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Muscular and pulmonary O 2 uptake kinetics during moderate‐ and high‐intensity sub‐maximal knee‐extensor exercise in humans
Author(s) -
Krustrup P.,
Jones A. M.,
Wilkerson D. P.,
Calbet J. A. L.,
Bangsbo J.
Publication year - 2009
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 - 10.1113/jphysiol.2008.166397
Subject(s) - intensity (physics) , kinetics , chemistry , vein , cardiology , medicine , nuclear medicine , physics , quantum mechanics
The purpose of this investigation was to determine the contribution of muscle O 2 consumption () to pulmonary O 2 uptake () during both low‐intensity (LI) and high‐intensity (HI) knee‐extension exercise, and during subsequent recovery, in humans. Seven healthy male subjects (age 20–25 years) completed a series of LI and HI square‐wave exercise tests in which (direct Fick technique) and (indirect calorimetry) were measured simultaneously. The mean blood transit time from the muscle capillaries to the lung (MTTc‐l) was also estimated (based on measured blood transit times from femoral artery to vein and vein to artery). The kinetics of and were modelled using non‐linear regression. The time constant (τ) describing the phase II kinetics following the onset of exercise was not significantly different from the mean response time (initial time delay +τ) for kinetics for LI (30 ± 3 vs 30 ± 3 s) but was slightly higher ( P < 0.05) for HI (32 ± 3 vs 29 ± 4 s); the responses were closely correlated ( r = 0.95 and r = 0.95; P < 0.01) for both intensities. In recovery, agreement between the responses was more limited both for LI (36 ± 4 vs 18 ± 4 s, P < 0.05; r =−0.01) and HI (33 ± 3 vs 27 ± 3 s, P > 0.05; r =−0.40). MTTc‐l was ∼17 s just before exercise and decreased to 12 and 10 s after 5 s of exercise for LI and HI, respectively. These data indicate that the phase II kinetics reflect kinetics during exercise but not during recovery where caution in data interpretation is advised. Increased probably makes a small contribution to during the first 15–20 s of exercise.