HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rossiter, H. B. Articles by Whipp, B. J. Search for Related Content PubMed PubMed Citation Articles by Rossiter, H. B. Articles by Whipp, B. J.

Intersample fluctuations in phosphocreatine concentration determined by ³¹P-magnetic resonance spectroscopy and parameter estimation of metabolic responses to exercise in humans

H. B. Rossiter*, F. A. Howe†, S. A. Ward‡, J. M. Kowalchuk*§, J. R. Griffiths†, and B. J. Whipp*

1. The ATP turnover rate during constant-load exercise is often estimated from the initial rate of change of phosphocreatine concentration ([PCr]) using ³¹P-magnetic resonance spectroscopy (MRS). However, the phase and amplitude characteristics of the sample-to-sample fluctuations can markedly influence this estimation (as well as that for the time constant () of the [PCr] change) and confound its physiological interpretation especially for small amplitude responses.

2. This influence was investigated in six healthy males who performed repeated constant-load quadriceps exercise of a moderate intensity in a whole-body MRS system. A transmit- receive surface coil was placed under the right quadriceps, allowing determination of intramuscular [PCr]; pulmonary oxygen uptake (V_O2) was simultaneously determined, breath-by-breath, using a mass spectrometer and a turbine volume measuring module.

3. The probability density functions (PDF) of [PCr] and V_O2 fluctuations were determined for each test during the steady states of rest and exercise and the PDF was then fitted to a Gaussian function. The standard deviation of the [PCr] and V_O2 fluctuations at rest and during exercise (s_r and s_w, respectively) and the peak centres of the distributions (xc_r and xc_w) were determined, as were the skewness (₁) and kurtosis (₂) coefficients.

4. There was no difference between s_r and s_w for [PCr] relative to the resting control baseline (s_r = 1·554 % (s.d. = 0·44), s_w = 1·514 % (s.d. = 0·35)) or the PDF peak centres (xc_r = -0·013 % (s.d. = 0·09), xc_w -0·197 % (s.d. = 0·18)). The standard deviation and peak centre of the 'noise' in V_O2 also did not vary between rest and exercise (s_r = 0·0427 l min^-1 (s.d. = 0·0104), s_w = 0·0640 l min^-1 (s.d. = 0·0292); xc_r = -0·0051 l min^-1 (s.d. = 0·0069), xc_w 0·0022 l min^-1 (s.d. = 0·0034)).

5. Our results demonstrate that the intersample 'noise' associated with [PCr] determination by ³¹P-MRS may be characterised as a stochastic Gaussian process that is uncorrelated with work rate, as previously described for V_O2. This 'noise' can significantly affect the estimation of [PCr] and especially the initial rate of change of [PCr], i.e. the fluctuations can lead to variations in estimation of the initial rate of change of [PCr] of more than twofold, if the inherent 'noise' is not accounted for. This 'error' may be significantly reduced in such cases if the initial rate of change is estimated from the time constant and amplitude of the response.

This article has been cited by other articles:

				A. R. Barker, J. R. Welsman, J. Fulford, D. Welford, and N. Armstrong Muscle phosphocreatine kinetics in children and adults at the onset and offset of moderate-intensity exercise J Appl Physiol, August 1, 2008; 105(2): 446 - 456. [Abstract] [Full Text] [PDF]

				A. M. Jones, D. P. Wilkerson, and J. Fulford Muscle [phosphocreatine] dynamics following the onset of exercise in humans: the influence of baseline work-rate J. Physiol., February 1, 2008; 586(3): 889 - 898. [Abstract] [Full Text] [PDF]

				A. M. Jones, D. P. Wilkerson, N. J. Berger, and J. Fulford Influence of endurance training on muscle [PCr] kinetics during high-intensity exercise Am J Physiol Regulatory Integrative Comp Physiol, July 1, 2007; 293(1): R392 - R401. [Abstract] [Full Text] [PDF]

				S. C. Forbes, J. M. Kowalchuk, R. T. Thompson, and G. D. Marsh Effects of hyperventilation on phosphocreatine kinetics and muscle deoxygenation during moderate-intensity plantar flexion exercise J Appl Physiol, April 1, 2007; 102(4): 1565 - 1573. [Abstract] [Full Text] [PDF]

				S. P. Dufour, E. Ponsot, J. Zoll, S. Doutreleau, E. Lonsdorfer-Wolf, B. Geny, E. Lampert, M. Fluck, H. Hoppeler, V. Billat, et al. Exercise training in normobaric hypoxia in endurance runners. I. Improvement in aerobic performance capacity J Appl Physiol, April 1, 2006; 100(4): 1238 - 1248. [Abstract] [Full Text] [PDF]

				H. B. Rossiter, J. M. Kowalchuk, and B. J. Whipp A test to establish maximum O2 uptake despite no plateau in the O2 uptake response to ramp incremental exercise J Appl Physiol, March 1, 2006; 100(3): 764 - 770. [Abstract] [Full Text] [PDF]

				L. F. Ferreira, A. J. Harper, and T. J. Barstow Frequency-domain characteristics and filtering of blood flow following the onset of exercise: implications for kinetics analysis J Appl Physiol, March 1, 2006; 100(3): 817 - 825. [Abstract] [Full Text] [PDF]

				O. Bernard, O. Alata, and M. Francaux On the modeling of breath-by-breath oxygen uptake kinetics at the onset of high-intensity exercises: simulated annealing vs. GRG2 method J Appl Physiol, March 1, 2006; 100(3): 1049 - 1058. [Abstract] [Full Text] [PDF]

				H. B. Rossiter, S. A. Ward, F. A. Howe, D. M. Wood, J. M. Kowalchuk, J. R. Griffiths, and B. J. Whipp Effects of dichloroacetate on VO2 and intramuscular 31P metabolite kinetics during high-intensity exercise in humans J Appl Physiol, September 1, 2003; 95(3): 1105 - 1115. [Abstract] [Full Text] [PDF]

				H. B. Rossiter, S. A. Ward, F. A. Howe, J. M. Kowalchuk, J. R. Griffiths, and B. J. Whipp Dynamics of intramuscular 31P-MRS Pi peak splitting and the slow components of PCr and O2 uptake during exercise J Appl Physiol, December 1, 2002; 93(6): 2059 - 2069. [Abstract] [Full Text] [PDF]