³¹P NMR spectroscopy investigation of muscle metabolism in hemodialysis patients. Calf muscle metabolism of six patients with end-stage chronic renal failure undergoing maintenance hemodialysis and of six control subjects was studied using ³¹P nuclear magnetic resonance spectroscopy at 4.7 Tesla. Spectra were obtained at rest, during exercise and recovery. At rest, the inorganic phosphate, ATP and phosphocreatine concentrations, and the intracellular pH were similar in both groups of subjects. In the patients, the maximum workload achieved at the end of exercise led to a 84% and 46% depletion of phosphocreatine and ATP, respectively; under this condition, the intracellular pH fell to 6.50 ± 0.09. In control subjects, a maximum workload caused no change in ATP concentration at the end of exercise, but a phosphocreatine depletion and an intracellular pH fall similar to those observed in the patients. Although the rate of phosphocreatine depletion during exercise was not different in the two groups of subjects, the decrease in intracellular pH was more rapid in the patients than in control subjects. At the end of maximum exercise, the rates of recovery of both phosphocreatine and intracellular pH were significantly reduced in the muscle of hemodialysis patients when compared to normal subjects. These results suggest that, in the calf muscle of hemodialysis patients, energy production via oxidative metabolism is impaired and compensated for by an increase in anaerobic glycolysis.