Control Mechanisms in Standing while Simultaneously Receiving Perturbations and Active Assistance from the Robotic Upright Stand Trainer (RobUST)
Tatiana Luna, Victor Santamaria, Isirame Omofumal, Moiz Khan, Sunil K. Agrawal
Abstract
In people with severe neuromotor deficits of trunk and lower extremities, rehabilitation of standing postural control is limited to rigid body support. To expand postural control training in standing, we have recently developed a Robotic Upright Stand Trainer (RobUST). In this study, we use RobUST to deliver body perturbations on the trunk while simultaneously providing direction-specific postural assistance on the pelvis. We study the effect that assist-as-needed forces has on postural imbalance on 10 able-bodied adults. We characterize postural imbalance with center of pressure (COP) variables such as excursion and root mean square COP. Surface electromyography (sEMG) was also applied to investigate muscle strategies. RobUST was designed for future training of participants with profound postural standing deficits. A common postural strategy, applied in such population, is to encourage the use of handlebars to maintain balance. Thus, we additionally investigate COP changes during trunk perturbations when ablebodied adults stood and held a handlebar. Results show that during perturbations, pelvic assistive forces decreased postural excursions and postural variability compared to quiet standing with no support. Interestingly, participants showed a similar level of postural stability, but with fewer muscle activity, with the use of an external fixed handlebar. Although, the maximum level of postural stability was observed when participants used the handlebar and received assistive forces. Our results show a significant promise of RobUST for future training of individuals with severe postural standing deficits.