Effects of short-term training and detraining on VO₂ kinetics: Faster VO₂ kinetics response after one training session

This study examined the time course of short-term training and detraining-induced changes in oxygen uptake (V ˙ O 2) kinetics. Twelve men (24±3 years) were assigned to either a 50% or a 70% of V ˙ O 2 m a x training intensity (n=6 per group). V ˙ O 2 was measured breath-by-breath. Changes in deoxygenated-hemoglobin concentration (Δ[HHb]) were measured by near-infrared spectroscopy. Moderate-intensity exercise on-transient V ˙ O 2 and Δ[HHb] were modeled with a mono-exponential and normalized (0-100% of response) and the [ H H b ] / V ˙ O 2 ratio was calculated. Similar changes in time constant of V ˙ O 2 (t V ˙ O 2) were observed in both groups. The combined group mean for t V ˙ O 2 decreased ∼14% (32.3 to 27.9s, P<0.05) after one training session with a further ∼11% decrease (27.9 to 24.8s, P<0.05) following two training sessions. The t V ˙ O 2 p remained unchanged throughout the remaining of training and detraining. A significant "overshoot" in the [ H H b ] / V ˙ O 2 ratio was decreased (albeit not significant) after one training session, and abolished (P<0.05) after the second one, with no overshoot observed thereafter. Speeding of V ˙ O 2 kinetics was remarkably quick with no further changes being observed with continuous training or during detraining. Improve matching of local O₂ delivery to O₂ utilization is a mechanism proposed to influence this response.