Postural abnormalities to multidirectional stance perturbations in Parkinson's disease

Area of Science:

• Neurology
• Biomechanics
• Movement Science

Background:

• Postural instability is a hallmark symptom of Parkinson's disease (PD).
• The pathophysiology of postural instability in PD, particularly concerning trunk control and protective responses, requires further elucidation.
• Understanding the effects of antiparkinsonian medication on these motor deficits is crucial.

Purpose of the Study:

• To investigate trunk control, protective arm movements, and electromyographic responses to multidirectional support-surface rotations in Parkinson's disease (PD) patients.
• To differentiate between motor control strategies on and off antiparkinsonian medication.
• To elucidate the pathophysiology of postural instability in PD.

Main Methods:

• Comparison of 10 PD patients with 11 age-matched healthy controls.
• Testing of 7 PD patients both with and without antiparkinsonian medication (OFF).
• Application of random rotational perturbations (7.5 deg amplitude) in six directions.

Main Results:

• PD patients demonstrated reduced trunk rotation and ankle torque, indicative of a stiffening response.
• This stiffening resulted from muscle co-contraction, increased agonist/antagonist muscle response amplitudes, and elevated background muscle activity.
• While deltoid responses were earlier in PD patients, arm movements were abnormally directed, offering no functional protection. Instability was greatest during backward falls. Medication partially improved arm responses and trunk roll instability.

Conclusions:

• Findings confirm previous observations of ankle muscle impairments in PD.
• New insights into balance deficits affecting hip, trunk, and arm responses in PD patients were provided.
• The study highlights the complex interplay of factors contributing to postural instability in PD.