral of the first contraction was significantly different between the three protocols, 2.4 +/- 0.2, 1.7 +/- 0.2 and 1.0 +/- 0.2 N s, respectively (P < 0.05). High-energy phosphate consumption was not significantly different between the three modes of exercise but a trend could be observed from lengthening (7.7 +/- 2.7 micromol approximately P muscle(-1)) to isometric (8.9 +/- 2.2 micromol approximately P muscle(-1)) to shortening contractions (10.4 +/- 1.6 micromol approximately P muscle(-1)). The ratio of high-energy phosphate consumption to force-time-integral was significantly lower for lengthening [0.3 +/- 0.1 micromol approximately P (N s)(-1)] and isometric [0.6 +/- 0.2 micromol approximately P (N s)(-1)] contractions compared with shortening [1.2 +/- 0.2 micromol approximately P (N s)(-1)] contractions (P < 0.05). CONCLUSION: The present results of maximally stimulated muscles are comparable with data in the literature for voluntary human exercise showing that the energy cost of force production during lengthening exercise is approximately 30% of that in shortening exercise. The present study suggests that this finding in humans probably does reflect intrinsic muscle properties rather than effects of differential recruitment and/or coactivation.

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October 2004
15 Reads

Voluntary activation level and muscle fiber recruitment of human quadriceps during lengthening contractions

J Appl Physiol (1985). 2004 Aug;97(2):619-26

Journal of applied Physiology

Abstract Voluntary activation levels during lengthening, isometric, and shortening contractions (angular velocity 60 degrees/s) were investigated by using electrical stimulation of the femoral nerve (triplet, 300 Hz) superimposed on maximal efforts. Recruitment of fiber populations was investigated by using the phosphocreatine-to-creatine ratio (PCr/Cr) of single characterized muscle fibers obtained from needle biopsies at rest and immediately after a series of 10 lengthening, isometric, and shortening contractions (1 s on/1 s off). Maximal voluntary torque was significantly higher during lengthening (270 +/- 55 N.m) compared with shortening contractions (199 +/- 47 N.m, P < 0.05) but was not different from isometric contractions (252 +/- 47 N.m). Isometric torque was higher than torque during shortening (P < 0.05). Voluntary activation level during maximal attempted lengthening contractions (79 +/- 8%) was significantly lower compared with isometric (93 +/- 5%) and shortening contractions (92 +/- 3%, P < 0.05). Mean PCr/Cr values of all fibers from all subjects at rest were 2.5 +/- 0.6, 2.0 +/- 0.7, and 2.0 +/- 0.7, respectively, for type I, IIa, and IIax fibers. After 10 contractions, the mean PCr/Cr values for grouped fiber populations (regardless of fiber type) were all significantly different from rest (1.3 +/- 0.2, 0.7 +/- 0.3, and 0.8 +/- 0.6 for lengthening, isometric, and shortening contractions, respectively; P < 0.05). The cumulative distributions of individual fiber populations after either contraction mode were significantly different from rest (P < 0.05). Curves after lengthening contractions were less shifted compared with curves from isometric and shortening contractions (P < 0.05), with a smaller shift for the type IIax compared with type I fibers in the lengthening contractions. The results indicate a reduced voluntary drive during lengthening contractions. PCr/Cr values of single fibers indicated a hierarchical order of recruitment of all fiber populations during maximal attempted lengthening contractions.

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August 2004
20 Reads

Metabolically assessed muscle fibre recruitment in brief isometric contractions at different intensities

Eur J Appl Physiol. 2004 Aug;92(4-5):485-92

European Journal of Applied Physiology

This study investigated the recruitment of type I, IIA and IIAX fibres after seven isometric contractions at 40, 70 and 100% maximal voluntary knee extension torque (MVC, 1 s on/1 s off). Biopsies of the vastus lateralis muscle were collected from seven subjects at rest and immediately post-exercise. Fibre fragments were dissected from the freeze-dried samples and characterized as type I, IIA and IIAX using mATPase staining. Phosphocreatine (PCr) and creatine (Cr) content were measured in the remaining part of characterized fibres. A decline in the ratio of PCr to Cr (PCr/Cr) was used as an indication of activation. The mean peak torques were, respectively, 39 (2), 72 (2) and 87 (6)% MVC. Cumulative distributions of type I and IIA fibres were significantly shifted to lower PCr/Cr ratios at all intensities (Kolmogorov-Smirnov test, P<0.05). The cumulative distribution of type IIAX fibres showed a significant leftward shift only at 87% MVC ( P<0.05). A hierarchical order of fibre activation with increasing intensity of exercise was found, with some indication of rate coding for type I and IIA fibres. Evidence for activation of type IIAX fibres was only found at 87% MVC.

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August 2004
15 Reads

Knee and ankle range of motion during stepping down in elderly compared to young men

Eur J Appl Physiol. 2004 Mar;91(2-3):287-95

European Journal of Applied Physiology

Abstract A major factor limiting mobility in elderly subjects is their difficulty with descending steps but the physiological and biomechanical basis of this problem is not well understood. To address this question we have compared the kinematics of stepping down in six elderly male subjects and six weight- and height-matched younger subjects. Five reflective markers were positioned on the lower limbs and subjects were filmed stepping down from four heights (200, 250, 300, and 335 mm). Maximum angular displacements for the knee and ankle of the supporting limb were expressed as a percentage of each subject's passive range of motion (ROM). Time spent in 'foot flat' during single support was also compared. The results show the elderly subjects sustained dorsiflexion and a 'foot flat' position of the support limb for a significantly ( P<0.05) longer period than the young (approximately 20%). Consequently, elderly subjects utilised a greater percentage of their passive ankle ROM compared to the young (elderly approximately 200%; young approximately 125%). We conclude that the elderly maintained a 'foot flat' position for a longer period possibly to increase the time spent on a larger base of support. These results suggest that exercise prescription in the elderly should include stretching in order to increase the ROM at the ankle joint

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March 2004
33 Reads

Changes in PCr/Cr ratio in single characterized muscle fibre fragments after only a few maximal voluntary contractions in humans

Acta Physiol Scand. 2004 Feb;180(2):187-93

Acta Physiologica Scandanavica

Abstract AIM: This methodological study investigated the number of brief maximal voluntary isometric contractions (MVC) needed to show evidence of fibre activation, as indicated by changes in the phosphocreatine to creatine (PCr/Cr) ratio. METHODS: Subjects performed series of four, seven and/or 10 MVC (1 s on, 1 s off) of the m. quadriceps (60 degrees -flexion angle). Biopsy samples of the m. vastus lateralis were taken at rest and immediately post-exercise. Single muscle fibres were dissected from the freeze-dried samples and classified as types I, IIA or IIAX, using mATPase stainings. Fragments of characterized fibres were analysed for PCr and Cr content. Analyses of variance were performed to investigate changes in PCr/Cr per fibre group over time, followed by Bonferroni post-hoc test (P < 0.01). The fifth percentile of resting values of each fibre group was determined. RESULTS: Mean PCr/Cr ratio after four, seven and 10 MVCs were significantly lower for all fibre groups (P < 0.01). The mean decreases were 44, 64 and 76%, respectively. However, only after seven and 10 contractions PCr/Cr ratios of all, but three type I and two type IIAX fibres, individual fibres were below the fifth percentile. CONCLUSION: In very short duration exercise, involving seven brief maximal voluntary contractions, changes in the PCr/Cr ratio indicated activation of different characterized muscle fibre fragments. The results suggest that this approach may be useful for investigating the pattern of fibre type activation in exercise of very short duration

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February 2004
18 Reads

Joint torques and dynamic joint stiffness in elderly and young men during stepping down

Clin Biomech (Bristol, Avon). 2003 Nov;18(9):848-55

Clinical Biomechanics

Abstract OBJECTIVE: To compare the joint torque pattern and dynamic joint stiffness at the knee and ankle in elderly and young men during stepping down. BACKGROUND: Adequate joint stiffness is critical during the single support phase to control forward and downward body momentum. DESIGN: Six active elderly men (mean 67.7) and six young men (mean 23.6) of similar body mass and height, were filmed stepping down from one force platform to another. Repeated trials were undertaken at three different step heights (200, 250, and 300 mm). METHOD: Joint torques were determined for the ankle and knee of the support limb throughout the single support phase. The gradient of the joint torque-angle graph was calculated to define dynamic joint stiffness of the ankle and knee in two phases; (I) from initiation of movement until heel-off of the supporting limb, and (II) from heel-off of the supporting limb to contra-limb touch down. RESULTS: Maximum ankle torque values were lower in the elderly and occurred at a larger dorsiflexion angle (P<0.05). Knee torque patterns were similar in both groups. Phase I ankle stiffness was significantly less in the elderly (4.0-5.2 Nm/ degrees ) at all step heights compared to the young (7.6 - 8.7 Nm/ degrees ). In both groups ankle stiffness in Phase II increased with step height, while knee joint stiffness decreased. CONCLUSIONS: The different torque pattern and lower dynamic ankle stiffness in the elderly, particularly for Phase I, suggested an altered control strategy. These findings highlight the importance of dynamic ankle joint stiffness in stepping down. RELEVANCE: Understanding how the elderly step down may be important in developing strategies to prevent falls.

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November 2003
14 Reads

Atrophy of non-locomotor muscle in patients with end-stage renal failure

Nephrol Dial Transplant. 2003 Oct;18(10):2074-81

Nephrology Dialysis and Transplantation

Abstract BACKGROUND: All previous histological studies of skeletal muscles of patients with renal failure have used locomotor muscle biopsies. It is thus unclear to what degree the observed abnormalities are due to the uraemic state and how much is due to disuse. The present study was undertaken to attempt to investigate this question by examining a non-locomotor muscle (rectus abdominis) in patients with end-stage renal failure. METHODS: Biopsies from rectus abdominis were obtained from 22 renal failure patients (RFPs) undergoing surgical Tenchkoff catheter implantation for peritoneal dialysis and 20 control subjects undergoing elective abdominal surgery. Histochemical staining of frozen sections and morphometric analysis was used to estimate the proportion of each fibre type, muscle fibre area and capillary density. Myosin heavy chain composition was examined by SDS-PAGE. RESULTS: There were no differences in fibre type distribution between RFPs and controls. All RFPs showed fibre atrophy [mean cross-sectional area (CSA) 3300 +/- 1100 microm2, compared to 4100 +/- 1100 microm2 in controls (P < 0.05)]. All fibre types were smaller in mean CSA in RFPs than in controls (15, 26 and 28% for types I, IIa and IIx, respectively). These differences could not be accounted for by differences in age, gender or cardiovascular or diabetic comorbidity. Muscle fibre capillarization, expressed as capillaries per fibre or capillary contacts per fibre, was significantly less in RFPs. CONCLUSIONS: Since a non-locomotor muscle was examined, the effects of disuse as a cause of atrophy have been minimized. It is likely, therefore, that the decreased muscle fibre CSA and capillary density of RFPs compared to controls were due predominantly to uraemia itself.

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October 2003
30 Reads

Effect of antagonist muscle fatigue on knee extension torque

Pflugers Arch. 2003 Sep;446(6):735-41

Pflugers Archiv

Abstract The effect of hamstring fatigue on knee extension torque was examined at different knee angles for seven male subjects. Before and after a dynamic flexion fatigue protocol (180 degrees s(-1), until dynamic torque had declined by 50%), maximal voluntary contraction extension torque was measured at four knee flexion angles (90 degrees, 70 degrees, 50 degrees and 30 degrees ). Maximal torque generating capacity and voluntary activation of the quadriceps muscle were determined using electrical stimulation. Average rectified EMG of the biceps femoris was determined. Mean dynamic flexion torque declined by 48+/-11%. Extensor maximal voluntary contraction torque, maximal torque generating capacity, voluntary activation and average rectified EMG at the four knee angles were unaffected by the hamstring fatigue protocol. Only at 50 degrees knee angle was voluntary activation significantly lower (15.7%) after fatigue ( P<0.05). In addition, average rectified EMG before fatigue was not significantly influenced by knee angle. It was concluded that a fatigued hamstring muscle did not increase the maximal voluntary contraction extension torque and knee angle did not change coactivation. Three possible mechanisms may explain the results: a potential difference in recruited fibre populations in antagonist activity compared with the fibres which were fatigued in the protocol, a smaller loss in isometric torque generating capacity of the hamstring muscle than was expected from the dynamic measurements and/or a reduction in voluntary activation.

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September 2003
50 Reads

Changes in muscle morphology in dialysis patients after 6 months of aerobic exercise training

Nephrol Dial Transplant. 2003 Sep;18(9):1854-61

Nephrololgy Dialysis Transplantation

Abstract BACKGROUND: In the present study we investigated the effect of a 6-month aerobic exercise programme on the morphology of the gastrocnemius muscle of end-stage renal disease (ESRD) patients. METHODS: Twenty-four ESRD patients volunteered to participate in the training programme and underwent muscle biopsy before training. Eighteen patients completed the training programme of whom nine agreed to a post-training biopsy (one woman and eight men, mean age 56 +/- 15 years). Data are presented for the nine subjects who were biopsied before (PRE) and after training (POST) and separately for the 15 subjects for whom we only have a biopsy before training (cross-sectional group). RESULTS: There were no significant differences (P > 0.05) in fibre type distribution or myosin heavy chain (MyHC) expression between the cross-sectional and PRE/POST groups. The mean cross-section fibre area after training (POST) increased by 46% compared with the PRE training status (P < 0.01). The proportion of atrophic fibres decreased significantly after training in type I, IIa and IIx fibre populations (from 51 to 15%, 58 to 21% and 62 to 32%, respectively). Significant differences were also found in capillary contact per fibre (CC/F), with the muscle having 24% (P < 0.05) more CC/F compared with the PRE training status. No significant differences in cytochrome c oxidase concentration were found between the groups. CONCLUSIONS: In conclusion, exercise appeared to be beneficial in renal rehabilitation by correcting the fibre atrophy, increasing the cross-section fibre area and improving the capillarization in the skeletal muscle of renal failure patients.

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September 2003
35 Reads

Quadriceps muscle strength and voluntary activation after polio.

Muscle Nerve 2003 Aug;28(2):218-26

Department of Rehabilitation Medicine, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, The Netherlands.

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http://dx.doi.org/10.1002/mus.10428DOI Listing
August 2003
10 Reads
2.283 Impact Factor

Quadriceps muscle strength and voluntary activation after polio

Muscle Nerve. 2003 Aug;28(2):218-26

Muscle & Nerve

Abstract Quadriceps strength, maximal anatomical cross-sectional area (CSA), maximal voluntary activation (MVA), and maximal relaxation rate (MRR) were studied in 48 subjects with a past history of polio, 26 with and 22 without postpoliomyelitis syndrome (PPS), and in 13 control subjects. It was also investigated whether, apart from CSA, MVA and MRR were determinants of muscle strength. Polio subjects had significantly less strength, CSA, and MRR in the more-affected quadriceps than control subjects. MVA was reduced in 18 polio subjects and normal in all controls. PPS subjects differed from non-PPS subjects only in that the MVA of the more-affected quadriceps was significantly lower. Both CSA and MVA were found to be associated with muscle strength. Quadriceps strength in polio subjects was dependent not only on muscle mass, but also on the ability to activate the muscles. Since impaired activation was more pronounced in PPS subjects, the new muscle weakness and functional decline in PPS may be due not only to a gradual loss of muscle fibers, but also to an increasing inability to activate the muscles.

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August 2003
24 Reads

Variability in fibre properties in paralysed human quadriceps muscles and effects of training.

Pflugers Arch. 2003 Mar;445(6):734-40

Pflugers Archiv

A spinal cord injury usually leads to an increase in contractile speed and fatigability of the paralysed quadriceps muscles, which is probably due to an increased expression of fast myosin heavy chain (MHC) isoforms and reduced oxidative capacity. Sometimes, however, fatigue resistance is maintained in these muscles and also contractile speed is slower than expected. To obtain a better understanding of the diversity of these quadriceps muscles and to determine the effects of training on characteristics of paralysed muscles, fibre characteristics and whole muscle function were assessed in six subjects with spinal cord lesions before and after a 12-week period of daily low-frequency electrical stimulation. Relatively high levels of MHC type I were found in three subjects and this corresponded with a high degree of fusion in 10-Hz force responses (r=0.88). Fatigability was related to the activity of succinate dehydrogenase (SDH) (r=0.79). Furthermore, some differentiation between fibre types in terms of metabolic properties were present, with type I fibres expressing the highest levels of SDH and lowest levels of alpha-glycerophosphate dehydrogenase. After training, SDH activity increased by 76+/-26% but fibre diameter and MHC expression remained unchanged. The results indicate that expression of contractile proteins and metabolic properties seem to underlie the relatively normal functional muscle characteristics observed in some paralysed muscles. Furthermore, training-induced changes in fatigue resistance seem to arise, in part, from an improved oxidative capacity

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March 2003
22 Reads

Repeated contractions alter the geometry of human skeletal muscle

J Appl Physiol (1985). 2002 Dec;93(6)

Journal of Applied Physiology

Abstract The aim of this study was to investigate the effect of repeated contractions on the geometry of human skeletal muscle. Six men performed two sets (sets A and B) of 10 repeated isometric plantarflexion contractions at 80% of the moment generated during plantarflexion maximal voluntary contraction (MVC), with a rest interval of 15 min between sets. By use of ultrasound, the geometry of the medial gastrocnemius (MG) muscle was measured in the contractions of set A and the displacement of the MG tendon origin in the myotendinous junction was measured in the contractions of set B. In the transition from the 1st to the 10th contractions, the fascicular length at 80% of MVC decreased from 34 +/- 4 (means +/- SD) to 30 +/- 3 mm (P < 0.001), the pennation angle increased from 35 +/- 3 to 42 +/- 3 degrees (P < 0.001), the myotendinous junction displacement increased from 5 +/- 3 to 10 +/- 3 mm (P < 0.001), and the average fascicular curvature remained constant (P > 0.05) at approximately 4.3 m(-1). No changes (P > 0.05) were found in fascicular length, pennation angle, and myotendinous junction displacement after the fifth contraction. Electrogoniometry showed that the ankle rotated by approximately 6.5 degrees during contraction, but no differences (P > 0.05) were obtained between contractions. The present results show that repeated contractions induce tendon creep, which substantially affects the geometry of the in-series contracting muscles, thus altering their potential for force and joint moment generation.

