Dynamic Responses of O sub(2) Uptake at the Onset and End of Exercise in Trained Subjects

• Published in: Canadian journal of applied physiology 2003-08, Vol.28 (4), p.630-641
• Main Authors: Cleuziou, C, Perrey, S, Borrani, F, Lecoq, A M, Candau, R, Courteix, D, Obert, P
• Format: Article
• Language: English
• ISSN: 1066-7814

Inconsistencies about dynamic asymmetry between the on- and off-transient responses in VO sub(2) are found in the literature. Therefore the purpose of this study was to examine VO sub(2)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) intensities. VO sub(2) kinetics in exercise and recovery were better described by a single exponential model (VT). For moderate exercise, we found a symmetry of VO sub(2) 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). Our results do not support a dynamically linear system model of VO sub(2) during cycling exercise in the heavy-intensity domain.