Comparison of forward and backward postural perturbations in mild-to-moderate Parkinson's disease.

Background: Assessing postural stability in Parkinson's disease (PD) often relies on measuring the stepping response to an imposed postural perturbation. The standard clinical technique relies on a brisk backwards pull at the shoulders by the examiner and judgement by a trained rater. In research settings, various quantitative measures and perturbation directions have been tested, but it is unclear which metrics and perturbation direction differ most between people with PD and controls.