Publications by authors named "David J Bishop"

146 Publications

Muscle contraction and mitochondrial biogenesis - A brief historical reappraisal.

Acta Physiol (Oxf) 2022 05 30;235(1):e13813. Epub 2022 Mar 30.

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

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http://dx.doi.org/10.1111/apha.13813DOI Listing
May 2022

Exercise and Training Regulation of Autophagy Markers in Human and Rat Skeletal Muscle.

Int J Mol Sci 2022 Feb 27;23(5). Epub 2022 Feb 27.

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

Autophagy is a key intracellular mechanism by which cells degrade old or dysfunctional proteins and organelles. In skeletal muscle, evidence suggests that exercise increases autophagosome content and autophagy flux. However, the exercise-induced response seems to differ between rodents and humans, and little is known about how different exercise prescription parameters may affect these results. The present study utilised skeletal muscle samples obtained from four different experimental studies using rats and humans. Here, we show that, following exercise, in the soleus muscle of Wistar rats, there is an increase in LC3B-I protein levels immediately after exercise (+109%), and a subsequent increase in LC3B-II protein levels 3 h into the recovery (+97%), despite no change in mRNA levels. Conversely, in human skeletal muscle, there is an immediate exercise-induced decrease in LC3B-II protein levels (-24%), independent of whether exercise is performed below or above the maximal lactate steady state, which returns to baseline 3.5 h following recovery, while no change in LC3B-I protein levels or mRNA levels is observed. /p62 protein and mRNA levels did not change in either rats or humans following exercise. By employing an ex vivo autophagy flux assay previously used in rodents we demonstrate that the exercise-induced decrease in LC3B-II protein levels in humans does not reflect a decreased autophagy flux. Instead, effect size analyses suggest a modest-to-large increase in autophagy flux following exercise that lasts up to 24 h. Our findings suggest that exercise-induced changes in autophagosome content markers differ between rodents and humans, and that exercise-induced decreases in LC3B-II protein levels do not reflect autophagy flux level.
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http://dx.doi.org/10.3390/ijms23052619DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8910616PMC
February 2022

Interpretation of exercise-induced changes in human skeletal muscle mRNA expression depends on the timing of the post-exercise biopsies.

PeerJ 2022 4;10:e12856. Epub 2022 Feb 4.

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

Background: Exercise elicits a range of adaptive responses in skeletal muscle, which include changes in mRNA expression. To better understand the health benefits of exercise training, it is important to investigate the underlying molecular mechanisms of skeletal muscle adaptation to exercise. However, most studies have assessed the molecular events at only a few time-points within a short time frame post-exercise, and the variations of gene expression kinetics have not been addressed systematically.

Methods: We assessed the mRNA expression of 23 gene isoforms implicated in the adaptive response to exercise at six time-points (0, 3, 9, 24, 48, and 72 h post exercise) over a 3-day period following a single session of high-intensity interval exercise.

Results: The temporal patterns of target gene expression were highly variable and the expression of mRNA transcripts detected was largely dependent on the timing of muscle sampling. The largest fold change in mRNA expression of each tested target gene was observed between 3 and 72 h post-exercise.

Discussion And Conclusions: Our findings highlight an important gap in knowledge regarding the molecular response to exercise, where the use of limited time-points within a short period post-exercise has led to an incomplete understanding of the molecular response to exercise. Muscle sampling timing for individual studies needs to be carefully chosen based on existing literature and preliminary analysis of the molecular targets of interest. We propose that a comprehensive time-course analysis on the exercise-induced transcriptional response in humans will significantly benefit the field of exercise molecular biology.
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http://dx.doi.org/10.7717/peerj.12856DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8820226PMC
February 2022

Transcription Factor Movement and Exercise-Induced Mitochondrial Biogenesis in Human Skeletal Muscle: Current Knowledge and Future Perspectives.

Int J Mol Sci 2022 Jan 28;23(3). Epub 2022 Jan 28.

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

In response to exercise, the oxidative capacity of mitochondria within skeletal muscle increases through the coordinated expression of mitochondrial proteins in a process termed mitochondrial biogenesis. Controlling the expression of mitochondrial proteins are transcription factors-a group of proteins that regulate messenger RNA transcription from DNA in the nucleus and mitochondria. To fulfil other functions or to limit gene expression, transcription factors are often localised away from DNA to different subcellular compartments and undergo rapid movement or accumulation only when required. Although many transcription factors involved in exercise-induced mitochondrial biogenesis have been identified, numerous conflicting findings and gaps exist within our knowledge of their subcellular movement. This review aims to summarise and provide a critical analysis of the published literature regarding the exercise-induced movement of transcription factors involved in mitochondria biogenesis in skeletal muscle.
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http://dx.doi.org/10.3390/ijms23031517DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8836245PMC
January 2022

Myths and methodologies: The use of equivalence and non-inferiority tests for interventional studies in exercise physiology and sport science.

