###### Abstract  
Individuals with Parkinson's disease (PD) have postural instability and gait dysfunction that lead to falls and disability with disease progression. Increased fall risk is particularly seen during challenging gait tasks such as obstacle-crossing. The purpose of this study was to determine if there were differences in dynamic postural control during self-paced walking and obstacle-crossing between persons with mild-to-moderate PD and healthy controls. Participants included nine individuals with PD and nine age- and gender-matched controls (CON). This study examined margin of stability metrics using instrumented 3D motion analysis during the two-step sequence of the obstacle-crossing task. Dynamic balance variables and spatiotemporal (ST) parameters at distinct gait events related to the leading (step one) and trailing leg (step two) were compared for the PD and CON groups using a mixed-model ANOVA. No differences were found between groups for ST gait parameters during obstacle-crossing, except for a significantly reduced step length (\(p\) = 0.005) for the trailing limb for the PD group. The PD group demonstrated significantly larger mean values for mediolateral center of pressure-center of mass (COP-COM) distance at first double support (\(p\) = 0.044) and center of pressure-extrapolated center of mass (COP-XCOM) distance at second double support (\(p\) = 0.016) for the second step. Our results suggest that the margin of stability may be useful in discerning postural control adaptations during obstacle negotiation in persons with PD. spatiotemporal gait parameters; center of pressure; center of mass; extrapolated center of mass; margin of stability +
Footnote †: journal: Applied Sciences  
during walking, where an individual's center of gravity continues to accelerate forward as their feet appear stuck to the floor or are moving in fast, small, shuffling steps, leading to significantly increased fall risk [4; 14]. Even individuals with very early stage PD may experience FOG (an estimated one in four persons), which can limit community mobility skills [15; 16; 17]. For those in advanced disease stages, the incidence of FOG is estimated as high as 75%, and this gait deficit can markedly contribute to injurious falls [15]. The underlying etiology of dynamic postural control impairments in individuals with PD is complex and not fully understood. Postural control requires multiple subsystems to interact simultaneously to maintain dynamic stability during both static and dynamic tasks as the individual interacts with a variety of environments. These subsystems include sensory organization, motor coordination, musculoskeletal properties, cognitive processes, and anticipatory and reactive postural control strategies [18; 19; 20]. Sensory integration for balance control involves the weighting of somatosensory, visual, and vestibular information based on environmental and task demands. Research indicates that individuals with PD have impaired sensory organization, as evidenced by dynamic posturography testing, including ineffective use of somatosensory and vestibular cues and an overreliance on visual information [21; 22; 23]. Reactive postural control, defined as the ability to bring in automatic postural responses following a perturbation or loss of balance, is a key contributor to increased fall risk in those with PD. Research demonstrates that individuals with PD have abnormal scaling and hypometric postural responses to perturbations both when standing and during walking tasks [18; 24; 25; 26]. Anticipatory postural control strategies are employed preceding self-generated movements, such as in reaching, bending, and walking tasks to maintain dynamic equilibrium. These anticipatory postural adjustments are less effective in individuals with PD because they are smaller in magnitude and are prolonged compared to healthy adults [19; 27; 28].