Publications by authors named "David J Bishop"

126 Publications

Fifteen days of moderate normobaric hypoxia does not affect mitochondrial function, and related genes and proteins, in healthy men.

Eur J Appl Physiol 2021 May 14. Epub 2021 May 14.

Institute for Health and Sport, Victoria University, Melbourne, VIC, Australia.

Purpose: To investigate within the one study potential molecular and cellular changes associated with mitochondrial biogenesis following 15 days of exposure to moderate hypoxia.

Methods: Eight males underwent a muscle biopsy before and after 15 days of hypoxia exposure (FiO = 0.140-0.154; ~ 2500-3200 m) in a hypoxic hotel. Mitochondrial respiration, citrate synthase (CS) activity, and the content of genes and proteins associated with mitochondrial biogenesis were investigated.

Results: Our main findings were the absence of significant changes in the mean values of CS activity, mitochondrial respiration in permeabilised fibers, or the content of genes and proteins associated with mitochondrial biogenesis, after 15 days of moderate normobaric hypoxia.

Conclusion: Our data provide evidence that 15 days of moderate normobaric hypoxia have negligible influence on skeletal muscle mitochondrial content and function, or genes and proteins content associated with mitochondrial biogenesis, in young recreationally active males. However, the increase in mitochondrial protease LON content after hypoxia exposure suggests the possibility of adaptations to optimise respiratory chain function under conditions of reduced O availability.
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http://dx.doi.org/10.1007/s00421-021-04706-4DOI Listing
May 2021

Genome wide association study of response to interval and continuous exercise training: the Predict-HIIT study.

J Biomed Sci 2021 May 13;28(1):37. Epub 2021 May 13.

Queensland University of Technology (QUT), Centre for Genomics and Personalised Health, Genomics Research Centre, School of Biomedical Sciences, Institute of Health and Biomedical Innovation, Kelvin Grove, Brisbane, QLD, Australia.

Background: Low cardiorespiratory fitness (V̇O) is highly associated with chronic disease and mortality from all causes. Whilst exercise training is recommended in health guidelines to improve V̇O, there is considerable inter-individual variability in the V̇O response to the same dose of exercise. Understanding how genetic factors contribute to V̇O training response may improve personalisation of exercise programs. The aim of this study was to identify genetic variants that are associated with the magnitude of V̇Opeak response following exercise training.

Methods: Participant change in objectively measured V̇Opeak from 18 different interventions was obtained from a multi-centre study (Predict-HIIT). A genome-wide association study was completed (n = 507), and a polygenic predictor score (PPS) was developed using alleles from single nucleotide polymorphisms (SNPs) significantly associated (P < 1 × 10) with the magnitude of V̇Opeak response. Findings were tested in an independent validation study (n = 39) and compared to previous research.

Results: No variants at the genome-wide significance level were found after adjusting for key covariates (baseline V̇Opeak individual study, principal components which were significantly associated with the trait). A Quantile-Quantile plot indicates there was minor inflation in the study. Twelve novel loci showed a trend of association with V̇Opeak response that reached suggestive significance (P < 1 × 10). The strongest association was found near the membrane associated guanylate kinase, WW and PDZ domain containing 2 (MAGI2) gene (rs6959961, P = 2.61 × 10). A PPS created from the 12 lead SNPs was unable to predict V̇Opeak response in a tenfold cross validation, or in an independent (n = 39) validation study (P > 0.1). Significant correlations were found for beta coefficients of variants in the Predict-HIIT (P < 1 × 10) and the validation study (P <  × 10), indicating that general effects of the loci exist, and that with a higher statistical power, more significant genetic associations may become apparent.

Conclusions: Ongoing research and validation of current and previous findings is needed to determine if genetics does play a large role in V̇Opeak response variance, and whether genomic predictors for V̇Opeak response trainability can inform evidence-based clinical practice. Trial registration Australian New Zealand Clinical Trials Registry (ANZCTR), Trial Id: ACTRN12618000501246, Date Registered: 06/04/2018, http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=374601&isReview=true .
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http://dx.doi.org/10.1186/s12929-021-00733-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8117553PMC
May 2021

Direct laser writing for cardiac tissue engineering: a microfluidic heart on a chip with integrated transducers.

Lab Chip 2021 05;21(9):1724-1737

Department of Mechanical Engineering, Boston University, Boston, MA 02215, USA. and Photonics Center, Boston University, Boston, MA 02215, USA and Department of Biomedical Engineering, Boston University, Boston, MA 02215, USA and Division of Materials Science and Engineering, Boston University, Boston, Massachusetts 02215, USA and Department of Physics, Boston University, Boston, MA 02215, USA.

We have developed a microfluidic platform for engineering cardiac microtissues in highly-controlled microenvironments. The platform is fabricated using direct laser writing (DLW) lithography and soft lithography, and contains four separate devices. Each individual device houses a cardiac microtissue and is equipped with an integrated strain actuator and a force sensor. Application of external pressure waves to the platform results in controllable time-dependent forces on the microtissues. Conversely, oscillatory forces generated by the microtissues are transduced into measurable electrical outputs. We demonstrate the capabilities of this platform by studying the response of cardiac microtissues derived from human induced pluripotent stem cells (hiPSC) under prescribed mechanical loading and pacing. This platform will be used for fundamental studies and drug screening on cardiac microtissues.
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http://dx.doi.org/10.1039/d0lc01078bDOI Listing
May 2021

High-intensity exercise training - too much of a good thing?

Nat Rev Endocrinol 2021 May 4. Epub 2021 May 4.

Institute for Health and Sport (iHeS), Victoria University, Melbourne, Victoria, Australia.

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http://dx.doi.org/10.1038/s41574-021-00500-6DOI Listing
May 2021

Reduced post-exercise muscle microvascular perfusion with compression is offset by increased muscle oxygen extraction: Assessment by contrast-enhanced ultrasound.

FASEB J 2021 May;35(5):e21499

Institute for Physical Activity and Nutrition (IPAN), School of Exercise and Nutrition Sciences, Deakin University, Geelong, VIC, Australia.

The microvasculature is important for both health and exercise tolerance in a range of populations. However, methodological limitations have meant changes in microvascular blood flow are rarely assessed in humans during interventions designed to affect skeletal muscle blood flow such as the wearing of compression garments. The aim of this study is, for the first time, to use contrast-enhanced ultrasound to directly measure the effects of compression on muscle microvascular blood flow alongside measures of femoral artery blood flow and muscle oxygenation following intense exercise in healthy adults. It was hypothesized that both muscle microvascular and femoral artery blood flows would be augmented with compression garments as compared with a control condition. Ten recreationally active participants completed two repeated-sprint exercise sessions, with and without lower-limb compression tights. Muscle microvascular blood flow, femoral arterial blood flow (2D and Doppler ultrasound), muscle oxygenation (near-infrared spectroscopy), cycling performance, and venous blood samples were measured/taken throughout exercise and the 1-hour post-exercise recovery period. Compared with control, compression reduced muscle microvascular blood volume and attenuated the exercise-induced increase in microvascular velocity and flow immediately after exercise and 1 hour post-exercise. Compression increased femoral artery diameter and augmented the exercise-induced increase in femoral arterial blood flow during exercise. Markers of blood oxygen extraction in muscle were increased with compression during and after exercise. Compression had no effect on blood lactate, glucose, or exercise performance. We provide new evidence that lower-limb compression attenuates the exercise-induced increase in skeletal muscle microvascular blood flow following exercise, despite a divergent increase in femoral artery blood flow. Decreased muscle microvascular perfusion is offset by increased muscle oxygen extraction, a potential mechanism allowing for the maintenance of exercise performance.
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http://dx.doi.org/10.1096/fj.202002205RRDOI Listing
May 2021

Ammonium chloride administration prior to exercise has muscle-specific effects on mitochondrial and myofibrillar protein synthesis in rats.

