title: Kinetics of oxygen uptake at the onset of exercise near or above peak oxygen uptake.
abstract: We tested the hypothesis that kinetics of O(2) uptake (VO(2)) measured in the transition to exercise near or above peak VO(2) (VO(2 peak)) would be slower than those for subventilatory threshold exercise. Eight healthy young men exercised at approximately 57, approximately 96, and approximately 125% VO(2 peak). Data were fit by a two- or three-component exponential model and with a semilogarithmic transformation that tested the difference between required VO(2) and measured VO(2). With the exponential model, phase 2 kinetics appeared to be faster at 125% VO(2 peak) [time constant (tau(2)) = 16.3 +/- 8.8 (SE) s] than at 57% VO(2 peak) (tau(2) = 29. 4 +/- 4.0 s) but were not different from that at 96% VO(2 peak) exercise (tau(2) = 22.1 +/- 2.1 s). VO(2) at the completion of phase 2 was 77 and 80% VO(2 peak) in tests predicted to require 96 and 125% VO(2 peak). When VO(2) kinetics were calculated with the semilogarithmic model, the estimated tau(2) at 96% VO(2 peak) (49.7 +/- 5.1 s) and 125% VO(2 peak) (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.
authors.affiliation: Department of Kinesiology, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1. hughson@healthy.uwaterloo.ca
authors.forename: R L
authors.initials: RL
authors.lastname: Hughson
authors.forename: D D
authors.initials: DD
authors.lastname: O'Leary
authors.forename: A C
authors.initials: AC
authors.lastname: Betik
authors.forename: H
authors.initials: H
authors.lastname: Hebestreit
mesh_terms: D000328:Adult; D004056:Differential Threshold; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D006801:Humans; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption; D012143:Respiratory Physiological Phenomena