Electro-mechanical failures and lactate production during fatigue.

The electrical and mechanical failures observed during sustained and intermittent electrically triggered (30 Hz) contractions of human flexor carpi ulnaris were compared with the blood lactate concentration. The changes recorded during contractions sustained for 60 s were compared with those observed during a series of sixty 1 s contractions separated by 1 s intervals, and also with the changes during the first 30 min of recovery. No significant (P less than 0.05) difference in force reduction or maximal venous lactate concentration was observed in either fatigue test, although electrical failure differed significantly (P less than 0.05). The recovery of electrical failure was poorly correlated with the reduction in lactate concentration following both sustained (r = -0.70) and intermittent contractions (r = 0.72). In contrast, the recovery in tetanic tension, rate of tension development and time to half relaxation correlated closely with the reduction in venous lactate concentration (r = -0.95, -0.93 and 0.96 respectively). It is suggested that, of the peripheral processes which appear to play a dominant role in peripheral fatigue, lactate production controls mechanical failure directly.