Evidence of Preserved Oxidative Capacity and Oxygen Delivery in the Plantar Flexor Muscles With Age

Studies examining the effect of aging on skeletal muscle oxidative capacity have yielded equivocal results; however, these investigations may have been confounded by differences in oxygen (O-2) delivery, physical activity, and small numbers of participants. Therefore, we evaluated skeletal muscle oxidative capacity and O-2 delivery in a relatively large group (N = 40) of young (22 +/- 2 years) and old (73 +/- 7 years) participants matched for physical activity. After submaximal dynamic plantar flexion exercise, phosphocreatine (PCr) resynthesis (P-31 magnetic resonance spectroscopy), muscle reoxygenation (near-infrared spectroscopy), and popliteal artery blood flow (Doppler ultrasound) were measured. The phosphocreatine recovery time constant (Tau) (young: 33 +/- 16; old: 30 +/- 11 seconds), maximal rate of adenosine triphosphate (ATP) synthesis (young: 25 +/- 9; old: 27 +/- 8 mM/min), and muscle reoxygenation rates determined by the deoxyhemoglobin/myoglobin recovery Tau (young: 48 +/- 5; old: 47 +/- 9 seconds) were similar between groups. Similarly, although tending to be higher in the old, there were no significant age-related differences in postexercise popliteal blood flow (area under the curve: young: 1,665 +/- 227 vs old: 2,404 +/- 357 mL, p =.06) and convective O-2 delivery (young: 293 +/- 146 vs old: 404 +/- 191 mL, p =.07). In conclusion, when physical activity and O-2 delivery are similar, oxidative capacity in the plantar flexors is not affected by aging. These findings reveal that diminished skeletal muscle oxidative capacity is not an obligatory accompaniment to the aging process.