Training effects of sub-maximal electrostimulation in a human muscle.

This paper compares the effects of 6 wk of sub-maximal training by electrostimulation (100 Hz) and voluntary contractions on the contractile properties of the adductor pollicis muscle in intact man. The daily training program consisted of ten series of twenty 1-s isotonic contractions (60 to 65% of maximum) separated by 1-s intervals. The observed increase in muscle force, tested in maximal voluntary and electrically evoked contractions, appears to be significantly smaller during electrostimulation than during a training session performed by voluntary contractions. The increase in force recorded during electrostimulation is not associated with changes in the tetanus rates of tension development and tension relaxation (dP0/dt). Conversely, the tetanus time course is found to be significantly accelerated in muscles trained by voluntary contractions. No change of the surface action potential total area was observed during both training procedures. Furthermore, electrostimulation does not improve muscle resistance to fatigue, which is observed to be significantly increased after training by voluntary contractions. This study indicates that electrostimulation augments the muscle force of contraction by changing peripheral processes associated with intra-cellular events, without modifying the nervous command of the contraction. The comparison of the peripheral changes recorded during sub-maximal training by electrostimulation and voluntary contractions suggests that electrostimulation is less efficient, but complementary to voluntary training because the number and the type of trained motor units are different in the two procedures.