Incomplete muscle activation after training with electromyostimulation.

Training with voluntary or electromyostimulation (EMS)-evoked eccentric contractions should produce complete muscle activation, since EMS and eccentric contractions preferentially recruit large motor units. Subjects (22 women ages 18-40) were randomly assigned to a voluntary (VOL; n = 8), EMS (n = 8), or control group. VOL and EMS groups trained the quadriceps at the same, increasing force levels 4 times/week for 6 weeks using voluntary or EMS-evoked eccentric contractions. VOL improved voluntary more than EMS-evoked eccentric strength. EMS improved EMS-evoked strength more than voluntary. EMS training improved EMS-evoked eccentric strength more than VOL training improved voluntary eccentric strength. EMS-evoked to voluntary force ratio increased from 0.57 (+/- 0.11) to 1.20 (+/- 0.35) in EMS and did not change in VOL (all changes p < .05). Six of eight EMS subjects produced greater EMS-evoked force posttraining, suggesting incomplete muscle activation after EMS training.