A comparison of voluntary versus stimulated strength training of the human adductor pollicis muscle.

The effects of voluntary versus electrically stimulated isometric strength training of the adductor pollicis on muscle strength were compared. The adductor pollicis of one hand was trained using voluntary contractions at 50% of the maximum voluntary contraction force, and the other with 30 Hz tetani (stimulated contractions), which produced a force equivalent to 30-50% of the maximum voluntary force. Tetani were delivered with surface electrodes placed over the ulnar nerve at the wrist. Both protocols resulted in large, significant increases in maximum voluntary strength of 79+/-44% (voluntary) and 74+/-41% (stimulated) (mean+/-s; P< 0.002). The time course of the changes was very similar for both protocols and there was no significant difference between the strength increases produced by the two protocols. The large gains resulting from stimulated training argues against central adaptations as a major contributor to the strength increases following training.