Physiol Rep 2021 Mar;9(6):e14797

Institute for Health and Sport (iHeS), Victoria University, Melbourne, Victoria, Australia.

Aim: Exercise is able to increase both muscle protein synthesis and mitochondrial biogenesis. However, acidosis, which can occur in pathological states as well as during high-intensity exercise, can decrease mitochondrial function, whilst its impact on muscle protein synthesis is disputed. Thus, the aim of this study was to determine the effect of a mild physiological decrease in pH, by administration of ammonium chloride, on myofibrillar and mitochondrial protein synthesis, as well as associated molecular signaling events.

Methods: Male Wistar rats were given either a placebo or ammonium chloride prior to a short interval training session. Rats were killed before exercise, immediately after exercise, or 3 h after exercise.

Results: Myofibrillar (p = 0.036) fractional protein synthesis rates was increased immediately after exercise in the soleus muscle of the placebo group, but this effect was absent in the ammonium chloride group. However, in the gastrocnemius muscle NH Cl increased myofibrillar (p = 0.044) and mitochondrial protein synthesis (0 h after exercise p = 0.01; 3 h after exercise p = 0.003). This was accompanied by some small differences in protein phosphorylation and mRNA expression.

Conclusion: This study found ammonium chloride administration immediately prior to a single session of exercise in rats had differing effects on mitochondrial and myofibrillar protein synthesis rates in soleus (type I) and gastrocnemius (type II) muscle in rats.
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http://dx.doi.org/10.14814/phy2.14797DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7995552PMC
March 2021

Blood-flow-restricted exercise: Strategies for enhancing muscle adaptation and performance in the endurance-trained athlete.

Exp Physiol 2021 Apr 10;106(4):837-860. Epub 2021 Feb 10.

Department of Internal Medicine, University of Utah, Salt Lake City, Utah, USA.

New Findings: What is the topic of this review? Blood-flow-restricted (BFR) exercise represents a potential approach to augment the adaptive response to training and improve performance in endurance-trained individuals. What advances does it highlight? When combined with low-load resistance exercise, low- and moderate-intensity endurance exercise and sprint interval exercise, BFR can provide an augmented acute stimulus for angiogenesis and mitochondrial biogenesis. These augmented acute responses can translate into enhanced capillary supply and mitochondrial function, and subsequent endurance-type performance, although this might depend on the nature of the exercise stimulus. There is a requirement to clarify whether BFR training interventions can be used by high-performance endurance athletes within their structured training programme.

Abstract: A key objective of the training programme for an endurance athlete is to optimize the underlying physiological determinants of performance. Training-induced adaptations are governed by physiological and metabolic stressors, which initiate transcriptional and translational signalling cascades to increase the abundance and/or function of proteins to improve physiological function. One important consideration is that training adaptations are reduced as training status increases, which is reflected at the molecular level as a blunting of the acute signalling response to exercise. This review examines blood-flow-restricted (BFR) exercise as a strategy for augmenting exercise-induced stressors and subsequent molecular signalling responses to enhance the physiological characteristics of the endurance athlete. Focus is placed on the processes of capillary growth and mitochondrial biogenesis. Recent evidence supports that BFR exercise presents an intensified training stimulus beyond that of performing the same exercise alone. We suggest that this has the potential to induce enhanced physiological adaptations, including increases in capillary supply and mitochondrial function, which can contribute to an improvement in performance of endurance exercise. There is, however, a lack of consensus regarding the potency of BFR training, which is invariably attributable to the different modes, intensities and durations of exercise and BFR methods. Further studies are needed to confirm its potential in the endurance-trained athlete.
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http://dx.doi.org/10.1113/EP089280DOI Listing
April 2021

A system for probing Casimir energy corrections to the condensation energy.

Microsyst Nanoeng 2020 28;6:115. Epub 2020 Dec 28.

Department of ECE, Boston University, Boston, MA 02215 USA.

In this article, we present a nanoelectromechanical system (NEMS) designed to detect changes in the Casimir energy. The Casimir effect is a result of the appearance of quantum fluctuations in an electromagnetic vacuum. Previous experiments have used nano- or microscale parallel plate capacitors to detect the Casimir force by measuring the small attractive force these fluctuations exert between the two surfaces. In this new set of experiments, we aim to directly detect the shifts in the Casimir energy in a vacuum due to the presence of the metallic parallel plates, one of which is a superconductor. A change in the Casimir energy of this configuration is predicted to shift the superconducting transition temperature () because of the interaction between it and the superconducting condensation energy. In our experiment, we take a superconducting film, carefully measure its transition temperature, bring a conducting plate close to the film, create a Casimir cavity, and then measure the transition temperature again. The expected shifts are smaller than the normal shifts one sees in cycling superconducting films to cryogenic temperatures, so using a NEMS resonator in situ is the only practical way to obtain accurate, reproducible data. Using a thin Pb film and opposing Au surface, we observe no shift in >12 µK down to a minimum spacing of ~70 nm at zero applied magnetic field.
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http://dx.doi.org/10.1038/s41378-020-00221-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7767790PMC
December 2020

The Effects of Regular Cold-Water Immersion Use on Training-Induced Changes in Strength and Endurance Performance: A Systematic Review with Meta-Analysis.

Sports Med 2021 Jan;51(1):161-174

Laboratory of Physiology and Sport Performance-LAFIDE, Postgraduate Program in Movement Sciences, School of Sciences, Department of Physical Education, São Paulo State University-UNESP, Av. Eng. Luiz Edmundo Carrijo Coube, 14-01, Vargem Limpa, Bauru, SP, 17033-360, Brazil.

Background: Cold-water immersion (CWI) is one of the main recovery methods used in sports, and is commonly utilized as a means to expedite the recovery of performance during periods of exercise training. In recent decades, there have been indications that regular CWI use is potentially harmful to resistance training adaptations, and, conversely, potentially beneficial to endurance training adaptations. The current meta-analysis was conducted to assess the effects of the regular CWI use during exercise training on resistance (i.e., strength) and endurance (i.e., aerobic exercise) performance alterations.

Methods: A computerized literature search was conducted, ending on November 25, 2019. The databases searched were MEDLINE, Cochrane Central Register of Controlled Trials, and SPORTDiscus. The selected studies investigated the effects of chronic CWI interventions associated with resistance and endurance training sessions on exercise performance improvements. The criteria for inclusion of studies were: (1) being a controlled investigation; (2) conducted with humans; (3) CWI performed at ≤ 15 °C; (4) being associated with a regular training program; and (5) having performed baseline and post-training assessments.

