Reduced muscle oxidative capacity is independent of O2 availability in elderly people.

摘要

Impaired O2 transport to skeletal muscle potentially contributes to the decline in aerobic capacity with aging. Thus, we examined whether (1) skeletal muscle oxidative capacity decreases with age and (2) O2 availability or mitochondrial capacity limits the maximal rate of mitochondrial ATP synthesis in vivo in sedentary elderly individuals. We used (31)P-magnetic resonance spectroscopy ((31)P-MRS) to examine the PCr recovery kinetics in six young (26?±?10 years) and six older (69?±?3 years) sedentary subjects following 4 min of dynamic plantar flexion exercise under different fractions of inspired O2 (FiO2, normoxia 0.2; hyperoxia 1.0). End-exercise pH was not significantly different between old (7.04?±?0.10) and young (7.05?±?0.04) and was not affected by breathing hyperoxia (old 7.08?±?0.08, P?>?0.05 and young 7.05?±?0.03). Likewise, end-exercise PCr was not significantly different between old (19?±?4 mM) and young (24?±?5 mM) and was not changed in hyperoxia. The PCr recovery time constant was significantly longer in the old (36?±?9 s) compared to the young in normoxia (23?±?8 s, P?