Delayed kinetics of VO2 in the transition from prior exercise. Evidence for O2 transport limitation of VO2 kinetics: a review.

The influence of prior exercise state on the kinetics of VO2, VE, and HR was studied in six subjects. The exercise conditions tested were square wave increases in work rate from rest to 80% of the work rate at anaerobic threshold (AT), from O W loadless pedaling to 80% AT, from rest to 40% AT, and from 40% to 80% AT. The kinetic response was evaluated by the time constant (tau) and mean response time (MRT = time to achieve 63% response) as determined by nonlinear regression. For both VO2 and HR, tau and MRT were not significantly different in the rest or O W to 80% AT tests, but were significantly faster in the rest to 40% AT test and significantly slower in the 40% to 80% AT test than the rest and O W to 80% AT tests. The tau for VE was significantly slower in the 40% to 80% AT tests than in the other tests. The coincident variation of HR and VO2 kinetics is taken as support for the hypothesis that VO2 kinetics are controlled by oxygen transport. Evidence from the literature that supports both the oxygen transport and the oxygen utilization for the control of VO2 kinetics is reviewed.