Electrical Stimulation to Modulate Human Ankle Impedance: Effects of Intervention on Balance Control in Quiet and Perturbed Stances

摘要

The ankle is the critical joint between the leg and foot that helps control physical interactions for propulsion, shock absorption, and balance of the body. This paper describes the effect of modulation of ankle impedance via functional electrical stimulation (FES) on balance control in humans while they are in quiet and perturbed stances. Subjects were instructed to stand on a computer-controlled treadmill while their kinematics and foot pressure were measured by an optical motion capture system and a force plate, respectively. The computer-controlled treadmill produced sinusoidal movement, which provided a mechanical perturbation to the subjects. While in quiet and perturbed stances, transcutaneous electrical stimulation with interferential current activated the agonist and antagonist muscles of the tibialis anterior and soleus muscles, which resulted in the co-contraction of the antagonistic ankle muscles. The experimental results show that simultaneous stimulation of the ankle antagonist muscle group using the interferential electrical stimulation (1) increases the root mean square (RMS) of the center of pressure (CoP) while in the quiet stance, and (2) decreases the RMS of the CoP and increases knee movement while in the perturbed stance. These findings highlight the different effects of FES-induced ankle impedance while in quiet and perturbed stances, suggesting that a simple modulation of ankle impedance via FES may not stabilize the postural sway in the quiet stance but rather may disturb it.