Exp Physiol 2022 03 26;107(3):201-212. Epub 2022 Jan 26.

Human Technology Interaction Group, Eindhoven University of Technology (TU/e), Eindhoven, The Netherlands.

Exercise physiology and sport science have traditionally made use of the null hypothesis of no difference to make decisions about experimental interventions. In this article, we aim to review current statistical approaches typically used by exercise physiologists and sport scientists for the design and analysis of experimental interventions and to highlight the importance of including equivalence and non-inferiority studies, which address different research questions from deciding whether an effect is present. Initially, we briefly describe the most common approaches, along with their rationale, to investigate the effects of different interventions. We then discuss the main steps involved in the design and analysis of equivalence and non-inferiority studies, commonly performed in other research fields, with worked examples from exercise physiology and sport science scenarios. Finally, we provide recommendations to exercise physiologists and sport scientists who would like to apply the different approaches in future research. We hope this work will promote the correct use of equivalence and non-inferiority designs in exercise physiology and sport science whenever the research context, conditions, applications, researchers' interests or reasonable beliefs justify these approaches.
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http://dx.doi.org/10.1113/EP090171DOI Listing
March 2022

Methods to match high-intensity interval exercise intensity in hypoxia and normoxia - A pilot study.

J Exerc Sci Fit 2022 Jan 27;20(1):70-76. Epub 2021 Dec 27.

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

The aim of this study was to compare high-intensity interval exercise (HIIE) sessions prescribed on the basis of a maximal value (peak power output, PPO) and a submaximal value (lactate threshold, LT) derived from graded exercise tests (GXTs) in normoxia and hypoxia.

Methods: A total of ten males (aged 18-37) volunteered to participate in this study. The experimental protocol consisted of a familiarization procedure, two GXTs under normoxia (FiO = 0.209) and two GXTs under normobaric hypoxia (FiO2 = 0.140), and three HIIE sessions performed in a random order. The HIIE sessions included one at hypoxia (HY) and two at normoxia (one matched for the absolute intensity in hypoxia, designated as NA, and one matched for the relative intensity in hypoxia, designated as NR).

Results: The data demonstrated that there was significant lower peak oxygen uptake (V̇O), peak heart rate (HR), PPO, and LT derived from GXTs in hypoxia, with higher respiratory exchange ratio (RER), when compared to those from GXTs performed in normoxia ( < 0.001). Among the three HIIE sessions, the NA session resulted in lower percentage of HR (85.0 ± 7.5% vs 94.4 ± 5.0%;  = 0.002) and V̇O (74.1 ± 9.1% vs 88.7 ± 7.7%;  = 0.005), when compared to the NR session. HIIE sessions in HY and NR resulted in similar percentage of HR and V̇O, as well as similar rating of perceived exertion and RER. The blood lactate level increased immediately after all the three HIIE sessions ( < 0.001), while higher blood lactate concentrations were observed immediately after the HY ( = 0.0003) and NR (p = 0.014) sessions when compared with NA.

Conclusion: Combining of PPO and LT derived from GXTs can be used to prescribe exercise intensity of HIIE in hypoxia.
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http://dx.doi.org/10.1016/j.jesf.2021.12.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8728434PMC
January 2022

Assessing mitochondrial respiration in permeabilized fibres and biomarkers for mitochondrial content in human skeletal muscle.

Acta Physiol (Oxf) 2022 02 21;234(2):e13772. Epub 2022 Jan 21.

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

Aim: Assessments of mitochondrial respiration and mitochondrial content are common in skeletal muscle research and exercise science. However, many sources of technical and biological variation render these analyses susceptible to error. This study aimed to better quantify the reliability of different experimental designs and/or techniques so as to assist researchers to obtain more reliable data.

Methods: We examined the repeatability of maximal mitochondrial oxidative phosphorylation in permeabilized muscle fibres via high-resolution respirometry, and citrate synthase activity (a biomarker for mitochondrial content) in a microplate with spectrophotometery.

