Bilateral asymmetric hip stiffness applied by a robotic hip exoskeleton elicits kinematic and kinetic adaptation

Abstract

Wearable robotic exoskeletons hold great promise for gait rehabilitation as portable, accessible tools. However, a better understanding of the potential for exoskeletons to elicit neural adaptation-a critical component of neurological gait rehabilitation-is needed. In this study, we investigated whether humans adapt to bilateral asymmetric stiffness perturbations applied by a hip exoskeleton, taking inspiration from the asymmetry augmentation strategies used in split-belt treadmill training. During walking, we applied torques about the hip joints to repel the thigh away from a neutral position on the left side and attract the thigh toward a neutral position on the right side. Six participants performed an adaptation walking trial on a treadmill while wearing the exoskeleton. The exoskeleton elicited time-varying changes and aftereffects in step length and propulsive/braking ground reaction forces, indicating behavioral signatures of neural adaptation. These responses resemble typical responses to split-belt treadmill training, suggesting that the proposed intervention with a robotic hip exoskeleton may be an effective approach to (re)training symmetric gait.

Gait Adaptation to Asymmetric Hip Stiffness Applied by a Robotic Exoskeleton

“…Based on these prior results, the positive and negative springs were intended to mimic the fast (which initially shorten step lengths) and slow belts (which initially lengthen step lengths), respectively, in the split-belt treadmill training paradigm. The specific stiffness values used in this experiment were chosen based on pilot testing to ensure safety and user comfort [23]. The stiffness controller was turned off by setting τ R = τ L = 0.…”

“…The results of an initial pilot study that investigated locomotor adaptation to the application of unilateral hip stiffness were presented in [22], and preliminary results of this study were presented in [23]. Compared to [23], this study presents results from a larger participant sample and incorporates extended analyses that encompass full lower body kinematics.…”

Gait adaptation to asymmetric hip stiffness applied by a robotic exoskeleton

“…Thus, the positive and negative springs were intended to mimic the fast (which initially shorten step lengths) and slow belts (which initially lengthen step lengths), respectively, in the split-belt treadmill training paradigm. The specific stiffness values used in this experiment were chosen based on pilot testing to ensure safety and user comfort [22]. The stiffness controller was turned off by setting τ R = τ L = 0.…”

“…We further predicted that with the perturbation applied, individuals would adapt their gait behavior back towards restoring gait symmetry over time (Hypothesis 2) and exhibit an aftereffect in an opposite direction to initially induced asymmetry after the perturbation is removed (Hypothesis 3). Preliminary reports of this study and an initial pilot study were presented in [21] and [22], respectively.…”