Results: Eight articles were included before the review process. A harmful effect of CWI associated with resistance training was verified for one-repetition maximum, maximum isometric strength, and strength endurance performance (overall standardized mean difference [SMD] = - 0.60; Confidence interval of 95% [CI95%] = - 0.87, - 0.33; p < 0.0001), as well as for Ballistic efforts performance (overall SMD = - 0.61; CI95% = - 1.11, - 0.11; p = 0.02). On the other hand, selected studies verified no effect of CWI associated with endurance training on time-trial (mean power), maximal aerobic power in graded exercise test performance (overall SMD = - 0.07; CI95% = - 0.54, 0.53; p = 0.71), or time-trial performance (duration) (overall SMD = 0.00; CI95% = - 0.58, 0.58; p = 1.00).

Conclusions: The regular use of CWI associated with exercise programs has a deleterious effect on resistance training adaptations but does not appear to affect aerobic exercise performance.

Trial Registration: PROSPERO CRD42018098898.
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http://dx.doi.org/10.1007/s40279-020-01362-0DOI Listing
January 2021

Exercise mitigates sleep-loss-induced changes in glucose tolerance, mitochondrial function, sarcoplasmic protein synthesis, and diurnal rhythms.

Mol Metab 2021 01 31;43:101110. Epub 2020 Oct 31.

Institute for Health and Sport, Victoria University, Melbourne, Australia.

Objective: Sleep loss has emerged as a risk factor for the development of impaired glucose tolerance. The mechanisms underpinning this observation are unknown; however, both mitochondrial dysfunction and circadian misalignment have been proposed. Because exercise improves glucose tolerance and mitochondrial function, and alters circadian rhythms, we investigated whether exercise may counteract the effects induced by inadequate sleep.

Methods: To minimize between-group differences of baseline characteristics, 24 healthy young males were allocated into one of the three experimental groups: a Normal Sleep (NS) group (8 h time in bed (TIB) per night, for five nights), a Sleep Restriction (SR) group (4 h TIB per night, for five nights), and a Sleep Restriction and Exercise group (SR+EX) (4 h TIB per night, for five nights and three high-intensity interval exercise (HIIE) sessions). Glucose tolerance, mitochondrial respiratory function, sarcoplasmic protein synthesis (SarcPS), and diurnal measures of peripheral skin temperature were assessed pre- and post-intervention.

Results: We report that the SR group had reduced glucose tolerance post-intervention (mean change ± SD, P value, SR glucose AUC: 149 ± 115 A.U., P = 0.002), which was also associated with reductions in mitochondrial respiratory function (SR: -15.9 ± 12.4 pmol O.s.mg, P = 0.001), a lower rate of SarcPS (FSR%/day SR: 1.11 ± 0.25%, P < 0.001), and reduced amplitude of diurnal rhythms. These effects were not observed when incorporating three sessions of HIIE during this period (SR+EX: glucose AUC 67 ± 57, P = 0.239, mitochondrial respiratory function: 0.6 ± 11.8 pmol O.s.mg, P = 0.997, and SarcPS (FSR%/day): 1.77 ± 0.22%, P = 0.971).

Conclusions: A five-night period of sleep restriction leads to reductions in mitochondrial respiratory function, SarcPS, and amplitude of skin temperature diurnal rhythms, with a concurrent reduction in glucose tolerance. We provide novel data demonstrating that these same detrimental effects are not observed when HIIE is performed during the period of sleep restriction. These data therefore provide evidence in support of the use of HIIE as an intervention to mitigate the detrimental physiological effects of sleep loss.
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http://dx.doi.org/10.1016/j.molmet.2020.101110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7704425PMC
January 2021

Short-Term Repeated-Sprint Training in Hot and Cool Conditions Similarly Benefits Performance in Team-Sport Athletes.

Front Physiol 2020 27;11:1023. Epub 2020 Aug 27.

School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Perth, WA, Australia.

This study compared the performance and physiological adaptations of short-term repeated-sprint training in HOT [40°C and 40% relative humidity (RH)] and COOL (20°C and 40% RH) conditions in team-sport athletes. Twenty-five trained males completed five training sessions of 60 min over 7 days in HOT ( = 13) or COOL ( = 12) conditions, consisting of a submaximal warm-up and four sets of maximal sprints. Before and after the intervention, intermittent shuttle running performance was assessed in cool and repeated-sprint ability in hot conditions; the latter preceded and followed by neuromuscular function testing. During the repeated-sprint training sessions, skin (~8.4°C) and core (~0.17°C) temperatures were higher in HOT than COOL ( < 0.05) conditions. Shuttle running distance increased after both interventions ( < 0.001), with a non-significant ( = 0.131) but larger effect in HOT (315 m, = 1.18) than COOL (207 m, = 0.51) conditions. Mean (~7%, < 0.001) and peak (~5%, < 0.05) power during repeated-sprinting increased following both interventions, whereas peak twitch force before the repeated-sprint assessment was ~10% lower after the interventions ( = 0.001). Heart rate during the repeated-sprint warm-up was reduced (~6 beats.min) following both interventions ( < 0.01). Rectal temperature was ~0.14°C lower throughout the repeated-sprint assessment after the interventions ( < 0.001), with larger effects in HOT than COOL during the warm-up ( = 0.082; = -0.53 vs. = -0.15) and repeated-sprints ( = 0.081; = -0.54 vs. = -0.02). Skin temperature ( = 0.004, = -1.11) and thermal sensation ( = 0.015, = -0.93) were lower during the repeated-sprints after training in HOT than COOL. Sweat rate increased (0.2 L.h) only after training in HOT ( = 0.027; = 0.72). The intensive nature of brief repeated-sprint training induces similar improvements in repeated-sprint cycling ability in hot conditions and intermittent running performance in cool conditions, along with analogous physiological adaptations, irrespective of the environmental conditions in which training is undertaken.
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http://dx.doi.org/10.3389/fphys.2020.01023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7493664PMC
August 2020

Are Alterations in Skeletal Muscle Mitochondria a Cause or Consequence of Insulin Resistance?

Int J Mol Sci 2020 Sep 22;21(18). Epub 2020 Sep 22.

Institute for Health and Sport (iHeS), Victoria University, Melbourne 8001, Australia.

As a major site of glucose uptake following a meal, skeletal muscle has an important role in whole-body glucose metabolism. Evidence in humans and animal models of insulin resistance and type 2 diabetes suggests that alterations in mitochondrial characteristics accompany the development of skeletal muscle insulin resistance. However, it is unclear whether changes in mitochondrial content, respiratory function, or substrate oxidation are central to the development of insulin resistance or occur in response to insulin resistance. Thus, this review will aim to evaluate the apparent conflicting information placing mitochondria as a key organelle in the development of insulin resistance in skeletal muscle.
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http://dx.doi.org/10.3390/ijms21186948DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7554894PMC
September 2020

An Examination and Critique of Current Methods to Determine Exercise Intensity.

Sports Med 2020 Oct;50(10):1729-1756

Institute for Health and Sport (IHES), Victoria University, Melbourne, Australia.

