Proactive adjustments to cued gait perturbations in people with and without chronic stroke.

Balance disturbances exist along a continuum from those that are fully unexpected to those that are predictable based on cues from the environment. When people experience predictable disturbances while walking, they may proactively adjust their gait to minimize losses of balance. However, one's ability to effectively implement these proactive control strategies may be impaired after a stroke due to a combination of motor and cognitive impairments that result from brain lesions. Here, we used explicit audiovisual cues to characterize the proactive and reactive control strategies implemented by people with and without stroke during unexpected versus expected gait perturbations. Following unexpected treadmill accelerations, both groups had smaller margins of stability on the recovery step than during unperturbed walking. When we provided audiovisual cues specifying the impending perturbation step, people without stroke performed less leg and joint work, especially at the ankle, during the cued perturbations and increased their subsequent margins of stability by approximately 3 cm on the recovery step. However, people post-stroke did not make these proactive adjustments. Instead, after any perturbation, they modified their stepping to maintain their center of mass position within their base of support, and this reactive strategy remained unchanged with audiovisual cues. Our findings suggest that people post-stroke rely on a general reactive control strategy rather than proactively modifying push-off work, even when given precise timing information about the impending gait perturbations.