Reactive Postural Control During Sit-to-Stand Motion

Moving from a seated position to a standing position is essential for performing daily functional tasks. However, a sit-to-stand task may lead to falls in people with neuromotor disorders. Previous studies have shown that perturbation-based training can improve individuals' reactive control and reduce the risk of falls. However, few studies have investigated individuals' reactive control while transitioning from sit-to-stand. The present study aims to understand how ten healthy adults react to physical perturbations when transitioning from sitting to standing. We delivered two types of perturbations to the participants. In one condition, we used a cable-driven robotic system to displace the user's pelvis. In the second condition, we used a treadmill to displace the participants' support surface. A set of perturbations were delivered until participants failed to maintain balance. The type of perturbation delivered, i.e., force applied on the pelvis or displacement of the support surface, was randomized within each set. In addition, the direction of the perturbation, i.e., anterior or posterior, was also randomized within each set. Joint angles, ground reaction forces, and muscle activity using surface electromyography were measured to characterize their balance control strategies. Our results show that perturbation directions had the most distinguishable change among participants. Participants also required an increase in trunk movement to stabilize as the perturbation intensities increased. These results provide important insights for designing future sit-to-stand perturbation-based training in individuals prone to falling.