Control of dynamic stability during gait termination on a slippery surface in Parkinson's disease

Abstract

This study investigated how Parkinson's disease (PD) affects the ability to switch from locomotion to gait termination (GT) during planned and cued GT and examined the effect of PD on the integration of a reactive, balance maintenance strategy into voluntary GT. After a series of stops on a stable surface, eight participants with and 10 without PD stopped on a surface, which slid quickly and unexpectedly forward mimicking a slippery surface. PD caused instability during the completely voluntary nonslippery stops (P = 0.012) but not during the slippery stops, which required a reactive movement. The PD group walked slower [0.9-1.0 m/s vs. 1.3 m/s, respectively (P < 0.001)] with shorter steps during the first step of nonslippery GT (P = 0.016) and with wider steps during all steps of nonslippery GT (P <or= 0.05). Similar to controls, the PD group increased lateral stability during planned GT compared to cued GT (P = 0.007). The timing of gait termination was similar between groups in all conditions. During the unexpected perturbation, both groups used a generalized slip response to regain balance after the perturbation. PD did not affect the ability to stop walking or to integrate a balance-correcting response into GT but did affect movement speed, size, and stability of the voluntary movement.

Figure 1

Average footfall locations for the first step of gait termination showing step length and width (+/− SE). PD group data are indicated by the darker markers. After the unexpectedly slippery stop, steps were significantly shorter and wider for the first planned stop (*) and then significantly shorter and wider again for the second planned stop (**) for both groups during the first step of GT. The PD group stepped significantly shorter than controls (^).

Figure 2

Average foot angle at contact on the force plate (+/− SE). Qualitative observation suggests that while the control group flattened the foot with repeated exposure, the PD group did not greatly adapt foot angle.

Figure 3

Average walking velocity (+/− SE). Walking velocity was significantly faster in the cued stops compared to the planned stops (*). The PD groups walked significantly slower than the control group (^).