LIMITS OF STABILITY OF INIVIDUALS WITH PARKINSON'S DISEASE

Abstract

INTRODUCTION: Postural instability has been considered one of the main features of with Parkinson?s disease (PD). Balance failure, apparent in postural instability of Parkinsonians, is believed to be correlated with impairments to control voluntary movements of center of mass (CM) over the base of support. Quantification of limits of stability may provide an important component of balance, since its reduction can affect the ability to perform daily tasks. OBJECTIVE: To determine if limits of stability in normal upright stance varied in individuals with PD. METHODS: A group of 12 individuals with idiopathic PD, aged 69.7 + 7.0 years and 12 control subjects aged 69.42 + 7.74 years, matched by body mass index and gender were included in the study. Percentage of body weight supported by each leg in upright stance was determined using the weight bearing test. Movement velocity (MV), maximal excursion (ME) and directional control (DC) of CM in forward, backward, right, and left directions were quantified by the limits of stability test of Balance Master System?. Since most variables related to MV, ME and DC did not have normal distributions, Mann-Whitney-U tests were used to investigate differences between PD and control group, at a significance level of α<0.05. RESULTS AND DISCUSSION: No significant differences between groups were found for percentages of body weight supported by the lower limbs. However, PD subjects demonstrated significant decreases in movement velocity in all directions. These findings were expected since bradykinesia, a typical feature of subjects with PD, prevents them from rapidly developing the muscular activation necessary to generate ground forces. Reductions in MV decrease the reaction forces and minimize the need for postural stability, which can be advantageous for subjects with PD. ME and DC were also significantly different in backward, right and left directions. Decreases in ME observed in PD subjects might be related to the presence of rigidity associated with reduced postural reactions, as well as changes in motor control, such as muscular co-activation between agonists and antagonists. It is possible that increases in the oscillations observed for the PD group occurred due to greater activity of reciprocal inhibition mechanisms, as previously observed in postural muscles of individuals with PD. CONCLUSIONS: The findings suggest that in a normal upright stance, limits of stability of subjects with PD were decreased in the backward, right and left directions.