[Muscle contractility in chronic disorders of neuromuscular transmission]

Muscle contractility of the thumb was studied in 24 normal subjects, 84 patients with myasthenia and 4 patients with hypothyrosis in response to supramaximal stimulation, on the basis of the time of contraction and semi-relaxation, staircase phenomena, and posttetanic potentiation. During hormonal therapy, the patients with myasthenia and those with hypothyrosis treated by substitution therapy manifested the normalization of the staircase and posttetanic potentiation, reduction of the contraction force and twitch time during single contraction. The comparison of the changes seen in the contraction force, staircase and posttetanic potentiation during examination of the patients over time suggested that the muscle has a regulatory system that determines the force and twitch time of muscle contraction.