title: Linear and nonlinear characteristics of oxygen uptake kinetics during heavy exercise.
abstract: We assessed the linearity of oxygen uptake (VO2) kinetics for several work intensities in four trained cyclists. VO2 was measured breath by breath during transitions from 33 W (baseline) to work rates requiring 38, 54, 85, and 100% of maximal aerobic capacity (VO2max). Each subject repeated each work rate four times over 8 test days. In every case, three phases (phases 1, 2, and 3) of the VO2 response could be identified. VO2 during phase 2 was fit by one of two models: model 1, a double exponential where both terms begin together close to the start of phase 2, and model 2, a double exponential where each of the exponential terms begins independently with separate time delays. VO2 rose linearly for the two lower work rates (slope 11 ml.min-1 W-1) but increased to a greater asymptote for the two heavier work rates. In all four subjects, for the two lighter work rates the double-exponential regression reduced to a single value for the time constant (average across subjects 16.1 +/- 7.7 s), indicating a truly monoexponential response. In addition, one of the responses to the heaviest work rate was monoexponential. For the remaining seven biexponential responses to the two heaviest work rates, model 2 produced a significantly better fit to the responses (P less than 0.05), with a mean time delay for the slow component of 105 +/- 46 s.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Medicine, Harbor-UCLA Medical Center, Torrance 90509.
authors.forename: T J
authors.initials: TJ
authors.lastname: Barstow
authors.forename: P A
authors.initials: PA
authors.lastname: Molé
mesh_terms: D000328:Adult; D004734:Energy Metabolism; D015444:Exercise / Q000502:physiology*; D005943:Gluconeogenesis; D006801:Humans; D007700:Kinetics; D008297:Male; D008954:Models, Biological; D010101:Oxygen Consumption / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology