The effect of continuous voluntary activation on neuromuscular transmission: a SFEMG study of myasthenia gravis and anterior horn cell disorders.

In normal subjects the neuromuscular jitter does not increase during continuous voluntary activation. In patients with myasthenia gravis, spinal muscular atrophy and motor neurone disease we have found that the neuromuscular jitter may increase during recordings of several minutes of continuous voluntary activation at steady innervation rates. In some units this led to impulse blocking, and in other units an initially normal jitter increased beyond the normal range. Measurement of jitter during continuous voluntary activation at steady innervation rates provides relevant information in the evaluation of neuromuscular transmission and fatigue in these disorders.