SKELETAL MUSCLE VO2MAX DECLINES WITH AGING INDEPENDENT OF CONVECTIVE OXYGEN DELIVERY

Abstract

It is well established that VO2max declines with age. Most studies examining this issue did so using whole body VO2. It is significant that during whole body exercise, O2 delivery to the working muscles declines from adulthood to old age and this alone can compromise aerobic performance. PURPOSE: To determine if muscle VO2max is reduced with aging independent of convective O2 delivery. METHODS: The distal muscles of a rat (Fisher 344 X Brown Norway F1 Hybrid) single hindlimb preparation perfused at matched rates of muscle convective O2 delivery, in young adult (8 mo old; mean ± SD, body mass: 416 ± 21 g) and late middle aged (28 mo old; 500 ± 58 g) animals, were electrically stimulated for 4 min (60 tetani min−1). Samples were drawn anaerobically every 30 s for measurement of O2 content in femoral arterial and venous blood. VO2max was determined by the product of blood flow and the arterio-venous O2 content difference across the hindlimb. Matching of muscle blood flow between each group was verified by examining the distribution of coloured microspheres infused after the experiment. RESULTS: Muscle O2 delivery was well matched between the 8 mo old (541 ± 96 μmol O2 min−1 100 g−1) and 28 mo old (532 ± 96 μmol O2 min−1 100 g−1) groups. VO2max was lower in the 28 mo old (308 ± 28 μmol O2 min−1 100 g−1) than the 8 mo old (388 ± 28 μmol O2, min−1 100 g−1; p < 0.05) rats. CONCLUSIONS: These results show that, at matched rates of muscle convective O2 delivery, VO2max is reduced with aging, suggesting that alterations in factors intrinsic to skeletal muscle (i.e., reduced capillarization, etc.) play a role in this response. Supported by CIHR (MOP 48185).