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December 2002
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In situ rat fast skeletal muscle is more efficient at submaximal than at maximal activation levels

J Appl Physiol (1985). 2002 May;92(5):2089-96

F. Abbate , C. J. De Ruiter , C. Offringa , A. J. Sargeant , A. De Haan

ABSTRACT The influence of stimulation frequency on efficiency (= total work output/high-energy phosphate consumption) was studied using in situ medial gastrocnemius muscle tendon complexes of the rat. The muscles performed 20 repeated concentric contractions (2/s) at 34°C. During these repeated contractions, the muscle was stimulated via the severed sciatic nerve with either 60, 90, or 150 Hz. The muscle was freeze-clamped immediately after these contractions, and high-energy phosphate consumption was determined by measuring intramuscular chemical change relative to control muscles. The average values (±SD) of efficiency calculated for 60, 90, and 150 Hz were 18.5 ± 1.5 (n = 7), 18.6 ± 1.5 (n = 9), and 14.7 ± 1.3 mJ/μmol phosphate (n = 9). The results indicate that the efficiency of the muscles that were submaximally activated (60 or 90 Hz) was higher (+26%,P < 0.05) than that of those maximally activated (150 Hz). Additional experiments showed that the low efficiency at maximal activation levels is unlikely to be the result of a higher energy turnover by the Ca2+-ATPase relative to the total energy turnover. Therefore, alternative explanations are discussed.

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May 2002
21 Reads

Effect of muscle temperature on rate of oxygen uptake during exercise in humans at different contraction frequencies

J Exp Biol. 2002 Apr;205(Pt 7):981-7

Journal of Experimental Biology

Abstract The effect of elevated human muscle temperature on energy turnover was investigated during cycling exercise (at 85 % of (VO(2)max)) at a contraction frequency of 60 revs min(-1). Muscle temperature was passively elevated prior to exercise by immersion of the legs in a hot water bath (42 degrees C). During exercise at this low pedalling rate, total energy turnover was higher (P<0.05) when muscle temperature was elevated compared with normal temperature (70.4+/-3.7 versus 66.9+/-2.4 kJ min(-1), respectively). Estimated net mechanical efficiency was found to be lower when muscle temperature was elevated. A second experiment was conducted in which the effect of elevated human muscle temperature on energy turnover was investigated during cycling exercise (at 85 % of (VO(2)max)) at a contraction frequency of 120 revs min(-1). Under the conditions of a high pedalling frequency, an elevated muscle temperature resulted in a lower energy turnover (P<0.05) compared with the normal muscle temperature (64.9+/-3.7 versus 69.0+/-4.7 kJ min(-1), respectively). The estimated net mechanical efficiency was therefore higher when muscle temperature was elevated. We propose that, in these experiments, prior heating results in an inappropriately fast rate of cross-bridge cycling when exercising at 60 revs min(-1), leading to an increased energy turnover and decreased efficiency. However, at the faster pedalling rate, the effect of heating the muscle shifts the efficiency/velocity relationship to the right so that cross-bridge detachment is more appropriately matched to the contraction velocity and, hence, energy turnover is reduced

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April 2002
22 Reads

Effects of training on contractile properties of paralyzed quadriceps muscle

Muscle Nerve. 2002 Apr;25(4):559-67.

Muscle & Nerve

Abstract Effects of two different training regimens on the contractile properties of the quadriceps muscle were studied in six individuals with spinal cord injury. Each subject had both limbs trained with the two regimens, consisting of stimulation with low frequencies (LF) at 10 HZ or high frequencies (HF) at 50 HZ; one limb of each subject was stimulated with the LF protocol and the other with the HF regimen. Twelve weeks of daily training increased tetanic tension by approximately 20%, which was not significantly different between training regimens. Interestingly, after HF but not LF training, the unusual high forces at the low frequency range of the force-frequency relationship decreased, possibly due to a reduced activation per impulse. After LF but not HF training, force oscillation amplitudes declined (by 33%) as relaxation tended to slow, which may have opposed possible effects of reduced activation as seen after HF training. Finally, fatigue resistance also increased rapidly after LF training (by 43%) but not after HF training. These results indicate that different types of training may selectively change different aspects of function in disused muscles.

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April 2002
25 Reads

Submaximal exercise capacity and maximal power output in polio subjects

Arch Phys Med Rehabil. 2001 Dec;82(12):1678-85.

Archives of Physical Medicine and Rehabilitation

Abstract OBJECTIVES: To compare the submaximal exercise capacity of polio subjects with postpoliomyelitis syndrome (PPS) and without (non-PPS) with that of healthy control subjects, to investigate the relationship of this capacity with maximal short-term power and quadriceps strength, and to evaluate movement economy. DESIGN: Cross-sectional survey. SETTING: University hospital. PARTICIPANTS: Forty-three polio subjects (25 PPS, 18 non-PPS) and 12 control subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Power output, oxygen uptake, and heart rate were measured in an incremental submaximal cycle ergometry test. Maximal short-term power was measured in 5-second all-out efforts. Knee extensor strength was measured on a chair dynamometer. RESULTS: The mean submaximal power +/- standard deviation at 80% of heart rate reserve of 83.8 +/- 29.9 watts in the polio subjects was significantly less than the mean submaximal power of 142.1 +/- 30.4 watts in the control group. However, expressed as a percentage of the maximal short-term power, submaximal power did not differ between the groups. Strength and maximal short-term power correlated significantly (p < .005) with submaximal power (r = .64 and .76, respectively). The oxygen uptake was higher than theoretically expected for the given submaximal power output in polio subjects, and appeared to increase with increasing asymmetry in strength and power between legs. No differences were found between PPS and non-PPS subjects. CONCLUSION: The submaximal work capacity of polio subjects was severely reduced, mainly in association with the reduced muscle capacity. And, because of a reduced movement economy, their energy cost was elevated. Although muscle loads in activities such as walking and climbing stairs differ from cycling, they also may require elevated relative levels of effort, predisposing subjects to premature fatigue in sustained activity.

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December 2001
28 Reads

Muscle oxygen uptake and energy turnover during dynamic exercise at different contraction frequencies in humans.

J Physiol. 2001 Oct 1;536(Pt 1):261-71.

Journal of Physiology

1. It has been established that pulmonary oxygen uptake is greater during cycle exercise in humans at high compared to low contraction frequencies. However, it is unclear whether this is due to more work being performed at the high frequencies and whether the energy turnover of the working muscles is higher. The present study tested the hypothesis that human skeletal muscle oxygen uptake and energy turnover are elevated during exercise at high compared to low contraction frequency when the total power output is the same. 2. Seven subjects performed single-leg dynamic knee-extensor exercise for 10 min at contraction frequencies of 60 and 100 r.p.m. where the total power output (comprising the sum of external and internal power output) was matched between frequencies (54 +/- 5 vs. 56 +/- 5 W; mean +/- S.E.M.). Muscle oxygen uptake was determined from measurements of thigh blood flow and femoral arterial - venous differences for oxygen content (a-v O(2) diff). Anaerobic energy turnover was estimated from measurements of lactate release and muscle lactate accumulation as well as muscle ATP and phosphocreatine (PCr) utilisation based on analysis of muscle biopsies obtained before and after each exercise bout. 3. Whilst a-v O(2) diff was the same between contraction frequencies during exercise, thigh blood flow was higher (P < 0.05) at 100 compared to 60 r.p.m. Thus, muscle V(O2) was higher (P < 0.05) during exercise at 100 r.p.m. Muscle V(O2) increased (P < 0.05) by 0.06 +/- 0.03 (12 %) and 0.09 +/- 0.03 l min(-1) (14 %) from the third minute to the end of exercise at 60 and 100 r.p.m., respectively, but there was no difference between the two frequencies. 4. Muscle PCr decreased by 8.1 +/- 1.7 and 9.1 +/- 2.0 mmol (kg wet wt)(-1), and muscle lactate increased to 6.8 +/- 2.1 and 9.8 +/- 2.5 mmol (kg wet wt)(-1) during exercise at 60 and 100 r.p.m., respectively. The total release of lactate during exercise was 48.7 +/- 8.8 and 64.3 +/- 10.6 mmol at 60 and 100 r.p.m. (not significant, NS). The total anaerobic ATP production was 47 +/- 8 and 61 +/- 12 mmol kg(-1), respectively (NS). 5. Muscle temperature increased (P < 0.05) from 35.8 +/- 0.3 to 38.2 +/- 0.2 degrees C at 60 r.p.m. and from 35.9 +/- 0.3 to 38.4 +/- 0.3 degrees C at 100 r.p.m. Between 1 and 7 min muscle temperature was higher (P < 0.05) at 100 compared to 60 r.p.m. 6. The estimated mean rate of energy turnover during exercise was higher (P < 0.05) at 100 compared to 60 r.p.m. (238 +/- 16 vs. 194 +/- 11 J s(-1)). Thus, mechanical efficiency was lower (P < 0.05) at 100 r.p.m. (24 +/- 2 %) compared to 60 r.p.m. (28 +/- 3 %). Correspondingly, efficiency expressed as work per mol ATP was lower (P < 0.05) at 100 than at 60 r.p.m. (22.5 +/- 2.1 vs. 26.5 +/- 2.5 J (mmol ATP)(-1)). 7. The present study showed that muscle oxygen uptake and energy turnover are elevated during dynamic contractions at a frequency of 100 compared with 60 r.p.m. It was also observed that muscle oxygen uptake increased as exercise progressed in a manner that was not solely related to the increase in muscle temperature and lactate accumulation.

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October 2001
41 Reads

Muscle oxygen uptake and energy turnover during dynamic exercise at different contraction frequencies in humans

J Physiol. 2001 Oct 1;536(Pt 1):261-71

Journal of Physiology

Abstract It has been established that pulmonary oxygen uptake is greater during cycle exercise in humans at high compared to low contraction frequencies. However, it is unclear whether this is due to more work being performed at the high frequencies and whether the energy turnover of the working muscles is higher. The present study tested the hypothesis that human skeletal muscle oxygen uptake and energy turnover are elevated during exercise at high compared to low contraction frequency when the total power output is the same. Seven subjects performed single-leg dynamic knee-extensor exercise for 10 min at contraction frequencies of 60 and 100 r.p.m. where the total power output (comprising the sum of external and internal power output) was matched between frequencies (54 ± 5 vs. 56 ± 5 W; mean ± S.E.M.). Muscle oxygen uptake was determined from measurements of thigh blood flow and femoral arterial–venous differences for oxygen content (a–v O2 diff). Anaerobic energy turnover was estimated from measurements of lactate release and muscle lactate accumulation as well as muscle ATP and phosphocreatine (PCr) utilisation based on analysis of muscle biopsies obtained before and after each exercise bout. Whilst a–v O2 diff was the same between contraction frequencies during exercise, thigh blood flow was higher (P < 0.05) at 100 compared to 60 r.p.m. Thus, muscle V̇O2 was higher (P < 0.05) during exercise at 100 r.p.m. Muscle V̇O2 increased (P < 0.05) by 0.06 ± 0.03 (12 %) and 0.09 ± 0.03 l min−1 (14 %) from the third minute to the end of exercise at 60 and 100 r.p.m., respectively, but there was no difference between the two frequencies. Muscle PCr decreased by 8.1 ± 1.7 and 9.1 ± 2.0 mmol (kg wet wt)−1, and muscle lactate increased to 6.8 ± 2.1 and 9.8 ± 2.5 mmol (kg wet wt)−1 during exercise at 60 and 100 r.p.m., respectively. The total release of lactate during exercise was 48.7 ± 8.8 and 64.3 ± 10.6 mmol at 60 and 100 r.p.m. (not significant, NS). The total anaerobic ATP production was 47 ± 8 and 61 ± 12 mmol kg−1, respectively (NS). Muscle temperature increased (P < 0.05) from 35.8 ± 0.3 to 38.2 ± 0.2 °C at 60 r.p.m. and from 35.9 ± 0.3 to 38.4 ± 0.3 °C at 100 r.p.m. Between 1 and 7 min muscle temperature was higher (P < 0.05) at 100 compared to 60 r.p.m. The estimated mean rate of energy turnover during exercise was higher (P < 0.05) at 100 compared to 60 r.p.m. (238 ± 16 vs. 194 ± 11 J s−1). Thus, mechanical efficiency was lower (P < 0.05) at 100 r.p.m. (24 ± 2 %) compared to 60 r.p.m. (28 ± 3 %). Correspondingly, efficiency expressed as work per mol ATP was lower (P < 0.05) at 100 than at 60 r.p.m. (22.5 ± 2.1 vs. 26.5 ± 2.5 J (mmol ATP)−1). The present study showed that muscle oxygen uptake and energy turnover are elevated during dynamic contractions at a frequency of 100 compared with 60 r.p.m. It was also observed that muscle oxygen uptake increased as exercise progressed in a manner that was not solely related to the increase in muscle temperature and lactate accumulation

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October 2001
12 Reads

Peripheral vascular changes after electrically stimulated cycle training in people with spinal cord injury

Arch Phys Med Rehabil. 2001 Jun;82(6):832-9

Archives of Physical Medicine and Rehabilitation

Abstract OBJECTIVE: To test whether a short period of training leads to adaptations in the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with spinal cord injury (SCI). DESIGN: Before-after trial. SETTING: Rehabilitation center, academic medical center. PARTICIPANTS: Nine men with spinal cord lesions. INTERVENTION: Six weeks of cycling using a functional electrically stimulated leg cycle ergometer (FES-LCE). MAIN OUTCOME MEASURES: Longitudinal images and simultaneous velocity spectra were measured in the common carotid (CA) and femoral (FA) arteries using quantitative duplex Doppler ultrasound examination. Arterial diameters, peak systolic inflow volumes (PSIVs), mean inflow volumes (MIVs), and a velocity index (VI), representing the peripheral resistance, were obtained at rest. PSIVs and VI were obtained during 3 minutes of hyperemia following 20 minutes of FA occlusion. RESULTS: Training resulted in significant increases in diameter (p < .01), PSIVs (p < .01), and MIVs (p < .05), and reduced VI (p < .01) of the FA, whereas values in the CA remained unchanged. Postocclusive hyperemic responses were augmented, indicated by significantly higher PSIVs (p <.01) and a trend toward lower VI. CONCLUSION: Six weeks of FES-LCE training increased the cross-sectional area of large conduit arteries and improved blood flow to the paralyzed legs of individuals with SCI.

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June 2001
21 Reads

Phosphocreatine and ATP content in human single muscle fibres before and after maximum dynamic exercise

Pflugers Arch. 2001 Jun;442(3):467-74

Pflugers Archiv

The recovery of high-energy phosphate levels in single human skeletal muscle fibres following short-term maximal (all-out) exercise was investigated. Three male volunteers exercised maximally for 25 s on an isokinetic cycling ergometer. Muscle biopsy samples from the vastus lateralis were collected at rest, immediately post-exercise and at 1.5 min of recovery. The subjects also performed a second exercise bout 1.5 min after the first, on a separate occasion. Single muscle fibres were dissected, characterized and assigned to one of four groups according to their myosin heavy chain (MyHC) isoform content; namely, type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC). Fibres were analysed for adenosine 5'-triphosphate (ATP), inosine-5'-monophosphate (IMP), phosphocreatine (PCr) and creatine (Cr) levels. Type I fibres had a lower Cr content than type II fibres (P<0.01). Within type II fibres resting [PCr] increased with increasing MyHC IIX isoform content (r=0.59, P<0.01). Post-exercise [PCr] was very low in all fibre groups (P<0.01 versus rest) while great reductions in ATP were also observed (P<0.01 versus rest), especially in the type II fibre groups. [PCr] at 1.5 min of recovery was still lower compared to rest for all fibre groups (P<0.01) especially in the IIAx and IIXa fibres.

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June 2001
37 Reads

Metabolism changes in single human fibres during brief maximal exercise

Exp Physiol. 2001 May;86(3):411-5

Experimental Physiology

Abstract Changes in high-energy phosphate levels in single human skeletal muscle fibres after 10 s of maximal (all-out) dynamic exercise were investigated. Muscle biopsies from vastus lateralis of two volunteers were collected at rest and immediately post exercise. Single muscle fibres were dissected from dry muscle and were assigned into one of four groups according to their myosin heavy chain (MyHC) isoform content: that is type I, IIA, IIAx and IIXa (the latter two groups containing either less or more than 50% IIX MyHC). Fragments of characterised fibres were analysed by HPLC for ATP, inosine-monophosphate (IMP), phosphocreatine (PCr) and creatine levels. After 10 s of exercise, PCr content ([PCr]) declined by approximately 46, 53, 62 and 59 % in type I, IIA, IIAx and IIXa fibres, respectively (P < 0.01 from rest). [ATP] declined only in type II fibres, especially in IIAx and IIXa fibres in which [IMP] reached mean values of 16 +/- 1 and 18 +/- 4 mmol (kg dry mass)(-1), respectively. While [PCr] was reduced in all fibre types during the brief maximal dynamic exercise, it was apparent that type II fibres expressing the IIX myosin heavy chain isoform were under a greatest metabolic stress as indicated by the reductions in [ATP].