Prescribing the frequency, duration, or volume of training is simple as these factors can be altered by manipulating the number of exercise sessions per week, the duration of each session, or the total work performed in a given time frame (e.g., per week). However, prescribing exercise intensity is complex and controversy exists regarding the reliability and validity of the methods used to determine and prescribe intensity. This controversy arises from the absence of an agreed framework for assessing the construct validity of different methods used to determine exercise intensity. In this review, we have evaluated the construct validity of different methods for prescribing exercise intensity based on their ability to provoke homeostatic disturbances (e.g., changes in oxygen uptake kinetics and blood lactate) consistent with the moderate, heavy, and severe domains of exercise. Methods for prescribing exercise intensity include a percentage of anchor measurements, such as maximal oxygen uptake ([Formula: see text]), peak oxygen uptake ([Formula: see text]), maximum heart rate (HR), and maximum work rate (i.e., power or velocity-[Formula: see text] or [Formula: see text], respectively), derived from a graded exercise test (GXT). However, despite their common use, it is apparent that prescribing exercise intensity based on a fixed percentage of these maximal anchors has little merit for eliciting distinct or domain-specific homeostatic perturbations. Some have advocated using submaximal anchors, including the ventilatory threshold (VT), the gas exchange threshold (GET), the respiratory compensation point (RCP), the first and second lactate threshold (LT and LT), the maximal lactate steady state (MLSS), critical power (CP), and critical speed (CS). There is some evidence to support the validity of LT, GET, and VT to delineate the moderate and heavy domains of exercise. However, there is little evidence to support the validity of most commonly used methods, with exception of CP and CS, to delineate the heavy and severe domains of exercise. As acute responses to exercise are not always predictive of chronic adaptations, training studies are required to verify whether different methods to prescribe exercise will affect adaptations to training. Better ways to prescribe exercise intensity should help sport scientists, researchers, clinicians, and coaches to design more effective training programs to achieve greater improvements in health and athletic performance.
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http://dx.doi.org/10.1007/s40279-020-01322-8DOI Listing
October 2020

The Molecular Adaptive Responses of Skeletal Muscle to High-Intensity Exercise/Training and Hypoxia.

Antioxidants (Basel) 2020 Jul 24;9(8). Epub 2020 Jul 24.

Institute for Health and Sport (iHeS), Victoria University, P.O. Box 14428, Melbourne 8001, Australia.

High-intensity exercise/training, especially interval exercise/training, has gained popularity in recent years. Hypoxic training was introduced to elite athletes half a century ago and has recently been adopted by the general public. In the current review, we have summarised the molecular adaptive responses of skeletal muscle to high-intensity exercise/training, focusing on mitochondrial biogenesis, angiogenesis, and muscle fibre composition. The literature suggests that (peroxisome proliferator-activated receptor gamma coactivator 1-alpha) PGC-1α, vascular endothelial growth factor (VEGF), and hypoxia-inducible factor 1-alpha (HIF1-α) might be the main mediators of skeletal muscle adaptations to high-intensity exercises in hypoxia. Exercise is known to be anti-inflammatory, while the effects of hypoxia on inflammatory signalling are more complex. The anti-inflammatory effects of a single session of exercise might result from the release of anti-inflammatory myokines and other cytokines, as well as the downregulation of Toll-like receptor signalling, while training-induced anti-inflammatory effects may be due to reductions in abdominal and visceral fat (which are main sources of pro-inflammatory cytokines). Hypoxia can lead to inflammation, and inflammation can result in tissue hypoxia. However, the hypoxic factor HIF1-α is essential for preventing excessive inflammation. Disease-induced hypoxia is related to an upregulation of inflammatory signalling, but the effects of exercise-induced hypoxia on inflammation are less conclusive. The effects of high-intensity exercise under hypoxia on skeletal muscle molecular adaptations and inflammatory signalling have not been fully explored and are worth investigating in future studies. Understanding these effects will lead to a more comprehensive scientific basis for maximising the benefits of high-intensity exercise.
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http://dx.doi.org/10.3390/antiox9080656DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7464156PMC
July 2020

Maternal exercise attenuates the lower skeletal muscle glucose uptake and insulin secretion caused by paternal obesity in female adult rat offspring.

J Physiol 2020 10 9;598(19):4251-4270. Epub 2020 Jul 9.

Institute for Health and Sport (IHES), Victoria University, Melbourne, Australia.

Key Points: Paternal obesity negatively influences metabolic outcomes in adult rat offspring. Maternal voluntary physical activity has previously been reported to improve glucose metabolism in adult rat offspring sired by healthy fathers. Here, we investigated whether a structured programme of maternal exercise training before and during gestation can attenuate the negative impacts that paternal obesity has on insulin sensitivity and secretion in female adult offspring. Exercise before and during pregnancy normalised the lower insulin sensitivity in skeletal muscle and the lower insulin secretion observed in female offspring sired by obese fathers. This paper presents a feasible, low-cost and translatable intervention strategy that can be applied perinatally to support multifactor interventions to break the cycle of metabolic dysfunction caused by paternal obesity.

Abstract: We investigated whether maternal exercise before and during gestation could attenuate the negative metabolic effects of paternal high-fat diet-induced obesity in female adult rat offspring. Fathers consumed a normal chow or high-fat diet before mating. Mothers exercised on a treadmill before and during gestation or remained sedentary. In adulthood, female offspring were assessed using intraperitoneal insulin and glucose tolerance tests (IPITT and IPGTT, respectively), pancreatic morphology, ex vivo skeletal muscle insulin-stimulated glucose uptake and mitochondrial respiratory function. Paternal obesity impaired whole-body and skeletal muscle insulin sensitivity and insulin secretion in adult offspring. Maternal exercise attenuated the lower insulin-stimulated glucose uptake in offspring sired by obese fathers but distal insulin signalling components (p-AKT Thr308 and Ser473, p-TBC1D4 Thr642 and GLUT4) remained unchanged (P > 0.05). Maternal exercise increased citrate synthase activity only in offspring sired by obese fathers. Maternal exercise also reversed the lower insulin secretion in vivo observed in offspring of obese fathers, probably due to an attenuation of the decrease in pancreatic beta cell mass. In summary, maternal exercise before and during pregnancy in rats attenuated skeletal muscle insulin resistance and attenuated the decrease in pancreatic beta cell mass and insulin secretion observed in the female offspring of obese fathers.
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http://dx.doi.org/10.1113/JP279582DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7586952PMC
October 2020

Resistance training upregulates skeletal muscle Na, K-ATPase content, with elevations in both α and α, but not β isoforms.

Eur J Appl Physiol 2020 Aug 3;120(8):1777-1785. Epub 2020 Jul 3.

Institute for Health and Sport (iHeS), Victoria University, PO Box 14428, Melbourne, VIC, 8001, Australia.

Purpose: The Na, K-ATPase (NKA) is important in regulating trans-membrane ion gradients, cellular excitability and muscle function. We investigated the effects of resistance training in healthy young adults on the adaptability of NKA content and of the specific α and β isoforms in human skeletal muscle.

Methods: Twenty-one healthy young males (22.9 ± 4.6 year; 1.80 ± 0.70 m, 85.1 ± 17.8 kg, mean ± SD) underwent 7 weeks of resistance training, training three times per week (RT, n = 16) or control (CON, n = 5). The training program was effective with a 39% gain in leg press muscle strength (p = 0.001). A resting vastus lateralis muscle biopsy was taken before and following RT or CON and assayed for NKA content ([H]ouabain binding site content) and NKA isoform (α, α, β β) abundances.

