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This Article Full Text Full Text (PDF) All Versions of this Article: 583/3/1093    most recent jphysiol.2007.138362v1 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 Lanza, I. R. Articles by Kent-Braun, J. A. Search for Related Content PubMed PubMed Citation Articles by Lanza, I. R. Articles by Kent-Braun, J. A. Related Collections Skeletal Muscle and Exercise

¹ Department of Kinesiology, University of Massachusetts, Amherst, MA, USA

We recently reported lower glycolytic flux (ATP_GLY) and increased reliance on oxidative ATP synthesis (ATP_OX) in contracting muscle of older compared to young humans. To further investigate this age-related difference in the pathways of ATP synthesis, we used magnetic resonance spectroscopy to determine the rates of ATP_OX, ATP_GLY and net phosphocreatine hydrolysis in vivo during maximal muscle contractions under free-flow (FF) and ischaemic (ISC) conditions in the ankle dorsiflexors of 20 young (27 ± 3 years; 10 male, 10 female) and 18 older (70 ± 5 years; 10 male, 8 female) adults. We hypothesized that ATP_GLY would be higher in young compared to old during FF contractions, but that old would be unable to increase ATP_GLY during ISC to match that of the young, which would suggest impaired glycolytic ATP synthesis with old age. Peak glycolytic flux during FF was lower in older (0.8 ± 0.1 mM ATP s^–1) compared to young (1.4 ± 0.1 mM ATP s^–1, P < 0.001) subjects. During ISC, peak ATP_GLY increased in old to a level similar to that of young (1.4 ± 0.2 mM ATP s^–1, 1.3 ± 0.2 mM ATP s^–1, respectively; P = 0.86), suggesting that glycolytic function remains intact in aged muscle in vivo. Notably, older adults fatigued less than young during both FF and ISC (P 0.004). These results provide novel evidence of unimpaired in vivo glycolytic function in the skeletal muscle of older adults during maximal isometric dorsiflexion, and suggest a potential role for differences in metabolic economy and as a result, metabolite accumulation, in the fatigue resistance of the old.

(Received 10 June 2007; accepted after revision 24 July 2007; first published online 2 August 2007)
Corresponding author J. A. Kent-Braun: Department of Kinesiology, Totman 108, University of Massachusetts, Amherst, MA 01003, USA. Email: janekb{at}kin.umass.edu

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