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May 2001
29 Reads

In vivo specific tension of human skeletal muscle

J Appl Physiol (1985). 2001 Mar;90(3):865-72

Journal of Applied Physiology

Abstract In this study, we estimated the specific tensions of soleus (Sol) and tibialis anterior (TA) muscles in six men. Joint moments were measured during maximum voluntary contraction (MVC) and during electrical stimulation. Moment arm lengths and muscle volumes were measured using magnetic resonance imaging, and pennation angles and fascicular lengths were measured using ultrasonography. Tendon and muscle forces were modeled. Two approaches were followed to estimate specific tension. First, muscle moments during electrical stimulation and moment arm lengths, fascicular lengths, and pennation angles during MVC were used (data set A). Then, MVC moments, moment arm lengths at rest, and cadaveric fascicular lengths and pennation angles were used (data set B). The use of data set B yielded the unrealistic specific tension estimates of 104 kN/m(2) in Sol and 658 kN/m(2) in TA. The use of data set A, however, yielded values of 150 and 155 kN/m(2) in Sol and TA, respectively, which agree with in vitro results from fiber type I-predominant muscles. In fact, both Sol and TA are such muscles. Our study demonstrates the feasibility of accurate in vivo estimates of human muscle intrinsic strength

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March 2001
40 Reads

Reproducibility of contractile properties of the human paralysed and non-paralysed quadriceps muscle

Clin Physiol. 2001 Jan;21(1):105-13

Clinical Physiology

Abstract This study assessed the reproducibility of electrically evoked, isometric quadriceps contractile properties in eight people with spinal cord injury (SCI) and eight able-bodied (AB) individuals. Over all, the pooled coefficients of variation (CVps) in the SCI group were significantly lower (ranging from 0.03 to 0.15) than in the AB group (ranging from 0.08 to 0.21) (P<0.05). Furthermore, in all subjects, the variability of force production increased as stimulation frequency decreased (P<0.01). In subjects with SCI, variables of contractile speed are clearly less reproducible than tetanic tension or resistance to fatigue. Contractile properties of quadriceps muscles of SCI subjects were significantly different from that of AB subjects. Muscles of people with SCI were less fatigue resistant (P<0.05) and produced force-frequency relationships that were shifted to the left, compared with AB controls (P<.01). In addition, fusion of force responses resulting from 10 Hz stimulation was reduced (P<.05) and speed of contraction (but not relaxation) was increased (P<0.05), indicating an increased contractile speed in paralysed muscles compared with non-paralysed muscles. These results correspond with an expected predominance of fast glycolytic muscle fibres in paralysed muscles. It is concluded that quadriceps dynamometry is a useful technique to study muscle function in non-paralysed as well as in paralysed muscles. Furthermore, these techniques can be reliably used, for example, to assess therapeutic interventions on paralysed muscles provided that expected differences in relative tetanic tension and fatigue resistance are larger than approximately 5% and differences in contractile speed are larger than approximately 15%

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January 2001
28 Reads

Total power output generated during dynamic knee extensor exercise at different contraction frequencies

J Appl Physiol (1985). 2000 Nov;89(5):1912-8

Journal of Applied Physiology

Abstract A novel approach has been developed for the quantification of total mechanical power output produced by an isolated, well-defined muscle group during dynamic exercise in humans at different contraction frequencies. The calculation of total power output comprises the external power delivered to the ergometer (i.e., the external power output setting of the ergometer) and the "internal" power generated to overcome inertial and gravitational forces related to movement of the lower limb. Total power output was determined at contraction frequencies of 60 and 100 rpm. At 60 rpm, the internal power was 18+/- 1 W (range: 16-19 W) at external power outputs that ranged between 0 and 50 W. This was less (P<0.05) than the internal power of 33+/-2 W (27-38 W) at 100 rpm at 0-50 W. Moreover, at 100 rpm, internal power was lower (P<0.05) at the higher external power outputs. Pulmonary oxygen uptake was observed to be greater (P<0.05) at 100 than at 60 rpm at comparable total power outputs, suggesting that mechanical efficiency is lower at 100 rpm. Thus a method was developed that allowed accurate determination of the total power output during exercise generated by an isolated muscle group at different contraction frequencies

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November 2000
41 Reads

In vivo measurement-based estimations of the human Achilles tendon moment arm

Eur J Appl Physiol. 2000 Nov;83(4 -5):363-9

European Journal of Applied Physiology

Abstract The aim of the present study was to estimate and compare in vivo measurement-based Achilles tendon moment arm lengths at rest and during isometric plantarflexion maximum voluntary contraction (MVC) using the centre-of-rotation (COR) and the tendon-excursion (TE) methods. Both methods were based on morphometric analysis of sagittal-plane magnetic resonance images of the foot. Using the COR method, moment arms were obtained at ankle angles from 15 degrees of dorsiflexion to 30 degrees of plantarflexion in steps of 15 degrees, digitizing the perpendicular distance from a moving centre of rotation in the tibio-talar joint to the Achilles tendon action line. The TE method was based on measurement of calcaneal displacement along the tibial axis during 15 degrees rotations of the ankle joint, from 30 degrees of dorsiflexion to 45 degrees of plantarflexion. The two methods gave similar estimations at rest varying from 4.3 to 5.6 cm. Using the COR method, the Achilles tendon moment arm during MVC was larger by 1-1.5 cm (22-27%, P < 0.01) than the respective resting value. In contrast, no difference (P > 0.05) was found between the resting and MVC moment arm estimations of the TE method. The disagreement in moment arms during MVC may be attributed to differences in the assumptions made between the two methods. The TE method has more limitations than the COR method and its estimations during MVC should be treated with caution. Resting Achilles tendon moment arm estimations of the COR method should be multiplied by 1.22-1.27 when maximal isometric plantarflexion joint moments, musculotendon forces and stresses are predicted using modelling

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November 2000
29 Reads

Altered contractile properties of the quadriceps muscle in people with spinal cord injury following functional electrical stimulated cycle training

Spinal Cord. 2000 Apr;38(4):214-23

Spinal Cord

Abstract STUDY DESIGN: A longitudinal training study. OBJECTIVES: To assess if contractile speed and fatigability of paralysed quadriceps muscles in individuals with spinal cord injury (SCI) can be altered by functional electrical stimulation leg cycle ergometry (FES-LCE) training. SETTINGS: The Sint Maartenskliniek rehabilitation centre and the University of Nijmegen, Nijmegen, the Netherlands. METHODS: Contractile properties of the quadriceps muscle were studied in seven people with motor-complete SCI who participated in a FES-LCE training program. Subjects trained for 30 min, three times per week for 6 weeks. Contractile speed and fatigue characteristics of electrically stimulated isometric contractions were compared before and after 6 weeks of FES-LCE. RESULTS: Fatigue resistance improved following FES-LCE training as indicated by the higher forces maintained in response to repetitive electrical stimulation. In contrast with an improved fatigue resistance, the maximal rate of force rise was unaffected, the speed of relaxation increased and the fusion of a 10 Hz force signal decreased. Furthermore, the force-frequency relationship shifted to the right at low stimulation frequencies, indicated by a decline in the ratio of 1 and 100 Hz force responses as well as the ratio of 10 and 100 Hz force responses. CONCLUSION: FES-LCE training can change the physiological properties of the quadriceps muscle in people with SCI. Even after a short period of training, the stimulated muscles become more resistant to fatigue. Furthermore, the increased speed of relaxation and associated decreased fusion and altered force-frequency relationship following training may be related to adaptations in the calcium handling processes, which reflect an early response of long-term disused muscles.

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April 2000
47 Reads

Influence of muscle temperature on the contractile properties of the quadriceps muscle in humans with spinal cord injury

Clin Sci (Lond). 2000 Jan;98(1):31-8

Clinical Science

Abstract Low muscle temperature in paralysed muscles of individuals with spinal cord injury may affect the contractile properties of these muscles. The present study was therefore undertaken to assess the effects of increased muscle temperature on the isometric contractile properties of electrically stimulated paralysed quadriceps muscles. When muscle temperature at a depth of 3 cm was increased from approximately 32 degrees C to approximately 36 degrees C by ultra-short-wave application, the half-relaxation time shortened and low-frequency force responses became less fused, but the maximal rate of increase in force remained unchanged. Heating had no effect upon either force decline or slowing of relaxation during fatiguing contractions. The force-frequency relationship of the paralysed quadriceps muscle was shifted to the right after the muscle was heated. Despite this shift, however, the relationship still resembled that in muscles of non-paralysed individuals, probably due to the unexplained high twitch forces. These results indicate that reduced muscle temperature in spinal-cord-injured individuals may lead to an underestimation of the changes in contractile properties in terms of relaxation rate or the degree of fusion with low-frequency stimulation. In addition, the force-frequency relationship of paralysed muscles does not accurately reflect the magnitude of these changes, even when the muscle is heated, and should therefore be treated with caution.

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January 2000
30 Reads

Effects of high-frequency initial pulses and posttetanic potentiation on power output of skeletal muscle.

J Appl Physiol (1985). 2000 Jan;88(1):35-40.

Journal of Applied Physiology

Abstract The effects of high-frequency initial pulses (HFIP) and posttetanic potentiation on mechanical power output during concentric contractions were examined in the in situ medial gastrocnemius of the rat with an intact origin on the femur and blood supply. Stimulation of the muscle was performed via the severed sciatic nerve. In the experiments, HFIP or the potentiating tetanus was followed by a stimulation of 80, 120, or 200 Hz. The results showed that both HFIP and the tetanus increased power output at high contraction velocities (>75 mm/s) when followed by a train of 80 or 120 Hz (200 Hz resulted in no effects). Mechanical power output was increased maximally by HFIP to 120 and 168% by the tetanus. Furthermore, when HFIP or the tetanus were followed by a train of 80 Hz, the peak power in the power-velocity curve tended to be shifted to a higher velocity.

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January 2000
30 Reads

Human muscle power generating capability during cycling at different pedalling rates.

Exp Physiol. 2000 Jan;85(1):117-24

Experimental Physiology

Abstract The effect of different pedalling rates (40, 60, 80, 100 and 120 rev min-1) on power generating capability, oxygen uptake (O2) and blood lactate concentration [La]b during incremental tests was studied in seven subjects. No significant differences in O2,max were found (mean +/- S.D., 5.31 +/- 0.13 l min-1). The final external power output delivered to the ergometer during incremental tests (PI,max) was not significantly different when cycling at 60, 80 or 100 rev min-1 (366 +/- 5 W). A significant decrease in PI,max of 60 W was observed at 40 and 120 rev min-1 compared with 60 and 100 rev min-1, respectively (P < 0.01). At 120 rev min-1 there was also a pronounced upward shift of the O2-power output (O2-P) relationship. At 50 W O2 between 80 and 100 rev min-1 amounted to +0.43 l min-1 but to +0.87 l min-1 between 100 and 120 rev min-1. The power output corresponding to 2 and 4 mmol l-1 blood lactate concentration (P[La]2 and P[La]4 ) was also significantly lower (> 50 W) at 120 rev min-1 (P < 0.01) while pedalling at 40, 60, 80 and 100 rev min-1 showed no significant difference. The maximal peak power output (PM, max) during 10 s sprints increased with pedalling rate up to 100 rev min-1. Our study indicates that with increasing pedalling rate the reserves in power generating capability increase, as illustrated by the PI,max/PM,max ratio (54.8, 44.8, 38.1, 34.6, 29.2%), the P[La]4/PM,max ratio (50.4, 38.9, 31.0, 27.7, 22.9%) and the P[La]2/PM,max ratio (42.8, 33.5, 25.6, 23.1, 15.6%) increases. Taking into consideration the O2,max, the PI,max and the reserve in power generating capability we concluded that choosing a high pedalling rate when performing high intensity cycling exercise may be beneficial since it provides greater reserve in power generating capability and this may be advantageous to the muscle in terms of resisting fatigue. However, beyond 100 rev min-1 there is a decrease in external power that can be delivered for an given O2 with an associated earlier onset of metabolic acidosis and clearly this will be disadvantageous for sustained high intensity exercise.

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January 2000
40 Reads

Temperature effect on the rates of isometric force development and relaxation in the fresh and fatigued human adductor pollicis muscle

Exp Physiol. 1999 Nov;84(6):1137-50

Experimental Physiology

Abstract The purpose of the present study was to investigate the effect of temperature on the rates of isometric force development and relaxation in electrically activated fresh and fatigued human adductor pollicis muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, muscle temperatures were approximately 37, 31, 25 and 22 C. Maximal isometric force was reduced by 16.8 +/- 1.5 % at 22 C. The stimulation frequency-force and -rate of force development relationships were shifted to the left at lower temperatures. Q10 values for the maximal rates of force development and relaxation, and the times for 100 to 50 % and 50 to 25 % force relaxation, were about 2.0 between 37 and 25 C and about 3.8 between 25 and 22 C. However, the time for 50 to 25 % force relaxation had a relatively high Q10 value between 25 and 22 C (6.9) and this parameter also appeared to be more sensitive to fatigue compared to the other indices of relaxation. Nevertheless, the effect of fatigue on all parameters decreased with cooling over the entire (37-22 C) temperature range

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November 1999
28 Reads

Changes in the tibialis anterior tendon moment arm from rest to maximum isometric dorsiflexion: in vivo observations in man

Clin Biomech (Bristol, Avon). 1999 Nov;14(9):661-6

Clinical Biomechanics

Abstract OBJECTIVE: In the present study, we examined the hypothesis that the tibialis anterior tendon moment arm increases during maximum isometric dorsiflexion as compared with rest. BACKGROUND: In musculoskeletal modelling applications, moment arms from passive muscles at rest are assumed representative of those measured during isometric muscle contraction. The validity of this assumption is questionable in musculotendon actuators enclosed by retinacular systems as in tibialis anterior. DESIGN AND METHODS: Sagittal-plane magnetic resonance images of the right ankle were taken in six subjects at rest and during maximum isometric dorsiflexion at six ankle angles between dorsiflexion and plantarflexion having the body placed in the supine position and the knee flexed at 90 degrees. Instant centres of rotation in the tibio-talar joint, tibialis anterior tendon action lines and moment arms were identified in the sagittal plane at ankle angles of -15 degrees, 0 degrees,+15 degrees and +30 degrees at rest and during maximum isometric dorsiflexion. RESULTS: At any given ankle angle, the tibialis anterior tendon moment arm during maximum isometric dorsiflexion increased by 0.9-1.5 cm (P<0.01) compared with rest. This was attributed to a displacement of both tibialis anterior tendon action line by 0.8-1.2 cm (P<0.01) and all instant centres of rotation by 0.3-0.4 cm (P<0. 01) distally in relation to their corresponding resting positions. CONCLUSIONS AND IMPLICATIONS: The assumption that the tibialis anterior tendon moment arm does not change from rest to maximum isometric dorsiflexion is invalid. Erroneous tendon forces, muscle stresses and joint moments by as much as 30% would be calculated using resting tibialis anterior tendon moment arms in the moment equilibrium equation around the ankle joint during maximum isometric dorsiflexion. RELEVANCE: A substantial increase in the tibialis anterior tendon moment arm occurs from rest to maximum isometric dorsiflexion. This needs to be taken into consideration when using planimetric musculoskeletal modelling for analysing maximal static ankle dorsiflexion loads.

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November 1999
55 Reads

Contractile properties of the quadriceps muscle in individuals with spinal cord injury

Muscle Nerve. 1999 Sep;22(9):1249-56

Muscle & Nerve

Abstract Selected contractile properties and fatigability of the quadriceps muscle were studied in seven spinal cord-injured (SCI) and 13 able-bodied control (control) individuals. The SCI muscles demonstrated faster rates of contraction and relaxation than did control muscles and extremely large force oscillation amplitudes in the 10-Hz signal (65 +/- 22% in SCI versus 23 +/- 8% in controls). In addition, force loss and slowing of relaxation following repeated fatiguing contractions were greater in SCI compared with controls. The faster contractile properties and greater fatigability of the SCI muscles are in agreement with a characteristic predominance of fast glycolytic muscle fibers. Unexpectedly, the SCI muscles exhibited a force-frequency relationship shifted to the left, most likely as the result of relatively large twitch amplitudes. The results indicate that the contractile properties of large human locomotory muscles can be characterized using the approach described and that the transformation to faster properties consequent upon changes in contractile protein expression following SCI can be assessed. These measurements may be useful to optimize stimulation characteristics for functional electrical stimulation and to monitor training effects induced by electrical stimulation during rehabilitation of paralyzed muscles.

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September 1999
61 Reads

The measurement of force/velocity relationships of fresh and fatigued human adductor pollicis muscle.

Eur J Appl Physiol Occup Physiol. 1999 Sep;80(4):386-93

European Journal of Applied Physiology

The purpose of the study was to obtain force/velocity relationships for electrically stimulated (80 Hz) human adductor pollicis muscle (n = 6) and to quantify the effects of fatigue. There are two major problems of studying human muscle in situ; the first is the contribution of the series elastic component, and the second is a loss of force consequent upon the extent of loaded shortening. These problems were tackled in two ways. Records obtained from isokinetic releases from maximal isometric tetani showed a late linear phase of force decline, and this was extrapolated back to the time of release to obtain measures of instantaneous force. This method gave usable data up to velocities of shortening equivalent to approximately one-third of maximal velocity. An alternative procedure (short activation, SA) allowed the muscle to begin shortening when isometric force reached a value that could be sustained during shortening (essentially an isotonic protocol). At low velocities both protocols gave very similar data (r2 = 0.96), but for high velocities only the SA procedure could be used. Results obtained using the SA protocol in fresh muscle were compared to those for muscle that had been fatigued by 25 s of ischaemic isometric contractions, induced by electrical stimulation at the ulnar nerve. Fatigue resulted in a decrease of isometric force [to 69 (3)%], an increase in half-relaxation time [to 431 (10)%], and decreases in maximal shortening velocity [to 77 (8)%] and power [to 42 (5)%]. These are the first data for human skeletal muscle to show convincingly that during acute fatigue, power is reduced as a consequence of both the loss of force and slowing of the contractile speed.

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September 1999
67 Reads

RNA content differs in slow and fast muscle fibers: implications for interpretation of changes in muscle gene expression

J Histochem Cytochem. 1999 Aug;47(8):995-1004

Journal of Histochemistry and Cytochemistry

Quantification of a specific muscle mRNA per total RNA (e.g., by Northern blot analysis) plays a crucial role in assessment of developmental, experimental, or pathological changes in gene expression. However, total RNA content per gram of a particular fiber type may differ as well. We have tested this possibility in the distinct fiber types of adult rat skeletal muscle. Sections of single fibers were hybridized against 28S rRNA as a marker for RNA content. Quantification of the hybridization showed that the 28S rRNA content decreases in the order I>IIA>IIX>IIB, where Type I fibers show a five- to sixfold higher expression level compared to Type IIB fibers. Results were verified with an independent biochemical determination of total RNA content performed on pools of histochemically defined freeze-dried single fibers. In addition, the proportion of myosin heavy chain (MHC) mRNA per microgram of total RNA was similar in slow and fast fibers, as demonstrated by Northern blot analysis. Consequently, Type I fibers contain five- to sixfold more MHC mRNA per microgram of tissue than IIB fibers. These differences are not reflected in the total fiber protein content. This study implies that proper assessment of mRNA levels in skeletal muscle requires evaluation of total RNA levels according to fiber type composition

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August 1999
60 Reads

Improved high-performance liquid chromatographic assay for the determination of "high-energy" phosphates in mammalian skeletal muscle. Application to a single-fibre study in man

J Chromatogr B Biomed Sci Appl. 1999 Jul 9;730(2):183-91

Journal of Chromotography

Abstract A sensitive and reproducible method for the determination of adenine nucleotides (ATP, IMP) and creatine compounds [creatine (Cr), phosphocreatine (PCr)] in freeze-dried single human muscle fibre fragments is presented. The method uses isocratic reversed-phase high-performance liquid chromatography of methanol extracts. Average retention times (min) of ATP, IMP and PCr, Cr from standard solutions were 10.6+/-0.42, 2.11+/-0.06 (n=6) and 10.5+/-0.31 and 1.19+/-0.02 (n=9), respectively. Detection limits in extracts from muscle fibre fragments were 2.0, 1.0, 3.0 and 2.0 mmol/kg dm, respectively. The assay was found successful for analysis of fibre-fragments weighing > or = 1 microg.

