Key result
Moderate physical activity is linked to higher energy-saving super-relaxed myosin states in type II muscle fibers.
Why the study?
It was unknown whether chronic physical activity in humans is associated with changes in the proportions of super-relaxed and disordered-relaxed skeletal myosins, which regulate resting ATP consumption and muscle metabolism.
Does physical activity level and training type influence resting skeletal muscle myosin conformation and ATP consumption in young men?
Cross-Sectional
Does physical activity level and training type influence resting skeletal muscle myosin conformation and ATP consumption in young men?
Physical activity and specific training regimens can dynamically rewire the molecular metabolism of human skeletal muscle by altering resting myosin conformations and ATP turnover.
Does not support practice changes; hypothesis-generating for activity effects on myosin energetics in type II fibers.
It has recently been established that myosin, the molecular motor protein, is able to exist in two conformations in relaxed skeletal muscle. These conformations are known as the super-relaxed (SRX) and disordered-relaxed (DRX) states and are finely balanced to optimize ATP consumption and skeletal muscle metabolism. Indeed, SRX myosins are thought to have a 5- to 10-fold reduction in ATP turnover compared with DRX myosins. Here, we investigated whether chronic physical activity in humans would be associated with changes in the proportions of SRX and DRX skeletal myosins. For that, we isolated muscle fibers from young men of various physical activity levels (sedentary, moderately physically active, endurance-trained, and strength-trained athletes) and ran a loaded Mant-ATP chase protocol. We observed that in moderately physically active individuals, the amount of myosin molecules in the SRX state in type II muscle fibers was significantly greater than in age-matched sedentary individuals. In parallel, we did not find any difference in the proportions of SRX and DRX myosins in myofibers between highly endurance- and strength-trained athletes. We did however observe changes in their ATP turnover time. Altogether, these results indicate that physical activity level and training type can influence the resting skeletal muscle myosin dynamics. Our findings also emphasize that environmental stimuli such as exercise have the potential to rewire the molecular metabolism of human skeletal muscle through myosin.
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Lewis et al. (2023) conducted a cross-sectional in Healthy individuals with varying physical activity levels. Physical activity and exercise training vs. Sedentary lifestyle was evaluated on Proportion of myosin molecules in the super-relaxed (SRX) state in type II muscle fibers (p=<0.05). Moderate physical activity is associated with a significantly higher proportion of resting skeletal muscle myosin molecules in the energy-saving super-relaxed state in type II muscle fibers compared to a sedentary lifestyle.
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