Effect of recovery time on V̇O_2 -ON kinetics in humans at the onset of moderate-intensity cycling exercise

Purpose τ of the primary phase of V̇O_2A kinetics during square-wave, moderate-intensity exercise mirrors that of PCr splitting ( τ PCr). Pre-exercise [PCr] and the absolute variations of PCr (∆[PCr]) occurring during transient have been suggested to control τ PCr and, in turn, to modulate V̇O_2A kinetics. In addition, V̇O_2A kinetics may be slower when exercise initiates from a raised metabolic level, i.e., from a less-favorable energetic state. We verified the hypothesis that: (i) pre-exercise [PCr], (ii) pre-exercise metabolic rate, or (iii) ∆[PCr] may affect the kinetics of muscular oxidative metabolism and, therefore, τ . Methods To this aim, seven active males (23.0 yy ± 2.3; 1.76 m ± 0.06, V̇O_2max : 3.32 L min −1 ± 0.67) performed three repetitions of series consisting of six 6-min step exercise transitions of identical workload interspersed with different times of recovery: 30, 60, 90, 120, 300 s. Results Mono-exponential fitting was applied to breath-by-breath V̇O_2A , so that τ was determined. τ decays as a first-order exponential function of the time of recovery ( τ = 109.5 × e (− t /14.0) + 18.9 r 2 = 0.32) and linearly decreased as a function of the estimated pre-exercise [PCr] ( τ = − 1.07 [PCr] + 44.9, r 2 = 0.513, P < 0.01); it was unaffected by the estimated ∆[PCr]. Conclusions Our results in vivo do not confirm the positive linear relationship between τ and pre-exercise [PCr] and ∆[PCr]. Instead, V̇O_2A kinetics seems to be influenced by the pre-exercise metabolic rate and the altered intramuscular energetic state.