Neuromuscular electrical stimulation affects the change in stretch tolerance by static stretching

Neuromuscular electrical stimulation (NMES) generates contractions by repetitive depolarization of axons under stimulating electrodes, and neural pathways activating motor units are affected by the stimulation parameters and delivery location. The present study examined the differences in acute effects of NMES applied over the nerve trunk and over the muscle belly on changes in range of motion and passive torque by static stretching. Effects of NMES or prolonged resting and 5-min stretching on the maximal dorsiflexion angle and passive torque were investigated. NMES consisted of 60 stimulation trains (10 s ON, 10 s OFF) at 10 Hz to the tibial nerve or triceps surae. Passive ankle dorsiflexion was performed before and after NMES and stretching interventions. Stretch tolerance and stiffness of the muscle-tendon unit were evaluated by the peak and slope of passive torques, respectively. Increases in the maximal dorsiflexion angle by stretching did not differ significantly among NMES over the nerve trunk (3 ± 2°), the over the muscle belly (2 ± 3°), and prolonged resting (2 ± 2°). Decreases in stiffness of the muscle-tendon unit by stretching were not significantly different among NMES over the nerve trunk (- 13.2 ± 7.1%), over the muscle belly (- 8.8 ± 11.3%), and prolonged resting (- 11.5 ± 11.5%). Significant increases in stretch tolerance by stretching were observed with NMES over the nerve trunk (9.0 ± 10.2%) and over the muscle belly (6.9 ± 14.6%), but not with prolonged resting (1.5 ± 8.7%). NMES tended to facilitate greater stretch tolerance by static stretching regardless of electrode location.