Analysis of Postural Instability in the Upright Position on Narrow Platforms and the Interactions with Postural Constraints

Training Postural Balance Control with Pelvic Force Field at the Boundary of Stability

This study characterizes the effects of a postural training program on balance and muscle control strategies in a virtual reality (VR) environment. The Robotic Upright Stand Trainer (RobUST), which applies perturbative forces on the trunk and assistive forces on the pelvis, was used to deliver perturbation-based balance training (PBT) in a sample of 10 healthy participants. The VR task consisted of catching, aiming, and throwing a ball at a target. All participants received trunk perturbations during the VR task with forces tailored to the participant's maximum tolerance. A subgroup of these participants additionally received assistive forces at the pelvis during training. Postural kinematics were calculated before and after RobUST training, including (i) maximum perturbation force tolerated, (ii) center of pressure (COP) and pelvic excursions, (iii) postural muscle activations (EMG), and (iv) postural control strategies (the ankle and hip strategies). We observed an improvement in the maximum perturbation force and postural stability area in both groups and decreases in muscle activity. The behavior of the two groups differed for perturbations in the posterior direction where the unassisted group moved towards greater use of the hip strategy. In addition, the assisted group changed towards a lower margin of stability and higher pelvic excursion. We show that training with force assistance leads to a reactive balance strategy that permits pelvic excursion but that is efficient at restoring balance from displaced positions while training without assistance leads to reactive balance strategies that restrain pelvic excursion. Patient populations can benefit from a platform that encourages greater use of their range of motion.

Situational factors that influence overreaching on a ladder during a gutter clearing task among older adults

Ladder falls from overreaching are a problem in older adults. Evidence suggests ladder use behavior to be dependent on interfacing user and environmental circumstances (i.e. situational factors). This study investigates the effects of situational factors (remaining debris, ladder position, time into task, hand dominant reach, reaching disposition) on reaching during a gutter clearing task on a ladder in 104 older adults. Reaching was quantified as the maximum lateral center of pressure (COP) displacement from the ladder's center. A reach was classified as an overreach when the COP displaced outside the ladder width, indicative of a ladder tip. Reaching disposition, remaining debris, ladder position, and the interaction of reaching disposition and remaining debris predicted 20% of the reaching variability during the ladder task. Overreaching was observed in 40% of participants accounting for 13% of all extended reaches (beyond ladder). This work can guide interventions on mitigating overreaching and improving ladder safety.