Cross-education after one session of unilateral surface electrical stimulation of the rectus femoris

Thirty-six adult men were randomly assigned to a remote stimulation group (RS; n = 18) or control group (CTL; n = 18). The RS group unilaterally performed a 10-minute surface electrical stimulation program (frequency 100 Hz, impulse 300 micros, 10 seconds on/10 seconds off) on the rectus femoris of the non-dominant leg. The subjects of the CTL group relaxed for 10 minutes without performing any training. Immediately before and after the surface electrical stimulation program, the isometric strength and the electromyographic (EMG) and mechanomyographic (MMG) response of the dominant leg was measured for all subjects. The dominant leg of the RS group showed a significant increase in the isometric force (5.11%; P < 0.001) and EMG activity of the agonist muscle (4.67%; P < 0.05), whereas a decrease in EMG activity of the antagonist muscles was observed (-10.27%; P < 0.05). The MMG activity did not show any alteration. No significant changes were observed for the CTL group. These results indicate that one unilateral surface electrical stimulation session on the rectus femoris improves the efficiency of the inactive leg. At a practical level, the results open a new way to rehabilitate muscle-skeletal injuries, especially weak members that cannot do any physical work. In this case, the muscle strength (and physical efficiency) can be improved by passive electrostimulation training on the healthy member.