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Excessive muscular fatigue in the postpoliomyelitis syndrome

Departments of Neurology, Radiology, and Medicine, California Pacific Medical Center, University of California, San Francisco, and the Magnetic Resonance Unit, VA Medical Center of San Francisco, CA.

To investigate anterior tibial muscle fatigability and metabolism in postpoliomyelitis syndrome patients and controls, we performed measurements of force and relaxation time, as well as ³¹P magnetic resonance spectroscopy, during intermittent, low-intensity, isometric, voluntary exercise. Both maximum voluntary contraction and tetanic force declined significantly more during exercise and subsequently recovered less in patients compared with controls, indicating greater fatigue in patients. However, intracellular pH and phosphocreatine were not different in the two groups at rest or during exercise or recovery, suggesting that the greater fatigue of the patients was not due to an excessive change of metabolites. Moreover, the pre-exercise half-relaxation time of the tetanus was significantly prolonged in patients compared with controls, and the decline in tetanic force during exercise was linearly related to the half-relaxation time of tetanus, suggesting impaired calcium kinetics. Taken together, the findings of increased fatigability, delayed recovery, and prolonged half-relaxation time, without differences in metabolites, suggest that the fatigue in postpoliomyelitis syndrome may be due to impaired activation beyond the muscle membrane.

Address correspondence and reprint requests to Dr. Robert G. Miller, California Pacific Medical Center, Department of Neurology, Room #545, 3698 California Street, San Francisco, CA 94118.

Presented in part a t the 44th annual meeting of the American Academy of Neurology, San Diego, CA, May 1992.

Received May 17, 1993. Accepted for publication in final form October 7, 1993

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