This study examined the time course of short-term training and detraining-induced changes in oxygen uptake (Symbol) kinetics. Twelve men (24 ± 3 years) were assigned to either a 50% or a 70% of Symbol training intensity (n = 6 per group). Symbol was measured breath-by-breath. Changes in deoxygenated-hemoglobin concentration (Δ[HHb]) were measured by near-infrared spectroscopy. Moderate-intensity exercise on-transient Symbol and Δ[HHb] were modeled with a mono-exponential and normalized (0–100% of response) and the Symbol ratio was calculated. Similar changes in time constant of Symbol (Symbol) were observed in both groups. The combined group mean for Symbol decreased ˜14% (32.3 to 27.9 s, P < 0.05) after one training session with a further ˜11% decrease (27.9 to 24.8 s, P < 0.05) following two training sessions. The Symbol remained unchanged throughout the remaining of training and detraining. A significant “overshoot” in the Symbol 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 Symbol 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.