Dynamic stability and compensatory stepping responses during anterior gait-slip perturbations in people with chronic hemiparetic stroke.

To examine the control of dynamic stability and characteristics of the compensatory stepping responses to an unexpected anterior gait slip induced under the non-involved limb in people with hemi-paretic stroke (PwHS) and to examine any resulting adaptive changes in these on the second slip due to experience from prior slip exposure. Ten PwHS experienced overground slip (S1) during walking on the laboratory walkway after 5-8 regular walking (RW) trials followed by a second consecutive slip trial (S2). The slip outcome (backward loss of balance, BLOB and no loss of balance, NLOB) and COM state (i.e. its COM position and velocity) stability were examined between the RW and S1 and S1 and S2 at touchdown (TD) of non-involved limb and at liftoff (LO) of the contralateral limb. At TD there was no difference in stability between RW and S1, however at LO, subjects demonstrated a lower stability on S1 than RW resulting in a 100% backward loss of balance (BLOB) with compensatory stepping response (recovery step, RS, 4/10 or aborted step, AS, 6/10). On S2, although there was no change in stability at TD, there was a significant improvement in stability at LO with a 40% decrease in BLOB. There was also a change in step strategy with a decrease in AS response (60% to 35%, p<0.05) which was replaced by an increase in the ability to step (increased compensatory step length, p<0.05) either via a recovery step or a walkover step. PwHS have the ability to reactively control COM state stability to decrease fall-risk upon a novel slip; prior exposure to a slip did not significantly alter feedforward control but improved the ability to use such feedback control for improved slip outcomes.