Skeletal Muscle Size, Function, and Adiposity with Lifelong Aerobic Exercise.

We examined the influence of lifelong aerobic exercise on skeletal muscle size, function, and adiposity. Young exercisers (YE; n=20, 10W, 25±1y), lifelong exercisers (LLE; n=28, 7W, 74±2y), and old-healthy non-exercisers (OH; n=20, 10W, 75±1y) were studied. On average, LLE exercised 5d/wk for 7h/wk over the past 52±1y. The LLE men were subdivided by exercise intensity (Performance: LLE-P, n=14; Fitness: LLE-F, n=7). Upper and lower leg muscle size and adiposity (intermuscular adipose tissue, IMAT) were determined via MRI and quadriceps isotonic and isometric function was assessed. For the quadriceps, aging decreased muscle size, isotonic and isometric strength, contraction velocity (men only), and power (P<0.05). In women, LLE did not influence muscle size or function. In men, LLE attenuated the decline in muscle size and isometric strength by ~50% (P<0.05). LLE did not influence other aspects of muscle function, nor did training intensity influence muscle size or function. For the triceps surae, aging decreased muscle size only in the women, while LLE (both sexes) and training intensity (LLE men) did not influence muscle size. In both sexes, aging increased thigh and calf IMAT by ~130% (P<0.05), while LLE attenuated the thigh increase by ~50% (P<0.05). Within the LLE men, higher training intensity decreased thigh and calf IMAT by ~30% (P<0.05). In summary, aging and lifelong aerobic exercise influenced muscle size, function, and adipose tissue infiltration in a sex and muscle-specific fashion. Higher training intensity throughout the lifespan provided greater protection against adipose tissue infiltration into muscle.