Dynamic asymmetry of phosphocreatine concentration and O-2 uptake between the on- and off-transients of moderate- and high-intensity exercise in humans

Rossiter, H.B., Ward, S.A., Kowalchuk, J.M., Howe, F.A., Griffiths, J.A. and Whipp, B.J. (2002) Dynamic asymmetry of phosphocreatine concentration and O-2 uptake between the on- and off-transients of moderate- and high-intensity exercise in humans. Journal of Physiology, 541, pp. 991-1002. (doi: 10.1113/jphysiol.2001.012910)

Abstract

<p>The on- and off-transient (i.e. phase II) responses of pulmonary oxygen uptake (V̇_O2) to moderate-intensity exercise (i.e. below the lactate threshold, θL) in humans has been shown to conform to both mono-exponentiality and ‘on-off’ symmetry, consistent with a system manifesting linear control dynamics. However above θL the V̇_O2 kinetics have been shown to be more complex: during high-intensity exercise neither mono-exponentiality nor ‘on-off’ symmetry have been shown to appropriately characterise the V̇_O2 response. Muscle [phosphocreatine] ([PCr]) responses to exercise, however, have been proposed to be dynamically linear with respect to work rate, and to demonstrate ‘on-off’ symmetry at all work intenisties. We were therefore interested in examining the kinetic characteristics of the V̇_O2 and [PCr] responses to moderate- and high-intensity knee-extensor exercise in order to improve our understanding of the factors involved in the putative phosphate-linked control of muscle oxygen consumption. We estimated the dynamics of intramuscular [PCr] simultaneously with those of V̇_O2 in nine healthy males who performed repeated bouts of both moderate- and high-intensity square-wave, knee-extension exercise for 6 min, inside a whole-body magnetic resonance spectroscopy (MRS) system. A transmit-receive surface coil placed under the right quadriceps muscle allowed estimation of intramuscular [PCr]; V̇_O2 was measured breath-by-breath using a custom-designed turbine and a mass spectrometer system. For moderate exercise, the kinetics were well described by a simple mono-exponential function (following a short cardiodynamic phase for V̇_O2,), with time constants (τ) averaging: τV̇_O2,on 35 ± 14 s (± s.d.), τ[PCr]on 33 ± 12 s, τV̇_O2,off 50 ± 13 s and τ[PCr]off 51 ± 13 s. The kinetics for both V̇_O2 and [PCr] were more complex for high-intensity exercise. The fundamental phase expressing average τ values of τV̇_O2,on 39 ± 4 s, τ[PCr]on 38 ± 11 s, τV̇_O2,off 51 ± 6 s and τ[PCr]off 47 ± 11 s. An associated slow component was expressed in the on-transient only for both V̇_O2 and [PCr], and averaged 15.3 ± 5.4 and 13.9 ± 9.1 % of the fundamental amplitudes for V̇_O2 and [PCr], respectively. In conclusion, the τ values of the fundamental component of [PCr] and V̇_O2 dynamics cohere to within 10 %, during both the on- and off-transients to a constant-load work rate of both moderate- and high-intensity exercise. On average, ≈90 % of the magnitude of the V̇_O2 slow component during high-intensity exercise is reflected within the exercising muscle by its [PCr] response.</p>

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Griffiths, Miss Jordon
• Authors: Rossiter, H.B., Ward, S.A., Kowalchuk, J.M., Howe, F.A., Griffiths, J.A., and Whipp, B.J.
• College/School: College of Medical Veterinary and Life Sciences > School of Cardiovascular & Metabolic Health
• Journal Name: Journal of Physiology
• ISSN: 0022-3751
• ISSN (Online): 1469-7793
• Published Online: 19 April 2002