Modulation of reactive response to slip-like perturbations: effect of explicit cues on paretic versus non-paretic side stepping and fall-risk.

Abstract

This study aimed to examine the effect of explicit cuing on reactive stepping with the paretic limb during slip-like perturbations in stroke survivors and to identify differences in postural stability and fall-risk while stepping with either limb. Eleven chronic hemiparetic stroke survivors received slip-like stance perturbations in no-cue (implicit, no instructions) and cued (explicit, instructions to step with paretic limb) conditions. Frequency of stepping with the paretic limb was recorded. Differences between non-paretic and paretic steps for falls, number of compensatory steps, relative center-of-mass position (X COM/BOS), and velocity (Ẋ(COM/BOS)), and vertical limb support (hip descent-Z hip) were analyzed. Stepping with the paretic limb increased from 6% in no-cue condition to 42% in cued condition with no significant difference in number of falls and steps regardless of stepping limb. At liftoff of the compensatory step, stability was greater (anterior X COM/BOS) with paretic than non-paretic limb stepping whereas, at touchdown (TD) of the step, stability with paretic limb reduced (posterior X COM/BOS and Ẋ(COM/BOS)) due to a smaller compensatory step taken with the paretic versus non-paretic limb. There was no significant difference in peak Z hip regardless of stepping limb; however, the timing of peak Z hip differed (occuring prior to TD during non-paretic stepping and post-TD during paretic stepping). Thus, fall onset was earlier with non-paretic versus paretic stepping. The results support that explicit cueing can facilitate initiation of reactive step from the paretic limb as compared with the no-cue condition. Stepping with the paretic limb in the cued condition however altered time of fall onset. Regardless of the stepping side, individuals demonstrated a fall risk suggesting the need for interventions focusing on reactive step training with both the limbs.