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July 1999
30 Reads

Human power output during repeated sprint cycle exercise: the influence of thermal stress

Eur J Appl Physiol Occup Physiol. 1999 Mar;79(4):360-6

European Journal of Applied Physiology

Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise. On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4 min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7 (1.5) degrees C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1 (0.5) degrees C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration. Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172) W vs 656 (58) W; P < 0.01] and sprint II [907 (150) vs 646 (37) W; P < 0.05]. Mean power output was higher in the heat compared to the normal environment in both sprint I [634 (91) W vs 510 (59) W; P < 0.05] and sprint II [589 (70) W vs 482 (47) W; P < 0.05]. There was a faster rate of fatigue (P < 0.05) when exercise was performed in the heat compared to the normal environment. Arterialised-venous blood samples were taken for the determination of acid-base status and blood lactate and blood glucose before exercise, 2 min after sprint I, and at several time points after sprint II. Before exercise there was no difference in resting acid-base status or blood metabolites between environmental conditions. There was a decrease in blood pH, plasma bicarbonate and base excess after sprint I and after sprint II. The degree of post-exercise acidosis was similar when exercise was performed in either of the environmental conditions. The metabolic response to exercise was similar between environmental conditions; the concentration of blood lactate increased (P < 0.01) after sprint I and sprint II but there were no differences in lactate concentration when comparing the exercise bouts performed in a normal and a hot environment. These data demonstrate that when brief intense exercise is performed in the heat, peak power output increases by about 25% and mean power output increases by 15%; this was due to achieving a higher pedal cadence in the heat

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March 1999
52 Reads

Disability and functional assessment in former polio patients with and without postpolio syndrome

Arch Phys Med Rehabil. 1999 Feb;80(2):136-43

Archives of Physical Medicine and Rehabilitation

Abstract OBJECTIVES: To compare perceived health problems and disability in former polio subjects with postpolio syndrome (PPS) and those without postpolio syndrome (non-PPS), and to evaluate perceived health problems, disability, physical performance, and muscle strength. DESIGN: Cross-sectional survey; partially blinded data collection. SUBJECTS: One hundred three former polio subjects, aged 32 to 60yrs. This volunteer sample came from referrals and patient contacts. Criterion for PPS: new muscle weakness among symptoms. MAIN OUTCOME MEASURES: Nottingham Health Profile (NHP), adapted D-code of the International Classification of Impairments, Disabilities and Handicaps, performance test, and muscle strength assessment. RESULTS: PPS subjects (n = 76) showed higher scores (p < .001) than non-PPS subjects (n = 27) within the NHP categories of physical mobility, energy, and pain. On a 16-item Polio Problems List, 78% of PPS subjects selected fatigue as their major problem, followed by walking outdoors (46%) and climbing stairs (41%). The disabilities of PPS subjects were mainly seen in physical and social functioning. No differences in manually tested strength were found between patient groups. PPS subjects needed significantly more time for the performance test than non-PPS subjects and their perceived exertion was higher. Perceived health problems (NHP-PhysMobility) correlated significantly with physical disability (r = .66), performance-time (r = .54), and muscle strength (r = .38). With linear regression analysis, 54% of the NHP-PhysMobility score could be explained by the performance test (time and exertion), presence of PPS, and muscle strength, whereas strength itself explained only 14% of the NHP-PhysMobility score. CONCLUSIONS: PPS subjects are more prone to fatigue and have more physical mobility problems than non-PPS subjects. In former polio patients, measurements of perceived health problems and performance tests are the most appropriate instruments for functional evaluation

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February 1999
36 Reads

Differences in human antagonistic ankle dorsiflexor coactivation between legs; can they explain the moment deficit in the weaker plantarflexor leg?

Exp Physiol. 1998 Nov;83(6):843-55

Experimental Physiology

The present study examined the hypothesis that the antagonistic ankle dorsiflexor coactivation level during maximum isometric voluntary plantarflexion (MVC) is a function of ankle angle. Six male subjects generated plantarflexion and dorsiflexion MVC trials at ankle angles of -15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg having the knee flexed at an angle of 90 deg. In all contractions surface EMG measurements were taken from tibialis anterior and soleus which were considered representative muscles of all dorsiflexors and plantarflexors, respectively. Antagonistic dorsiflexor coactivation was expressed as normalized EMG and moment. Calculations of the antagonistic dorsiflexor moment were based on the tibialis anterior EMG-dorsiflexor moment relationship from contractions at 50, 40, 30, 20 and 10 % of the dorsiflexion MVC moment. In both legs dorsiflexor coactivation level followed an open U-shaped pattern as a function of ankle angle. Differences of 9 and 14 % (P < 0.05) were found in the measured net plantarflexion MVC moment between legs at ankle angles of -15 and +30 deg, respectively. No difference (P > 0.05) was found in the calf circumference between legs. Differences were found in the antagonistic dorsiflexor coactivation between legs at ankle angles of -15 and +30 deg. In the weaker leg the antagonistic EMG measurements were higher by 100 and 45 % (P < 0.01) and the estimated antagonistic moments were higher by 70 and 43 % (P < 0.01) compared with the weaker leg at -15 and +30 deg, respectively. This finding was associated with a decreased range of motion (ROM) in the weaker leg (14 %, P < 0.01), such that no difference (P > 0.05) was found in dorsiflexor antagonistic coactivation between legs at end-range ankle angles. The findings of the study (i) have to be taken into consideration when estimating musculoskeletal loads in the lower extremity, (ii) imply that stretching training can result in a stronger plantarflexion at end-range ankle angles through inhibition of the dorsiflexors, and (iii) imply a neural drive inadequacy during a plantarflexion MVC at end-range angles

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November 1998
24 Reads

In vivo measurements of the triceps surae complex architecture in man: implications for muscle function

J Physiol. 1998 Oct 15;512 ( Pt 2):603-14

Journal of Physiology

1. The objectives of this study were to (1) quantify experimentally in vivo changes in pennation angle, fibre length and muscle thickness in the triceps surae complex in man in response to changes in ankle position and isometric plantarflexion moment and (2) compare changes in the above muscle architectural characteristics occurring in the transition from rest to a given isometric plantarflexion intensity with the estimations of a planimetric muscle model assuming constant thickness and straight muscle fibres. 2. The gastrocnemius medialis (GM), gastrocnemius lateralis (GL) and soleus (SOL) muscles of six males were scanned with ultrasonography at different sites along and across the muscle belly at rest and during maximum voluntary contraction (MVC) trials at ankle angles of -15 deg (dorsiflexed direction), 0 deg (neutral position), +15 deg (plantarflexed direction) and +30 deg. Additional images were taken at 80, 60, 40 and 20% of MVC at an ankle angle of 0 deg. 3. In all three muscles and all scanned sites, as ankle angle increased from -15 to +30 deg, pennation increased (by 6-12 deg, 39-67%, P < 0.01 at rest and 9-16 deg, 29-43%, P < 0.01 during MVC) and fibre length decreased (by 15-28 mm, 32-34%, P < 0.01 at rest and 8-10 mm, 27-30%, P < 0.05 during MVC). Thickness in GL and SOL increased during MVC compared with rest (by 5-7 mm, 36-47%, P < 0.01 in GL and 6-7 mm, 38-47%, P < 0.01 in SOL) while thickness of GM did not differ (P > 0.05) between rest and MVC. 4. At any given ankle angle the model underestimated changes in GL and SOL occurring in the transition from rest to MVC in pennation angle (by 9-12 deg, 24-38%, P < 0.01 in GL and 9-14 deg, 25-28%, P < 0.01 in SOL) and fibre length (by 6-15 mm, 22-39%, P < 0.01 in GL and 6-8 mm, 23-24%, P < 0.01 in SOL). 5. The findings of the study indicate that the mechanical output of muscle as estimated by the model used may be unrealistic due to errors in estimating the changes in muscle architecture during contraction compared with rest

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October 1998
48 Reads

Changes in Achilles tendon moment arm from rest to maximum isometric plantarflexion: in vivo observations in man

J Physiol. 1998 Aug 1;510 ( Pt 3):977-85

Journal of Physiology

Abstract The purpose of the present study was to examine the effect of a plantarflexor maximum voluntary contraction (MVC) on Achilles tendon moment arm length. Sagittal magnetic resonance (MR) images of the right ankle were taken in six subjects both at rest and during a plantarflexor MVC in the supine position at a knee angle of 90 deg and at ankle angles of -30 deg (dorsiflexed direction), -15 deg, 0 deg (neutral ankle position), +15 deg (plantarflexed direction), +30 deg and +45 deg. A system of mechanical stops, support triangles and velcro straps was used to secure the subject in the above positions. Location of a moving centre of rotation was calculated for ankle rotations from -30 to 0 deg, -15 to +15 deg, 0 to +30 deg and +15 to +45 deg. All instant centres of rotation were calculated both at rest and during MVC. Achilles tendon moment arms were measured at ankle angles of -15, 0, +15 and +30 deg. At any given ankle angle, Achilles tendon moment arm length during MVC increased by 1-1.5 cm (22-27%, P < 0.01) compared with rest. This was attributed to a displacement of both Achilles tendon by 0.6-1.1 cm (P < 0.01) and all instant centres of rotation by about 0.3 cm (P < 0.05) away from their corresponding resting positions. The findings of this study have important implications for estimating loads in the musculoskeletal system. Substantially unrealistic Achilles tendon forces and moments generated around the ankle joint during a plantarflexor MVC would be calculated using resting Achilles tendon moment arm measurements

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August 1998
63 Reads

Shortening-induced force depression in human adductor pollicis muscle

J Physiol. 1998 Mar 1;507 ( Pt 2):583-91

Journal of Physiology

Abstract The effects of single isovelocity shortening contractions on force production of the electrically stimulated human adductor pollicis muscle were investigated in seven healthy male subjects. Redeveloped isometric force immediately following isovelocity shortening was always depressed compared with the isometric force recorded at the same muscle length but without preceding shortening. The maximal isometric force deficit (FD) was (mean ± S.E.M.) 37 ± 2 % after 38 deg of shortening at 6.1 deg s−1. The FD was positively correlated with angular displacement (r2 > 0.98) and decreased with increasing velocity of the shortening step. Stimulation at 20 Hz instead of 50 Hz reduced absolute force levels during the contractions to about 73 % and the FD was decreased to a similar extent. Eighty-nine per cent of the velocity-related variation in the FD could be explained by the absolute force levels during shortening. FD was largely abolished by allowing the muscle to relax briefly (approximately 200 ms), a time probably too short for significant metabolic recovery. At all but the highest velocities there was a linear decline in force during the latter part of the isovelocity shortening phase, suggesting that the mechanisms underlying FD were active during shortening. Our results show that shortening-induced force deficit is a significant feature of human muscle working in situ and is proportional to the work done by the muscle-tendon complex. This finding has important implications for experimental studies of force-velocity relationships in the intact human.

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March 1998
20 Reads

Comparison of the molecular, antigenic and ATPase determinants of fast myosin heavy chains in rat and human: a single-fibre study

Pflugers Arch. 1997 Dec;435(1):151-63

Pflugers Archiv

Abstract Combined methodologies of histochemistry, immunohistochemistry, sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), reverse transcriptase polymerase chain reaction (RT-PCR) and a histochemical method specific for myofibrillar ATPase (mATPase) of the type IIX myosin heavy chain (MyHC) isoform were used to study human and rat single fibres to examine the homology between type II MyHC isoform-based fibres of both species. We demonstrate that human type II fibres exhibit antigenic mATPase and 3'-untranslated region (3'-UTR) sequence determinants homologous to the IIA and IIX but not the IIB MyHC isoforms of the rat. Both immunolabelling with anti-MyHC monoclonal antibodies and the mATPase method used with frozen sections confirmed that all human type II fibres express type IIA and/or type IIX MyHC. Quantitative immunohistochemistry failed to recognize human fibres with antigenic characteristics corresponding to hybrid IIXB MyHC-based fibres. Ca2+-stimulated maximum myosin ATPase activity, determined by quantitative histochemistry, revealed that human IIX fibres (with an optical density or OD = 0.707) display enzyme activity which is comparable to that of the rat type IIX (OD = 0.687) but lower than that of the rat type IIB fibres (OD = 0.836). The results do not support the notion that MyHC IIB is expressed in human limb muscles, even in hybrid fibres. We conclude that human type II fibres have been misclassified in numerous previous publications and that this has important implications in attempts to compare the physiological characteristics of fibre types, particularly when animal models are used.

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December 1997
17 Reads

Myosin heavy chain isoform expression and high energy phosphate content in human muscle fibres at rest and post-exercise

J Physiol. 1996 Oct 15;496 ( Pt 2):583-588

Journal of Physiology

Abstract 1. The relationship between myosin heavy chain (MyHC) isoforms and high energy phosphate content was studied in human muscle fibres at rest and following maximal dynamic exercise lasting 25 s. 2. Single fibre fragments were characterized as type I, type IIA, type IIX or type IIAX. These latter fibres were subdivided into five groups on the basis of the proportion of MyHC IIX isoform present. 3. Resting ATP concentration in type I fibres was 10% lower than in type II fibres (P < 0.05), but no differences were found amongst type IIA, IIX and IIAX fibre groups. Phosphocreatine (PCr) content was lower in type I than in type II fibres (P < 0.01) and, amongst type II fibres, increased progressively with the amounts of MyHC IIX expressed. 4. After 25 s of maximal dynamic exercise ATP concentration was reduced in all fibres. The decrease was approximately 25% in type I fibres and between 47 and 66% in the type II subgroups. 5. Post-exercise PCr content was low in all fibre types. Fibre groups with the lowest post-exercise PCr also had the lowest ATP and the highest inosine monophosphate contents. delta PCr (rest to post-exercise) was smallest in type I fibres and showed a progressive increase in the type II fibre groups as the proportion of the faster IIX myosin heavy chain isoform increased.

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October 1996
35 Reads

In vivo IIX and IIB fiber recruitment in gastrocnemius muscle of the rat is compartment related

J Appl Physiol (1985). 1996 Aug;81(2):933-42

Journal of Applied Physiology

The purpose of the present study was to investigate to what extent fast-twitch IIX and IIB fiber recruitment was related to the natural existing muscle compartments (subvolumes of muscle innervated by different primary nerve branches) in rat medial gastrocnemius. Three groups (n = 6) of rats trotted on a motor-driven treadmill (20 degrees incline) at different speeds. A fourth group served as controls, and a fifth group received in situ electrical stimulation of all medial gastrocnemius muscle fibers. Postexercise glycogen levels (periodic acid-Schiff staining intensities) were made. Running caused more and in situ stimulation caused less glycogen breakdown in the proximal IIX and IIB fibers compared with the fibers of the same type in the most distal compartment. Furthermore, the boundaries of the most distal compartment could often be recognized in the periodic acid-Schiff-stained cross sections. It was concluded that during running the proximal IIX and IIB fibers were recruited to a greater extent (and at lower treadmill speeds) compared with the distal IIX and IIB fibers, respectively

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August 1996
30 Reads

Fast-twitch muscle unit properties in different rat medial gastrocnemius muscle compartments

J Neurophysiol. 1996 Jun;75(6):2243-54

Journal of Neurophysiology

1. The effect of muscle unit (MU) localization on physiological properties was investigated within the fast-twitch fatigue-resistant (FR) and fast-fatigable (FF) MU populations of rat medial gastrocnemius (MG) muscle. Single MG MUs were functionally isolated by microdissection of the ventral roots. FR and FF MU properties of the most proximal and distal muscle compartments were compared. The most proximal and distal compartment are subvolumes of the MG innervated by the most proximal and distal primary nerve branch, respectively. A subsample of the isolated units was glycogen depleted and muscle cross sections were stained for glycogen and myosin-adenosinetriphosphatase. 2. It was shown that proximal FF and FR units reached optimum length for force production at shorter muscle lengths compared with the distal FR and FF units. 3. The fast MUs of the proximal compartment had small territories that were located close to and/or within the mixed region (containing type I, IIA, IIX, and IIB fibers) of the muscle. The fast MUs of the distal compartment had greater territories that were located in the more superficial muscle part (containing only type IIX and IIB fibers) and in some cases spanned the entire area of the distal muscle compartment. 4. FR and FF MUs consisted of muscle fibers identified histochemically as type IIX and IIB, respectively. 5. Within each of the FR and FF MU populations, MUs that were located in the most proximal muscle compartment were more resistant to fatigue compared with the units located in the most distal compartment. 6. Cross-sectional fiber areas were smaller for the proximal FR and FF fibers, but specific force did not differ among units. Consequently, when account was taken of the innervation ratio, the proximal FR and FF units produced less force than distal units of the same type. Tetanic forces were 87 +/- 27 (SD) mN (proximal FR), 154 +/- 53 (SD) mN (distal FR), 142 +/- 25 (SD) mN (proximal FF), and 229 +/- 86 (SD) mN (distal FF). 7. The present findings suggest that with increasing demand placed on rat MG during in vivo locomotion, recruitment is likely to proceed from proximal to distal muscle parts within the FR and FF MU populations.

View Article
June 1996
38 Reads

Repeated force production and metabolites in two medial gastrocnemius muscle compartments of the rat

J Appl Physiol (1985). 1995 Dec;79(6):1855-61

Journal of Applied Physiology

The most proximal and distal motor nerve branches in the rat medial gastrocnemius innervate discrete muscle compartments dominated by fast-twitch oxidative and fast-twitch glycolytic fibers, respectively. The functional consequences of the difference in oxidative capacity between these compartments were investigated. Wistar rats were anesthetized with pentobarbital sodium (90 mg/kg ip). Changes in force of both compartments during 21 isometric contractions (train duration 200 ms, stimulation frequency 120 Hz, 3 s between contractions) were studied in situ with and without blood flow. Without blood flow, force and phosphocreatine declined to a greater extent in the proximal than the distal compartment compared with the run with intact flow. After the protocol without blood flow, when flow was restored, the time constants for force recovery (which were closely associated to the recovery of phosphocreatine) were 37 +/- 7 (SD) (proximal compartment) and 148 +/- 20 s (distal compartment). It was concluded that the proximal compartment had a four times higher oxidative capacity and, therefore, a superior ability for repeated force production.

