Effects of Mechanical Perturbation Magnitude on Human Gait Entrainment

Gait entrainment is a relatively new robot-aided rehabilitation approach, and its underlying mechanisms remain underexplored. Investigating how different periodic perturbation parameters influence entrainment characteristics could help bridge this knowledge gap and improve gait rehabilitation protocol designs. This study examines the effect of varying magnitudes of periodic mechanical perturbations on gait entrainment characteristics in lower extremity joints during walking, such as success rate, phase variability, and onset latency. Two distinct soft robotic devices were utilized to perturb the ankle and hip joints, with perturbation magnitudes controlled by adjusting the actuator pressure. Fifteen healthy participants performed walking tasks in separate studies for each joint, with each device perturbing the respective joint at predetermined magnitudes. In the ankle study, a perturbation magnitude corresponding to 3.4% of the peak ankle torque achieved a consistently high entrainment success rate (75.6%). Similarly, in the hip study, a perturbation magnitude equivalent to 7.8% of the peak hip torque yielded a high entrainment success rate (80.0%). Both studies exhibited plateauing trends in entrainment success rate, phase variability, and onset latency, indicating that increases beyond their respective critical magnitude thresholds did not lead to further improvements. These results may be attributed to the recruitment of somatosensory feedback networks as well as mechanisms for optimizing mechanical assistance, which are not necessarily mutually exclusive. Identifying these magnitude thresholds provides a foundation for developing personalized rehabilitation protocols aimed at enhancing neuromotor learning through consistent gait entrainment.