Preparation for compensatory forward stepping in Parkinson's disease

Area of Science:

• Neuroscience
• Biomechanics
• Movement Disorders

Background:

• Parkinson's disease (PD) impairs motor control and balance.
• Compensatory stepping is a crucial protective response to external perturbations.
• Preparation for stepping, including anticipatory postural adjustments (APAs), is vital for effective balance recovery.

Purpose of the Study:

• To characterize the preparation phase of compensatory stepping in individuals with PD compared to healthy controls.
• To investigate the effect of levodopa medication on the preparation and execution of compensatory steps in PD.
• To identify factors associated with altered stepping preparation in PD.

Main Methods:

• Observational study in an outpatient neuroscience laboratory.
• Nineteen participants with idiopathic PD (tested on and off levodopa) and 17 healthy controls.
• Participants responded to a movable platform translating posteriorly, with analysis of anticipatory postural adjustments (APAs) and step parameters (latency, length, center of mass velocity/displacement).

Main Results:

• Individuals with PD demonstrated significantly more lateral APAs (57% off-medication, 42% on-medication) compared to controls (10%).
• PD participants with APAs had later, shorter steps, greater forward center of mass displacement at foot-off, and required more steps to regain equilibrium.
• Levodopa did not influence APA presence or step execution parameters. Poor axial scores and freezing on the United Parkinson's Disease Rating Scale correlated with APA use.

Conclusions:

• Lateral postural preparation (APAs) before compensatory stepping in PD is associated with inefficient balance recovery from external perturbations.
• The findings suggest that altered postural preparation strategies contribute to balance deficits in PD.
• Levodopa does not appear to ameliorate these specific motor preparation deficits in compensatory stepping.