The influences of skeletal muscle mitochondria and sex on critical torque and fatigue in humans
Date
2022-08-17
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Abstract
Mitochondria provide ATP through oxidative phosphorylation (OXPHOS) to generate muscular force and maintain cellular homeostasis during exercise. The critical torque (CT) represents the highest intensity of intermittent isometric contractions that can be supported entirely by aerobic metabolism as well as a phase transition between distinct profiles of performance muscle fatigability (PMF) development. The purpose of this study was to investigate whether skeletal muscle mitochondrial content and sex were related to variation in CT and the magnitude of PMF induced by aerobic, small muscle mass exercise. Twelve females and 12 males matched for aerobic fitness underwent vastus lateralis muscle biopsy sampling to determine their myosin heavy chain (MHC) composition (i.e., fibre type), mitochondrial protein content, and citrate synthase (CS) activity. Once recovered, participants completed 3-4 intermittent isometric knee extension trials to task failure, including one trial at a fixed intensity for all participants, to determine CT and the curvature constant (W’), and two 30-min trials of intermittent isometric knee extensor exercise 10% below CT to assess PMF. The absolute CT and relative CT were not significantly different between males and females (p>0.05). There was no significant difference across sexes for the content of any OXPHOS proteins or CS activity (p>0.05); however, males had significantly lower proportions of MHC I compared to females (p=0.021). Multiple biomarkers of mitochondrial content were correlated with CT, and a few of these markers correlated with indices of fatigability at exercise intensities above CT, but none correlated with indices of fatigue below CT. Thirty minutes of isometric knee extensor exercise 10% below CT caused peripheral and central fatigue (p<0.05) for all variables, but males and females demonstrated similar declines in maximum voluntary contraction, potentiated twitch force, low- frequency fatigue, and voluntary activation (p>0.05). Results were similar for exercise performed above the CT. In summary, CT was correlated with skeletal muscle properties related to mitochondrial content in fitness-matched males and females, but CT and mitochondrial content were not different across sexes. Furthermore, the magnitude of PMF induced by exercise near the CT was also similar between sexes, and PMF was only related to skeletal muscle properties for exercise above the CT.
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Keywords
Human physiology, muscle physiology, muscle fatigue
Citation
McDougall, R. M. (2022). The influences of skeletal muscle mitochondria and sex on critical torque and fatigue in humans (Master thesis). University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca .