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Muscle metabolism and activation heterogeneity by combined 31P chemical shift and T2 imaging, and pulmonary O2 uptake during incremental knee-extensor exercise.

Cannon, DT; Howe, FA; Whipp, BJ; Ward, SA; McIntyre, DJ; Ladroue, C; Griffiths, JR; Kemp, GJ; Rossiter, HB (2013) Muscle metabolism and activation heterogeneity by combined 31P chemical shift and T2 imaging, and pulmonary O2 uptake during incremental knee-extensor exercise. Journal of Applied Physiology, 115 (6). pp. 839-849. https://doi.org/10.1152/japplphysiol.00510.2013
SGUL Authors: Howe, Franklyn Arron

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Abstract

The integration of skeletal muscle substrate depletion, metabolite accumulation, and fatigue during large muscle-mass exercise is not well understood. Measurement of intramuscular energy store degradation and metabolite accumulation is confounded by muscle heterogeneity. Therefore, to characterize regional metabolic distribution in the locomotor muscles, we combined 31P magnetic resonance spectroscopy, chemical shift imaging, and T2-weighted imaging with pulmonary oxygen uptake during bilateral knee-extension exercise to intolerance. Six men completed incremental tests for the following: (1) unlocalized 31P magnetic resonance spectroscopy; and (2) spatial determination of 31P metabolism and activation. The relationship of pulmonary oxygen uptake to whole quadriceps phosphocreatine concentration ([PCr]) was inversely linear, and three of four knee-extensor muscles showed activation as assessed by change in T2. The largest changes in [PCr], [inorganic phosphate] ([Pi]) and pH occurred in rectus femoris, but no voxel (72 cm3) showed complete PCr depletion at exercise cessation. The most metabolically active voxel reached 11 ± 9 mM [PCr] (resting, 29 ± 1 mM), 23 ± 11 mM [Pi] (resting, 7 ± 1 mM), and a pH of 6.64 ± 0.29 (resting, 7.08 ± 0.03). However, the distribution of 31P metabolites and pH varied widely between voxels, and the intervoxel coefficient of variation increased between rest (∼10%) and exercise intolerance (∼30-60%). Therefore, the limit of tolerance was attained with wide heterogeneity in substrate depletion and fatigue-related metabolite accumulation, with extreme metabolic perturbation isolated to only a small volume of active muscle (<5%). Regional intramuscular disturbances are thus likely an important requisite for exercise intolerance. How these signals integrate to limit muscle power production, while regional "recruitable muscle" energy stores are presumably still available, remains uncertain.

Item Type: Article
Additional Information: Copyright © 2013 the American Physiological Society Licensed under Creative Commons Attribution CC-BY 3.0: the American Physiological Society
Keywords: exercise, magnetic resonance spectroscopy, oxygen uptake, quadriceps, skeletal muscle, Adult, Exercise, Exercise Test, Humans, Hydrogen-Ion Concentration, Kinetics, Knee, Magnetic Resonance Spectroscopy, Male, Muscle, Skeletal, Oxygen, Oxygen Consumption, Phosphocreatine, Phosphorus, Quadriceps Muscle, Young Adult, Humans, Muscle, Skeletal, Oxygen, Phosphorus, Phosphocreatine, Exercise Test, Magnetic Resonance Spectroscopy, Exercise, Oxygen Consumption, Kinetics, Adult, Quadriceps Muscle, Knee, Young Adult, Hydrogen-Ion Concentration, Male, Physiology, 06 Biological Sciences, 11 Medical And Health Sciences
SGUL Research Institute / Research Centre: Academic Structure > Molecular and Clinical Sciences Research Institute (MCS)
Academic Structure > Molecular and Clinical Sciences Research Institute (MCS) > Neuroscience (INCCNS)
Journal or Publication Title: Journal of Applied Physiology
Language: eng
Dates:
DateEvent
15 September 2013Published
Publisher License: Creative Commons: Attribution 3.0
Projects:
Project IDFunderFunder ID
058420Wellcome Trusthttp://dx.doi.org/10.13039/100004440
064898Wellcome Trusthttp://dx.doi.org/10.13039/100004440
BB/I001174/1Biotechnology and Biological Sciences Research Councilhttp://dx.doi.org/10.13039/501100000268
BB/I00162X/1Biotechnology and Biological Sciences Research Councilhttp://dx.doi.org/10.13039/501100000268
MR/K006312/1Medical Research Councilhttp://dx.doi.org/10.13039/501100000265
11562Cancer Research UKhttp://dx.doi.org/10.13039/501100000289
PubMed ID: 23813534
Go to PubMed abstract
URI: https://openaccess.sgul.ac.uk/id/eprint/107474
Publisher's version: https://doi.org/10.1152/japplphysiol.00510.2013

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