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December 1995
39 Reads

Non-linear relationship between O2 uptake and power output at high intensities of exercise in humans

J Physiol. 1995 Oct 1;488 ( Pt 1):211-7

Journal of Physiology

1. A slow component to pulmonary oxygen uptake (VO2) is reported during prolonged high power exercise performed at constant power output at, or above, approximately 60% of the maximal oxygen uptake. The magnitude of the slow component is reported to be associated with the intensity of exercise and to be largely accounted for by an increased VO2 across the exercising legs. 2. On the assumption that the control mechanism responsible for the increased VO2 is intensity dependent we hypothesized that it should also be apparent in multi-stage incremental exercise tests with the result that the VO2-power output relationship would be curvilinear. 3. We further hypothesized that the change in the VO2-power output relationship could be related to the hierarchical recruitment of different muscle fibre types with a lower mechanical efficiency. 4. Six subjects each performed five incremental exercise tests, at pedalling rates of 40, 60, 80, 100 and 120 rev min-1, over which range we expected to vary the proportional contribution of different fibre types to the power output. Pulmonary VO2 was determined continuously and arterialized capillary blood was sampled and analysed for blood lactate concentration ([lactate]b). 5. Below the level at which a sustained increase in [lactate]b was observed pulmonary VO2 showed a linear relationship with power output; at high power outputs, however, there was an additional increase in VO2 above that expected from the extrapolation of that linear relationship, leading to a positive curvilinear VO2-power output relationship. 6. No systematic effect on the magnitude or onset of the 'extra' VO2 was found in relation to pedalling rate, which suggests that it is not related to the pattern of motor unit recruitment in any simple way.

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October 1995
27 Reads

The mATPase histochemical profile of rat type IIX fibres: correlation with myosin heavy chain immunolabelling

Histochem J. 1995 Sep;27(9):715-22

Journal of Histochemistry

In the present study we report a novel histochemical method which, by sequential pre-incubations in alkaline and acidic media, selectively differentiates muscle fibres expressing myosin heavy chain IIX, on the basis of a specific profile for myofibrillar actomyosin ATPase (mATPase) activity. The enzyme reactions were tested for specificity by means of anti-myosin heavy chain monoclonal antibodies, which were characterized on Western blots of muscle homogenates. Enzyme histochemical reactions with the traditional pH buffers were compared to those of the new method and, in conjunction with the immunoreactions, used to confirm the relationship between MyHC expression and the distinct profiles for mATPase. Immunohistochemical reactions demonstrated that the new method only differentiates those fibres expressing myosin heavy chain IIX. The method revealed a continuum in which the intermediate staining intensities corresponded to hybrid fibres expressing myosin heavy chain IIX in combination with either the IIA or IIB forms. Quantitative histochemistry and immunohistochemistry (by image analysis), used to examine the relationship between staining intensities for mATPase and amounts of myosin heavy chain IIX expression, revealed that the new method discriminates well between hybrid fibres expressing variable amounts of the IIX isoform (r2 = 0.93)

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September 1995
31 Reads

Air friction and rolling resistance during cycling

Med Sci Sports Exerc. 1995 Jul;27(7):1090-5

Medicine and Science in Sports and Exercise

To calculate the power output during actual cycling, the air friction force Fa and rolling resistance Fr have to be known. Instead of wind tunnel experiments or towing experiments at steady speed, in this study these friction forces were measured by coasting down experiments. Towing experiments at constant acceleration (increasing velocity) were also done for comparison. From the equation of motion, the velocity-time curve v(t) was obtained. Curve-fitting procedures on experimental data of the velocity v yielded values of the rolling resistance force Fr and of the air friction coefficient k = Fa/v2. For the coasting down experiments, the group mean values per body mass m (N = 7) were km = k/m = (2.15 +/- 0.32) x 10(-3)m-1 and ar = Fr/m = (3.76 +/- 0.18) x 10(-2)ms-2, close to other values from the literature. The curves in the phase plane (velocity vs acceleration) and the small residual sum of squares indicated the validity of the theory. The towing experiments were not congruent with the coasting down experiments. Higher values of the air friction were found, probably due to turbulence of the air.

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July 1995
46 Reads

Fatigue and recovery of voluntary and electrically elicited dynamic force in humans

J Physiol. 1995 Apr 1;484 ( Pt 1):227-235

Journal of Physiology

1. Percutaneous electrical stimulation of the human quadriceps muscle has been used to assess the loss of central activation immediately after a bout of fatiguing exercise and during the recovery period. 2. Fatigue was induced in eight healthy males by a maximal effort lasting 25 s performed on an isokinetic cycle ergometer at a constant pedal frequency of 60 revolutions per minute. The cranks of the ergometer were driven by an electric motor. Before and after the sprint, subjects allowed their legs to be passively taken round by the motor. During the passive movement the knee extensors were stimulated (4 pulses; 100 Hz). Peak voluntary force (PVF) during the sprint and peak stimulated forces (PSF) before and in recovery were recorded via strain gauges in the pedals. Recovery of voluntary force was assessed in a series of separate experiments in which subjects performed a second maximal effort after recovery periods of different durations. 3. Peak stimulated forces were reduced to 69f8 + 9 3 % immediately after the maximal effort, (P< 0 05), but had returned to pre-exercise values after 3 min. The maximum rate of force development (MRFD) was also reduced following fatigue to 68f8 + 11 0% (P < 0'05) of control and was fully recovered after 2 min. PVF was reduced to 72-0 + 9 4% (P< 0 05) of the control value following the maximal effort. After 3 min voluntary force had fully recovered. 4. The effect of changing the duration of the fatiguing exercise (10, 25 and 45 s maximal effort) resulted in an increased degree of voluntary force loss as the duration of the maximal effort increased. This was associated with an increased reduction in PSF measured immediately after the exercise. 5. The close association between the changes in stimulated force and voluntary force suggests that the fatigue in this type of dynamic exercise may be due to changes in the muscle itself and not to failure of central drive.

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April 1995
33 Reads

Physiological characteristics of two extreme muscle compartments in gastrocnemius medialis of the anaesthetized rat

Acta Physiol Scand. 1995 Apr;153(4):313-24

Acta Physiologica Scandavica

Rat medial gastrocnemius (GM) muscle is a compartmentalized muscle. The functional properties and fibre type composition of the most proximal and most distal compartment were studied in in situ preparations. The proximal compartment contained predominantly fast twitch oxidative fibres. The distal compartment was mainly composed of fast twitch glycolytic fibres. With the use of two small electrodes placed around the primary nerve branches, both compartments could be separately stimulated within the same muscle. The length-force relationship was less broad and maximal twitch and tetanic forces were obtained at lower muscle lengths for the proximal compartment. The differences (mm) were 0.9 +/- 0.2 and 1.2 +/- 0.2 for maximal twitch and tetanic force (120 Hz) production, respectively (P < 0.001). The shortening velocity for maximal power production was lower (P < 0.001) for the proximal compartment (proximal: 57.1 +/- 2.7 mm s-1, distal: 73.1 +/- 3.0 mm s-1). During a standard fatigue test the fatiguability was significantly lower for the proximal compared with the distal fibres. Our findings suggest that the proximal compartment is likely to be activated in vivo during activities requiring relatively low power outputs for longer time periods. In contrast the distal compartment is probably recruited only during high power demanding short lasting activities. The presented model makes it possible to study fatigue related changes in power production of the 'red' and 'white' areas of the GM separately in a way that is probably meaningful with respect to in vivo function.

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April 1995
44 Reads

Diaphragmatic breathing reduces efficiency of breathing in patients with chronic obstructive pulmonary disease

Am J Respir Crit Care Med. 1995 Apr;151(4):1136-42

American Journal of Respiratory and Critical Care Medicine

The effects of diaphragmatic breathing learning on chest wall motion, mechanical efficiency of the respiratory muscles, breathing pattern, and dyspnea sensation were studied in seven patients with severe chronic obstructive pulmonary disease (COPD) (FEV1 34 +/- 7% of the predicted value) during loaded and unloaded breathing. Chest wall motion was studied focusing on amplitude and phase relation of rib cage and abdominal motion. Mechanical efficiency was defined as the ratio of added external power output and added oxygen consumption during inspiratory threshold loading (40% maximal inspiratory pressure [Plmax]). After 2 wk run-in, all subjects participated in a diaphragmatic breathing program for 3 wk. Variables obtained during diaphragmatic breathing were compared with those obtained during natural breathing. During diaphragmatic breathing the ratio of rib cage to abdominal motion decreased significantly during unloaded (0.86 versus 0.37; p < 0.01) as well as during loaded breathing (0.97 versus 0.50; p < 0.01). Chest wall motion became more asynchronous during diaphragmatic breathing in the unloaded conditions (mean phase difference for natural breathing 3.5 versus 10.4% for diaphragmatic breathing; p < 0.02) and loaded conditions (mean phase difference for natural breathing 6 versus 11.4% for diaphragmatic breathing; p < 0.02). Surprisingly, mechanical efficiency decreased significantly during diaphragmatic breathing (2.57 +/- 0.76%) in comparison with natural breathing (3.35 +/- 1.48%; p < 0.01). Tidal volume, respiratory frequency, and duty cycle did not change significantly during diaphragmatic breathing. Dyspnea sensation tended to increase during diaphragmatic breathing.

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April 1995
36 Reads

New method for the accurate characterization of single human skeletal muscle fibres demonstrates a relation between mATPase and MyHC expression in pure and hybrid fibre types

J Muscle Res Cell Motil. 1995 Feb;16(1):21-34

Journal of Muscle Research and Cell Motility

In the present study we have developed a method which, by combining histochemical, immunohistochemical, electrophoretic and immunoblotting analyses on a single fibre, enables a sensitive characterization of human skeletal muscle fibres dissected from freeze-dried biopsy samples. For histochemical (and immunohistochemical) analysis fibre fragments (500 microns) of individual fibres were mounted in an embedding medium to allow cryostat sections of normalized thickness to be reproducibly obtained. The specificity of the myofibrillar Ca2+ ATPase (mATPase) staining profiles in gelatin-embedded single fibre sections was tested by immunohistochemical reactions with anti-myosin heavy chain (MyHC) monoclonal antibodies specific to human MyHC I, IIA, IIB and IIA + IIB and by gel electrophoresis. The combined methodologies demonstrated the specificity of the mATPase staining patterns which correlated to the expression of distinct MyHC isoforms. In addition the results provide evidence that many fibres co-expressed different MyHC isoforms in variable relative amounts, forming a continuum. Staining intensities for mATPase, converted into optical density values by image analysis revealed that a relationship between mATPase and MyHC expression holds for hybrid fibres even when displaying one MyHC type with overwhelming dominance. The results also revealed that three MyHC isoforms I, IIA and IIB can be co-expressed on a single muscle fibre. In such a case mATPase alone, with the current protocols, does not allow an accurate characterization of the specific MyHC-based fibre type(s). Although some hybrid fibres may have displayed a non-uniform expression of myosins along their lengths, most fibres from the IIA/B group (type) remained very stable with respect to the relative amounts of the MyHCs expressed. Finally, a second slow MyHC isoform was recognized on immunoblots of a mixed muscle sample.

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February 1995
71 Reads

Characterization of human skeletal muscle fibres according to the myosin heavy chains they express

J Muscle Res Cell Motil. 1995 Feb;16(1):35-43

Journal of Muscle Research and Cell Motility

Using a method of single muscle fibre analysis, we investigated the presence of RNA transcripts for various isoforms of the myosin heavy chain (MyoHC) gene in histochemically, immunohistochemically and electrophoretically characterized individual muscle fibres (n = 65) from adult human vastus lateralis muscle. A cDNA clone isolated in this study was shown to contain the 3' end of a previously uncharacterized human MyoHC gene which is expressed specifically in human fast IIA muscle fibres and we conclude that this clone contains part of the human fast IIA MyoHC gene. In all the fibres histochemically, immunohistochemically and electrophoretically characterized as containing the previously classified IIB MyoHC (n = 23), it was shown that the human equivalent to the rat type IIX MyoHC gene is expressed. This observation was taken to suggest that the previously classified IIB muscles fibres in human muscle express a MyoHC isoform equivalent to the rat IIX, not the IIB, and would therefore be more accurately classified as IIX fibres.

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February 1995
49 Reads

The significance of motor unit variability in sustaining mechanical output of muscle

Adv Exp Med Biol. 1995;384:323-38

Advances in Experimental Medicine and Biology

Neuromuscular function and fatigue have been studied using a wide variety of preparations. These range from sections of single fibers from which the cell membrane has been removed to whole muscles or groups of muscles acting about a joint in the intact animal. Each type of preparation has its merits and limitations. There is no ideal preparation; rather the question to be answered will determine the most appropriate model in each case and sometimes a combination of approaches will be needed. In particular, it is important to understand how the mechanical output of whole muscle can be sustained to meet the demands of a task and to take into account the organized variability of the constituent motor units.

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January 1995
83 Reads

Relationships between energy expenditure and positive and negative mechanical work in repetitive lifting and lowering

J Appl Physiol (1985). 1994 Jul;77(1):420-426

Journal of Applied Physiology

Determining the separate energy costs of the positive and negative mechanical work in repetitive lifting or lowering is quite complex, as a mixture of both work components will always be involved in the up- and downward motion of the lifter's body mass. In the current study, a new method was tested in which coefficients specifically related to the positive and negative work were estimated by multiple regression on a data set of weight-lifting and weight-lowering tasks. The energy cost was obtained from oxygen uptake measurements. The slopes of the regression lines for energy cost and mechanical work were steeper for positive than for negative work. The cost related to the negative work was approximately 0.3-0.5 times the cost of the positive work. This finding is well in line with data obtained directly from other isolated activities of either positive or negative work (e.g., ladder climbing vs. descending). However, the intercept values of the regression lines were not significantly different from zero or were even negative. This was most likely due to the metabolic energy not related to processes that yield mechanical work (e.g., isometric muscle actions) that was not constant among trials.

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July 1994
27 Reads

Effect of growth on efficiency and fatigue in extensor digitorum longus muscle of the rat

Eur J Appl Physiol Occup Physiol. 1994;69(5):429-434

European Journal of Applied Physiology

The effect of growth on work output, energy consumption and efficiency during repetitive dynamic contractions was determined using extensor digitorum longus muscles of 40-, 60-, 120- and 700-day-old male Wistar rats. When work output of each contraction was normalized to the work output of the first contraction it was found that work output initially increased over the first 10-20 contractions by approximately 8% in each age group. Thereafter a faster decrease in work output was found in the youngest group (approximately 2% each contraction) compared to the older groups (approximately 0.7% each contraction). After 40 contractions the reduction in work output was significantly different only between the youngest group and the two oldest groups (-30% vs -5%). These differences in fatigue were not associated with differences in adenosine 5'-triphosphate and phosphocreatine concentrations or in lactate production. Total work output and high-energy phosphate consumption increased by approximately 555% and 380% from age 40 to 120 days, respectively. Consequently, efficiency was significantly higher (approximately 32%) in the older groups compared to 40-day-old animals. Normalized for muscle mass, mean rate of high-energy phosphate consumption was similar in all groups whereas mean power output was significantly lower in the youngest group (approximately 46%). Thus, the difference in efficiency between the young and the other groups may be attributed to a lower external power production in the youngest group rather than changes in energy turnover

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May 1994
53 Reads

Human power output and muscle fatigue

Int J Sports Med. 1994 Apr;15(3):116-121

International Journal of Sports Medicine

In human locomotion the ability to generate and sustain power output is of fundamental importance. This review examines the implications for power output of having variability in the metabolic and contractile properties within the population of muscle fibres which comprise the major locomotory muscles. Reference is made to studies using an isokinetic cycle ergometer by which the global power/velocity relationship for the leg extensor muscles can be determined. The data from these studies are examined in the light of the force velocity characteristics of human type I and type II muscle fibres. The 'plasticity' of fibre properties is discussed with reference to the 'acute' changes elicited by exercise induced fatigue and changes in muscle temperature and 'chronic' changes occurring following intensive training and ageing.

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April 1994
30 Reads

Measurement of directional force and power during human submaximal and maximal isokinetic exercise

Eur J Appl Physiol Occup Physiol. 1994;68(2):177-81

European Journal of Applied Physiology

An isokinetic cycle ergometer has been developed to measure power output generated over a wide range of constant velocities. The ergometer system has two operating modes and it can be instantly switched from one to another. In its conventional mode the cycle ergometer is connected to a conventional electrically braked cycle ergometer so that the subjects can perform submaximal steady-state exercise. For maximal power measurements the system can be instantly switched to an isokinetic control mechanism which allows a constant pedalling rate to be set in the range of 23-180 rev.min-1. In both operating modes the forces generated on the pedals are monitored by strain-gauges mounted inside the pedals. This enables information to be obtained regarding the direction of forces generated at the foot-pedal interface. The output from the strain-gauges was A-D converted and stored along with data giving pedal and crank position. Data was sampled 150 times in each revolution of the crank. Force data are usually analysed for maximal peak power (highest instantaneous power generated during each revolution), mean power (power generated over a complete revolution), extension and flexion power (power generated during leg extension and leg flexion respectively). This system allows characterisation of the relationship between maximal leg power and pedalling rate, both under control and exercise-induced potentiation and fatigue conditions. Thus it is possible for example to quantify instantly the magnitude of fatigue induced by preceding dynamic exercise of a given duration, intensity or contraction velocity.

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February 1994
31 Reads

Changes in acid-base status of marathon runners during an incremental field test. Relationship to mean competitive marathon velocity

Eur J Appl Physiol Occup Physiol. 1993;67(1):71-6

European Journal of Applied Physiology

Four top-class runners who regularly performed marathon and long-distance races participated in this study. They performed a graded field test on an artificial running track within a few weeks of a competitive marathon. The test consisted of five separate bouts of running. Each period lasted 6 min with an intervening 2-min rest bout during which arterialized capillary blood samples were taken. Blood was analysed for pH, partial pressure of oxygen and carbon dioxide (PO2 and PCO2) and lactate concentration ([la-]b). The values of base excess (BE) and bicarbonate concentration ([HCO3-]) were calculated. The exercise intensity during the test was regulated by the runners themselves. The subjects were asked to perform the first bout of running at a constant heart rate fc which was 50 beats.min-1 below their own maximal fc. Every subsequent bout, each of which lasted 6 min, was performed with an increment of 10 beats.min-1 as the target fc. Thus the last, the fifth run, was planned to be performed with fc amounting to 10 beats.min-1 less than their maximal fc. The results from these runners showed that the blood pH changed very little in the bouts performed at a running speed below 100% of mean marathon velocity (nu m). However, once nu m was exceeded, there were marked changes in acid-base status. In the bouts performed at a velocity above the nu m there was a marked increase in [la-]b and a significant decrease in pH, [HCO3-], BE and pCO2. The average marathon velocity (nu m) was 18.46 (SD 0.32) km.h-1.(ABSTRACT TRUNCATED AT 250 WORDS)

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July 1993
32 Reads

Age-related changes in force and efficiency in rat skeletal muscle

Acta Physiol Scand. 1993 Apr;147(4):347-55

Acta Physiologica Scandanavica

We investigated the effect of age on (the reduction of) work output, efficiency and muscle fibre type composition. Rat medial gastrocnemius muscles of three age-groups performed a series of 15 repeated contractions within 6 s (blood flow was arrested). Stimulation and shortening velocities were chosen as optimal for each group, while all muscles shortened over the same relative fibre lengths. The fibre type composition showed a higher proportion of the oxidative type IIBd fibres in the middle-aged group [5 months old; 39.8 +/- 6.8 vs. 23.6 +/- 4.2% of the fibre area in the young rats (1.3 months old)] in contrast to the type IIBm fibres (52.9 vs. 67.9%, respectively), while the old group (22 months old) was not different from the middle-aged group. Work output in the last contraction (relative to the first contraction) was not different between the age-groups (53.1 +/- 18.1; 48.0 +/- 6.5 and 61.1 +/- 6.2%, respectively). High-energy phosphate utilization was not different between the groups (150.6 +/- 11.2; 154.6 +/- 15.6 and 157.2 +/- 7.0 mumol g-1 dry wt, respectively). However, the efficiency was approximately 30% lower in the muscles of the youngest group, which corresponds with a lower specific power and specific tension. Since the change in fibre type composition is unlikely to be the cause of the low efficiency in the young animals, the causes remain unclear, but may be related to the rapid growth of the young rats in our study.

