Entrainment During Human Locomotion Using a Lightweight Soft Robotic Hip Exosuit (SR-HExo)

A gait entrainment study was conducted using a lightweight soft robotic hip exosuit (SR-HExo) that can apply perturbations at the hip joint during treadmill walking. Periodic mechanical perturbations were applied by flat fabric Pneumatic Artificial Muscle (ff-PAM) actuators starting at a subject's preferred gait frequency and increasing up to 15% higher in 3% increments. Anterior hip flexion perturbations and posterior hip extension perturbations were tested in two separate experiments. All 11 healthy participants showed successful entrainment in all 12 experimental conditions (i.e., from preferred gait frequency to 15% higher in both flexion and extension perturbation directions). This study confirmed that there exists a single stable point attractor during gait entrainment to unilateral, unidirectional hip perturbations, which is consistent with previous ankle studies. Phase-locking was consistently observed around toe-off phase of the gait cycle (GC). Group averaged results showed gait synchronization with extension perturbations occurred earlier in the gait cycle (around 50% GC where the hip angle reaches maximum extension) than with flexion perturbations (just after 60% GC where the transition from maximum hip extension towards hip flexion occurs). Other gait entrainment characteristics (specifically, success rate of entrainment, basin of entrainment, and transient response) observed in this study posits the potential of the SR-HExo for entrainment-based gait training in rehabilitative contexts.