Adipose depot distribution in the lower limbs: influence of aging and lifelong endurance exercise in women

Objective and Hypothesis: The objective of this study was to investigate the influence of aging and lifelong lower body endurance exercise on adipose distribution within the intramuscular (within skeletal muscle), intermuscular (between skeletal muscle), and subcutaneous adipose depots of the upper and lower leg in women. We hypothesized that engagement with lifelong lower body endurance exercise would, at least partly, prevent the age-related adipose accumulation in each of these three main adipose depots. Methods: Intramuscular, intermuscular, and subcutaneous adipose levels were measured across the upper (mid-thigh) and lower (widest portion of the calf) leg via magnetic resonance imaging (MRI) in 27 women: young exercisers (YE, n=10, 25±1y, 60±2kg, VO2max: 44±2ml/kg/min), old healthy non-exercisers (OH, n=10, 75±1y, 65±1kg, VO2max: 18±1ml/kg/min), and lifelong endurance exercisers (LLE, n=7, 72±2y, 61±4kg, VO2max: 26±2ml/kg/min). LLE engaged with primarily running and cycling endurance exercise for ~50 years (4-5d/wk, ~7h/wk). Results: Age-related adipose accumulation (YE < OH, p≤0.05) occurred in both the upper (+65%) and lower (+68%) leg. The greatest proportional age-related adipose accumulation (YE < OH, p≤0.05) occurred in the intramuscular depot (upper leg: +8-fold, lower leg: +4-fold), with similar proportional increases for intermuscular (upper leg: +2-fold, lower leg: +2-fold) and subcutaneous depots (upper leg: +2-fold, lower leg: +2-fold). The largest contributor to the absolute amount of age-related adipose accumulation (YE < OH, p≤0.05) occurred in the subcutaneous depot (upper leg: +2789mm2, lower leg: +1042mm2), with less absolute increases in the intermuscular (upper leg: +452mm2, lower leg: +85mm2) and intramuscular depots (upper leg: +270mm2, lower leg: +109mm2). The LLE cohort demonstrated no age-related adipose accumulation in any of the three adipose depots in the upper and lower leg (YE vs LLE, p > 0.05). Conclusions: These data suggest that, in women: 1) Age-related adipose accumulation occurs in a depot-specific manner (intramuscular > intermuscular > subcutaneous) in the upper and lower leg. 2) Lifelong lower body endurance exercise training eliminates adipose accumulation in the main adipose depots of the upper and lower leg. 3) Engagement with regular endurance exercise training across the lifespan can positively impact metabolic and skeletal muscle health. 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.