Increase and Decrease in Velocity and Force During Exercise with a Hybrid Robotic-FES Rehabilitation System.

Early rehabilitation is beneficial for stroke patients, but it is often delayed since the patients are often bedbound due to their general condition. New robotic rehabilitation devices such as ROBERT® enable patients to exercise even while bedbound. During pilot testing of an automated FES-delivery system combined with ROBERT®, we observed both increased and decreased exerted velocity and interaction force during repetitive exercising with the system. The goal of the current study was thus to investigate the extent of both potentiation and fatigue, as assessed in the velocity and interaction force produced in response to repetitive robotic-FES exercising. Eight healthy subjects completed 50 repetitions of leg-press exercises using the hybrid robotic-FES system. For individual subjects, significant changes were found for both mean and maximal velocities and interaction forces exerted during the exercise. Roughly half of the subjects had an increase in maximal velocity and interaction force during the exercise, and half exhibited an increase in mean velocity, whereas three subjects had an increase in mean interaction force during the exercise. The changes in mean velocity were in the range of -40.6 to 30.9% and for the maximal velocity they were in the range of -21.9 to 22.0%. The changes for mean interaction force were in the range of -5.8 to 11.0%, while for the maximal interaction force, they were in the range of -7.8 to 14.4%. These changes might pose significant challenges for future developments of hybrid robotic-FES rehabilitation systems, as the system must be able to comply with the observed changes, and appropriately adapt to them in order to maintain efficacy and safety.