The Effects of Age and Long-Term Endurance Training on VO2 Kinetics
The kinetics of the adjustment of pulmonary oxygen uptake (VO2) was examined during step transitions from 20 W to moderate-intensity cycling in young (Y), middle-aged (M), and older (O) endurance trained and untrained men. VO2p was measured breath-by-breath and changes in deoxygenated hemoglobin ([HHb]) were measured by near-infrared spectroscopy. VO2p and [HHb] were modeled with a monoexponential model. The kinetic time constant for VO2 (τVO2p) was not different across age-groups (P > 0.05) in the trained group (17 ± 8, 18 ± 5, and 20 ± 5 s, in Y, M, and O, respectively). For untrained, τVO2p was greater (P < 0.05) only in the O (26 ± 7, 24 ± 7, and 42 ± 11 s for Y, M, and O, respectively). The overall adjustment of [HHb] was faster than τVO2p in O untrained, resulting in an [HHb]/VO2p “overshoot” during the exercise transient; this may reflect a microvascular blood flow limitation. The present study suggests that long-term endurance training can abolish the age-related slowing of τVO2p via improved matching of local O2 delivery to muscle VO2.
O2 uptake kinetics, aging, trained, near-infrared spectroscopy
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