Shifting the balance of human standing: Inter-limb coordination for the control of a robotic balance simulation

Learning to maintain standing balance in the presence of a paretic limb is an important recovery process for many stroke survivors. In this study, we used a robotic balance simulator to investigate whether manipulating medial-lateral or anterior-posterior torque contributions (i.e. input gains) could shift the control of balance toward a targeted lower limb in healthy controls. Manipulation of medial-lateral (ML) torque gains shifted the vertical load distribution toward the virtually weakened limb, but did not result in a significant shift in anterior-posterior (AP) torque control. Instead individual participants were observed to shift AP torque control in either direction, although participants more often shifted control toward the virtually weakened limb at larger ML asymmetries. In contrast, manipulation of AP torque gains did not produce any observable changes in measured torque signals. The shift in torque contributions during ML manipulations shows promise as an implicit training method for reducing weight-bearing asymmetry. However, further work is required to ensure both vertical load and AP torque control shift in the desired direction as well as to determine the applicability of the protocol in a patient population.