Human gait is quite complex, especially when considering the irregular and uncertain environments that humans are able to walk in. While unperturbed gait in a controlled environment is understood to a large degree, gait in more unique environments, such as asymmetric compliant terrain, is not understood to the same degree. In this study, we build upon a neuromuscular gait model and extend it to allow for walking on unilaterally compliant (soft) surfaces. This model is then compared to and verified by experimental human data. The model can successfully walk with step length trends similar to human data. Additionally, the model shows similar behaviors with respect to kinematics and muscle activity. We believe this work contributes significantly to a better understanding of the control of human gait and could lead to model-informed, patient-specific rehabilitation strategies that can advance the field of rehabilitation robotics, as well as the development of bio-inspired controllers for bipedal robots that would be able to traverse through dynamic and complaint terrains.

Due to hemiparesis, stroke survivors frequently develop a dysfunctional gait that is often characterized by an overall decrease in walking speed and a unilateral decrease in step length. With millions currently affected by this dys-functional gait, robust and effective rehabilitation protocols are needed. Although robotic devices have been used in numerous rehabilitation protocols for gait, the lack of significant afteref-fects that translate to effective therapy makes their application still questionable. This paper proposes a novel type of robot-assisted intervention that results in significant aftereffects that last much longer than any other previous study. With the utilization of a novel robotic device, the Variable Stiffness Treadmill (VST), the stiffness of the walking surface underneath one leg is decreased for a number of steps. This unilateral stiffness perturbation results in a significant aftereffect that is both useful for stroke rehabilitation and often lasts for over 200 gait cycles after the intervention has concluded. More specifically, the aftereffect created is an increase in both left and right step lengths, with the unperturbed step length increasing significantly more than the perturbed. These effects may be helpful in correcting two of the most common issues in post-stroke gait: overall decrease in walking speed and a unilateral shortened step length. The results of this work show that a robot-assisted therapy protocol involving repeated unilateral stiffness perturbations can lead to a more permanent and effective solution to post-stroke gait.