Effects of age and long-term endurance training on VO₂ kinetics

PURPOSE: This study examined the effects of age and training status on the pulmonary oxygen uptake (VO₂p) kinetics of untrained and chronically trained young, middle-age, and older groups of men. METHODS: Breath-by-breath VO₂p and near-infrared spectroscopy-derived muscle deoxygenation ([HHb]) were monitored continuously in young (20-39 yr) trained (YT, n = 8) and untrained (YuT, n = 8), middle-age (40-59 yr) trained (MT, n = 9) and untrained (MuT, n = 9), and older (60-85 yr) trained (OT, n = 9) and untrained (OuT, n = 8) men. On-transient VO₂p and [HHb] responses to cycling exercise at 80% of the estimated lactate threshold (three repeats) were modeled as monoexponential. Data were scaled to a relative percentage of the response (0%-100%), the signals time aligned, and the individual [HHb]-to-VO₂p ratio was calculated as the average [HHb]/VO₂ during the 20- to 120-s period after exercise onset. RESULTS: The time constant for the adjustment of phase II pulmonary VO₂ (τVO₂p) was larger in OuT (42.0 ± 11.3 s) compared with that in YT (17.0 ± 7.5 s), MT (18.1 ± 5.3 s), OT (19.8 ± 5.4 s), YuT (25.7 ± 6.6 s), and MuT (24.4 ± 7.4 s) (P < 0.05). Similarly, the [HHb]/VO₂ ratio was larger than 1.0 in OuT (1.30 ± 0.13, P < 0.05) and this value was larger than that observed in YT (1.01 ± 0.07), MT (1.04 ± 0.05), OT (1.04 ± 0.04), YuT (1.05 ± 0.03), and MuT (1.02 ± 0.09) (P < 0.05). CONCLUSIONS: This study showed that the slower VO₂ kinetics typically observed in older individuals can be prevented by long-term endurance training interventions. Although the role of O₂ delivery relative to peripheral use cannot be elucidated from the current measures, the absence of age-related slowing of VO₂ kinetics seems to be partly related to a preservation of the matching of O₂ delivery to O₂ utilization in chronically trained older individuals, as suggested by the reduction in the [HHb]/VO₂ ratio.