The Sensitivity of Muscle Activity to Magnitude, Duration and Timing of Small Plantarflexion Torque Pulses During Walking

Small perturbations can modulate gait characteristics and therefore have potential as a gait therapy for aged or clinical populations. To understand how the neuro-musculoskeletal system interacts with small perturbations, we investigated the response and sensitivity of different muscles activities to the torque pulse characteristics. We explored three pulse characteristics: 1) onset timing, 2) duration, and 3) magnitude. Electromyography (EMG) in five leg muscles showed how muscles activities changed depending on the perturbation characteristics. Six participants (four men and two women) walked on a treadmill at their preferred speed while wearing Bowden cable ankle exoskeletons on both legs. The exoskeleton applied Trapezoidal torque pulses with varying magnitudes and durations at five different gait cycle timings. EMG signals from the Tibialis Anterior, Gastrocnemius Medialis and Lateralis, Soleus, and Rectus Femoris muscles were collected. We calculated the coefficient of determination (R²) between EMG envelopes of perturbed and unperturbed strides to assess muscle response. Results indicated that torque pulse magnitude are more likely to significantly change EMG envelope of strides compared to pulse duration. Also, we observed that muscles show less change in activity, when the pulses are applied at push-off.