Transfer of reactive balance adaptation from stance-slip perturbation to stance-trip perturbation in chronic stroke survivors.

BACKGROUND: Chronic stroke survivors demonstrate the potential to acquire reactive adaptations to external perturbations. However, such adaptations in postural stability and compensatory stepping responses are perturbation-type specific and the ability to generalize such adaptation to an opposing perturbation has not been studied. OBJECTIVE: The study aimed to examine whether improved reactive balance control acquired through prior slip-perturbation training would positively transfer to, or interfere with, the reactive response to an unexpected novel trip. METHODS: Twenty-six chronic stroke survivors were assigned to either the training group (TR) who received treadmill-induced slips (12 m/s2) while standing followed by a novel trip (16.8 m/s2) or the control group (TC) who experienced a single unannounced trip. The primary outcome measure was postural stability (examined by relative center of mass position (RCoMP) and velocity (RCoMV)) with step length and trunk angle being secondary measures. Perturbation outcome (fall vs recovery) and number of compensatory steps were also recorded. RESULTS: The TR group showed an anterior shift in RCoMP via longer compensatory backward step and reduced number of steps from first to last slip-perturbation (p < 0.05). Post-slip adaptation, the TR group exhibited a more posterior RCoMP on the novel trip along with a longer forward step and decreased trunk flexion compared to the TC group (p < 0.05). CONCLUSIONS: Chronic stroke survivors demonstrated improved direction-specific compensatory stepping response on a novel trip-perturbation following reactive adaptation to large-magnitude, stance-slip perturbation training.The present study investigates the ability of chronic stroke survivors to generalize motor adaptation from stance-slip perturbation training to a novel, diametrically opposing trip-perturbation. We report that people with chronic hemi-paretic stroke could execute the acquired adaptation in reactive postural stability to improve reactive stepping responses to a novel stance-trip perturbation via generation of a direction-specific effective compensatory stepping response, such that the training group demonstrated a longer forward compensatory step and better control of postural stability than the control group.