Stroke often results in hemiparesis and gait asymmetries, such as spatial, temporal, or kinematic asymmetries between the paretic and nonparetic legs. Asymmetric gaits have been correlated with higher metabolic cost, slower walking speeds, and lower mobility. These gaits can also cause joint pain due to repetitive high loads on the nonparetic limb. For these reasons, physical therapists try to decrease gait asymmetries, and their interventions have been shown to be effective. However, sessions are expensive, limiting access. More automated rehabilitation techniques have been developed, but they have not been more effective than conventional physical therapy. A better understanding of the mechanisms driving gait asymmetry could allow for the development of more targeted, effective, and accessible gait interventions.

In my doctoral research, I first studied the correlation between step length asymmetry and metabolic cost in individuals with chronic stroke and in unimpaired participants. Participants were tasked with altering their step length asymmetry using biofeedback. All participants were able to significantly alter their step length asymmetry. Unimpaired participants self-selected a symmetric step length asymmetry that correlated to the lowest energy cost. However, for individuals with chronic stroke, metabolic cost minimization did not explain self-selected step length asymmetry. I then built a unilateral knee-ankle exoskeleton emulator that can actuate knee flexion, knee extension, and ankle plantarflexion. I designed a knee position controller to track desirable knee kinematics and demonstrated the mechatronic capabilities of the emulator system on one unimpaired participant and one participant with chronic stroke. The knee position controller was able to prevent negative impacts at the knee when plantarflexion torques were applied, and the position controller could track different desired knee trajectories with low tracking error.

The results from these studies could better inform the design of future rehabilitation tools and assistive devices. Our results suggest that metabolic energy consumption probably will not be a barrier to therapists who seek to improve step length asymmetry. Additionally, we found that active ankle plantarflexion assistance can cause increased knee extension which might lead to long-term tissue damage with constant use. Assistive devices simultaneously assisting the ankle and knee could prevent these poor knee responses. This might allow for a more comfortable application of larger magnitude ankle torques which could potentially improve metabolic reductions. These projects have led to a new experimental tool that can be used to discover beneficial participant-specific assistance strategies for individuals with chronic stroke.