Premium
Inferences from pulmonary O 2 uptake with respect to intramuscular [phosphocreatine] kinetics during moderate exercise in humans
Author(s) -
Rossiter H. B.,
Ward S. A.,
Doyle V. L.,
Howe F. A.,
Griffiths J. R.,
Whipp B. J.
Publication year - 1999
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.1469-7793.1999.0921p.x
Subject(s) - phosphocreatine , kinetics , chemistry , medicine , endocrinology , cardiology , nuclear magnetic resonance , energy metabolism , physics , quantum mechanics
1 In the non‐steady state of moderate intensity exercise, pulmonary O 2 uptake (V̇ p,O2 ) is temporally dissociated from muscle O 2 consumption (V̇ m,O2 ) due to the influence of the intervening venous blood volume and the contribution of body O 2 stores to ATP synthesis. A monoexponential model of V̇ p,O2 without a delay term, therefore, implies an obligatory slowing of V̇ p,O2 kinetics in comparison to V̇ m,O2 . 2 During moderate exercise, an association of V̇ m,O2 and [phosphocreatine] ([PCr]) kinetics is a necessary consequence of the control of muscular oxidative phosphorylation mediated by some function of [PCr]. It has also been suggested that the kinetics of V̇ p,O2 will be expressed with a time constant within 10 % of that of V̇ m,O2 . 3 V̇ p,O2 and intramuscular [PCr] kinetics were investigated simultaneously during moderate exercise of a large muscle mass in a whole‐body NMR spectrometer. Six healthy males performed prone constant‐load quadriceps exercise. A transmit‐receive coil under the right quadriceps allowed determination of intramuscular [PCr]; V̇ p,O2 was measured breath‐by‐breath, in concert with [PCr], using a turbine and a mass spectrometer system. 4 Intramuscular [PCr] decreased monoexponentially with no delay in response to exercise. The mean of the time constants (τ PCr ) was 35 s (range, 20–64 s) for the six subjects. 5 Two temporal phases were evident in the V̇ p,O2 response. When the entire V̇ p,O2 response was modelled to be exponential with no delay, its time constant (τ′ V̇p,O2 ) was longer in all subjects (group mean = 62 s; range, 52–92 s) than that of [PCr], reflecting the energy contribution of the O 2 stores. 6 Restricting the V̇ p,O2 model fit to phase II resulted in matching kinetics for V̇ p,O2 (group mean τ V̇p,O2 = 36 s; range, 20–68 s) and [PCr], for all subjects. 7 We conclude that during moderate intensity exercise the phase II τ V̇p,O2 provides a good estimate of τ PCr and by implication that of V̇ m,O2 (τ V̇m,O2 ).