Kinetics of oxygen uptake at the onset of exercise near or above peak oxygen uptake

We tested the hypothesis that kinetics of O2uptake (V̇O2) measured in the transition to exercise near or above peak V̇O2(V̇O(2peak)) would be slower than those for subventilatory threshold exercise. Eight healthy young men exercised at ~57, ~96, and ~125% V̇O(2peak). Data were fit by a two- or three-component exponential model and with a semi-logarithmic transformation that tested the difference between required V̇O2and measured V̇O2. With the exponential model, phase 2 kinetics appeared to be faster at 125% V̇O(2peak) [time constant (τ2) = 16.3 ± 8.8 (SE) s] than at 57% V̇O(2peak) (τ2= 29.4 ± 4.0 S) but were not different from that at 96% V̇O(2peak) exercise (τ2= 22.1 ± 2.1 s). V̇O2at the completion of phase 2 was 77 and 80% V̇O(2peak) in tests predicted to require 96 and 125% V̇O(2peak). When V̇O2kinetics were calculated with the semi-logarithmic model, the estimated τ2at 96% V̇O(2peak) (49.7 ± 5.1 s) and 125% V̇O(2peak) (40.2 ± 5.1 s) were slower than with the exponential model. These results are consistent with our hypothesis and with a model in which the cardiovascular system is compromised during very heavy exercise.