Effects Of Age And Aerobic Exercise Training On The Oxygen Cost Of Leg Cycling

Abstract

PURPOSE Leg muscle strength, size and oxidative capacity decline with age, contributing to reduced VO2peak but it is less clear whether age also alters the oxygen cost of leg cycling (economy). Since muscle structure and metabolic capacity are reported to change with age we tested the hypothesis that suggest oxygen cost of leg cycling would decline with age but would be improved with aerobic exercise training. METHODS Healthy, non-exercise trained men and women (n = 58, age 21–81) were tested before and after 4 months of aerobic bicycle exercise (3–4 d/wk at 65–80% of HRpeak for 20–40 min). VO2 was measured during seated rest on the bike and at workloads eliciting ∼50%, 70% and 100% VO2peak. RESULTS At baseline there were age related reductions (p<0.01) in leg muscle size (4%/decade), isokinetic knee extensor strength (9%/decade) and VO2peak (7%/decade). However, the slope of the regression line between VO2 and workload (watts) averaged 10.6±0.1 ml/W and did not differ across age, or between women and men. VO2 at submaximal and peak workloads was positively associated with leg muscle size and strength (r = 0.65–0.85, p<0.01). Training resulted in significant (p<0.01) increases in VO2peak (9%) and leg strength (8%) but not leg muscle size (2.5%, p = 0.19). At the same absolute submaximal workloads used before training, VO2, HR, VE and RER were all reduced 3–8% (p<0.01). The slope between VO2 and workload was also reduced 6% (p<0.01) after training. None of these training adaptations varied with age or sex. We previously reported that several markers of muscle oxidative capacity in these subjects declined with age in both men and women and improved in response to training in both young and older people. CONCLUSIONS These data demonstrate that reductions in aerobic cycling performance with age in healthy men and women are not due to changes in economy, but are instead related to declining muscle strength and oxidative capacity. The improvement in exercise economy with training is related to increases in muscle oxidative capacity and strength, all of which remain adaptable in older people.