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.