Unilateral stiffness modulation with a robotic hip exoskeleton elicits adaptation during gait

Wearable robotic exoskeletons show promise in their ability to provide gait assistance and rehabilitation in real-world contexts. However, a better understanding is needed of how exoskeletons contribute to neural adaptation in locomotion, a critical component of neurological gait rehabilitation. We tested whether unilateral perturbations elicit neural adaptation in healthy participants using a novel robotic hip exoskeleton, taking inspiration from asymmetry augmentation strategies used in split-belt treadmill training. We found that applying a virtual stiffness parallel to the hip joint on one side elicited changes in hip range of motion and step length, and that these changes were time varying, indicating an adaptation response. However, participants converged on asymmetric hip ranges of motion and step lengths both with and without applied stiffness from the exoskeleton. These results suggest that while adaptation appears to have occurred, it was not solely driven by the nervous system reducing gait asymmetry. Our findings indicate that applying mechanical impedance asymmetrically to the joints may be an effective gait training and rehabilitation approach, as well as a method to elicit a novel adaptation response to further study neuromotor control of locomotion.