Neuromuscular Electrical Stimulation Primes Feedback Control During a Novel Single Leg Task

FMRI studies support that neuromuscular electrical stimulation can modulate the excitability of the somatosensory cortex. We studied whether practice and electrical stimulation of the quadriceps would enhance learning during a weight-bearing task. 20 healthy individuals (10 male) and 8 control subjects participated in a 2-day study. Day 1 consisted of a pretest, a training session, and a post-test; day 2 consisted of a pretest, 2 bouts of electrical stimulation to the quadriceps muscles, and a post-test. The single limb squat task was performed at varying knee resistance and target velocities and a random unexpected perturbation was administered. Feedforward error was calculated during a 50 ms time window before the unexpected event. Feedback error was calculated during a 150 ms window after the unexpected event. Peak error score decreased by 2.98 degrees (p < 0.001) immediately following training. Error was improved by 1.78 degrees (p < 0.001) during the feedforward phase and 1.44 degrees (p < 0.001) during the feedback phase. All subjects plateaued after day 1; except for the electrical stimulation group that showed a decrease of 1.206 degrees during the perturbed cycles (p = 0.024). Electrical stimulation triggered additional learning, beyond practice, during the unexpected event at a latency associated with the transcortical reflex.