Results: For mitochondrial respiration using permeabilized skeletal muscle fibres, the variability was reduced using three chambers and removing outliers compared to two chambers (CV reduced from 12.7% to 11.0%), and the minimal change that can be detected with 10 participants reduced from 17% to 13% according to modelling. For citrate synthase activity, the within-plate CV (3.5%) increased when the assay was repeated after 4 hours (CV = 10.2%) and 4 weeks (CV = 30.5%). The readings were correlated, but significantly different after 4 hours and 4 weeks.

Conclusion: This research provides evidence for important technical considerations when measuring mitochondrial respiration and content using citrate synthase activity as a biomarker. When assessing mitochondrial respiration in human skeletal muscle, the technical variability of high-resolution respirometry can be reduced by increasing technical repeats and excluding outliers, practices which are not currently common. When analysing citrate synthase activity, our results highlight the importance of analysing all samples from the same study at the same time.
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http://dx.doi.org/10.1111/apha.13772DOI Listing
February 2022

Aerobic-interval exercise with blood flow restriction potentiates early markers of metabolic health in man.

Acta Physiol (Oxf) 2022 02 16;234(2):e13769. Epub 2022 Jan 16.

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

Aim: This study examined whether aerobic-interval exercise with blood flow restriction (BFR) potentiates early markers of metabolic health compared to exercise with systemic hypoxia or normoxia in man.

Methods: In a randomized-crossover fashion, eight healthy men completed nine 2-minute running bouts at 105% of their lactate threshold on three occasions separated by one week, either with BFR (BFR-trial), systemic hypoxia (HYP-trial) or normoxia (control; CON-trial). Near-infrared spectroscopy was used to assess the muscle level of hypoxia. A muscle biopsy was collected at rest and 3 hours after exercise to quantify genes involved in cholesterol synthesis (PGC-1α2), glucose disposal (GLUT4) and capillary growth (HIF-1α; VEGFA), as well as mitochondrial respiration (PGC-1α2/3), uncoupling (UCP3) and expansion (p53; COXIV-1/2; CS; AMPKα1/2).

Results: The muscle level of hypoxia was matched between the BFR-trial and HYP-trial (~90%; P > .05), which was greater than the CON-trial (~70%; P < .05). PGC-1α2 increased most in the BFR-trial (16-fold vs CON-trial; 11-fold vs HYP-trial; P < .05). GLUT4 and VEGFA selectively increased by 2.0 and 3.4-fold, respectively in BFR-trial (P < .05), which was greater than CON-trial (1.2 and 1.3 fold) and HYP-trial (1.2 and 1.8 fold; P < .05). UCP3 increased more in BFR-trial than the HYP-trial (4.3 vs 1.6 fold), but was not different between BFR-trial and CON-trial (2.1 fold) or between CON-trial and HYP-trial (P > .05). No trial differences were evident for other genes (P > .05).

Conclusion: Independent of the muscle level of hypoxia, BFR-exercise potentiates early markers of metabolic health associated with the regulation of cholesterol production and glucose homeostasis in man.
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http://dx.doi.org/10.1111/apha.13769DOI Listing
February 2022

Factors Influencing AMPK Activation During Cycling Exercise: A Pooled Analysis and Meta-Regression.

Sports Med 2022 Jun 8;52(6):1273-1294. Epub 2021 Dec 8.

Sports Performance Research Institute New Zealand (SPRINZ), Auckland University of Technology, Auckland, New Zealand.

Background: The 5' adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a cellular energy sensor that is activated by increases in the cellular AMP/adenosine diphosphate:adenosine triphosphate (ADP:ATP) ratios and plays a key role in metabolic adaptations to endurance training. The degree of AMPK activation during exercise can be influenced by many factors that impact on cellular energetics, including exercise intensity, exercise duration, muscle glycogen, fitness level, and nutrient availability. However, the relative importance of these factors for inducing AMPK activation remains unclear, and robust relationships between exercise-related variables and indices of AMPK activation have not been established.

Objectives: The purpose of this analysis was to (1) investigate correlations between factors influencing AMPK activation and the magnitude of change in AMPK activity during cycling exercise, (2) investigate correlations between commonly reported measures of AMPK activation (AMPK-α2 activity, phosphorylated (p)-AMPK, and p-acetyl coenzyme A carboxylase (p-ACC), and (3) formulate linear regression models to determine the most important factors for AMPK activation during exercise.

Methods: Data were pooled from 89 studies, including 982 participants (93.8% male, maximal oxygen consumption [[Formula: see text]] 51.9 ± 7.8 mL kg min). Pearson's correlation analysis was performed to determine relationships between effect sizes for each of the primary outcome markers (AMPK-α2 activity, p-AMPK, p-ACC) and factors purported to influence AMPK signaling (muscle glycogen, carbohydrate ingestion, exercise duration and intensity, fitness level, and muscle metabolites). General linear mixed-effect models were used to examine which factors influenced AMPK activation.

