Oxygen uptake kinetics during incremental- and decremental-ramp cycle ergometry

Abstract

The pulmonary oxygen uptake (VO2) response to incremental-ramp cycle ergometry typically demonstrates lagged-linear first-order kinetics with a slope of similar to 10-11 ml.min(-1).W-1, both above and below the lactate threshold (theta(L)), i.e. there is no discernible VO2 slow component (or "excess" VO2) above theta(L). We were interested in determining whether a reverse ramp profile would yield the same response dynamics. Ten healthy males performed a maximum incremental -ramp (15-30 W.min(-1), depending on fitness). On another day, the work rate (WR) was increased abruptly to the incremental maximum and then decremented at the same rate of 15-30 W. min(-1) (step-decremental ramp). Five subjects also performed a sub-maximal ramp-decremental test from 90% of theta(L). VO2 was determined breath-by-breath from continuous monitoring of respired volumes (turbine) and gas concentrations (mass spectrometer). The incremental-ramp VO2-WR slope was 10.3 +/- 0.7 ml.min(-1).W-1, whereas that of the descending limb of the decremental ramp was 14.2 +/- 1.1 ml.min(-1).W-1 (p < 0.005). The sub-maximal decremental-ramp slope, however, was only 9.8 +/- 0.9 ml.min(-1).W-1: not significantly different from that of the incremental-ramp. This suggests that the VO2 response in the supra-theta(L) domain of incremental-ramp exercise manifest not actual, but pseudo, first-order kinetics.