Entrainment During Human Locomotion Using a Soft Wearable Ankle Robot

An entrainment study was conducted with a novel soft robotic ankle-foot orthosis (SR-AFO) consisting of a pair of flat fabric pneumatic artificial muscles (ff-PAM). Entrainment capabilities of a lighter soft robotic orthosis were compared with heavy rigid robotic counterparts reported previously. To measure the SR-AFO's capacity to manifest gait entrainment, periodic pneumatic plantarflexion perturbations equal to the calculated increase from the subject's preferred gait frequency were applied to the ankle. Two days of experiments were conducted. In the Day 1 experiment, perturbations were applied from the baseline to a 15% increase in the gait frequency with steps of 3% at a fixed treadmill speed of the subject's preferred walking speed. In the Day 2 experiment, in order to investigate the maximum entrainment capability with the SR-AFO, perturbations were applied from the baseline with steps of 5% with proportionally increasing walking speed until subjects failed to maintain phase locking for 50 or more consecutive steps. In the Day 1 experiment, all 10 subjects were entrained at the highest 15% condition. In the Day 2 experiments, the average basin of entrainment was 39.3
$\pm$
9.2%. Importantly, phase locking was always observed in the push-off phase of the gait cycle in both days of experiments. The observed basin of entrainment with the SR-AFO was substantially higher than the previously reported value (+7%) with a heavy rigid ankle robot, confirming the potential of the SR-AFO to significantly extend the effectiveness of the entrainment paradigm in gait adaptation and rehabilitation.