title: Dynamic responses of O2 uptake at the onset and end of exercise in trained subjects.
abstract: 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 .VO2on- 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.
authors.affiliation: Laboratoire de physiologie de l'exercice musculaire, Faculté des sports et de l'EP, Université d'Orléans la source, 45067 Orléans cedex 2, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Cleuziou
authors.forename: Stéphane
authors.initials: S
authors.lastname: Perrey
authors.forename: Fabio
authors.initials: F
authors.lastname: Borrani
authors.forename: Anne Marie
authors.initials: AM
authors.lastname: Lecoq
authors.forename: Robin
authors.initials: R
authors.lastname: Candau
authors.forename: Daniel
authors.initials: D
authors.lastname: Courteix
authors.forename: Philippe
authors.initials: P
authors.lastname: Obert
mesh_terms: D000328:Adult; D001642:Bicycling / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption; D010806:Physical Education and Training; D010807:Physical Endurance