Jeroen A.L. Jeneson1, Joep P. Schmitz1, Johannes H. van Dijk2, Dick F. Stegeman2, Peter A. Hilbers1, Klaas Nicolay1
1Biomedical Engineering, Eindhoven University of Technology, Eindhoven, Netherlands; 2Clinical Neurophysiology, University Medical Center St Radboud, Nijmegen, Netherlands
Muscle fatigue is a primary symptom in human myopathy. Its molecular basis remains hotly debated. We tested the in vivo significance of two leading hypotheses i.e., Pi accumulation and muscle acidification using bicycle ergometry, 31P MR spectroscopy and multi-channel surface electromyography. The experimental design allowed quasi-independent manipulation of intramuscular concentrations of Pi and H+ at the start of exercise. It was found that the ability of a subject to exercise against a supramaximal load maintaining a pedaling frequency of 80 rpm was neither affected by low intramuscular pH or high Pi but required a minimal phosphocreatine concentration of 5 mM.