Objective and Hypothesis: The objective of this study was to investigate the influence of aging and lifelong lower body endurance exercise on two key parameters of skeletal muscle health (muscle mass and adipose accumulation) in nearly all of the lower limb muscles. We hypothesized that lifelong lower body endurance exercise would be, at least partially, beneficial for the age-related changes in skeletal muscle mass and adipose accumulation. Methods: Skeletal muscle volume and adipose accumulation was measured via magnetic resonance imaging (MRI) in 10 upper (rectus femoris, vastii, adductor longus, adductor magnus, gracilis, sartorius, biceps femoris long head, biceps femoris short head, semimembranosus, semitendinosus) and 7 lower (anterior tibial muscles, posterior tibialis, peroneals, flexor digitorum longus, lateral gastrocnemius, medial gastrocnemius, soleus) leg muscles in 34 men: young exercisers (YE, n=10, 25±1y, 75±8kg, VO 2 max: 53±8ml/kg/min), old healthy non-exercisers (OH, n=10, 75±2y, 88±9kg, VO 2 max: 22±4ml/kg/min), and lifelong endurance exercisers (LLE, n=14, 74±4y, 77±7kg, VO 2 max: 38±4ml/kg/min). LLE completed endurance exercise, primarily running and cycling, for ~50 years (4-6d/wk, ~8h/wk). Results: Age-related skeletal muscle atrophy was found in 7 of the 17 muscles (YE > OH, p≤0.05), ranging from approximately -20% to -40%. LLE reduced age-related atrophy in 4 of these 7 muscles (LLE vs YE, p>0.05). Age-related skeletal muscle adipose accumulation was found in 14 of the 17 muscles (YE 0.05). Conclusions: The current data suggest: 1) Not all (~50%) lower limb skeletal muscles atrophy with aging. 2) Age-related skeletal muscle adipose accumulation (i.e., myosteatosis) occurs in most ( >80%) of the lower limb muscles, and in some muscles the magnitude of this age-related response is substantial. 3) Lifelong lower body endurance exercise has positive effects on those skeletal muscles that undergo age-related atrophy and adipose accumulation, with a much greater influence on reducing adipose infiltration. Funding: This research was supported by the National Institutes of Health Grant R01-AG038576 and the Ball State University Human Bioenergetics Program This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Yoon et al. (Fri,) studied this question.