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April 1993
24 Reads

Effect of prior exercise at different pedalling frequencies on maximal power in humans

Eur J Appl Physiol Occup Physiol. 1993;66(2):102-107

European Journal of Applied Physiology

The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev.min-1, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake (VO2max), whether performed at a pedalling frequency of 60 or 120 rev.min-1, reduced maximal STPO generated at 120 rev.min-1 to a much greater extent than maximal STPO at 60 rev.min-1. After 6-min submaximal exercise at 60 rev.min-1 mean reductions in maximal STPO measured at 120 and 60 rev.min-1 were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev.min-1, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev.min-1. Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev.min-1. Nevertheless, maximal STPO generated at 120 rev.min-1 was reduced after exercise at 120 rev.min-1 [20 (SD 13)%, P < 0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

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February 1993
14 Reads

Changes in morphological and functional characteristics of male rat EDL muscle during growth

J Muscle Res Cell Motil. 1993 Feb;14(1):47-53

Journal of Muscle Research and Cell Motility

Morphological and functional changes as well as changes in fibre-type composition were investigated in the left extensor digitorum longus (EDL) muscles of male Wistar rats of approximately 40, 60, 120 and 700 days old. A number of morphological changes occurred in the EDL muscle during growth. While from 40 to 120 days muscle mass and cross-sectional area (CSA) increased by 247 and 192%, changes in muscle and fibre lengths were much smaller (44 and 17%, respectively). Besides morphological changes tetanic force was also found to increase (approximately 307%) up to 120 days. Because this increase in force was greater than the increase in CSA, specific force increased by approximately 29% between 40 and 60 days. Thereafter, specific force stayed rather constant. From 40 until 60 days changes were also found in the force-frequency and force-velocity curve, which indicate a slowing of the muscles (until 60 days). Changes in fibre-type composition of the EDL muscle were found to occur later during growth between 60 and 120 days. In this period an increase in the relative total area of Type IIBd fibres and a decrease in the relative total area of Type IIBm fibres (corresponding to the Type 2X and IIB fibres, respectively), were found; this was apparently due to a conversion of many Type IIBm into Type IIBd fibres and not to a difference in cross-sectional growth between these fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

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February 1993
17 Reads

Aerobic exercise in the adjunctive treatment of depression: a randomized controlled trial

J R Soc Med. 1992 Sep;85(9):541-4

Journal of The Royal Society of Medicine

Two clinical trials have been conducted in a sample of depressed patients to determine whether the addition of an aerobic exercise programme to their usual treatment improved outcome after 12 weeks. In the first trial, an aerobic exercise group had a superior outcome compared with a control group in terms of trait anxiety and a standard psychiatric interview. A second trial was then conducted to compare an aerobic exercise programme with low intensity exercise. Both groups showed improvement but there were no significant differences between the groups. In neither trial was there any correlation between the extent of change in the subjects' physical fitness due to aerobic exercise and the extent of the improvement of psychiatric scores.

View Article
September 1992
115 Reads

Growth-related change in specific force but not in specific power of rat fast skeletal muscle

Exp Physiol. 1992 May;77(3):505-508

Experimental Physiology

The effect of growth on the dynamic performance of rat medial gastrocnemius muscle was studied. From approximately 1.5 to 5 months of age specific force increased by 18%. Reductions were found in both optimal stimulation frequency (from 120 to 100 Hz) and optimal shortening velocity (by 16%) indicating that the fibres became slower. Specific power did not change during growth but was obtained at a lower shortening velocity. Possible mechanisms for the observed changes are discussed

View Article
May 1992
15 Reads

Effect of fatigue on maximal power output at different contraction velocities in humans

J Appl Physiol (1985). 1991 Dec;71(6):2332-7

Journal of Applied Physiology

The effect of fatigue as a result of a standard submaximal dynamic exercise on maximal short-term power output generated at different contraction velocities was studied in humans. Six subjects performed 25-s maximal efforts on an isokinetic cycle ergometer at five different pedaling rates (60, 75, 90, 105, and 120 rpm). Measurements of maximal power output were made under control conditions [after 6 min of cycling at 30% maximal O2 uptake (VO2max)] and after fatiguing exercise that consisted of 6 min of cycling at 90% VO2max with a pedaling rate of 90 rpm. Compared with control values, maximal peak power measured after fatiguing exercise was significantly reduced by 23 +/- 19, 28 +/- 11, and 25 +/- 11% at pedaling rates of 90, 105, and 120 rpm, respectively. Reductions in maximum peak power of 11 +/- 8 and 14 +/- 8% at 60 and 75 rpm, respectively, were not significant. The rate of decline in peak power during the 25-s control measurement was least at 60 rpm (5.1 +/- 2.3 W/s) and greatest at 120 rpm (26.3 +/- 13.9 W/s). After fatiguing exercise, the rate of decline in peak power at pedaling rates of 105 and 120 rpm decreased significantly from 21.5 +/- 9.0 and 26.3 +/- 13.9 W/s to 10.0 +/- 7.3 and 13.3 +/- 6.9 W/s, respectively. These experiments indicate that fatigue induced by submaximal dynamic exercise results in a velocity-dependent effect on muscle power. It is suggested that the reduced maximal power at the higher velocities was due to a selective effect of fatigue on the faster fatigue-sensitive fibers of the active muscle mass.

View Article
December 1991
18 Reads

Effect of lowered muscle temperature on the physiological response to exercise in men

Eur J Appl Physiol Occup Physiol. 1991;63(5):387-92

European Journal of Applied Physiology

The effect of low muscle temperature on the response to dynamic exercise was studied in six healthy men who performed 42 min of exercise on a cycle ergometer at an intensity of 70% of their maximal O2 uptake. Experiments were performed under control conditions, i.e. from rest at room temperature, and following 45 min standing with legs immersed in a water bath at 12 degrees C. The water bath reduced quadriceps muscle temperature (at 3 cm depth) from 36.4 (SD 0.5) degrees C to 30.5 (SD 1.7) degrees C. Following cooling, exercise heart rate was initially lower, the mean difference ranged from 13 (SD 4) beats.min-1 after 6 min of exercise, to 4 (SD 2) beats.min-1 after 24 min of exercise. Steady-state oxygen uptake was consistently higher (0.2 l.min-1). However, no difference could be discerned in the kinetics of oxygen uptake at the onset of exercise. During exercise after cooling a significantly higher peak value was found for the blood lactate concentration compared to that under control conditions. The peak values were both reached after approximately 9 min of exercise. After 42 min of exercise the blood lactate concentrations did not differ significantly, indicating a faster rate of removal during exercise after cooling. We interpreted these observations as reflecting a relatively higher level of muscle hypoxia at the onset of exercise as a consequence of a cold-induced vasoconstriction. The elevated steady-state oxygen uptake may in part have been accounted for by the energetic costs of removal of the extra lactate released into the blood consequent upon initial tissue hypoxia

View Article
November 1991
27 Reads

Effect of shortening velocity on work output and energy cost during repeated contractions of the rat EDL muscle

Eur J Appl Physiol Occup Physiol. 1991;62(6):430-5

European Journal of Applied Physiology

The effect of shortening velocity on the reduction in work output, energy consumption and efficiency during repetitive contractions has been determined in rat extensor digitorum longus muscle. Muscles in situ (with occluded blood flow, 37 degrees C) were stimulated to perform 40 successive contractions (at 4 Hz) with a total duration of the exercise period of 10 s and shortening velocities of either 25, 50 or 75 mm.s-1 (whole muscle-tendon complex). Care was taken that work output during the shortening phase of the first contraction was the same for the different velocities used. Total work output of the 40 contractions was not significantly different between the three groups with different shortening velocities; nor was there a significant difference in the high-energy phosphate consumption over this 10-s exercise period. However, when the ratio of total work output and total energy consumption was calculated a significantly higher efficiency (25-30% in comparison with the efficiency of the other two velocities) was found with the shortening velocity of 50 mm.s-1. There was no significant difference in efficiency between shortening velocities of 25 and 75 mm.s-1. This suggests that with this protocol efficiency showed a velocity-dependent pattern that may have the same shape as the power/velocity curve. Whereas total work output during the 10-s exercise period was not significantly different between the velocities studied, the time course of the changes in work output was quite different. With shortening velocities of 50 and 75 mm.s-1 work output initially increased by maximally 6% and 12% respectively in contrast to a steady level in the contractions with a velocity of 25 mm.s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

View Article
June 1991
19 Reads

Influence of an active pre-stretch on fatigue of skeletal muscle

Eur J Appl Physiol Occup Physiol. 1991;62(4):268-273

European Journal of Applied Physiology

In activities such as running, many muscles of the lower extremities appear to be actively stretched before they are allowed to shorten. In this study we investigated the effect of an active pre-stretch on the fatigability of muscles. Thus muscle contractions were compared in which shortening was preceded by an active isometric phase or by an active stretch. Rat medial gastrocnemius muscle-tendon complexes (with arrested blood flow) performed a series of ten repeated contractions (1.s-1) with either an active stretch or an isometric phase preceding the shortening. Contraction duration (0.45 s), and shortening duration (0.3 s), distance (6 mm) and velocity (20 mm.s-1) were the same in both types of contraction. Work output during the ten shortening phases was approximately 40% higher in the contractions with an active pre-stretch; in contrast, high-energy phosphate utilization was similar. Over the ten repeated contractions reduction of work output during the shortening phases of both types of contraction was similar in absolute terms (approx. 9.5 mJ). It is suggested that all the extra work performed during the shortening phases after a pre-stretch originated from sources other than cross-bridge cycling, which are hardly affected by fatigue. However, reduction of work output in relative terms, which is how the reduction is often expressed in voluntary exercise, was less after a pre-stretch (26% vs 32%), giving the impression of protection against fatigue by an active pre-stretch.

View Article
April 1991
15 Reads

Seat height in handrim wheelchair propulsion

J Rehabil Res Dev. 1989 Fall;26(4):31-50

Journal of Rehabilitation Research and Development

To study the effect of seat height on the cardiorespiratory system and kinematics in handrim wheelchair ambulation, nine non-wheelchair users participated in a wheelchair exercise experiment on a motor-driven treadmill. The subjects conducted five progressive exercise tests. After an initial try-out test, four tests were performed at different standardized seat heights of 100, 120, 140, and 160 degrees elbow extension (subject sitting erect, hands on the rim in top-dead-center = 12.00 hrs; full extension = 180 degrees). Each test consisted of four 3-minute exercise blocks at speeds of respectively 0.55, 0.83, 1.11, and 1.39 m.s-1 (2-5 km.hr-1). Analysis of variance revealed significant effects of seat height (P less than 0.05) on gross mechanical efficiency (ME), oxygen cost, push range, and push duration, and on the ranges of motion in the different arm segments and trunk. Mean ME appeared higher at the lower seat heights of 100 and 120 degrees elbow extension. This is reflected in an enhanced oxygen consumption at seat heights of 140 and 160 degrees elbow extension. Simultaneously, the push range showed a 15 to 20 degree decrease with increasing seat height, which is reflected in a decreased push duration. In the push phase, decreases in retroflexion and abduction/adduction of the upper arm were seen. The trunk shifted further forward, and the motion range in the elbow joint shifted to extension with increasing seat height. No shifts in minimum and maximum angular velocities were seen with increasing seat height. The results showed an interrelationship between wheelchair seat height and both cardiorespiratory and kinematic parameters. With respect to the cardiorespiratory system, the optimization of the wheelchair geometry, based on functional characteristics of the user, appears beneficial.

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September 1989
23 Reads

Age-related effects of fatigue and recovery from fatigue in rat medial gastrocnemius muscle

Q J Exp Physiol. 1989 Sep;74(5):715-26

Quarterley Journal of Experimental Physiology

Force-velocity, power-velocity and unloaded shortening data were obtained from in situ medial gastrocnemius muscle-tendon complexes (stimulated at 60 Hz) with intact circulation of mature male rats (approximately 125 days old). Measurements were carried out at the end of a long (15 s) contraction (fatigued muscles) or with a short (1 s) contraction either in the fresh state (fresh muscles) or in muscles which had recovered for 15 min after a long contraction. Compared to the fresh state fatigue reduced isometric force by 57%, maximal shortening velocity by approximately 40% and maximal power output by 81%. These reductions were similar to data previously obtained with younger rats (40 days old). However, the velocity data of the muscles which had recovered for 15 min after a long contraction showed a greater reduction in the mature rats. This difference between the two age groups together with a difference in the changes in the initial parts of the isometric force time curves suggest an age-dependent response of the fast-fatigable fibre population of these mixed muscles. In a separate series of experiments the underlying mechanism of the recovery from fatigue was studied in a group of young rats. Fatigue was induced with five long (15 s) contractions (each at 5 min intervals). The recovery of isometric force and power output was monitored with short contractions which indicated a plateau of recovery but the absolute values were still reduced after 60 min (85 and 71% of prefatigue values, respectively). Phosphocreatine concentration recovered rapidly, whereas the ATP concentration was still markedly reduced after 1 h of recovery. The time courses of recovery of inosine-5'-monophosphate (IMP) and lactate concentrations resembled those of force and power output. Thus it is possible that age-dependent differences in IMP and/or lactate production may play a role in fatigue and recovery from fatigue.

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September 1989
13 Reads

Optimum cycle frequencies in hand-rim wheelchair propulsion. Wheelchair propulsion technique

Eur J Appl Physiol Occup Physiol. 1989;58(6):625-32

European Journal of Applied Physiology

To study the effect of different cycle frequencies on cardio-respiratory responses and propulsion technique in hand-rim wheelchair propulsion, experienced wheelchair sportsmen (WS group; n = 6) and non-wheelchair users (NW group; n = 6) performed wheelchair exercise tests on a motor-driven treadmill. The WS group wheeled at velocities of 0.55, 0.83, 1.11 and 1.39 m.s-1 and a slope of 2 degrees. The NW group wheeled at 0.83, 1.11 and 1.39 m.s-1 and a 1 degree slope. In each test, a 3-min period at a freely chosen cycle frequency (FCF: 100%) was followed by four 3-min blocks of paced cycle frequencies at 60%, 80%, 120% and 140% FCF. Effects of both cycle frequency and velocity on physiological and propulsion technique parameters were studied. Analysis of variance showed a significant effect (p less than 0.05) of cycle frequency on oxygen cost and gross mechanical efficiency in both the WS and NW group. This indicated the existence of an optimum cycle frequency which is close to the FCF at any given velocity. The optimum cycle frequency increased with velocity from 0.67 to 1.03 cps over the range studied (p less than 0.05). Oxygen cost was approximately 10% less at 100% FCF than at 60% or 140% FCF. Gross mechanical efficiency for the WS group at 100% FCF was 8.5%, 9.7%, 10.4% and 10.1%, respectively, at the four velocities.(ABSTRACT TRUNCATED AT 250 WORDS)

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June 1989
17 Reads

Changes in velocity of shortening, power output and relaxation rate during fatigue of rat medial gastrocnemius muscle

Pflugers Arch. 1989 Feb;413(4):422-8

Pflugers Archiv

The force-velocity characteristics of rat medial gastrocnemius muscle have been determined by measuring the force sustained during constant velocity releases of the muscle stimulated in situ at an ambient temperature of 26 degrees C. The velocity of unloaded shortening was determined using the "slack" test and rate of relaxation from the half time of force loss at the end of stimulation. Measurements were first made on fresh muscles using short contractions and then during a series which consisted of a 15 s contraction (fatigued muscle), followed by 15 min recovery and a 1 s contraction (recovered muscle). After a 5 min recovery period the sequence was repeated. Comparison was made between the fatigued and recovered state in each preparation in order to allow for any change in the preparation during the course of the experiment. After 15 s contraction the fatigued muscles showed a marked reduction in all parameters measured. In fatigued muscles the isometric force fell to 48 +/- 15% (mean +/- SD) and there was a decrease in maximum velocity of shortening to 66%. These changes in the force-velocity relationship were accompanied by slowing of relaxation so that the half time of relaxation nearly doubled. The consequence of these changes was that the maximum power output was reduced by a much greater extent than was the isometric force (75% vs. 52%). It is suggested that the changes in force-velocity characteristics reflect a reduction in cross-bridge cycling in fatigued muscle.

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February 1989
17 Reads

Propelling efficiency of front-crawl swimming

J Appl Physiol (1985). 1988 Dec;65(6):2506-12

Journal of Applied Physiology

In this study the propelling efficiency (ep) of front-crawl swimming, by use of the arms only, was calculated in four subjects. This is the ratio of the power used to overcome drag (Pd) to the total mechanical power (Po) produced including power wasted in changing the kinetic energy of masses of water (Pk). By the use of an extended version of the system to measure active drag (MAD system), Pd was measured directly. Simultaneous measurement of O2 uptake (VO2) enabled the establishment of the relationship between the rate of the energy expenditure (PVO2) and Po (since when swimming on the MAD system Po = Pd). These individual relationships describing the mechanical efficiency (8-12%) were then used to estimate Po in free swimming from measurements of VO2. Because Pd was directly measured at each velocity studied by use of the MAD system, ep could be calculated according to the equation ep = Pd/(Pd + Pk) = Pd/Po. For the four top class swimmers studied, ep was found to range from 46 to 77%. Total efficiency, defined as the product of mechanical and propelling efficiency, ranged from 5 to 8%.

