Does Ankle Exoskeleton Assistance Impair Stability During Walking in Individuals with Cerebral Palsy?

Lower-limb exoskeletons have the potential to improve mobility in individuals with movement disabilities, such as cerebral palsy (CP). The goal of this study was to assess the impact of plantar-flexor assistance from an untethered ankle exoskeleton on dynamic stability during unperturbed and perturbed walking in individuals with CP. Seven participants with CP (Gross Motor Function Classification System levels I-III, ages 6-31 years) completed a treadmill walking protocol under their normal walking condition and while wearing an ankle exoskeleton that provided adaptive plantar-flexor assistance. Pseudo-randomized treadmill perturbations were delivered during stance phase by accelerating one side of a split-belt treadmill. Treadmill perturbations resulted in a significant decrease in anteroposterior minimum margin-of-stability (- 32.1%, p < 0.001), and a significant increase in contralateral limb step length (8.1%, p = 0.005), integrated soleus activity during unassisted walking (23.4%, p = 0.02), and peak biological ankle moment (9.6%, p = 0.03) during stance phase. Plantar-flexor assistance did not significantly alter margin-of-stability, step length, soleus activity, or ankle moments during both unperturbed and perturbed walking. These results indicate that adaptive plantar-flexor assistance from an untethered ankle exoskeleton does not significantly alter dynamic stability maintenance during unperturbed and perturbed walking for individuals with CP, supporting future research in real-world environments.