Visuomotor Ankle Training on a Stiffness-Controlled Robotic Platform Improves Ankle Motor Control and Lower Extremity Function in Chronic Stroke Survivors

This study demonstrated the feasibility of a 6-week, visuomotor ankle training program using a stiffness-controlled, 2 degree-of-freedom robotic platform and investigated its effectiveness on paretic ankle motor control and lower extremity function in patients with stroke. In this feasibility study, two chronic stroke survivors with right hemiparesis participated in the training involving ankle motor control for 12 sessions over 6 weeks. While standing on a compliant robotic platform that simulated rotational stiffness comparable to the ankle joint stiffness of unimpaired individuals, participants performed visually-guided target reaching ankle movement tasks in the sagittal and frontal planes, i.e., dorsiflexion, plantarflexion, inversion, and eversion directions, totaling 160 trials per session. Both participants successfully completed the 6-week training without any discomfort or safety issues. This visuomotor ankle training on the compliant robotic platform contributed to the significant improvement of paretic ankle motor control, evidenced by less variable, smoother, and faster ankle movements. At the conclusion of the training, a significant improvement in the fast walking speed was observed in both participants (over 20% in one subject and over 50% in the other), validating clinical relevance of the training. The Berg Balance Scale score evaluating postural balance was also improved, but only one subject showed a clinically significant improvement (8 points), while the other did not reach the clinical significance (2 points). These results suggest the potential benefits of the visuomotor ankle training program using a stiffness-controlled robotic platform to patients with stroke by providing a desirable therapeutic target towards improved ankle motor control and lower extremity function.