The effect of handrail shape and size on the speed and accuracy of reach-to-grasp reactions following induced balance loss

Gosine, Philippa (1,2), Collins, Mackenzie (2,3), Komisar, Vicki (4), Novak, Alison (2,5)

1: Institute of Biomaterials and Biomedical Engineering, University of Toronto

2: Toronto Rehabilitation Institute - University Health Network

3: Systems Design Engineering, University of Waterloo

4: Department of Biomedical Physiology and Kinesiology, Simon Fraser University

5: Department of Occupational Science and Occupational Therapy, University of Toronto

Reach-to-grasp reactions toward handrails are often performed following balance loss on stairs. The speed and accuracy of volitional reach-to-grasp movements depend on age and object properties. This study evaluates the effect of handrail profile on the speed and accuracy of reach-to-grasp reactions following balance loss.

Fourteen older (>60y) and 14 young adults (18-35y) experienced surface translations, which led to backward and forward balance loss. Participants were instructed to reach and grasp the nearby handrail. To evaluate full reliance on the handrail, we incrementally increased the perturbation magnitude until the participant reached an acceleration of 5m/s/s or was no longer able to recover their balance without stepping or relying on the harness. During the trial prior to the failure trial, we determined the speed and movement time of the hand using a marker on the wrist. Errors and adjustments in grasping were determined from videos and load cells in the handrail were used to determine contact time. Seven handrail profiles were tested: 1.5” round, and 2.5” and 3” round, tapered and decorative handrails. Repeated-measures ANOVAs were conducted to determine significant differences between groups and within handrail profiles and Tukey post-hoc tests were performed if a significant main effect was found (p<0.05).

Young adults withstood higher perturbations than older adults (p=0.0004). For forward balance loss, participants withstood higher perturbations with the 1.5” round handrail than the tapered and round handrails (main effect: p=0.001, Tukey post-hoc: p<0.05). Handrail contact time and the time from peak resultant wrist velocity to contact were not significantly affected by age or handrail profile. Young adults had higher peak resultant wrist velocity (p<0.04) than older adults. In terms of accuracy, the largest numbers of errors were observed with the tapered and 3” decorative handrails, each resulting in a total of 15 errors over 56 trials, and tapered handrails resulted in the largest number of grip adjustments after contact.

Compensatory reach-to-grasp reactions can be challenging, indicated by error rates, particularly with the larger handrails. Participants did not significantly change the timing of their reach-to-grasp based on handrail profile, indicating that they did not modulate their movement to account for handrail shape or size. This is the first step in determining the effect of handrail profile on balance recovery.