Training effects on muscle fatigue in man.

Effects of 3 months training, on electrical and mechanical failures during fatigue, were studied in human adductor pollicis muscle. Eight subjects carried out a daily training program of 10 series of 20 fast (0.5 s) voluntary contractions, against a load equivalent to 30-40% of the muscle maximal force. Contractile properties in control and trained muscles are tested by delivering supramaximal electrical pulses (30 Hz) to the motor nerve, thereby triggering series of 60 1-s contractions separated by 1-s intervals. Training produces significant increase in tension development during a 30 Hz isometric tetanus (+ 13%; P less than 0.001). Concimitant rates of tension development and of relaxation are respectively augmented by + 18% (P less than 0.001) and + 12% (P less than 0.001). No significant change of surface muscle action potential (SAP) is observed after training. The considerable loss of force recorded during fatigue in control muscles (-36%) is significantly smaller (P less than 0.001) after training (-17%). Slowing of tension development and of tension relaxation, observed during fatigue in control muscles (respectively -47% and -79%) is smaller after training (respectively -28% and -65%). Analysis of electrical failure indicates that training significantly (P less than 0.01) reduces augmentation of muscle SAP duration and area recorded during fatigue. Comparison of time courses of mechanical and electrical failures in control and trained muscles, supports the idea that intracellular processes play the major role in tension decay associated with fatigue in human adductor pollicis muscle.