Effect of discrepant gait assistance on the motion and stability of unplanned gait termination.

For the development and widespread adoption of wearable robots, ensuring the safety of the wearers is critical. The gait instability risks specific to wearable gait-assist robots arise from the motion interference of the robot. Such motion interference occurs due to sudden changes in the wearer's gait. This study focuses on unplanned gait termination, an abrupt stopping motion during walking. The primary objective of this study was to clarify the effects of discrepant assistance provided continuously during gait termination, in contrast to the wearers' intention. In the experiments, unplanned gait termination was induced while walking with a gait-assist robot, and the wearers' motions were compared between conditions with and without discrepant assistance in terms of gait termination distance, time, and physical stability. The results showed that discrepant assistance facilitated leg swings and significantly increased the step length required to stop. This extension impedes the wearers' ability to stop within short distances and may increase situational hazards such as collision or misstep risk in spatially constrained environments. Regression analysis indicated that joint kinematics during the late swing phase were most strongly associated with this extension. Conversely, the anterior mechanical stability margin increased. These findings indicate that discrepant assistance may increase risks specific to unplanned gait termination, highlighting the need to consider such risks beyond the conventional focus on fall prevention. The effect of discrepant assistance revealed in this study provides insight into the design of gait assistance that ensures the safety of gait-assist robots.