Excessive muscular fatigue in patients with spastic paraparesis.

We used intermittent tetanic contractions and 31P magnetic resonance spectroscopy to investigate human tibialis anterior muscle metabolism and fatigability in a group of patients with spastic paraparesis and in normal controls. During intermittent tetanic stimulation, the decline in tension was significantly greater in patients than in controls, and the half-relaxation time of the tetanus was more prolonged. Moreover, the decline in phosphocreatine and intracellular pH was significantly greater in patients than in controls. These observations suggest that biochemical changes in the muscles of patients with upper motor neuron lesions may contribute to their excessive fatigability.