While persons with early stage Parkinson’s disease (EPD) typically demonstrate minor levels of physical impairment and disability,^10,21 they often have difficulty with transitional movements.66 To date, most of the studies evaluating such transitional movements in persons with PD have focused on those individuals in advanced stages of the disease;​ little is known in regards to persons with EPD. The primary objective of this dissertation was to characterize dynamic postural control utilized in response to increased task demands during transitional locomotor tasks in persons with EPD. To achieve this goal, three separate studies were undertaken.

The purpose of study #1 was to compare dynamic postural control, between persons with EPD and HC participants, during preplanned and unplanned gait termination. Center of pressure (COP) and full body kinematics (i.e., extrapolated center of mass [eCOM]) were used to quantify dynamic postural control in 15 persons with EPD and 10 HC participants during preplanned and unplanned stopping tasks. Compared to HC subjects, persons with EPD exhibited significantly shorter distances in the AP direction, between the COP and the eCOM during both stopping tasks. Group differences, however, were not influenced by task type. These findings suggest that persons with EPD adopt a more cautious postural control strategy, reducing the COM momentum during both stopping tasks. Moreover, the results suggest that dynamic postural control during gait termination is altered even in the early stages of PD.

The purpose of study #2 was to compare dynamic postural control between persons with EPD and HC participants, during preplanned step turning. Participant criteria, instrumentation, and data analysis for this experiment were described in study #1. Participants were instructed to walk at self-selected pace to a designated location and turn to the side of their dominant limb at a 90° angle. The turning cycle was divided into two phases, based upon the three steps (approach, pivot, and acceleration) required to complete the turn. The peak distance between the COP and the eCOM was calculated during each phase. Individuals with EPD demonstrated significantly shorter COP-eCOM distances compared to HC subjects during both phases. These group differences were influenced by both a shorter distance between the COP and the COM, and a slower COM velocity. These findings further support that persons with EPD adopt a more cautious movement strategy when transitioning from one walking direction to another.

The purpose of study #3 was to:​ 1) compare turning preferences between persons with EPD and HC participants, 2) examine the influence of EPD on postural control during the spin turn, and 3) determine whether postural control differences between subjects with EPD and HC participants are influenced by turn type. Participant criteria for this experiment and details of instrumentation and data analysis are described in study #1. The frequency of the step- and spin-turn strategies was recorded for each participant. In addition, the peak COPeCOM distances produced during preplanned step and spin turns were examined. Persons with EPD used the step turn strategy 1.4 times more frequently than the spin turn when compared to age matched control subjects. Compared to the control group, persons with EPD utilized shorter COP-eCOM distances during both the step turn and the spin turn. Peak COP-eCOM distances were similar between the two types of turn strategies within each group.

Taken together, findings from this dissertation provides evidence that persons with EPD select a postural control strategy that decreases disequilibrium and mobility, and increases stability, during more complex locomotor tasks. Additionally, it demonstrates that functional impairments can be detected during more complex locomotor activities, even in the early stages of PD, when clinical signs of gait disturbance are often absent. This information may be used to quantify disease severity, develop task specific interventions for persons with EPD, and examine the effects of such interventions.