Herrero, AJ, Martín, J, Martín, T, Abadía, O, Fernández, B, and García-López, D. Short-term effect of strength training with and without superimposed electrical stimulation on muscle strength and anaerobic performance. A randomized controlled trial. Part I. J Strength Cond Res 24 (6): 1609-1615, 2010-The purpose of this study was to compare strength training with and without superimposed electromyostimulation (EMS) on muscle strength and anaerobic power. Twenty-eight subjects were assigned to: weight+ EMS (ES), weight (VOL), or control group (CG). ES and VOL performed 4 training sessions per week during 4 weeks on a knee extension machine (8 sets; 8 repetitions; 1-second concentric phase from 90 to 0, 1-second eccentric phase from 0 to 90, 1-second rest at 90; 3-minute rest between sets; 70% maximal voluntary contraction). Group ES received EMS in the concentric phase of each action (120 Hz, 400 microseconds). Before training, after training, and 2 weeks after the end of the training (detraining), maximal voluntary contraction, squat jump, countermovement jump (CMJ), countermovement jump with free arms (CMJ A), and 20-m sprint time were analyzed. After the training period, ES and VOL increased their muscle strength (40.2% and 31.4%, respectively, p< 0.001). After the detraining period, this gain remained above baseline values for ES and VOL (49.1% and 24.5%, respectively, p< 0.001). Changes in muscle strength between baseline and detraining were higher in ES than in VOL (p< 0.01). Anaerobic performance was not affected by training in any group, but percentage change between baseline and after training suggests that the CMJ and CMJ A with free arms performance were impaired in ES with respect to VOL and CG. Superimposed EMS onto voluntary contractions increases strength more than voluntary training alone; nevertheless, a detraining period should be respected to observe this delayed adaptation. To improve anaerobic power with superimposed EMS, a complementary and specific work such as plyometrics should be carried out.