Bio-energetic changes in human gastrocnemius muscle 1-2 days after strenuous exercise.

[31P]magnetic resonance spectroscopy was used to study the metabolic sequelae of intense muscular activity in gastrocnemius of seven subjects 1-2 days after a 67-mile bicycle ride. The muscle was examined at rest, during a test exercise and during recovery from test exercise. Post-ride and pre-ride results were compared. At rest, the ratio of phosphocreatine to ATP (PCr/ATP) was increased post-ride; during test exercise PCr/(PCr+Pi) was lower post-ride; and the recoveries of PCr, Pi and PCr/(PCr+Pi) after test exercise were delayed, with decreased 'overshoot' of PCr/(PCr+Pi) (which is due to recovery of Pi to below its resting value). Mild mitochondrial damage (perhaps due to exposure to high cytosolic [Pi] during the bicycle ride) may explain some of these results. In contrast to reports of largely eccentric exercise there was no increase in resting Pi/ATP. We have thus demonstrated perturbations of muscle bio-energetics 1-2 days after strenuous exercise, in the absence of convincing enzymological evidence of muscle damage.