Time required for the restoration of normal heavy exercise Vo(2) kinetics following prior heavy exercise

Prior heavy exercise markedly alters the O2 uptake (O2) response to subsequent heavy exercise. However, the time required for O2 to return to its normal profile following prior heavy exercise is not known. Therefore, we examined the O2 responses to repeated bouts of heavy exercise separated by five different recovery durations. On separate occasions, nine male subjects completed two 6-min bouts of heavy cycle exercise separated by 10, 20, 30, 45, or 60 min of passive recovery. The second-by-second O2 responses were modeled using nonlinear regression. Prior heavy exercise had no effect on the primary O2 time constant (from 25.9 ± 4.7 s to 23.9 ± 8.8 s after 10 min of recovery; P = 0.338), but it increased the primary O2 amplitude (from 2.42 ± 0.39 to 2.53 ± 0.41 l/min after 10 min of recovery; P = 0.001) and reduced the O2 slow component (from 0.44 ± 0.13 to 0.21 ± 0.12 l/min after 10 min of recovery; P <0.001). The increased primary amplitude was also evident after 20–45 min, but not after 60 min, of recovery. The increase in the primary O2 amplitude was accompanied by an increased baseline blood lactate concentration (to 5.1 ± 1.0 mM after 10 min of recovery; P <0.001). Baseline blood lactate concentration was still elevated after 20–60 min of recovery. The priming effect of prior heavy exercise on the O2 response persists for at least 45 min, although the mechanism underpinning the effect remains obscure.