Aerobic power declines with aging in rat skeletal muscles perfused at matched convective O2 delivery

1 Faculty of Kinesiology and 2 Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada T2N 1N4 Although it is well established that maximal O 2 uptake ( O 2 max ) declines from adulthood to old age, the role played by alterations in skeletal muscle is unclear. Specifically, because during whole body exercise reductions in convective O 2 delivery to the working muscles from adulthood to old age compromise aerobic performance, this obscures the influence of alterations within the skeletal muscles. We sought to overcome this limitation by using an in situ pump-perfused hindlimb preparation to permit matching of muscle convective O 2 delivery in young adult (8 mo; muscle convective O 2 delivery = 569 ± 42 µmol O 2 · min 1 · 100 g 1 ) and late middle-aged (28-30 mo; 539 ± 62 µmol O 2 · min 1 · 100 g 1 ) Fischer 344 × Brown Norway F1 hybrid rats. The distal hindlimb muscles were electrically stimulated for 4 min (60 tetani/min), and O 2 max was determined. O 2 max normalized to the contracting muscle mass was 22% lower in the 28- to 30-mo-old (344 ± 17 µmol O 2 · min 1 · 100 g 1 ) than the 8-mo-old (441 ± 20 µmol O 2 · min 1 · 100 g 1 ; P