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J Appl Physiol 94: 2391-2397, 2003. First published February 28, 2003; doi:10.1152/japplphysiol.00589.2002
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Vol. 94, Issue 6, 2391-2397, June 2003

ATP synthesis and proton handling in muscle during short periods of exercise and subsequent recovery

David Bendahan1, Graham J. Kemp2, Magali Roussel1, Yann Le Fur1, and Patrick J. Cozzone1

1 Faculté de Médecine, Centre de Resonance Magnetique Biologique et Medicale, Unité Mixte de Recherche 6612 Centre National de la Recherche Scientifique, Marseille 13005, France; and 2 Department of Musculoskeletal Science, University of Liverpool, Liverpool L69 3GA, United Kingdom

We used 31P-magnetic resonance spectroscopy to study proton buffering in finger flexor muscles of eight healthy men (25-45 yr), during brief (18-s) voluntary finger flexion exercise (0.67-Hz contraction at 10% maximum voluntary contraction; 50/50 duty cycle) and 180-s recovery. Phosphocreatine (PCr) concentration fell 19 ± 2% during exercise and then recovered with half time = 0.24 ± 0.01 min. Cell pH rose by 0.058 ± 0.003 units during exercise as a result of H+ consumption by PCr splitting, which (assuming no lactate production or H+ efflux) implies a plausible non-Pi buffer capacity of 20 ± 3 mmol · l intracellular water-1 · pH unit-1. There was thus no evidence of significant glycogenolysis to lactate during exercise. Analysis of PCr kinetics as a classic linear response suggests that oxidative ATP synthesis reached 48 ± 2% of ATP demand by the end of exercise; the rest was met by PCr splitting. Postexercise pH recovery was faster than predicted, suggesting "excess proton" production, with a peak value of 0.6 ± 0.2 mmol/l intracellular water at 0.45 min of recovery, which might be due to, e.g., proton influx driven by cellular alkalinization, or a small glycolytic contribution to PCr resynthesis in recovery.

bioenergetics; buffer capacity; glycogenolysis; phosphorus-31 magnetic resonance spectroscopy; skeletal muscle


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