Results: Significant correlations (r = 0.19-0.55, p < .05) with AMPK activity were found between end-exercise muscle glycogen, exercise intensity, and muscle metabolites phosphocreatine, creatine, and free ADP. All markers of AMPK activation were significantly correlated, with the strongest relationship between AMPK-α2 activity and p-AMPK (r = 0.56, p < 0.001). The most important predictors of AMPK activation were the muscle metabolites and exercise intensity.

Conclusion: Muscle glycogen, fitness level, exercise intensity, and exercise duration each influence AMPK activity during exercise when all other factors are held constant. However, disrupting cellular energy charge is the most influential factor for AMPK activation during endurance exercise.
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http://dx.doi.org/10.1007/s40279-021-01610-xDOI Listing
June 2022

High-intensity training induces non-stoichiometric changes in the mitochondrial proteome of human skeletal muscle without reorganisation of respiratory chain content.

Nat Commun 2021 12 3;12(1):7056. Epub 2021 Dec 3.

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

Mitochondrial defects are implicated in multiple diseases and aging. Exercise training is an accessible, inexpensive therapeutic intervention that can improve mitochondrial bioenergetics and quality of life. By combining multiple omics techniques with biochemical and in silico normalisation, we removed the bias arising from the training-induced increase in mitochondrial content to unearth an intricate and previously undemonstrated network of differentially prioritised mitochondrial adaptations. We show that changes in hundreds of transcripts, proteins, and lipids are not stoichiometrically linked to the overall increase in mitochondrial content. Our findings suggest enhancing electron flow to oxidative phosphorylation (OXPHOS) is more important to improve ATP generation than increasing the abundance of the OXPHOS machinery, and do not support the hypothesis that training-induced supercomplex formation enhances mitochondrial bioenergetics. Our study provides an analytical approach allowing unbiased and in-depth investigations of training-induced mitochondrial adaptations, challenging our current understanding, and calling for careful reinterpretation of previous findings.
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http://dx.doi.org/10.1038/s41467-021-27153-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8642543PMC
December 2021

Exercise does not improve insulin resistance and mitochondrial characteristics together.

J Endocrinol 2021 12 9;252(2):91-105. Epub 2021 Dec 9.

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

The aim of this study was to investigate the relationship between mitochondrial content and respiratory function and whole-body insulin resistance in high-fat diet (HFD) fed rats. Male Wistar rats were given either a chow diet or an HFD for 12 weeks. After 4 weeks of the dietary intervention, half of the rats in each group began 8 weeks of interval training. In vivo glucose and insulin tolerance were assessed. Mitochondrial respiratory function was assessed in permeabilised soleus and white gastrocnemius (WG) muscles. Mitochondrial content was determined by the measurement of citrate synthase (CS) activity and protein expression of components of the electron transport system (ETS). We found HFD rats had impaired glucose and insulin tolerance but increased mitochondrial respiratory function and increased protein expression of components of the ETS. This was accompanied by an increase in CS activity in WG. Exercise training improved glucose and insulin tolerance in the HFD rats. Mitochondrial respiratory function was increased with exercise training in the chow-fed animals in soleus muscle. This exercise effect was absent in the HFD animals. In conclusion, exercise training improved insulin resistance in HFD rats but without changes in mitochondrial respiratory function and content. The lack of an association between mitochondrial characteristics and whole-body insulin resistance was reinforced by the absence of strong correlations between these measures. Our results suggest that improvements in mitochondrial respiratory function and content are not responsible for improvements in whole-body insulin resistance in HFD rats.
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http://dx.doi.org/10.1530/JOE-21-0242DOI Listing
December 2021

Revisiting the contribution of mitochondrial biology to the pathophysiology of skeletal muscle insulin resistance.

Biochem J 2021 11;478(21):3809-3826

Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Canada.

