SYNOPSIS In two subjects with paramyotonia congenita the isometric torque generated by the abductor digiti minimi and the surface EMG recorded over ADM decreased during prolonged or repetitive contractions, whether these were voluntarily or electrically induced. Isometric twitch times did not alter significantly during this muscle fatigue. Cooling greatly accelerated the fatiguing process. It is suggested that this local muscle weakness is due to a progressive decrease in excitability of the muscle cell membrane.

SYNOPSIS In two subjects with paramyotonia congenita myotonic delay in muscle relaxation, recorded electromyographically and with a displacement transducer, was found to increase with repeated forceful contractions. Myotonia was elicited readily in warm temperatures, was initially aggravated by cooling, but was invariably lost as muscle fatigue developed. The EMG evidence of myotonia usually subsided before complete muscle relaxation had occurred, suggesting that a defect of the contractile mechanism was present over and above any defect at membrane level.