Effects Of Old Age And Physical Activity On Oxidative Capacity In Human Skeletal Muscle

Abstract

Studies of the effects of old age on muscle oxidative capacity have led to contradictory results. These discrepancies may be due in part to muscle-specific differences in the effects of altered physical activity patterns in the elderly. PURPOSE: To determine if training status has differential effects on oxidative capacity in vivo in two lower limb muscles, tibialis anterior (TA) and vastus lateralis (VL), in young and older men. METHODS: We used phosphorus magnetic resonance spectroscopy (MRS) to measure muscle oxidative capacity non-invasively in young (n=8, 25±4 yrs, mean±SD) and older (n=8, 69±4) healthy, untrained men; and young (n=7, 28±3) and older (n=3, 71±8) male runners. In separate trials, subjects performed a 16-s and a 24-s maximal voluntary isometric contraction of the TA and VL, respectively, while phosphocreatine (PCr) was measured using a 4 tesla MRS system. Resynthesis of [PCr] followed a mono-exponential time course with a rate constant, kPCr, that is attributable to ATP synthesis from oxidative phosphorylation. A three-way (group, muscle, age) ANOVA was applied. RESULTS: There was a main effect of group such that kPCr was higher in trained than untrained men (p<0.001). There was also an age-by-muscle interaction such that kPCr was greater in young compared to older men in VL (p=0.009), but not in TA, regardless of training status.TableCONCLUSION: The decrease in oxidative capacity observed in the VL but not the TA of both older groups provides evidence of a muscle-specific effect of aging that is independent of training status. These results also confirm greater muscle oxidative capacity in vivo in two muscles of the lower limb in trained compared to untrained men. NIH/NIA R01 AG21094, K02 023582; ACSM Student Grant (RGL)