While the etiology of type 2 diabetes is multifaceted, the induction of insulin resistance in skeletal muscle is a key phenomenon, and impairments in insulin signaling in this tissue directly contribute to hyperglycemia. Despite the lack of clarity regarding the specific mechanisms whereby insulin signaling is impaired, the key role of a high lipid environment within skeletal muscle has been recognized for decades. Many of the proposed mechanisms leading to the attenuation of insulin signaling - namely the accumulation of reactive lipids and the pathological production of reactive oxygen species (ROS), appear to rely on this high lipid environment. Mitochondrial biology is a central component to these processes, as these organelles are almost exclusively responsible for the oxidation and metabolism of lipids within skeletal muscle and are a primary source of ROS production. Classic studies have suggested that reductions in skeletal muscle mitochondrial content and/or function contribute to lipid-induced insulin resistance; however, in recent years the role of mitochondria in the pathophysiology of insulin resistance has been gradually re-evaluated to consider the biological effects of alterations in mitochondrial content. In this respect, while reductions in mitochondrial content are not required for the induction of insulin resistance, mechanisms that increase mitochondrial content are thought to enhance mitochondrial substrate sensitivity and submaximal adenosine diphosphate (ADP) kinetics. Thus, this review will describe the central role of a high lipid environment in the pathophysiology of insulin resistance, and present both classic and contemporary views of how mitochondrial biology contributes to insulin resistance in skeletal muscle.
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http://dx.doi.org/10.1042/BCJ20210145DOI Listing
November 2021

Impacts of high-intensity exercise on the metabolomics profile of human skeletal muscle tissue.

Scand J Med Sci Sports 2022 Feb 3;32(2):402-413. Epub 2021 Nov 3.

Laboratory of Exercise Physiology, Faculty of Physical Education, University of Campinas (UNICAMP), Campinas, Brazil.

The study aimed to identify and quantify the metabolites profile and metabolic pathways in human muscle tissue engaged during exhaustive high-intensity cycling exercise. Seven healthy physically active men performed a graded exercise test and an exhaustive supramaximal effort at 115% of maximal aerobic power with muscles biopsies performed in rest and immediately after exhaustion for quantifying of muscle metabolites changes by H-NMR spectroscopy. The time until exhaustion (tlim) recorded was 224.7 ± 35.5 s whereas the muscle pH at exhaustion was 6.48 ± 0.05. A total of 54 metabolites were identified and quantified. The most enriched and impacted pathways included: beta oxidation of very long chain fatty acids, mitochondrial electron transport chain, alanine aspartate, and glutamate metabolism, citric acid cycle, arginine biosynthesis, propanoate metabolism, threonine and 2-oxobutanoate degradation and pyruvate metabolism. In addition, the muscle concentrations in Post exercise, compared to Pre increased significantly (p < 0.0398) for fumarate (42.0%), succinate (101.2%), glucose (249.7%), lactate (122.8%), O-acetylcarnitine (164.7%), glycerol (79.3%), AMP (288.2%), 2-oxobutyrate (121.0%), and methanol (58.5%), whereas decreased significantly (p < 0.010) for creatine phosphate (-70.2%), ADP (-56.5%), carnitine (-33.5%), and glutamate (-42.3%). Only the succinate was significantly correlated with tlim (r = -0.76; p = 0.0497). Besides the classical expected contribution of glycolytic and phosphagen energetic pathways, it was demonstrated that the high-intensity exercise is also associated with pathways indicatives of amino acid and fatty acid oxidation metabolisms, highlighting the inverse relation between changes in the intramuscular succinate levels and tlim.
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http://dx.doi.org/10.1111/sms.14086DOI Listing
February 2022

Effects of mild heat exposure on fatigue responses during two sets of repeated sprints matched for initial mechanical output.

J Sci Med Sport 2022 Mar 30;25(3):249-254. Epub 2021 Sep 30.

Research and Scientific Support, Aspetar Orthopaedic and Sports Medicine Hospital, Qatar; School of Human Sciences (Exercise and Sport Science), The University of Western Australia, Australia. Electronic address:

Objectives: We examined whether mild heat exposure alters performance, perceptual responses and neural drive to the quadriceps during two sets of repeated sprints matched for initial mechanical output.

Design: Repeated measures.

Methods: Twelve males performed 10 × 6-s sprints (recovery = 30 s), followed 6 min later by 5 × 6-s sprints (recovery = 30 s) in either COOL (24 °C/30% rH) or HOT (35 °C/40% rH) conditions. Subsequently, two sets of five consecutive sprints matched for initial mechanical output were compared.

Results: On the basis of peak power, performance in sprint 2 was not significantly different to sprint 11 in both conditions (p ≥ 0.32). Average peak power across the five sprints compared (i.e., sprints 2-6 and 11-15, respectively) was 2.6 ± 3.4% higher in HOT compared to COOL (p = 0.025). Electromyographic activity (root mean square value) of the vastus lateralis muscle remained unchanged. Core (sprints 2-6: 37.85 ± 0.21 vs. 37.53 ± 0.19 °C, sprints 11-15: 38.26 ± 0.33 vs. 37.89 ± 0.24 °C; p < 0.001) and skin (sprints 2-6: 36.21 ± 0.29 vs. 30.72 ± 0.52 °C, sprints 11-15: 36.37 ± 0.28 vs. 30.99 ± 0.55 °C; p < 0.001) temperatures were overall higher in HOT compared to COOL. Heart rate, thermal sensation and comfort were significantly elevated in HOT compared to COOL (p ≤ 0.02), irrespective of sprint number.

