title: 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 ~10-11 ml·min(-1)·W(-1), both above and below the lactate threshold (θL), i.e. there is no discernible VO2 slow component (or "excess" VO2) above θL. 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 θL. 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-θL domain of incremental-ramp exercise manifest not actual, but pseudo, first-order kinetics. Key pointsThe slope of the decremental-ramp response is appreciably greater than that of the incremental.The response dynamics in supra-θL domain of the incremental-ramp appear not to manifest actual first-order kinetics.The mechanisms underlying the different dynamic response behaviour for incremental and decremental ramps are presently unclear.
authors.affiliation: Dept of Physiology, St George's Hospital Medical School , London, United Kingdom ; Dept of Physiology, Uludag University Medical School , Bursa, Turkey.
authors.forename: Fadil
authors.initials: F
authors.lastname: Ozyener
authors.forename: Harry B
authors.initials: HB
authors.lastname: Rossiter
authors.forename: Susan A
authors.initials: SA
authors.lastname: Ward
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Whipp
keywords: Oxygen uptake-work rate gain; decremental-ramp exercise; incremental-ramp exercise; system linearity.