Results: After RT, each of NKA content (12%, 311 ± 76 vs 349 ± 76 pmol g wet weight, p = 0.01), NKA α (32%, p = 0.01) and α (10%, p < 0.01) isoforms were increased, whereas β (p = 0.18) and β (p = 0.22) isoforms were unchanged. NKA content and isoform abundances were unchanged during CON.

Conclusions: Resistance training increased muscle NKA content through upregulation of both α and α isoforms, which were independent of β isoform changes. In animal models, modulations in α and α isoform abundances in skeletal muscle may affect fatigue resistance during exercise, muscle hypertrophy and strength. Whether similar in-vivo functional benefits of these NKA isoform adaptations occurs in human muscle with resistance training remains to be determined.
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http://dx.doi.org/10.1007/s00421-020-04408-3DOI Listing
August 2020

Order of same-day concurrent training influences some indices of power development, but not strength, lean mass, or aerobic fitness in healthy, moderately-active men after 9 weeks of training.

PLoS One 2020 14;15(5):e0233134. Epub 2020 May 14.

Institute for Health and Sport, Victoria University, Melbourne, Australia.

Background: The importance of concurrent exercise order for improving endurance and resistance adaptations remains unclear, particularly when sessions are performed a few hours apart. We investigated the effects of concurrent training (in alternate orders, separated by ~3 hours) on endurance and resistance training adaptations, compared to resistance-only training.

Materials And Methods: Twenty-nine healthy, moderately-active men (mean ± SD; age 24.5 ± 4.7 y; body mass 74.9 ± 10.8 kg; height 179.7 ± 6.5 cm) performed either resistance-only training (RT, n = 9), or same-day concurrent training whereby high-intensity interval training was performed either 3 hours before (HIIT+RT, n = 10) or after resistance training (RT+HIIT, n = 10), for 3 d.wk-1 over 9 weeks. Training-induced changes in leg press 1-repetition maximal (1-RM) strength, countermovement jump (CMJ) performance, body composition, peak oxygen uptake ([Formula: see text]), aerobic power ([Formula: see text]), and lactate threshold ([Formula: see text]) were assessed before, and after both 5 and 9 weeks of training.

Results: After 9 weeks, all training groups increased leg press 1-RM (~24-28%) and total lean mass (~3-4%), with no clear differences between groups. Both concurrent groups elicited similar small-to-moderate improvements in all markers of aerobic fitness ([Formula: see text] ~8-9%; [Formula: see text] ~16-20%; [Formula: see text] ~14-15%). RT improved CMJ displacement (mean ± SD, 5.3 ± 6.3%), velocity (2.2 ± 2.7%), force (absolute: 10.1 ± 10.1%), and power (absolute: 9.8 ± 7.6%; relative: 6.0 ± 6.6%). HIIT+RT elicited comparable improvements in CMJ velocity only (2.2 ± 2.7%). Compared to RT, RT+HIIT attenuated CMJ displacement (mean difference ± 90%CI, -5.1 ± 4.3%), force (absolute: -8.2 ± 7.1%) and power (absolute: -6.0 ± 4.7%). Only RT+HIIT reduced absolute fat mass (mean ± SD, -11.0 ± 11.7%).

Conclusions: In moderately-active males, concurrent training, regardless of the exercise order, presents a viable strategy to improve lower-body maximal strength and total lean mass comparably to resistance-only training, whilst also improving indices of aerobic fitness. However, improvements in CMJ displacement, force, and power were attenuated when RT was performed before HIIT, and as such, exercise order may be an important consideration when designing training programs in which the goal is to improve lower-body power.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0233134PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7224562PMC
August 2020

CYP1A2 genotype and acute effects of caffeine on resistance exercise, jumping, and sprinting performance.

J Int Soc Sports Nutr 2020 Apr 15;17(1):21. Epub 2020 Apr 15.

Institute for Health and Sport (IHES), Victoria University, Melbourne, Australia.

Background: It has been suggested that polymorphisms within CYP1A2 impact inter-individual variation in the response to caffeine. The purpose of this study was to explore the acute effects of caffeine on resistance exercise, jumping, and sprinting performance in a sample of resistance-trained men, and to examine the influence of genetic variation of CYP1A2 (rs762551) on the individual variation in responses to caffeine ingestion.

Methods: Twenty-two men were included as participants (AA homozygotes n = 13; C-allele carriers n = 9) and were tested after the ingestion of caffeine (3 mg/kg of body mass) and a placebo. Exercise performance was assessed with the following outcomes: (a) movement velocity and power output in the bench press exercise with loads of 25, 50, 75, and 90% of one-repetition maximum (1RM); (b) quality and quantity of performed repetitions in the bench press exercise performed to muscular failure with 85% 1RM; (c) vertical jump height in a countermovement jump test; and (d) power output in a Wingate test.

Results: Compared to placebo, caffeine ingestion enhanced: (a) movement velocity and power output across all loads (effect size [ES]: 0.20-0.61; p <  0.05 for all); (b) the quality and quantity of performed repetitions with 85% of 1RM (ES: 0.27-0.85; p <  0.001 for all); (c) vertical jump height (ES: 0.15; p = 0.017); and (d) power output in the Wingate test (ES: 0.33-0.44; p <  0.05 for all). We did not find a significant genotype × caffeine interaction effect (p-values ranged from 0.094 to 0.994) in any of the analyzed performance outcomes.

Conclusions: Resistance-trained men may experience acute improvements in resistance exercise, jumping, and sprinting performance following the ingestion of caffeine. The comparisons of the effects of caffeine on exercise performance between individuals with the AA genotype and AC/CC genotypes found no significant differences.

Trial Registration: Australian New Zealand Clinical Trials Registry. ID: ACTRN12619000885190.
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http://dx.doi.org/10.1186/s12970-020-00349-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7161272PMC
April 2020

Modulation of Countermovement Jump-Derived Markers of Neuromuscular Function With Concurrent vs. Single-Mode Resistance Training.

J Strength Cond Res 2020 Jun;34(6):1497-1502

School of Exercise and Nutrition Sciences, Deakin University, Melbourne, Australia.

Pattison, KJ, Drinkwater, EJ, Bishop, DJ, Stepto, NK, and Fyfe, JJ. Modulation of countermovement jump-derived markers of neuromuscular function with concurrent vs. single-mode resistance training. J Strength Cond Res 34(6): 1497-1502, 2020-This study assessed changes in countermovement jump (CMJ)-derived markers of neuromuscular function with concurrent training vs. resistance training (RT) alone and determined associations between changes in CMJ parameters and other neuromuscular adaptations (e.g., maximal strength gain). Twenty-three recreationally active men performed 8 weeks of RT alone (RT group, n = 8) or combined with either high-intensity interval training cycling (HIIT + RT group, n = 8) or moderate-intensity continuous cycling (MICT + RT group, n = 7). Maximal strength and CMJ performance were assessed before (PRE), after 4 weeks of training (MID), and >72 hours (maximal strength) or >5-7 days (CMJ performance) after (POST) the training intervention. Improvements in CMJ relative peak force from both PRE to MID and PRE to POST were attenuated for both HIIT + RT (effect size [ES]: -0.44; ±90% confidence limit, ±0.51 and ES: -0.72; ±0.61, respectively) and MICT + RT (ES: -0.74; ±0.49 and ES: -1.25; ±0.63, respectively). Compared with RT alone, the change in the flight time to contraction time ratio (FT:CT) was attenuated from PRE to MID for MICT + RT (ES: -0.38; ±0.42) and from PRE to POST for both MICT + RT (ES: -0.60; ±0.55) and HIIT + RT (ES: -0.75; ±0.30). PRE to POST changes in both CMJ relative peak force and flight time:contraction time (F:C) ratio were also associated with relative 1 repetition maximum leg press strength gain (r = 0.26 and 0.19, respectively). These findings highlight the utility of CMJ testing for monitoring interference to improvements in neuromuscular function with concurrent training.
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http://dx.doi.org/10.1519/JSC.0000000000003587DOI Listing
June 2020

ADOR2A C Allele Carriers Exhibit Ergogenic Responses to Caffeine Supplementation.

