Understanding Recovery Reactions Following Balance Loss: The Effect of Age and Handrail Cross-sectional Design

Abstract

Falls on stairs are a common cause of injury and hospitalizations, particularly for older adults. To recover balance after a destabilization, fast, accurate and appropriate balance recovery strategies must be employed to arrest a fall. While handrails have been shown to decrease the likelihood of falls, it is unknown how handrail shape and size affect the ability to support successful balance recovery. With a lack of guiding data to support design, national and international standards and regulations permit a variety of handrail cross-sectional sizes and shapes. This thesis aims to better understand balance recovery on stairs and how the design of handrails affects the reach-to-grasp balance recovery responses. I conducted four experimental studies to address the overall research objective. In the first two studies, I characterized the demands of balance recovery during stair descent. Novel methods were used to induce unexpected forward and backward balance loss during stair descent in younger adults. To recover from both forward and backward balance loss, participants used a variety of strategies, including compensatory stepping, counter-balancing trunk and arm movement and grasping environmental features. Of those participants who grasped the handrail, participants applied a range of forces, from light touch to 30% of their body weight. Many participants also had errors in grasping, particularly in backward balance loss. Building on this work, Studies 3 and 4 aimed to further understand the effect of handrail shape and size on the speed and accuracy of reach-to-grasp reactions and ability to generate necessary forces to arrest a fall for older and younger adults. A ramp-up perturbation protocol was used to induce balance loss that was repeatable and demanding for all handrail cross-sections. Of the seven handrails tested, the 1.5” round handrails allowed participants to apply the highest forces and to withstand the greatest magnitudes of perturbation with the fewest errors for both younger and older adults. In contrast, large complex handrails resulted in reduced forces, lower withstood perturbations with more errors. This research provides empirical evidence that can be used to guide standard development and clinical recommendations for safer stairways.