Why do stroke survivors fall?

Lobes of the brain

Claire Honeycut

Assistant professor, School of Biological and Health Systems Engineering
Arizona State University

Half of the 6.5 million stroke survivors in the United States will fall, making falls the most common and expensive medical complication in stroke survivors. Despite this statistic, we know little about the mechanisms of why and how these individuals fall. While balance and postural stability following stroke has been studied extensively, a thorough analysis of stroke survivors response during a fall is relatively untouched. Our objective was to determine the key characteristics of a stroke survivor’s response that leads to a fall during perturbations of the treadmill that simulate “trips.” We collected kinematic and muscle activity data from 18 stroke survivors during perturbations of the treadmill. Backward perturbations elicit a compensatory stepping response. We evaluated key variables during this first step including: step length, reaction time, trunk & shank flexion and velocity, etc. Clinical scores (e.g.Berg Balance, 5 times sit-to-stand), physical activity scale, BMI, and standing asymmetry were also evaluated. We hypothesized that the mechanics of the compensatory step as well as the body’s position before the step would relate to a fall. The experimental protocol consisted of three phases: 1) 6 perturbations of varying amplitude (3 levels) and direction (backward, forward), 2) 15 backward perturbations of the same amplitude, and 3) repeat of the initial 6 perturbations. Eleven of the 18 subjects fell at least once in response to the backward perturbations resulting in 19 percent of all trials being a fall. The trunk, shank and center-of-mass positions immediately preceding the compensatory step and at the completion of the step were the most important factors relating to a fall in stroke survivors. Clinical measures and most muscle activation latencies were not different between falls and non-falls. Interestingly, the reaction time and the step length were not important indicating that it was the mechanics of the step and not the speed of the step that was important. These results indicate that training programs should target enhancing the compensatory stepping response and that clinical measures are not appropriately tuned to predict who will be a “faller” in stroke survivors.

Janet Neisewander
ASU School of Life Sciences
https://sols.asu.edu/
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Computing Commons room 120