Conclusions: When two sets of repeated sprints were matched for initial mechanical output, performance was enhanced with mild heat exposure. This occurred despite higher thermal, cardiovascular, and perceptual strain, and without alterations in quadriceps neural drive.
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http://dx.doi.org/10.1016/j.jsams.2021.09.009DOI Listing
March 2022

Analysis of a Casimir-driven parametric amplifier with resilience to Casimir pull-in for MEMS single-point magnetic gradiometry.

Microsyst Nanoeng 2021 7;7:73. Epub 2021 Sep 7.

Department of Mechanical Engineering, Boston University, Boston, MA 02215 USA.

The Casimir force, a quantum mechanical effect, has been observed in several microelectromechanical system (MEMS) platforms. Due to its extreme sensitivity to the separation of two objects, the Casimir force has been proposed as an excellent avenue for quantum metrology. Practical application, however, is challenging due to attractive forces leading to stiction and device failure, called Casimir pull-in. In this work, we design and simulate a Casimir-driven metrology platform, where a time-delay-based parametric amplification technique is developed to achieve a steady-state and avoid pull-in. We apply the design to the detection of weak, low-frequency, gradient magnetic fields similar to those emanating from ionic currents in the heart and brain. Simulation parameters are selected from recent experimental platforms developed for Casimir metrology and magnetic gradiometry, both on MEMS platforms. While a MEMS offers many advantages to such an application, the detected signal must typically be at the resonant frequency of the device, with diminished sensitivity in the low frequency regime of biomagnetic fields. Using a Casimir-driven parametric amplifier, we report a 10,000-fold improvement in the best-case resolution of MEMS single-point gradiometers, with a maximum sensitivity of 6 Hz/(pT/cm) at 1 Hz. Further development of the proposed design has the potential to revolutionize metrology and may specifically enable the unshielded monitoring of biomagnetic fields in ambient conditions.
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http://dx.doi.org/10.1038/s41378-021-00289-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433440PMC
September 2021

Probing the subcellular nanostructure of engineered human cardiomyocytes in 3D tissue.

Microsyst Nanoeng 2021 27;7:10. Epub 2021 Jan 27.

Department of Mechanical Engineering, Boston University, Boston, MA 02215 USA.

The structural and functional maturation of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) is essential for pharmaceutical testing, disease modeling, and ultimately therapeutic use. Multicellular 3D-tissue platforms have improved the functional maturation of hiPSC-CMs, but probing cardiac contractile properties in a 3D environment remains challenging, especially at depth and in live tissues. Using small-angle X-ray scattering (SAXS) imaging, we show that hiPSC-CMs matured and examined in a 3D environment exhibit a periodic spatial arrangement of the myofilament lattice, which has not been previously detected in hiPSC-CMs. The contractile force is found to correlate with both the scattering intensity (  = 0.44) and lattice spacing (  = 0.46). The scattering intensity also correlates with lattice spacing (  = 0.81), suggestive of lower noise in our structural measurement than in the functional measurement. Notably, we observed decreased myofilament ordering in tissues with a myofilament mutation known to lead to hypertrophic cardiomyopathy (HCM). Our results highlight the progress of human cardiac tissue engineering and enable unprecedented study of structural maturation in hiPSC-CMs.
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http://dx.doi.org/10.1038/s41378-020-00234-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433147PMC
January 2021

100 pT/cm single-point MEMS magnetic gradiometer from a commercial accelerometer.

Microsyst Nanoeng 2020 10;6:71. Epub 2020 Aug 10.

Department of Mechanical Engineering, Boston University, Boston, MA 02215 USA.

