Age-related changes in oxidative capacity differ between locomotory muscles and are associated with physical activity behavior

There is discrepancy in the literature regarding the degree to which old age affects muscle bioenergetics. These discrepancies are likely influenced by several factors, including variations in physical activity (PA) and differences in the muscle group investigated. To test the hypothesis that age may affect muscles differently, we quantified oxidative capacity of tibialis anterior (TA) and vastus lateralis (VL) muscles in healthy, relatively sedentary younger (8 YW, 8 YM; 21- 35 years) and older (8 OW, 8 OM; 65-80 years) adults. To investigate the effect of physical activity on muscle oxidative capacity in older adults, we compared older sedentary women to older women with mild-to-moderate mobility impairment and lower physical activity (OIW, n = 7), and older sedentary men with older active male runners (OAM, n = 6). Oxidative capacity was measured in vivo as the rate constant, kPCr, of postcontraction phosphocreatine recovery, obtained by 31P magnetic resonance spectroscopy following maximal isometric contractions. While kPCr was higher in TA of older than activitymatched younger adults (28%; p = 0.03), older adults had lower kPCr in VL (23%; p = 0.04). In OIW compared with OW, kPCr was lower in VL (~45%; p = 0.01), but not different in TA. In contrast, OAM had higher kPCr than OM (p = 0.03) in both TA (41%) and VL (54%). In older adults, moderate-to-vigorous PA was positively associated with kPCr in VL (r = 0.65, p < 0.001) and TA (r = 0.41, p = 0.03). Collectively, these results indicate that age-related changes in oxidative capacity vary markedly between locomotory muscles, and that altered PA behavior may play a role in these changes.