Nutrients 2020 Mar 11;12(3). Epub 2020 Mar 11.

Institute for Health and Sport (IHES), Victoria University, Melbourne 3011, Australia.

Caffeine's ergogenic effects on exercise performance are generally explained by its ability to bind to adenosine receptors. is the gene that encodes A subtypes of adenosine receptors. It has been suggested that gene polymorphisms may be responsible for the inter-individual variations in the effects of caffeine on exercise performance. In the only study that explored the influence of variation in -in this case, a common polymorphism (rs5751876)-on the ergogenic effects of caffeine on exercise performance, C allele carriers were identified as "non-responders" to caffeine. To explore if C allele carriers are true "non-responders" to the ergogenic effects of caffeine, in this randomized, double-blind study, we examined the acute effects of caffeine ingestion among a sample consisting exclusively of C allele carriers. Twenty resistance-trained men identified as C allele carriers (CC/CT genotype) were tested on two occasions, following the ingestion of caffeine (3 mg/kg) and a placebo. Exercise performance was evaluated with movement velocity, power output, and muscle endurance during the bench press exercise, countermovement jump height, and power output during a Wingate test. Out of the 25 analyzed variables, caffeine was ergogenic in 21 (effect size range: 0.14 to 0.96). In conclusion, (rs5751876) C allele carriers exhibited ergogenic responses to caffeine ingestion, with the magnitude of improvements similar to what was previously reported in the literature among samples that were not genotype-specific. Therefore, individuals with the CT/CC genotype may still consider supplementing with caffeine for acute improvements in performance.
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http://dx.doi.org/10.3390/nu12030741DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7146260PMC
March 2020

Effects of Sodium Bicarbonate Supplementation on Muscular Strength and Endurance: A Systematic Review and Meta-analysis.

Sports Med 2020 Jul;50(7):1361-1375

Institute for Health and Sport (IHES), Victoria University, Melbourne, VIC, Australia.

Background: The effects of sodium bicarbonate on muscular strength and muscular endurance are commonly acknowledged as unclear due to the contrasting evidence on the topic.

Objective: To conduct a systematic review and meta-analysis of studies exploring the acute effects of sodium bicarbonate supplementation on muscular strength and endurance.

Methods: A search for studies was performed using five databases. Meta-analyses of standardized mean differences (SMDs) were performed using a random-effects model to determine the effects of sodium bicarbonate supplementation on muscular strength (assessed by changes in peak force [N], peak torque [N m], or maximum load lifted [kg]) and muscular endurance (assessed by changes in the number of repetitions performed, isokinetic total work, or time to maintain isometric force production). Subgroup meta-analyses were conducted for the muscular endurance of small vs. large muscle groups and muscular strength tested in a rested vs. fatigued state. A random-effects meta-regression analysis was used to explore possible trends in the effects of: (a) timing of sodium bicarbonate ingestion; and (b) acute increase in blood bicarbonate concentration (from baseline to pre-exercise), on muscular endurance and muscular strength.

Results: Thirteen studies explored the effects of sodium bicarbonate on muscular endurance and 11 on muscular strength. Sodium bicarbonate supplementation was found to be ergogenic for muscular endurance (SMD = 0.37; 95% confidence interval [CI]: 0.15, 0.59; p = 0.001). The performance-enhancing effects of sodium bicarbonate were significant for both small (SMD = 0.31; 95% CI: 0.04, 0.59; p = 0.025) and large muscle groups (SMD = 0.40; 95% CI: 0.13, 0.66; p = 0.003). Sodium bicarbonate ingestion was not found to enhance muscular strength (SMD = - 0.03; 95% CI: - 0.18, 0.12; p = 0.725). No significant effects were found regardless of whether the testing was carried out in a rested (SMD = 0.02; 95% CI: - 0.09, 0.13; p = 0.694) or fatigued (SMD = - 0.16; 95% CI: - 0.59, 0.28; p = 0.483) state. No significant linear trends in the effects of timing of sodium bicarbonate ingestion or acute increase in blood bicarbonate concentrations on muscular endurance or muscular strength were found.

Conclusions: Overall, sodium bicarbonate supplementation acutely improves muscular endurance of small and large muscle groups, but no significant ergogenic effect on muscular strength was found.
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http://dx.doi.org/10.1007/s40279-020-01275-yDOI Listing
July 2020

Neuromuscular and perceptual responses during repeated cycling sprints-usefulness of a "hypoxic to normoxic" recovery approach.

Eur J Appl Physiol 2020 Apr 21;120(4):883-896. Epub 2020 Feb 21.

Athlete Health and Performance Research Center, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.

Purpose: We investigated the consequence of varying hypoxia severity during an initial set of repeated cycling sprints on performance, neuromuscular fatigability, and exercise-related sensations during a subsequent set of repeated sprints in normoxia.

Methods: Nine active males performed ten 4-s sprints (recovery = 30 s) at sea level (SL; FiO ~ 0.21), moderate (MH; FiO ~ 0.17) or severe normobaric hypoxia (SH; FiO ~ 0.13). This was followed, after 8 min of passive recovery, by five 4-s sprints (recovery = 30 s) in normoxia.

Results: Mean power decrement during Sprint 10 was exacerbated in SH compared to SL and MH (- 34 ± 12%, - 22 ± 13%, - 25 ± 14%, respectively, p < 0.05). Sprint performance during Sprint 11 recovered to that of Sprint 1 in all conditions (p = 0.267). All exercise-related sensations at Sprint 11 recovered significantly compared to Sprint 1, with no difference for Set 2 (p > 0.05). Ratings of overall perceived discomfort, difficulty breathing, and limb discomfort were exacerbated during Set 1 in SH versus SL (p < 0.05). Compared to SL, the averaged MPO value for Set 2 was 5.5 ± 3.0% (p = 0.003) lower in SH. Maximal voluntary force and twitch torque decreased similarly in all conditions immediately after Set 1 (p < 0.05), without further alterations after Set 2. Peripheral and cortical voluntary activation values did not change (p > 0.05).

Conclusion: Exercise-related sensations, rather than neuromuscular function integrity, may play a pivotal role in influencing performance of repeated sprints and its recovery.
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http://dx.doi.org/10.1007/s00421-020-04327-3DOI Listing
April 2020

The effect of sleep restriction, with or without high-intensity interval exercise, on myofibrillar protein synthesis in healthy young men.

J Physiol 2020 04 11;598(8):1523-1536. Epub 2020 Mar 11.

