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Abstract #1024

31P-MRS reveals oxidative capacities of red and white fibers in human muscle differ 7-fold in vivo

Jeroen A Jeneson1,2, Laura E Habets1, Melissa T Hooijmans2, Sandra M van den Berg2, Bart Bartels1, W Ludo van der Pol3, and Aart J Nederveen2
1Child Health, University Medical Center Utrecht, Utrecht, Netherlands, 2Radiology and Nuclear Medicine, Amsterdam University Medical Center|location AMC, Amsterdam, Netherlands, 3Neurology and Neurosurgery, University Medical Center Utrecht, Utrecht, Netherlands


31P MRS has been used to non-invasively diagnose muscular mitochondrial dysfunction in disease. However, shifts in muscle fiber type composition due to muscle disuse are potential confounders since mitochondrial and capillary densities differ between fiber types. We obtained new quantitative information on this subject matter on basis of dynamic in vivo 31P MRS recordings from upper arm muscle of fourteen healthy subjects performing a maximal arm-cycling test. Analysis of the post-exercise time course of Pi in red and white myofiber pools distinguished by myoplasmic pH revealed a sevenfold difference in oxidative capacity between these fiber types in vivo.

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