Prolongation of twitch potentiating mechanism throughout muscle fatigue and recovery.

Measurements have been made of twitch amplitudes in human ankle dorsiflexor muscles during and following fatiguing electrical stimulation. In six subjects, studied with the arterial circulation occluded, the twitch was observed to undergo an early potentiation (mean, 99 +/- 50%) followed by complete disappearance. A second, smaller phase of potentiation (mean, 25 +/- 30%) occurred during recovery and gave way to prolonged depression of the twitch. A comparison of these results with those obtained with an intact circulation suggested that the four phases in the behavior of the twitch were the net result of two processes, potentiation and fatigue, with different time courses. Provided they are timed appropriately, observations of twitch amplitude can provide useful information concerning the development of, and recovery from, muscle fatigue.