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The Off‐Transient Pulmonary Oxygen Uptake (V O2 ) Kinetics Following Attainment of a Particular V O2 During Heavy‐Intensity Exercise in Humans
Author(s) -
Cunningham D. A.,
Croix C. M.,
Paterson D. H.,
Özyener F.,
Whipp B. J.
Publication year - 2000
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1111/j.1469-445x.2000.01919.x
Subject(s) - time constant , work (physics) , kinetics , transient (computer programming) , oxygen , amplitude , work rate , chemistry , intensity (physics) , anaerobic exercise , transient response , constant (computer programming) , thermodynamics , mechanics , analytical chemistry (journal) , physics , heart rate , medicine , chromatography , optics , programming language , physiology , organic chemistry , quantum mechanics , computer science , blood pressure , electrical engineering , engineering , operating system
The oxygen uptake response to moderate‐intensity exercise (i.e. < anaerobic threshold (θ an )) has been characterised with a gain (i.e. response amplitude per increment of work rate) and time constant that do not vary appreciably at different work rates or between the on‐ and off‐transients. Above θ an , the response becomes more complex with an early component that typically projects to a value that has a gain similar to that of the < θ an response, but which is supplemented by the addition of a delayed slow kinetic component. We therefore established a constant target V O2 (V O2 1 ) for each subject such that with different imposed work rates the contribution to V O2 1 from the slow phase varied over a wide range. Work rates were chosen so that V O2 1 was attained at 2‐24 min. Five subjects (aged 21‐58 years) cycled at four to five different work rates. V O2 was measured breath‐by‐breath, at V O2 1 the work rate was abruptly reduced and the subject recovered by cycling unloaded for 15 min. Unlike the on‐transient, for which the slow component shows a long delay, the off‐transient was best fitted as two simultaneous exponential components. The slower off‐transient component had a small amplitude and long time constant, but did not differ significantly among the various tests. The off‐transient kinetics for V O2 therefore was independent of the magnitude of the contribution to the slow phase from the on‐transient kinetics.