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December 1988
24 Reads

Age-related changes in power output during repetitive contractions of rat medial gastrocnemius muscle

Pflugers Arch. 1988 Oct;412(6):665-7

Pflugers Archiv

Changes in isometric force, power output and relaxation rate have been measured during repetitive tetanic contractions in 2 groups of rats of different ages. During the first 5 contractions there were no differences between a young and mature group. In contrast to isometric force production, which decreased about 3% per contraction, power output initially increased to 108% of the power output in the first contraction. A greater reduction in power output and relaxation rate after the 5th contraction indicated a greater reduction of the cross-bridge cycling rate in the younger rats. ATP, phosphocreatine and lactate concentrations after the last contraction were not different between the age-groups. In contrast IMP production, which has been suggested may play a regulatory role during fatigue was twice as high in the young rats. Judged by isometric force production there is no age-related difference in fatiguability. However, profound differences were observed in power output, which indicates that quantification of fatigue as a loss of isometric force may be seriously misleading when considering the functional status of the muscle for normal dynamic contractions.

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October 1988
17 Reads

Influence of muscle dimensions on economy of isometric exercise in rat medial gastrocnemius muscles in situ

Eur J Appl Physiol Occup Physiol. 1988;57(1):64-9

European Journal of applied Physiology

The effect of muscle dimensions on economy (force-time integral divided by the amount of energy utilized) was investigated in male rats (body mass range 95-490 g), anaesthetized with pentobarbital. The medial gastrocnemius muscle in situ performed 6 maximal isometric contractions of 350 ms duration (1.s-1) at twitch optimum length at 35 degrees C. The areas under the 6 time-force curves were added to obtain force-time integral of the experiment. Differences of concentrations of ATP, phosphocreatine and lactate between experimental and contralateral (resting) muscles were used to calculate high-energy phosphate consumption due to stimulation. Muscle mass and cross-sectional area increased (approximately +400% and +300%, respectively) over the rat body mass range studied. Muscle length and length of the most distal fibre bundle increased by approximately 17 mm and 4 mm, respectively. Force-time integral (N.s) increased proportional to cross-sectional area whereas high-energy phosphate consumption (mumoles) increased proportional to muscle mass. The relative fraction of the total energy consumption utilized for force-independent processes was independent of rat body mass. The economy of the actomyosin system was unaffected during growth, whereas economy of the whole muscle decreased during growth by approximately 30% (p less than 0.001). The effect of muscle dimensions on economy is discussed with respect to human endurance capacity measured by voluntary isometric contractions.

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July 1988
20 Reads

Applied physiology of speed skating

J Sports Sci. 1987 Winter;5(3):249-59

Journal of Sports Science

Speed skating exercise can be better understood by taking account of physiological and biomechanical considerations. Comparison with other sports shows the unique and peculiar way of skating propulsion. The relatively long lasting isometric muscle contractions during the gliding phase, alternated with high power output push-offs, place unusual demands on the (local) energy delivering systems. The short and explosive push-off needs a specific pattern of motor unit recruitment. Some mixture of slow twitch (to sustain skating posture) and fast twitch fibres (to effect push off) in the hip and knee extensors seems necessary for optimal skating performance.

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December 1987
24 Reads

Effect of prior exercise on maximal short-term power output in humans

J Appl Physiol (1985). 1987 Oct;63(4):1475-80

Journal of Applied Physiology

The effect of prior exercise (PE) on subsequent maximal short-term power output (STPO) was examined during cycling exercise on an isokinetic ergometer. In the first series of experiments the duration of PE at a power output equivalent to 98% maximum O2 uptake (VO2max) was varied between 0.5 and 6 min before measurement of maximal STPO. As PE duration increased subsequent STPO fell to approximately 70% of control values after 3-6 min. In series ii the effect of varying the intensity of PE of fixed 6-min duration was studied in five subjects. After PE less than 60% VO2max there was an increase of 12% in STPO, but after greater than 60% VO2max there was a progressive fall in STPO as PE intensity increased, indicating a reduction of approximately 35% at 100% VO2max compared with control values. In series iii we examined the effect on STPO of allowing a recovery period after a fixed intensity (mean = 87% VO2max) of 6 min PE before measurement of STPO. This indicated a rapid recovery of dynamic function with a half time of approximately 32 s, which is similar to the kinetics of PC resynthesis and taken with the other findings suggests the dominant role that PC exerts on the STPO under these conditions.

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October 1987
19 Reads

Effect of muscle temperature on leg extension force and short-term power output in humans

Eur J Appl Physiol Occup Physiol. 1987;56(6):693-8

European Journal of Applied Physiology

The effect of changing muscle temperature on performance of short term dynamic exercise in man was studied. Four subjects performed 20 s maximal sprint efforts at a constant pedalling rate of 95 crank rev.min-1 on an isokinetic cycle ergometer under four temperature conditions: from rest at room temperature; and following 45 min of leg immersion in water baths at 44; 18; and 12 degrees C. Muscle temperature (Tm) at 3 cm depth was respectively 36.6, 39.3, 31.9 and 29.0 degrees C. After warming the legs in a 44 degrees C water bath there was an increase of approximately 11% in maximal peak force and power (PPmax) compared with normal rest while cooling the legs in 18 and 12 degrees C water baths resulted in reductions of approximately 12% and 21% respectively. Associated with an increased maximal peak power at higher Tm was an increased rate of fatigue. Two subjects performed isokinetic cycling at three different pedalling rates (54, 95 and 140 rev.min-1) demonstrating that the magnitude of the temperature effect was velocity dependent: At the slowest pedalling rate the effect of warming the muscle was to increase PPmax by approximately 2% per degree C but at the highest speed this increased to approximately 10% per degree C.

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June 1987
28 Reads

Human muscle function following prolonged eccentric exercise

Eur J Appl Physiol Occup Physiol. 1987;56(6):704-11

European Journal of Applied Physiology

4 subjects performed repeated eccentric contractions with leg extensors during prolonged downhill walking (-25% gradient) at 6.44 km.h-1 until collapse due to muscle weakness (range of exercise duration 29 to 40 min). During the exercise oxygen uptake rose progressively from approximately 45% of the previously determined VO2max at 10 min to approximately 65% at the end of the exercise. Following the exercise there was an immediate, significant, and sustained reduction in maximal voluntary isometric contraction, and short term (anaerobic) power output measured concentrically on an isokinetic ergometer. These reductions in muscle function persisted for 96 hours post exercise, and were reflected by significant reductions in the tension generated at low frequency (20 Hz) relative to higher frequency (50 Hz) percutaneous stimulation of the quadriceps. All four subjects showed an increase in plasma levels of creatine kinase post eccentric exercise. Performing concentric contractions by walking uphill for one hour at a significantly greater metabolic cost failed to induce comparable reductions in muscle function. These results provide evidence for the consequences of prolonged eccentric work upon dynamic function which complements earlier reports of structural, enzymatic, and static function changes

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June 1987
43 Reads

The effect of oral supplementation with L-carnitine on maximum and submaximum exercise capacity

Eur J Appl Physiol Occup Physiol. 1987;56(4):457-60

European Journal of Applied Physiology

Two trials were conducted to investigate the effects of L-carnitine supplementation upon maximum and submaximum exercise capacity. Two groups of healthy, untrained subjects were studied in double-blind cross-over trails. Oral supplementation of 2 g per day L-carnitine was used for 2 weeks in the first trial and the same dose but for 4 weeks in the second trial. Maximum and submaximum exercise capacity were assessed during a continuous progressive cycle ergometer exercise test performed at 70 rpm. In trial 1, plasma concentrations of lactate and beta-hydroxybutyrate were measured pre- and post-exercise. In trial 2, pre- and post-exercise plasma lactate were measured. The results of treatment with L-carnitine demonstrated no significant changes in maximum oxygen uptake (VO2max) or in maximum heart rate. In trial 1, there was a small improvement in submaximal performance as evidenced by a decrease in the heart-rate response to a work-load requiring 50% of VO2max. The more extensive trial 2 did not reproduce the significant result obtained in trial 1, that is, there was no significant decrease in heart rate at any given submaximal exercise intensity, under carnitine-supplemented conditions. Plasma metabolic concentrations were unchanged following L-carnitine, in both trials. It is concluded, that in contrast to other reports, carnitine supplementation may be of little benefit to exercise performance since the observed effects were small and inconsistent.

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April 1987
22 Reads

Strength training and power output: Transference effects in the human quadriceps muscle

J Sports Sci. 1986 Autumn;4(2):101-7

Journal of Sports Sciences

The effects of strength training of the quadriceps on peak power output during isokinetic cycling has been investigated in group of 17 young healthy volunteers. Subjects trained by lifting near-maximal loads on a leg extension machine for 12 weeks. Measurements of maximal voluntary isometric force were made at 2-3 week intervals and a continual record was kept of the weights lifted in training. Peak power output was measured at 110 rev min-1 and at either 70 or 80 rev min-1 before and after the 12 week training period. Measurements of maximum oxygen uptake (VO2max) were made on 12 subjects before and after training. The greatest change was in the weights lifted in training which increased by 160-200%. This was accompanied by a much smaller increase in maximum isometric force (3-20%). There was no significant change in peak power output at either speed. The VO2max remained unchanged with training. The role of task specificity in training is discussed in relation to training regimes for power athletes and for rehabilitation of patients with muscle weakness.

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September 1986
26 Reads

A constant-velocity cycle ergometer for the study of dynamic muscle function

J Appl Physiol Respir Environ Exerc Physiol. 1983 Jul;55(1 Pt 1):212-7

Journal of Applied Physiology

A cycle ergometer has been designed to measure the force exerted on the pedal cranks during maximum effort at a variety of constant velocities. Preset crank velocities of 13-166 rpm are established by a controlled 3-hp motor and cannot be overcome by the subject. Torque is measured by strain gauges bonded to the crank shafts; peak torque, peak power, work, and average power are derived for each pedal cycle. Studies in 30 healthy male subjects established reproducibility and normal standards. During exercise for 45 s at a constant velocity of 60 rpm, there was a wide intersubject variation in both maximal torque (118-226 N . m) and the percentage decline in torque (27.2-52.0%). The decline in torque was inversely related to maximal O2 intake (r = 0.84). During short (10-s) periods of exercise at six crank velocities between 60-160 rpm, a linear inverse relationship between maximal peak torque and pedal crank velocity was observed. The peak torque-velocity relationship and the percentage decline in peak torque during 30 s exercise at 60, 100, and 140 rpm were reproducible within a given subject, the coefficient of variation was less than 10%

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July 1983
17 Reads

Maximum leg force and power output during short-term dynamic exercise

J Appl Physiol Respir Environ Exerc Physiol. 1981 Nov;51(5):1175-82

Journal of Applied Physiology

Force exerted and power generated were measured during short-term exercise performed on a bicycle ergometer that had been modified by the addition of an electric motor driving the cranks at a chosen constant velocity. Five subjects made a series of 20-s maximum efforts at different crank velocities (range 23--171 rev/min). The forces exerted were continuously monitored with strain gauges bonded to the cranks. Peak force was exerted at approximately 90 degrees past top dead center in each revolution. During the 20-s effort peak force declined from the maximum level (PFmax) attained near the start of exercise, the rate of decline being velocity dependent. PFmax was found to be inversely and linearly related to crank velocity and when standardized for upper leg muscle (plus bone) volume (ULV) was given by PFmax (kgf/l ULV) = 27.51--0.125 crank velocity (rev/min). Integration of the force records with pedal velocity enabled power output to be calculated. Maximum power output was a parabolic function of crank velocity, the apex of the relationship indicating that the velocity for greatest power output was 110 rev/min. At this velocity our subjects achieved a maximum mean power output, averaged over a complete revolution, of 840 +/- 153 W (85 +/- 5 W/l ULV). This was compared with the calculated value for maximum mechanical power output from aerobic sources, which was 272 +/- 49 W (30 +/- 1 W/l ULV).

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November 1981
63 Reads

Ventilation in exercise studied with circulatory occlusion

J Appl Physiol Respir Environ Exerc Physiol. 1981 Apr;50(4):718-23

Journal of Applied Physiology

Five male subjects exercised on a cycle ergometer (100 W) for 8 min; circulation to the legs was occluded by cuffs during the first 2 and last 2 min. Ventilation (VE), oxygen intake (VO2), and carbon dioxide output (VCO2) were measured breath by breath. Repeat studies were used to follow arterial PCO2 (PaCO2) and rebreathing mixed venous PCO2 (PVCO2). The results were compared to studies without cuffing, but which were otherwise identical. The initial period of cuffing was associated with marked hyperpnea, high VE/VCO2 ratio, and low PaCO2 and PVCO2. Following release of occlusion at the end of the first 2 min, there was an immediate fall in VE, followed by an increase after an average of 12 s. VE/VCO2 fell and end-tidal PCO2 rose after 4-5 s and reached control values after 12 s. Studies during rebreathing established that CO2 reached the lungs from the legs 4-5 s after release of occlusion, and control PVCO2 was reached after 12 s. Repeated occlusion for the final 2 min of exercise was associated with hyperpnea of similar degree to the initial occlusion. An identical study performed in a patient with absent ventilatory response to CO2 and reduced ventilatory response to exercise showed normal hyperventilatory response to cuffing but did not show an increase in ventilation associated with the arrival of CO2 in the lungs, following release of occlusion. The studies confirmed the importance of CO2 in mediating rapid changes in ventilation during exercise.

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April 1981
30 Reads

The effects of atropine and practolol on the perception of exertion during treadmill exercise.

Ergonomics. 1979 Oct;22(10):1141-6.

Ergonomics

Research into the physiological cues related to heart rate that might determine the perceived exertion in human exercise.

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October 1979
60 Reads

Physiologic responses to exercise in myocardial infarction patients following residential rehabilitation

Arch Phys Med Rehabil. 1979 Mar;60(3):121-5.

Archives of Physical Medicine and Rehabilitation

The physiological responses to exercise were studied in 16 men (33-52 years of age), 8--12 weeks after a first uncomplicated myocardial infarction and following a 3--4 week period of attendance at a residential rehabilitation center at which the patients were required to participate in a controlled program of exercise, sport and recreation. Data were also collected on an inactive, but otherwise healthy group of men of the same age and occupational status, and on an occupationally and recreationally active healthy group. The patient group were indistinguishable from the healthy inactive group in their response to submaximal exercise, although both of these groups showed differences when compared with the active group. Symptom-limited maximal data were also collected and these are reported in relation to the energy requirements of some common leisure, occupational and domestic activities.

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March 1979
18 Reads

Measurement of forces applied and work performed in pedalling a stationary bicycle ergometer

Ergonomics. 1978 Jan;21(1):49-53

Ergonomics

The early development of strain gauge technology applied to the cranks of a stationary cycle ergometer using phosphor bronze contacts and sliding ring design.Research initiated by Tony Sargeant but absolutely dependent on the brilliant engineering expertise of Alec Charters (instrument maker) and Ted Reeves (electrical engineer).

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January 1978
19 Reads

The effect of disuse muscular atrophy on the forces generated in dynamic exercise

Clin Sci Mol Med. 1977 Aug;53(2):183-8

Clinical Science and Molecular Medicine

1. Six patients were studied after prolonged immobilization of an injured leg resulting in muscle atrophy. 2. The forces exerted by the atrophied and normal legs during continuous dynamic exercise (one- and two-leg cycling) were examined by a specially adapted ergometer. 3. In one-leg cycling the peak force exerted on the crank at a given work rate, the net work rate performed on the crank, and the proportion of work rate performed in leg extension and flexion phases of the cycle were the same whether the atrophied or normal limb was used. 4. Despite these similarities there was an unexplained reduction in efficiency when using the atrophied leg to perform one-leg cycling. 5. In two-leg cycling the peak force exerted at a given work rate by the atrophied leg was reduced by about 40% as compared with the normal leg, which reflected a similar reduction in the contribution of that leg to the total net work rate. Possible reasons and implications for this disproportionate sharing of work between the normal and atrophied leg are discussed

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August 1977
22 Reads

Functional and structural changes after disuse of human muscle

Clin Sci Mol Med. 1977 Apr;52(4):337-42

Clinical Science and Molecular Medicine

1. Seven patients who had suffered unilateral leg fracture were studied after removal of immobilizing plaster casts. 2. Leg volume measured anthropometrically was reduced by 12% in the injured leg (5-68 +/- 1-05 litres) compared with the uninjured (6-43 +/- 0-87 litres). Associated with this loss was a similar reduction in the net maximum oxygen uptake achieved in one-leg cycling, from 1-89 +/- 0-21 1/min in the uninjured leg to 1-57 +/- 0-18 1/min in the injured. 3. Measured by a percutaneous needle biopsy technique, a reduction of 42% was found in the cross-sectional area of the muscle fibres sampled from the vastus lateralis of the injured compared with the uninjured leg. 4. Staining for myosin adenosine triphosphatase activity showed that both type I and II fibres were affected, being reduced respectively from 3410 to 1840 micronm2 and from 3810 to 2390 micronm2 cross-sectional area. 5. Possible reasons and implications are discussed for the discrepancy between the magnitude of the difference observed in the gross measurement of leg function (maximum oxygen uptake) and structure (leg volume) as compared with the cellular level (cross-sectional fibre area).

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April 1977
12 Reads

Forces applied to cranks of a bicycle ergometer during one- and two-leg cycling

J Appl Physiol Respir Environ Exerc Physiol. 1977 Apr;42(4):514-8

Journal of Applied Physiology

An examination was made of the comparability of one- and two-leg exercise performed pedaling a stationary bicycle ergometer. The pattern of force exerted on both cranks was examined by means of a specially adapted ergometer which is described. The mean of the peak force in each cycle (MPF) was linearly related to work load (W) in both forms of exercise, and if account was taken of the doubled work output in two-leg cycling there was no significant difference between the MPF/W relationships; these are given by the equations one-leg: MPF (kg) = 11.23 + 0.065 (W in kpm/min) two-leg MPF (kg) = 10.76 + 0.032 (W in kpm/min). Calculation from the force records of the work performed on the cranks (WCR net) showed good agreement (r = 0.98, P less than 0.001) with the work load set on the ergometer. Analysis of the proportion of work done in leg extension and flexion phases of cycling revealed no differences between one- and two-leg exercise or between the right and left legs. The majority (approximately 80%) of Wer net being performed in leg extension is described by: Wer net (extension)) = 10.6 +/- 0.8 (W cr net total). In one-leg exercise (W greater than 900 kpm/min) the variation in rotation speed during a normal cycle ranged from +20 to --30% of the mean speed compared with +/- 10% in two-leg exercise.

