Dynamic postural stability during the sit-to-walk transition in individuals with Parkinson's disease

Postural control during dynamic activities requires the integration of multiple sensory and motor pathways so that the central nervous system can coordinate the anticipatory/postural and intentional/movement components of the task. Persons with Parkinson's disease (PD) exhibit a marked deficit in maintaining equilibrium during transitions between states of static and dynamic equilibrium, such as gait initiation (GI) and (STS) where momentum must be generated and controlled. A more common functional task that has received little attention is initiating gait from a seated position (sit to walk or STW), which represents a merging of GI and STS. Thus, STW is a complex transitional task that imposes challenges to both the locomotor and dynamic postural control systems and its biomechanical evaluation may provide valuable insight into postural control deficits in this population. The purpose of the study was to evaluate motor performance during STW in a PD population (n=12) compared to healthy age-matched older adults (HOA) (n=12) and healthy young subjects (HYA) (n=12). STW performance was captured at 120 Hz using an 8 camera 3D Optical motion system and 2 force plates. In general, there appears to be a continuum of STW performance whereby the HYA performed the task more efficiently than the HOA and the HOA performed the tasks more efficiently than the PD patients. The HYA appeared to merge the two tasks around seat-off, while the HOA demonstrated both merged and some movement sequenced characteristics. However, the PD patients were unable to merge the two tasks into one continuous movement and they appeared to complete STS before performing GI. These findings have potential implications in understanding the risk of falls in PD patients during dynamic transitional movements and can provide a structure for studying the STW motor task.