Magnetic sensing is present in our everyday interactions with consumer electronics and demonstrates the potential for the measurement of extremely weak biomagnetic fields, such as those of the heart and brain. In this work, we leverage the many benefits of microelectromechanical system (MEMS) devices to fabricate a small, low-power, and inexpensive sensor whose resolution is in the range of biomagnetic fields. At present, biomagnetic fields are measured only by expensive mechanisms such as optical pumping and superconducting quantum interference devices (SQUIDs), suggesting a large opportunity for MEMS technology in this work. The prototype fabrication is achieved by assembling micro-objects, including a permanent micromagnet, onto a postrelease commercial MEMS accelerometer using a pick-and-place technique. With this system, we demonstrate a room-temperature MEMS magnetic gradiometer. In air, the sensor's response is linear, with a resolution of 1.1 nT cm, spans over 3 decades of dynamic range to 4.6 µT cm, and is capable of off-resonance measurements at low frequencies. In a 1 mTorr vacuum with 20 dB magnetic shielding, the sensor achieves a 100 pT cm resolution at resonance. This resolution represents a 30-fold improvement compared with that of MEMS magnetometer technology and a 1000-fold improvement compared with that of MEMS gradiometer technology. The sensor is capable of a small spatial resolution with a magnetic sensing element of 0.25 mm along its sensitive axis, a >4-fold improvement compared with that of MEMS gradiometer technology. The calculated noise floor of this platform is 110 fT cm Hz, and thus, these devices hold promise for both magnetocardiography (MCG) and magnetoencephalography (MEG) applications.
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http://dx.doi.org/10.1038/s41378-020-0173-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8433323PMC
August 2020

International Society of Sports Nutrition position stand: sodium bicarbonate and exercise performance.

J Int Soc Sports Nutr 2021 Sep 9;18(1):61. Epub 2021 Sep 9.

Performance & Physique Enhancement Laboratory, University of South Florida, Tampa, FL, 33612, USA.

Based on a comprehensive review and critical analysis of the literature regarding the effects of sodium bicarbonate supplementation on exercise performance, conducted by experts in the field and selected members of the International Society of Sports Nutrition (ISSN), the following conclusions represent the official Position of the Society: 1. Supplementation with sodium bicarbonate (doses from 0.2 to 0.5 g/kg) improves performance in muscular endurance activities, various combat sports, including boxing, judo, karate, taekwondo, and wrestling, and in high-intensity cycling, running, swimming, and rowing. The ergogenic effects of sodium bicarbonate are mostly established for exercise tasks of high-intensity that last between 30 s and 12 min. 2. Sodium bicarbonate improves performance in single- and multiple-bout exercise. 3. Sodium bicarbonate improves exercise performance in both men and women. 4. For single-dose supplementation protocols, 0.2 g/kg of sodium bicarbonate seems to be the minimum dose required to experience improvements in exercise performance. The optimal dose of sodium bicarbonate dose for ergogenic effects seems to be 0.3 g/kg. Higher doses (e.g., 0.4 or 0.5 g/kg) may not be required in single-dose supplementation protocols, because they do not provide additional benefits (compared with 0.3 g/kg) and are associated with a higher incidence and severity of adverse side-effects. 5. For single-dose supplementation protocols, the recommended timing of sodium bicarbonate ingestion is between 60 and 180 min before exercise or competition. 6. Multiple-day protocols of sodium bicarbonate supplementation can be effective in improving exercise performance. The duration of these protocols is generally between 3 and 7 days before the exercise test, and a total sodium bicarbonate dose of 0.4 or 0.5 g/kg per day produces ergogenic effects. The total daily dose is commonly divided into smaller doses, ingested at multiple points throughout the day (e.g., 0.1 to 0.2 g/kg of sodium bicarbonate consumed at breakfast, lunch, and dinner). The benefit of multiple-day protocols is that they could help reduce the risk of sodium bicarbonate-induced side-effects on the day of competition. 7. Long-term use of sodium bicarbonate (e.g., before every exercise training session) may enhance training adaptations, such as increased time to fatigue and power output. 8. The most common side-effects of sodium bicarbonate supplementation are bloating, nausea, vomiting, and abdominal pain. The incidence and severity of side-effects vary between and within individuals, but it is generally low. Nonetheless, these side-effects following sodium bicarbonate supplementation may negatively impact exercise performance. Ingesting sodium bicarbonate (i) in smaller doses (e.g., 0.2 g/kg or 0.3 g/kg), (ii) around 180 min before exercise or adjusting the timing according to individual responses to side-effects, (iii) alongside a high-carbohydrate meal, and (iv) in enteric-coated capsules are possible strategies to minimize the likelihood and severity of these side-effects. 9. Combining sodium bicarbonate with creatine or beta-alanine may produce additive effects on exercise performance. It is unclear whether combining sodium bicarbonate with caffeine or nitrates produces additive benefits. 10. Sodium bicarbonate improves exercise performance primarily due to a range of its physiological effects. Still, a portion of the ergogenic effect of sodium bicarbonate seems to be placebo-driven.
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http://dx.doi.org/10.1186/s12970-021-00458-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8427947PMC
September 2021

Caffeine during High-Intensity Whole-Body Exercise: An Integrative Approach beyond the Central Nervous System.

