Using Generic Upper-Body Movement Strategies in a Free Walking Setting to Detect Gait Initiation Intention in a Lower-Limb Exoskeleton

In recent years, lower-limb exoskeletons have been marketed to become a possible alternative to wheelchairs for people with walking impairments or paralysis. However, most assistive exoskeletons rely on constraining control strategies based on remote controls or torso tilting events. One approach to build more intuitive control interfaces would be to exploit knowledge on human motor control, and the coordination between upper and lower limb movements during gait events, such as the anticipatory postural adjustments that precede gait initiation. In this study, it was hypothesized that generic trunk and arm movements preceding gait in a free walking setting in able-bodied users can still be retrieved while wearing an assistive lower-limb exoskeleton that constrains their leg movements. This was evaluated on a group of eight unimpaired participants, and analysis of upper-body wearable IMU signals showed similarity of postural adjustments between the free and exoskeleton-constrained settings. Additionally, a classification architecture showed that the walking state of the robot can be correctly triggered based on free-walking data gathered from all participants with an accuracy rate of 95%. This suggests that interlimb coordination still exists in a constrained setting, and could pave the road towards the elaboration of more natural controls for assistive lower-limb exoskeletons.