Several studies of training programs have tested the impact of electro stimulation on strength gain. In rugby players, for example, isolated stimulation of the quadriceps femoris, gluteus maximus and triceps surae muscles during a 12-week period led to a marked increase in the strength and power of these muscles . However, the technical skills of rugby, as scrummaging and sprinting, did not benefit from these improvements. In another study, the combination of electro stimulation and plyometric training improved the maximal strength of the quadriceps femoris, as well as vertical jump and sprint but electrostimulation alone reduced the sprint velocity and its benefits did generally not exceed those observed when applied in combination with plyometric training.
In a recent review, electrostimulation combined with fast concentric (1808/s) or eccentric training was acknowledged to increase maximal concentric moment. However, these examples, as in most of the published studies on the subject, have poor methodological qualities. In this systematic review, showed that electrical stimulation is more effective to increase the quadriceps femoris strength, only compared to no exercise, and even more effective when the stimulation was combined with simultaneous voluntary activity . Electrical stimulation was still not more effective than classical training, except when associated with eccentric training. Thus, as summarized by Vanderthommen and Duchateau , strength gains due to electrostimulation do not seem to be higher than those due to training with voluntary contractions. Because these gains are likely due to the intensity of the stimulation, it is extremely important to use comfortable currents, even if no standardized method exists. Electrostimulation in healthy subjects and athletes looks more like a complement to classical strengthening programs, particularly in combination with simultaneous voluntary contraction. Its main advantages are to increase the muscle workload, as a complement to classical training, and to induce a contraction pattern different from the pattern during voluntary contraction . Finally, even if strength gain could be transferred to sports activities, negative outcomes suggest that skill training is always needed to improve the muscle coordination necessary for the task to be trained.