Dynamic responses of oxygen uptake at the onset and end of moderate and heavy exercise in trained subjects.
Inconsistencies about dynamic asymmetry between the on- and off-transient responses in VO2 are found in the literature. Therefore the purpose of this study was to examine VO2 on- and off-transients during moderate- and heavy-intensity cycling exercise in trained subjects. Ten men underwent an initial incremental test for the estimation of ventilatory threshold (VT) and, on different days, two bouts of square-wave exercise at moderate (<VT) and heavy (>VT) intensities. VO2 kinetics in exercise and recovery were better described by a single exponential model (<VT), or by a double exponential with two time delays (>VT). For moderate exercise, we found a symmetry of VO2 kinetics between the on- and off-transients (i.e., fundamental component), consistent with a system manifesting linear control dynamics. For heavy exercise, a slow component superimposed on the fundamental phase was expressed in both the exercise and recovery, with similar parameter estimates. But the on-transient values of the time constant were appreciably faster than the associated off-transient, and independent of the work rate imposed (<VT and >VT). Our results do not support a dynamically linear system model of VO2 during cycling exercise in the heavy-intensity domain.
University of Orléans, France.
Christophe
C
Cleuziou
Stéphane
S
Perry
Fabio
F
Borrani
Anne Marie
AM
Lecoq
Robin
R
Candau
Daniel
D
Courteix
Philippe
P
Obert
D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D001642:Bicycling / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D016018:Least-Squares Analysis; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption; D010806:Physical Education and Training; D010807:Physical Endurance; D011659:Pulmonary Gas Exchange