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April 1977
9 Reads

Limb volume, composition, and maximum aerobic power output in relation to habitual 'preference' in young male subjects

Ann Hum Biol. 1977 Jan;4(1):49-55

Annals of Human Biology

Anthropometric data are presented for the preferred and non-preferred limbs of normal subjects together with measurements of one-limb maximum aerobic power output (V O2 max). The habitually preferred arms and legs were significantly larger in total volume (LV) when compared with the contralateral limbs (5 per cent, P less than 0-01; and 2 per cent, P less than 0-01 respectively). These differences were mainly attributable to variation in the size of the muscle component. Expressed in absolute terms, V O2 max achieved in exercise with the preferred legs was significantly larger than the non-preferred legs (2-84 cf. 2-74 l/min; P less than 0-01) and a similar but non-significant difference was found between the arms (1-10 cf. 1-05 l/min). If, however, V O2 max is standardized for the size of the active muscle mass (LV, muscle plus bone) these differences between the preferred and non-preferred limbs disappear. The implications of these observations are discussed.

View Article
January 1977
16 Reads

Effects of exercise therapy on total and component tissue leg volumes of patients undergoing rehabilitation from lower limb injury

Ann Hum Biol. 1975 Oct;2(4):327-37

Annals of Human Biology

Anthropometric and X-ray data were collected on 20 young male patients undergoing a systematic programme of exercise therapy following fracture of the leg and consequent immobilization for 25--254 (mean 117) days. Estimates of total leg volume, calculated from X-ray or from anthropometric measurements, were essentially interchangeable in both the injured and uninjured legs. A procedure for estimating muscle volume from total leg volume is given. At the start of rehabilitation, muscle volume was significantly smaller (860 ml, 16 per cent) in the injured than in the uninjured leg. By the end of rehabilitation (mean 50 days) the injured leg had siginficantly increased by 360 ml (8 per cent) over its initial volume, and the uninjured one had increased but not significantly (120 ml, 2 per cent), so that the injured leg was still approximately 11 per cent (620 ml) small than the uninjured. The initial degree of atrophy and the period of immobilization were not significantly correlated, although the latter showed a negative relationship (P greater than 0.05) with the rate of increase of muscle volume in the injured leg. No significant correlation was found between the ratio of injured/uninjured leg volumes and muscle width measurements at 1/3 subischial, at 12.7 cm above the knee joint space or at the maximum calf. In systematic studies involving atrophy muscle volume must therefore be estimated either by anthropometry or by X-ray measurements.

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October 1975
10 Reads

Aerobic power prediction in patients recovering from limb injury

Arch Phys Med Rehabil. 1975 Aug;56(8):340-5

Archives of Physical Medicine and Rehabilitation

Procedures for the prediction of one-leg and two-leg maximal aerobic power output (VO2 max) have been examined in a group of 15 young men having had fracture of one leg and consequent immobilization resulting in muscle atrophy. Extrapolation of the submaximal cardiac frequency (FH) and oxygen intake (VO2) responses to an assumed FH amx of 175 in one-leg and 195 in two-leg work resulted in a systematic overestimation of VO2 max. This overestimation could be removed by applying the appropriate regression equations, but the overall accuracy of the extrapolation method was limited to +/- 15% in the case of the injured leg and +/- 8% for either the uninjured leg or both legs combined. Prediction of VO2 max from leg muscle (plus bone) volume gave the same order of accuracy. However, it was shown that the VO2 max of the injured leg could be predicted with an accuracy of +/- 5%, if the observed VO2 max data of the uninjured leg and two legs were combined and utilized in the following formula: VO2 max (injured leg) = (A X 2) - VO2 max (uninjured leg), where A is the mean one-leg VO2 max predicted from the two-leg VO2 max observed. It was concluded that wherever possible the one-leg and two-leg VO2 max of patients undergoing rehabilitation therapy should be measured directly. If the patient is unable to pedal the bicycle ergometer with his injured leg alone then the VO2 max of this limb may be predicted from leg volume measurements or from the observed uninjured and two-leg VO2 max with an accuracy of approximately 8%.

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August 1975
27 Reads

Circadian variation in physiological responses to exercise on a stationary bicycle ergometer

Br J Ind Med. 1975 May;32(2):110-4

British Journal of Industrial Medicine

The responses of six healthy male subjects to submaximal and maximal exercise on a stationary bicycle ergometer have been investigated over a 24-hour period. Measurements were made on each subject at approximately three-hourly intervals and they included minute ventilation at a carbon dioxide output of 1-5 1 min-minus 1 (VE 1-5), tidal volume at a fixed VE of 30 1 min-minus 1 (VT 30), oxygen intake (VO2) at a work load (W) of 150 W (VO2 150), tympanic temperature (Tty) and cardiac frequency at a VO2 of 1-5 1 min-minus 1 (fH 1-5). The experiments were conducted in three parts: on the first occasion two subjects were measured during exercise; on the second occasion a further four subjects were observed in a similar way but starting from a baseline of zero load, and the measurements also included an estimate of cardiac output (Q) using a rebreathing technique. Finally the maximum aerobic power output (VO2max) was measured in three of the subjects in early morning and late evening. Diet and habitual physical activity were held constant between the exercise test on all three occasions. The results show that in the first two subjects fH 1-5 and Tty had a rhythmic pattern of variation with time of day whereas VE 1-5, VT30, and VO2 150 remained fairly constant. The variation in fH 1-5 was associated with Tty; the two variables reached a minimum at similar to 0500 hr and a maximum at similar 1200 hr. These results were confirmed on the remaining subjects but the changes in fH 1-5 and Tty were shown to be more variable and reduced in magnitude. Further, if the changes were calculated from a baseline of zero load, it was shown that the absolute changes observed in fH 1-5 and Tty were not due to the exercise per se but to changes in the basal level from which each subject operated. In addition it was shown that VO2 max and Q remained constant and were independent of the time of day. It is concluded that provided the exercise test conditions are rigidly standardized and subjects exercise from a controlled baseline there is no evidence for circadian variation in the change of responses to work at submaximal or maximal effort.

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May 1975
18 Reads

Cardiopulmonary responses to exercise in obese girls and young women

J Appl Physiol. 1975 Mar;38(3):373-6

Journal of Applied Physiology

A study of exercise performance was carried out in 17 obese girls and young adults. During submaximal steady-state bicycle exercise oxygen intake (Vo2) for a given work output (W) was raised in obese subjects but minute ventilation at a fixed carbon dioxide output, gas exchange, blood gases, and cardiac output at a given VO2 were similar to the values previously found for normals. In obese subjects high levels of VO2 for fixed W were also obtained on the treadmill but when these were standardized for body weight (unlike the bicycle test) it was shown that the obese girls and women exercised within the normal (expected) range of aerobic energy expenditure. During maximal performance the absolute VO2 max was the same in obese and nonobese subjects but for a given body weight, lean body mass, and leg muscle (plus) bone volume, VO2max was reduced by 23.8, 16.3, and 24.5% respectively, in the former group. It was concluded that obesity though having minimal affect on responses to submaximal exercise is nevertheless associated with a marked reduction in physiological performance at or near maximal effort.

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March 1975
18 Reads

Effects of training on the physiological responses to one- and two-leg work

J Appl Physiol. 1975 Mar;38(3):377-5

Journal of Applied Physiology

The effects of training resulting from one-leg exercise on a stationary bicycle ergometer have been studied. Seven subjects were habituated to one- and two-leg progressive exercise tests on 11 successive days and were then trained for 60 min-day-1 (30 min each leg) 3 times per wk for 5-6 wk at approximately 80% of their one-leg VO2 max. VE max increased (P less than 0.05) by approximately 14 1-min-1 and VO2 max by approximately 0.34 1-min-1 (+14%; P less than 0.05) in one-leg exercise. This latter increase was not, however, reflected in the two-leg VO2 max which only increased 145 ml-min-1 (4.7%). It was concluded that training is specific and in one-leg work the phenomenon is mainly peripheral in origin, but in two-leg work the limitation to maximal exercise is still provided by the capacity of the central cardiovascular system to transport oxygen to a given effective muscle mass.

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March 1975
14 Reads

Changes in physiological performance of the lower limb after fracture and subsequent rehabilitation.

Clin Sci Mol Med. 1975 Feb;48(2):107-14.

Clinical Science and Molecular Medicine

1. Eight patients who had suffered a fracture of one leg were studied before and after a 7 weeks period of rehabilitation during work with one leg and both legs on a bicycle ergometer. 2. In submaximal exercise minute ventilation for a given carbon dioxide output and tidal volume at a given minute ventilation remained unchanged throughout the period of therapy for both one- and two-leg exercise: oxygen intake for a given work output and cardiac frequency for a given oxygen intake decreased in both the injured and uninjured limb during one-leg work, although in two-leg exercise there was no significant change. 3. Oxygen intake at zero load was subtracted from the maximum oxygen intake measured during loaded exercise to give net values for each limb exercised separately or both legs exercised together. The net maximum oxygen intake thus calculated increased 8-9% (*17 1/min) in the uninjured leg and 17-4% (*29 1/min) in the injured leg during one-leg exercise. In two-leg exercise the increase was 17-2% (*43 1/min), which approximately equals the increase in the two legs measured separately. 4. In both legs there was an increase in leg muscle (plus bone) volume although this was significant in the injured leg only. 5. The maximum oxygen intake attained in two-leg exercise for a given leg volume in the patients at discharge was not significantly different from that found previously in a cross-sectional survey of young healthy (naval) servicemen. Thus the rehabilitation programme investigated appears to be effective, although the spontaneous recovery without a rehabilitation programme is unknown.

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February 1975
11 Reads

Physiological responses to exercise in patients following fracture of the lower limb

Scand J Rehabil Med. 1975;7(2):45-50

Scandanavian Journal of Rehabilitation Medicine

Twenty-five patients with healed fractures of the lower limb and nine normal control subjects were measured anthropometrically and during maximal and submaximal one- and two-leg bicycle exercise. Oxygen intake at a given submaximal work level of 450 kmp min-1 and cardiac frequency at an oxygen intake of 1.5 I min-1 were significantly higher (p less than 0.001) in the injured compared with the uninjured limbs of the patients and normal subjects. The maximum aerobic power of the injured and uninjured limbs of the patients and normal subjects. The maximum aerobic power of the injured and uninjured limbs of the patients were 18.8% (0.44 I min-1) and 25.6% (0.61 I min-1) respectively lower than the right and left legs of the control subjects. The corresponding value for 2-leg work was 17.6% (0.51 I min-1). The deterioration in 1-leg performance of the patients was associated with a concomitant decrease in leg muscle (plus bone) volume. In 2-leg work this factor was also probably combined with a deterioration in performance due to general cardiovascular deconditioning.

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February 1975
16 Reads

Use of anthropometry and radiography for the estimation of limb (and component tissue) volume of patients recovering from leg fractures

J Physiol. 1975 Jan;244(1):13P-14P

Journal of Physiology

A research report of methodologies for the assessment of limb tissues (fat, muscle, bone).

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January 1975
36 Reads

Physiological responses to one- and two-leg exercise following training

J Physiol. 1975 Jan;244(1):50P

Journal of Physiology

The first preliminary publication of research initiated by Anthony J Sargeant as part of his PhD thesis.

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January 1975
24 Reads

Physiological responses to exercise following fracture of the leg and subsequent rehabilitation

J Physiol. 1974 Oct;242(2):134P-135P

Journal of Physiology

Preliminary report of one part of the research that formed the PHd thesis of Anthony J Sargeant

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October 1974
32 Reads

The assessment of physiological changes occurring during rehabilitation of lower limb injuries at the Joint Services Medical Rehabilitation Unit.

Proc R Soc Med. 1974 Jun;67(6 Pt 1):498.

Proceedings of The Royal Society of Medicine

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1645738/pdf/procrsmed00321-0104.pdf Anthony J Sargeant and colleagues preliminary research report on plans to study rehabilitation strategies in injured military personnel.The Assessment of Physiological Changes Occurring During Rehabilitation of Lower Limb Injuries at the Joint Services Medical Rehabilitation Unit by C T M Davies PhD, R H Fox MB LRCP, A J Hackett, F J Imms MB PhD, Sally James BSC, S P Prestidge and A J Sargeant BEd (MRC Environmental Physiology Unit, London School ofHygiene and Tropical Medicine, and Division ofHuman Physiology, National Institutefor Medical Research, London NW3)1 The research programme aims to record the improvement of general fitness and the return of function in the injured limb. Such data will be of value in assessing the efficacy of present therapies and in the design and evaluation ofnew treatments. Heart rate is monitored during the working day by recording the electrocardiogram using a small portable tape recorder which is strapped to the subject and causes minimum inconvenience. Resting heart rates and cardiac responses to exercise therapy are obtained. Preliminary results show that the therapeutic regimes seldom raise the heart rate above 160 beats/min. Mean night-time heart rates are recorded using an E cell SAMI. Exercise testing is performed in the laboratory using a bicycle ergometer on which the subjects initially work only the non-affected limb. When they are able to use the injured limb the work capacity of the two limbs is compared. The recovery of function in the injured limb is assessed by frequent anthropometry of the legs and measurement of joint mobility, the testing of muscle power and analysis of the gait. Muscle power is measured isometrically using a strain gauge to which either a direct pull or a torque can be applied. On admission there is marked reduction of power in the injured limb. This limitation of voluntary muscle power may be due to a combination of apprehension or pain together with actual loss of contractile force. The gait is analysed using a metal track on which the subject walks whilst wearing shoes fitted with metal contacts. Contact between the foot and the track completes a circuit and the event is recorded. The period of swing of the right and left strides may be compared and the floor contact times of each heel and toe measured. Initially the gait is asymmetrical as regards both swing times and contact times. Movement is further assessed by taking a cinefilm of the subject walking and performing simple acts such as sitting and rising from a chair and climbing stairs. These films are examined for abnormalities of movement and elimination of these abnormalities is studied in serial films. 1 Requests for reprints should be sent to: Dr F J Imms MRC, Environmental Physiology Unit, London School

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June 1974
17 Reads

Effects of hypoxic training on normoxic maximal aerobic power output

Eur J Appl Physiol Occup Physiol. 1974;33(3):227-36

European Journal of Applied Physiology

A research project to examine when whether a hypoxia (as might occur at altitude) is an important factor in training for aerobic power output.

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March 1974
13 Reads

The physiological responses to running downhill

Eur J Appl Physiol Occup Physiol. 1974 Mar 28;32(3):187-94

European Journal of Applied Physiology

Anthony J Sargeant did this rare research into downhill running for which Brian Smith (an experienced runner) was the subject and student. It involved many hours of careful measurement by Anthony J Sargeant on just one subject. In the days of demanding statistical significance a rare achievement. (Rodolfo Margaria was a reviewer when the paper was submitted and tried to block its publication because it did not agree with the "definitive work of Margaria" (actually the only other study at the time of downhill running - published in Italian - and actually it did so agree with the data presented by Margaria - just not his description and conclusions!)

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March 1974
26 Reads

Plasma catecholamine concentration during dynamic exercise involving different muscle groups

Eur J Appl Physiol Occup Physiol. 1974 Mar 28;32(3):195-206

European Journal of Applied Physiology

Explores the circulatory response to exercise using different muscle groups and heart rate response.

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March 1974
25 Reads

Indirect determination of maximal aerobic power output during work with one or two limbs

Eur J Appl Physiol Occup Physiol. 1974 Mar 28;32(3):207-15

European Journal of Applied Physiology

Part of the one/two leg response to exercise research that was initiated by Anthony J Sargeant as part of hie PhD research which explores the peripheral and central limitations to human exercise performance.

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March 1974
13 Reads

Physiological responses to one- and two-leg exercise breathing air and 45 percent oxygen

J Appl Physiol. 1974 Feb;36(2):142-8

Journal of Applied Physiology

Anthony J Sargeant proposed this approach to using a reduced muscle mass to examine the limitation to maximum oxygen uptake (100% 0xygen cannot be used - hence 45%) enhanced oxygen increases Maximum Oxygen Uptake in 2-leg exercise where cardiac output is limiting - but does not increase the maximum oxygen uptake in 1-leg exercise where the limitation is not the delivery of oxygen but the muscle enzyme systems capability to take up and utilize the oxygen.

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February 1974
22 Reads

Physiological responses to standardised arm work

Ergonomics. 1974 Jan;17(1):41-9

Ergonomics

Reported differences in the power output and efficiency of arm work compared to leg work are an artefact. Typical arm work research actually study arm work plus a contribution from upper body muscles. When the upper body contribution is eliminated by restraining movement so that arm cranking is only performed by arm muscles the efficiencies and power are not significantly different to leg work.

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January 1974
28 Reads

Plasma catecholamine concentration during exercise involving different muscle groups

J Physiol. 1974 Jan;236(1):21P-22P

Journal of Physiology

A preliminary report to The Physiological Society (later published in full : see Eur J Appl Physiol Occup Physiol. 1974 Mar 28;32(3):195-206.

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January 1974
20 Reads

Perceived exertion during rhythmic exercise involving different muscle masses

J Hum Ergol (Tokyo). 1973 Sep;2(1):3-11

Journal of Human Ergology

This was a by-product of research looking at exercise performed with different muscle masses. It was thought that it might help the understanding of which physiological cues were important in determining the perception of exertion.

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September 1973
22 Reads

Electromyographic, kinesiological and metabolic examination of running on a treadmill

J Physiol. 1973 Aug;233(1):7P

Journal of Physiology

A careful examination of the difference between running on the treadmill compared to runnning on flat ground. It should have been written-up as a full research paper but Peter Cavanagh, who was a key member of the team and held the data, moved to the USA before we could draft the paper.

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August 1973
20 Reads

Physiological responses to one- and two-limb work in the sitting position

J Physiol. 1973 Jul;232(2):91P-92P

Journal of Physiology

A preliminary report to The Physiological Society of research seeking to understand the limitations to maximum exercise.

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July 1973
15 Reads

PARTICIPATION OF WEST INDIAN BOYS IN ENGLISH SCHOOLS’ SPORTS TEAMS

Educational Research 1972: 14 (3), 225-230

Educational Research

This paper reports the results of an investigation into the proportional participation of West Indian boys in secondary school sports teams. Information on participation in the first two years was obtained by questionnaire from 969 third‐year boys of whom 13 per cent were West Indian, and analysed in two groupings, the top and botton half streams. An overwhelming predominance of West Indian boys proportionate to their numbers were found in soccer, cricket and athletics. A secondary finding was a high correlation between academic ability and participation; both West Indian and white English participation was proportionally higher in the top streams.

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March 1972
34 Reads

Body temperature in exercise. Effects of acclimatisation to heat and habituation to work

Int Z Angew Physiol. 1971;30(1):10-9

European Journal of Applied Physiology (International Zeitschrift fur angewandte physiology)

Anthony J Sargeant completed this research for his Bachelor degree research dissertation. It shows how exercise results in heat acclimatisation.

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January 1971
17 Reads