Miyata, T.; Izumi, N.; Kimura, K.; Yamaguchi, T.; Yamamoto, S.; Masani, K.

Functional electrical stimulation is commonly used to enhance human movement through low-level electrical activation of muscles. More recently, dysfunctional electrical stimulation (DFES) has been proposed as a method to perturb gait by artificially inducing discomfort and mimicking inadequate muscle activity. Here we investigated strategies to induce internal perturbations during treadmill walking using DFES by systematically varying the timing and target muscle. Eleven healthy participants walked at three different speeds while DFES was applied to the tibialis anterior (TA), soleus (SOL), rectus femoris (RF), and biceps femoris (BF) muscles at 25%, 50%, 75%, and 100% of the gait cycle, each for a duration of 0.2 seconds. The gait cycle was time-locked to heel contact (0%). Results showed a significant reduction in the anterior-posterior margin of stability compared to baseline, particularly when DFES was applied to the SOL at 75%, the RF at 50%, and the BF at 75% of the gait cycle. Under these conditions, increased knee flexion and shorter stride intervals were observed relative to baseline. In conclusion, we identified effective DFES conditions to induce postural instability during walking. By mimicking inadequate muscle activity, DFES provides a promising method to study dynamic balance control and mechanisms underlying falls in neurological populations.