Exploring the effects of lifelong aerobic exercise on early skeletal muscle remodeling between 8 and 14 months in the rat.

The insidious onset and progression of sarcopenia make it vital to understand the early skeletal muscle changes and explore therapies to slow its progression. This study explored the gastrocnemius remodeling at an early stage of aging (14 months of age) and the effects of lifelong aerobic exercise. For that, 2-month-old male Wistar rats underwent a 12-month treadmill exercise program. Sedentary age-matched, young sedentary, and young exercised for 6 months rats were considered. The results highlighted an age-related decrease in the relative gastrocnemius muscle mass, suggestive of loss or atrophy of some fibers, which was mitigated by lifelong aerobic exercise. Consequently, an age-related compensatory hypertrophy was suggested to be triggered in the gastrocnemius muscle. Data proposed that aging reduced mitochondrial density, indicated by citrate synthase (CS) activity, which was prevented by lifelong aerobic exercise. The reduced CS activity correlated with increased ATP-dependent 6-phosphofructokinase (PFKM)/ATP synthase subunit beta (ATPB) ratio, suggesting that at an early stage of aging, the skeletal muscle favors the glycolytic metabolism in response to decreased mitochondrial content. The results also pointed to an age-induced AMP-activated protein kinase (AMPK) activation and an AMPK-related apoptosis inhibition, perchance to reduce fiber loss or atrophy. The basal phosphorylated AMPK/AMPK ratio decreased with lifelong aerobic exercise, possibly reflecting the exercise-induced increase in CS activity. This work highlights the importance of studying early skeletal muscle changes in aging for timely disease management and prevention.