Direction-specific limits of stability are reduced in mild to moderate Parkinson's disease individuals

Abstract

Postural instability in Parkinson's disease (PD) has been associated with decreases of the limits of stability (LOS) in the anterior-posterior (AP) directions. Although LOS changes in the latero-lateral (LL) directions have been suggested, they have not been evaluated in studies with PD, especially when the LOS tests involve intentional displacements of the body center of mass (COM). The aim of this study was to investigate the LOS in standing posture during voluntary movements that promote movement of the COM in AP and LL directions of individuals with and without PD. Twelve subjects with PD (Hoehn & Yahr stages of II and III) and 12 without the disease performed the LOS tests in the anterior, posterior, right and left directions. The movement velocity (MV), maximum excursion (ME), and directional control (DC) of the COM were evaluated in all investigated directions. Individuals with PD demonstrated smaller COM displacements in all directions (p<0.05). There were no significant differences between the groups regarding the ME and DC in the anterior direction (p>0.05). However, the ME and DC of the COM were smaller for the PD group in the backward, right, and left directions (p<0.05). Individuals with mild to moderate PD demonstrated decreases in the LOS in the posterior and LL directions, when compared to individuals without the disease. These findings suggested that such directions should be trained in the standing position with voluntary movements of the COM from the early stages of PD.