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 skeletal muscles (intramuscular), between the skeletal muscles (intermuscular), and in the subcutaneous tissue of the upper and lower leg. We hypothesized that lifelong lower body endurance exercise would, at least partially, prevent the age-related adipose accumulation in 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 33 men: young exercisers (YE, n=10, 25±1y, 75±8kg, VO2max: 53±8ml/kg/min), old healthy non-exercisers (OH, n=10, 75±2y, 88±9kg, VO2max: 22±4ml/kg/min), and lifelong endurance exercisers (LLE, n=13, 74±4y, 77±7kg, VO2max: 38±4ml/kg/min). LLE completed endurance exercise, primarily running and cycling, for ~50 years (4-6d/wk, ~8h/wk). Results: There was age-related (YE 0.05) depot. LLE was similar to YE (p > 0.05) with regards to upper and lower leg total adipose accumulation, as well as accumulation in all of the adipose depots (intramuscular, intermuscular, and subcutaneous) with one exception: the lower leg intramuscular adipose accumulation in LLE was greater than YE (+5-fold; p≤0.05) and ~40% lower than OH (p≤0.10). Conclusions: These data suggest that: 1) Age-related adipose accumulation appears to be depot-specific (intramuscular > intermuscular > subcutaneous) in the upper and lower leg. 2) Lifelong lower body endurance exercise has a powerful effect on reducing adipose accumulation in the main adipose depots of the upper and lower leg. 3) Given the known negative health outcomes associated with adipose accumulation, these findings support the beneficial effects of lifelong endurance exercise on skeletal muscle and overall metabolic 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.
Yoon et al. (Fri,) studied this question.