Institute for Health and Sport, Victoria University, Melbourne, Australia.

Key Points: Sleep restriction has previously been associated with the loss of muscle mass in both human and animal models. The rate of myofibrillar protein synthesis (MyoPS) is a key variable in regulating skeletal muscle mass and can be increased by performing high-intensity interval exercise (HIIE), although the effect of sleep restriction on MyoPS is unknown. In the present study, we demonstrate that participants undergoing a sleep restriction protocol (five nights, with 4 h in bed each night) had lower rates of skeletal muscle MyoPS; however, rates of MyoPS were maintained at control levels by performing HIIE during this period. Our data suggest that the lower rates of MyoPS in the sleep restriction group may contribute to the detrimental effects of sleep loss on muscle mass and that HIIE may be used as an intervention to counteract these effects.

Abstract: The present study aimed to investigate the effect of sleep restriction, with or without high-intensity interval exercise (HIIE), on the potential mechanisms underpinning previously-reported sleep-loss-induced reductions to muscle mass. Twenty-four healthy, young men underwent a protocol consisting of two nights of controlled baseline sleep and a five-night intervention period. Participants were allocated into one of three parallel groups, matched for age, , body mass index and habitual sleep duration; a normal sleep (NS) group [8 h time in bed (TIB) each night], a sleep restriction (SR) group (4 h TIB each night), and a sleep restriction and exercise group (SR+EX, 4 h TIB each night, with three sessions of HIIE). Deuterium oxide was ingested prior to commencing the study and muscle biopsies obtained pre- and post-intervention were used to assess myofibrillar protein synthesis (MyoPS) and molecular markers of protein synthesis and degradation signalling pathways. MyoPS was lower in the SR group [fractional synthetic rate (% day ), mean ± SD, 1.24 ± 0.21] compared to both the NS (1.53 ± 0.09) and SR+EX groups (1.61 ± 0.14) (P < 0.05). However, there were no changes in the purported regulators of protein synthesis (i.e. p-AKT and p-mTOR ) and degradation (i.e. Foxo1/3 mRNA and LC3 protein) in any group. These data suggest that MyoPS is acutely reduced by sleep restriction, although MyoPS can be maintained by performing HIIE. These findings may explain the sleep-loss-induced reductions in muscle mass previously reported and also highlight the potential therapeutic benefit of HIIE to maintain myofibrillar remodelling in this context.
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http://dx.doi.org/10.1113/JP278828DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7217042PMC
April 2020

Transcriptomic profiling of skeletal muscle adaptations to exercise and inactivity.

Nat Commun 2020 01 24;11(1):470. Epub 2020 Jan 24.

Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden.

The molecular mechanisms underlying the response to exercise and inactivity are not fully understood. We propose an innovative approach to profile the skeletal muscle transcriptome to exercise and inactivity using 66 published datasets. Data collected from human studies of aerobic and resistance exercise, including acute and chronic exercise training, were integrated using meta-analysis methods (www.metamex.eu). Here we use gene ontology and pathway analyses to reveal selective pathways activated by inactivity, aerobic versus resistance and acute versus chronic exercise training. We identify NR4A3 as one of the most exercise- and inactivity-responsive genes, and establish a role for this nuclear receptor in mediating the metabolic responses to exercise-like stimuli in vitro. The meta-analysis (MetaMEx) also highlights the differential response to exercise in individuals with metabolic impairments. MetaMEx provides the most extensive dataset of skeletal muscle transcriptional responses to different modes of exercise and an online interface to readily interrogate the database.
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http://dx.doi.org/10.1038/s41467-019-13869-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6981202PMC
January 2020

Mitochondrial respiration variability and simulations in human skeletal muscle: The Gene SMART study.

FASEB J 2020 02 9;34(2):2978-2986. Epub 2020 Jan 9.

Institute for Health and Sport (iHeS), Victoria University, Melbourne, Victoria, Australia.

Mitochondrial respiration using the oxygraph-2k respirometer (Oroboros) is widely used to estimate mitochondrial capacity in human skeletal muscle. Here, we measured mitochondrial respiration variability, in a relatively large sample, and for the first time, using statistical simulations, we provide the sample size required to detect meaningful respiration changes following lifestyle intervention. Muscle biopsies were taken from healthy, young men from the Gene SMART cohort, at multiple time points. We utilized samples for each measurement with two technical repeats using two respirometer chambers (n = 160 pairs of same muscle after removal of low-quality samples). We measured the Technical Error of measurement (TE ) and the coefficient of variation (CV) for each mitochondrial complex. There was a high correlation between measurements from the two chambers (R > 0.7 P < .001) for all complexes, but the TE was large (7.9-27 pmol s  mg ; complex dependent), and the CV was >15% for all complexes. We performed statistical simulations of a range of effect sizes at 80% power and found that 75 participants (with duplicate measurements) are required to detect a 6% change in mitochondrial respiration after an intervention, while for interventions with 11% effect size, ~24 participants are sufficient. The high variability in respiration suggests that the typical sample sizes in exercise studies may not be sufficient to capture exercise-induced changes.
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http://dx.doi.org/10.1096/fj.201901997RRDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7384122PMC
February 2020

Forty high-intensity interval training sessions blunt exercise-induced changes in the nuclear protein content of PGC-1α and p53 in human skeletal muscle.

Am J Physiol Endocrinol Metab 2020 02 3;318(2):E224-E236. Epub 2019 Dec 3.

Institute for Health and Sport, Victoria University, Melbourne, Victoria, Australia.

Exercise-induced increases in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and p53 protein content in the nucleus mediate the initial phase of exercise-induced mitochondrial biogenesis. Here, we investigated whether exercise-induced increases in these and other markers of mitochondrial biogenesis were altered after 40 sessions of twice-daily high-volume, high-intensity interval training (HVT) in human skeletal muscle. Vastus lateralis muscle biopsies were collected from 10 healthy recreationally active participants before, immediately postexercise, and 3 h after a session of high-intensity interval exercise (HIIE) performed at the same absolute exercise intensity before and after HVT (pre-HVT and post-HVT, respectively). The protein content of common markers of exercise-induced mitochondrial biogenesis was assessed in nuclear- and cytosolic-enriched fractions by immunoblotting; mRNA contents of key transcription factors and mitochondrial genes were assessed by qPCR. Despite exercise-induced increases in PGC-1α, p53, and plant homeodomain finger-containing protein 20 (PHF20) protein content, the phosphorylation of p53 and acetyl-CoA carboxylase (p-p53 Ser and p-ACC Ser, respectively), and PGC-1α mRNA Pre-HVT, no significant changes were observed post-HVT. Forty sessions of twice-daily high-intensity interval training blunted all of the measured exercise-induced molecular events associated with mitochondrial biogenesis that were observed pre-HVT. Future studies should determine whether this loss relates to the decrease in relative exercise intensity, habituation to the same exercise stimulus, or a combination of both.
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http://dx.doi.org/10.1152/ajpendo.00233.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7052577PMC
February 2020

Compression Garments Reduce Muscle Movement and Activation during Submaximal Running.

Med Sci Sports Exerc 2020 03;52(3):685-695

Institute for Health and Sport (iHeS), Victoria University, VIC, AUSTRALIA.

Purpose: The purpose of this study was to investigate the effectiveness of sports compression tights in reducing muscle movement and activation during running.

