Time required for the restoration of normal heavy exercise Vo2 kinetics following prior heavy exercise

Prior heavy exercise markedly alters the 02 uptake (Vo(2)) response to subsequent heavy exercise. However, the time required for Vo(2) to return to its normal profile following prior heavy exercise is not known. Therefore, we examined the Vo(2) 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 VO2 responses were modeled using nonlinear regression. Prior heavy exercise had no effect on the primary VO2 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 Vo(2) amplitude (from 2.42 +/- 0.39 to 2.53 +/- 0.41 l/min after 10 min of recovery; P = 0.001) and reduced the Vo(2) 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 Vo(2) 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 Vo(2) response persists for at least 45 min, although the mechanism underpinning the effect remains obscure.