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Influence of exercise intensity on the on‐ and off‐transient kinetics of pulmonary oxygen uptake in humans
Author(s) -
Özyener F.,
Rossiter H. B.,
Ward S. A.,
Whipp B. J.
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.t01-1-00891.x
Subject(s) - kinetics , chemistry , oxygen , intensity (physics) , cardiology , cycle ergometer , transient (computer programming) , heart rate , medicine , physics , blood pressure , organic chemistry , quantum mechanics , computer science , operating system
1 The maximal oxygen uptake (V̇ O2,peak ) during dynamic muscular exercise is commonly taken as a crucial determinant of the ability to sustain high‐intensity exercise. Considerably less attention, however, has been given to the rate at which V̇ O2 increases to attain this maximum (or to its submaximal requirement), and even less to the kinetic features of the response following exercise. 2 Six, healthy, male volunteers (aged 22 to 58 years), each performed 13 exercise tests: initial ramp‐incremental cycle ergometry to the limit of tolerance and subsequently, on different days, three bouts of square‐wave exercise each at moderate , heavy , very heavy and severe intensities. Pulmonary gas exchange variables were determined breath by breath throughout exercise and recovery from the continuous monitoring of respired volumes (turbine) and gas concentrations (mass spectrometer). 3 For moderate exercise, the V̇ O2 kinetics were well described by a simple mono‐exponential function, following a short cardiodynamic phase, with the on‐ and off‐transients having similar time constants (τ 1 ); i.e. τ 1,on averaged 33 ± 16 s (± S.D.) and τ 1,off 29 ± 6 s. 4 The on‐transient V̇ O2 kinetics were more complex for heavy exercise. The inclusion of a second slow and delayed exponential component provided an adequate description of the response; i.e. τ 1,on = 32 ± 17 s and τ 2,on = 170 ± 49 s. The off‐transient V̇ O2 kinetics, however, remained mono‐exponential (τ 1,off = 42 ± 11 s). 5 For very heavy exercise, the on‐transient V̇ O2 kinetics were also well described by a double exponential function (τ 1,on = 34 ± 11 s and τ 2,on = 163 ± 46 s). However, a double exponential, with no delay, was required to characterise the off‐transient kinetics (i.e. τ 1,off = 33 ± 5 s and τ 2,off = 460 ± 123 s). 6 At the highest intensity ( severe ), the on‐transient V̇ O2 kinetics reverted to a mono‐exponential profile (τ 1,on = 34 ± 7 s), while the off‐transient kinetics retained a two‐component form (τ 1,off = 35 ± 11 s and τ 2,off = 539 ± 379 s). 7 We therefore conclude that the kinetics of V̇ O2 during dynamic muscular exercise are strikingly influenced by the exercise intensity, both with respect to model order and to dynamic asymmetries between the on‐ and off‐transient responses.