Methods: A total of 27 recreationally active males were recruited across two separate studies. For study 1, 13 participants (mean ± SD = 84.1 ± 9.4 kg, 22 ± 3 yr) completed two 4-min treadmill running bouts (2 min at 12 and 15 km·h) under two conditions: a no-compression control (CON1) and compression (COMP). For study 2, 14 participants (77.8 ± 8.4 kg, 27 ± 5 yr) completed four 9-min treadmill running bouts (3 min at 8, 10, and 12 km·h) under four conditions: a no-compression control (CON2) and three different commercially available compression tights (2XU, Nike, and Under Armor). Using Vicon 3D motion capture technology, lower limb muscle displacement was investigated in both study 1 (thigh and calf) and study 2 (vastus lateralis + medialis [VAS]; lateral + medial gastrocnemius [GAS]). In addition, study 2 investigated the effects of compression on soft tissue vibrations (root-mean-square of resultant acceleration, RMS Ar), muscle activation (iEMG), and running economy (oxygen consumption, V˙O2) during treadmill running.

Results: Wearing compression during treadmill running reduced thigh and calf muscle displacement as compared with no compression (both studies), which was evident across all running speeds. Compression also reduced RMS Ar and iEMG during treadmill running, but it had no effect on running economy (study 2).

Conclusion: Lower limb compression garments are effective in reducing muscle displacement, soft tissue vibrations, and muscle activation associated with the impact forces experienced during running.
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http://dx.doi.org/10.1249/MSS.0000000000002182DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7034367PMC
March 2020

What Dose of Caffeine to Use: Acute Effects of 3 Doses of Caffeine on Muscle Endurance and Strength.

Int J Sports Physiol Perform 2019 Sep 9:1-8. Epub 2019 Sep 9.

Purpose: To explore the effects of 3 doses of caffeine on muscle strength and muscle endurance.

Methods: Twenty-eight resistance-trained men completed the testing sessions under 5 conditions: no-placebo control, placebo control, and with caffeine doses of 2, 4, and 6 mg·kg-1. Muscle strength was assessed using the 1-repetition-maximum test; muscle endurance was assessed by having the participants perform a maximal number of repetitions with 60% 1-repetition maximum.

Results: In comparison with both control conditions, only a caffeine dose of 2 mg·kg-1 enhanced lower-body strength (d = 0.13-0.15). In comparison with the no-placebo control condition, caffeine doses of 4 and 6 mg·kg-1 enhanced upper-body strength (d = 0.07-0.09) with a significant linear trend for the effectiveness of different doses of caffeine (P = .020). Compared with both control conditions, all 3 caffeine doses enhanced lower-body muscle endurance (d = 0.46-0.68). For upper-body muscle endurance, this study did not find significant effects of caffeine.

Conclusions: This study revealed a linear trend between the dose of caffeine and its effects on upper-body strength. The study found no clear association between the dose of caffeine and the magnitude of its ergogenic effects on lower-body strength and muscle endurance. From a practical standpoint, the magnitude of caffeine's effects on strength is of questionable relevance. A low dose of caffeine (2 mg·kg-1)-for an 80-kg individual, the dose of caffeine in 1-2 cups of coffee-may produce substantial improvements in lower-body muscle endurance with the magnitude of the effect being similar to that attained using higher doses of caffeine.
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http://dx.doi.org/10.1123/ijspp.2019-0433DOI Listing
September 2019

Effects of Dietary Supplements on Adaptations to Endurance Training.

Sports Med 2020 Jan;50(1):25-53

Institute for Health and Sport, Victoria University, Melbourne, VIC, Australia.

Endurance training leads to a variety of adaptations at the cellular and systemic levels that serve to minimise disruptions in whole-body homeostasis caused by exercise. These adaptations are differentially affected by training volume, training intensity, and training status, as well as by nutritional choices that can enhance or impair the response to training. A variety of supplements have been studied in the context of acute performance enhancement, but the effects of continued supplementation concurrent to endurance training programs are less well characterised. For example, supplements such as sodium bicarbonate and beta-alanine can improve endurance performance and possibly training adaptations during endurance training by affecting buffering capacity and/or allowing an increased training intensity, while antioxidants such as vitamin C and vitamin E may impair training adaptations by blunting cellular signalling but appear to have little effect on performance outcomes. Additionally, limited data suggest the potential for dietary nitrate (in the form of beetroot juice), creatine, and possibly caffeine, to further enhance endurance training adaptation. Therefore, the objective of this review is to examine the impact of dietary supplements on metabolic and physiological adaptations to endurance training.
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http://dx.doi.org/10.1007/s40279-019-01185-8DOI Listing
January 2020

Cold water immersion attenuates anabolic signaling and skeletal muscle fiber hypertrophy, but not strength gain, following whole-body resistance training.

J Appl Physiol (1985) 2019 11 12;127(5):1403-1418. Epub 2019 Sep 12.

Institute for Health and Sport (iHeS), Victoria University, Melbourne, Australia.

We determined the effects of cold water immersion (CWI) on long-term adaptations and post-exercise molecular responses in skeletal muscle before and after resistance training. Sixteen men (22.9 ± 4.6 y; 85.1 ± 17.9 kg; mean ± SD) performed resistance training (3 day/wk) for 7 wk, with each session followed by either CWI [15 min at 10°C, CWI (COLD) group, = 8] or passive recovery (15 min at 23°C, control group, = 8). Exercise performance [one-repetition maximum (1-RM) leg press and bench press, countermovement jump, squat jump, and ballistic push-up], body composition (dual X-ray absorptiometry), and post-exercise (i.e., +1 and +48 h) molecular responses were assessed before and after training. Improvements in 1-RM leg press were similar between groups [130 ± 69 kg, pooled effect size (ES): 1.53 ± 90% confidence interval (CI) 0.49], whereas increases in type II muscle fiber cross-sectional area were attenuated with CWI (-1,959 ± 1,675 µM ; ES: -1.37 ± 0.99). Post-exercise mechanistic target of rapamycin complex 1 signaling (rps6 phosphorylation) was blunted for COLD at post-training (POST) +1 h (-0.4-fold, ES: -0.69 ± 0.86) and POST +48 h (-0.2-fold, ES: -1.33 ± 0.82), whereas basal protein degradation markers (FOX-O1 protein content) were increased (1.3-fold, ES: 2.17 ± 2.22). Training-induced increases in heat shock protein (HSP) 27 protein content were attenuated for COLD (-0.8-fold, ES: -0.94 ± 0.82), which also reduced total HSP72 protein content (-0.7-fold, ES: -0.79 ± 0.57). CWI blunted resistance training-induced muscle fiber hypertrophy, but not maximal strength, potentially via reduced skeletal muscle protein anabolism and increased catabolism. Post-exercise CWI should therefore be avoided if muscle hypertrophy is desired. This study adds to existing evidence that post-exercise cold water immersion attenuates muscle fiber growth with resistance training, which is potentially mediated by attenuated post-exercise increases in markers of skeletal muscle anabolism coupled with increased catabolism and suggests that blunted muscle fiber growth with cold water immersion does not necessarily translate to impaired strength development.
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http://dx.doi.org/10.1152/japplphysiol.00127.2019DOI Listing
November 2019