The Effects of a Virtual Environment and Robot-Generated Haptic Forces on the Coordination of the Lower Limb During Gait in Chronic Stroke Using Planar and 3D Phase Diagrams

Previous studies have combined robot-controlled haptic tensile forces with virtual reality (VR) to produce gait adaptation and post-adaptation effects in spatiotemporal gait and postural outcomes in healthy young, elderly, and chronic stroke individuals. The present study focuses on kinematic and dynamic adaptation and post-adaptation effects of lower limb segment coordination, during and after a 15 N tensile force exposure by presenting two representations of 3D coordination - planar and phase diagrams. One chronic stroke subject (73 y.o., 8 months post-stroke, RH) and one age-matched control subject (71 y.o, RH) walked on a self-paced treadmill in a virtual environment holding a robot-controlled haptic leash. The paradigm consisted of a 30 s pre-force baseline epoch, followed by a 60 s tensile force and a 60 s post-force epoch. Both the chronic stroke and control subject showed evidence of changes in bilateral intersegmental coordination of the lower limb to accompany gait speed increases during force and post-force epochs. In particular, both subjects increased dorsiflexion of the non-dominant leg during and after the 15 N force exposure. Changes in limb segment coordination also corresponded to bilateral increases in 3D intersegmental trajectory areas. While there was no evidence of increased symmetry based on left and right leg plane comparisons, slight increases in angular velocity were noted just prior to and during the swing phase of the paretic leg during force and post-force epochs. These findings were further substantiated by Sobolev norms which increased bilaterally and proportionally for force and post-force epochs. Adaptation and post-adaptation effects seen in bilateral lower limb coordination when haptic forces were present and released suggest proportional increases in the kinematic and dynamic outcomes. Further investigation involving a wider range of chronic stroke functional levels should be conducted.