Nutrients 2021 Jul 22;13(8). Epub 2021 Jul 22.

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

Caffeine is one of the most consumed ergogenic aids around the world. Many studies support the ergogenic effect of caffeine over a large spectrum of exercise types. While the stimulatory effect of caffeine on the central nervous system is the well-accepted mechanism explaining improvements in exercise performance during high-intensity whole-body exercise, in which other physiological systems such as pulmonary, cardiovascular, and muscular systems are maximally activated, a direct effect of caffeine on such systems cannot be ignored. A better understanding of the effects of caffeine on multiple physiological systems during high-intensity whole-body exercise might help to expand its use in different sporting contexts (e.g., competitions in different environments, such as altitude) or even assist the treatment of some diseases (e.g., chronic obstructive pulmonary disease). In the present narrative review, we explore the potential effects of caffeine on the pulmonary, cardiovascular, and muscular systems, and describe how such alterations may interact and thus contribute to the ergogenic effects of caffeine during high-intensity whole-body exercise. This integrative approach provides insights regarding how caffeine influences endurance performance and may drive further studies exploring its mechanisms of action in a broader perspective.
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http://dx.doi.org/10.3390/nu13082503DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8400708PMC
July 2021

Sports compression garments improve resting markers of venous return and muscle blood flow in male basketball players.

J Sport Health Sci 2021 Jul 24. Epub 2021 Jul 24.

Institute for Health and Sport (iHeS), Victoria University, Footscray, VIC 3011, Australia; Department of Physiology, Australian Institute of Sport, Bruce, ACT 2617, Australia.

Background: The benefits associated with sports compression garments are thought to be closely related to enhanced blood flow. However, findings are equivocal, possibly due to heterogeneity in the techniques used for measuring blood flow, the garment types used, and the pressures applied. This study combined Doppler ultrasound and near-infrared spectroscopy technologies to provide the first comprehensive assessment of the effects of 3 sports compression garment types on markers of venous return and muscle blood flow at rest.

Methods: Resting lower-limb blood flow measures (markers of venous return, muscle blood flow, and muscle oxygenation) of 22 elite, junior, male basketball players (age = 17.2 ± 0.9 years, mean ± SD) were assessed in 4 separate conditions: no compression (CON), compression tights (TIGHTS), compression shorts (SHORTS), and compression socks (SOCKS). Markers of venous return (cross-sectional area, time-averaged mean and peak blood flow velocity, and venous blood flow) were measured via Doppler ultrasound at the popliteal and common femoral veins. Muscle blood flow and muscle oxygenation were measured in the gastrocnemius medialis and vastus lateralis using near-infrared spectroscopy.

Results: Popliteal markers of venous return were higher in TIGHTS compared to CON (p < 0.01) and SHORTS (p < 0.01), with SOCKS values higher compared with CON (p < 0.05). Common femoral vein markers of venous return were higher for all conditions compared to CON (p < 0.05), with TIGHTS values also higher compared to SOCKS (p < 0.05). Gastrocnemius medialis blood flow was higher for TIGHTS compared to CON (p = 0.000), SOCKS (p = 0.012), and SHORTS (p = 0.000), with SOCKS higher compared to SHORTS (p = 0.046). Vastus lateralis blood flow was higher for TIGHTS compared to CON (p = 0.028) and SOCKS (p = 0.019), with SHORTS also higher compared to CON (p = 0.012) and SOCKS (p = 0.005). Gastrocnemius medialis oxygenation was higher for TIGHTS compared to CON (p = 0.003), SOCKS (p = 0.033), and SHORTS (p = 0.003), with SOCKS higher compared to CON (p = 0.044) and SHORTS (p = 0.032). Vastus lateralis oxygenation was higher for TIGHTS compared to CON (p = 0.020) and SOCKS (p = 0.006).

Conclusion: Markers of venous return, muscle blood flow, and muscle oxygenation are increased with sports compression garments. TIGHTS are most effective, potentially because of the larger body area compressed.
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http://dx.doi.org/10.1016/j.jshs.2021.07.010DOI Listing
July 2021

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

Eur J Appl Physiol 2021 Aug 14;121(8):2323-2336. 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
August 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 07;17(7):385-386

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
July 2021

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

FASEB J 2021 05;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 03;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 04 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
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