Adaptation of inter-limb control during robot-simulated human standing balance

Re-learning to maintain standing balance in the presence of a paretic lower limb is important for many stroke survivors. Models of inter-limb adaptations of the central nervous system performing its role as the balance controller can aid the development of post-stroke balance therapies. This thesis quantifies such inter-limb adaptations in healthy participants. Two studies examine whether asymmetrically manipulating the limbs’ contributions to simulated standing balance (i.e., ankle torque gains) using a robotic balance platform can shift balance control toward a targeted limb. In the first study, virtually weakening (decreasing the contribution, or input gain, to the simulation from) a limb in the medial-lateral direction significantly shifted weight distribution, but not anterior-posterior torque variance, towards the virtually weakened limb. Asymmetrically manipulated anterior-posterior limb contributions also did not produce observable changes in torque, despite expectations for the balance controller to adapt and prefer using the virtually strengthened (gain-increased) limb. The second study further investigates manipulating anterior-posterior limb contributions and whether the balance controller is optimally adaptive. The protocol’s torque gain values, unlike those of the previous study, required the balance controller to adopt a new strategy to remain upright. The targeted limb was virtually strengthened by a factor of two (gain of two) while the other limb was virtually reversed (gain of negative one). Two measures of balance contribution were calculated using (1) root mean square torque during quiet stance and (2) the balance controller’s frequency response functions identified during perturbed stance. Over a two-day protocol with gains alternating between normal and manipulated values in each day, significant shifts of balance contributions were observed within and between days. The results demonstrate that the central nervous system can adapt inter-limb balance coordination in the absence of sensory feedback that explicitly communicates the asymmetrical manipulation of the balance dynamics. Anterior-posterior torque gain manipulations show promise as therapy for reducing balance asymmetries, which is crucial for restoring the mobility and independence of stroke survivors. As an additional mode of balance therapy, this novel method may enhance the effectiveness of existing stroke rehabilitation programs. Future work will address the applicability of this protocol to patient populations.Applied Science, Faculty ofMechanical Engineering, Department ofGraduat