Effort to reduce postural sway affects both cognitive and motor performances in individuals with Parkinson's disease

To assess the effects of voluntarily reducing postural sway on postural control and to determine the attention level needed to do so in healthy adults (n=16, 65.9±9.7) and persons with PD (n=25, 65.8±9.5 years). Tasks: quiet and still standing conditions with and without a category task. Cognitive performance, center of pressure (CoP) displacement variability (RMSCoP) and velocity (VCoP) were assessed in the anterior-posterior (AP) and medial-lateral (ML) directions. Controls showed larger RMSCoP (AP) and VCoP (AP and ML) during still versus quiet standing (p<0.01), while the PD group demonstrated no changes. In the PD group, RMSCoP and VCoP (ML) increased in still standing when performed with the cognitive task (p<0.05). In both groups, cognitive responses decreased in still standing (p<0.05). In PD, attempting to reduce postural sway did not affect postural control under single task conditions, however ML CoP variability and velocity did increase as a dual task. In older adults, increased displacement and velocity in both AP and ML directions was observed during single, but not dual task conditions. Therefore standing still might not be an adequate postural strategy as it increases the attentional demand and affects motor performance, putting persons with PD at greater risk for falls.