Effects of age and pathology on stance modifications in response to increased postural threat.

This study investigated modifications to standing posture in response to elevated postural anxiety evoked by a potential physical threat to stability. Sixteen young adults, 16 older adults and 16 patients diagnosed with Parkinson's disease (PD) stood with or without the expectation of a threat to their posture (i.e., external trunk perturbation). This method allowed for the assessment of the effects of anticipatory anxiety on standing posture associated with an ecologically valid and direct threat to stability. Our manipulation was successful as all participants, independent of age and disease, reported significant increases in postural anxiety when anticipating a threat to their posture. The trunk sway modifications observed in response to elevated postural anxiety were dependent on age and disease. Young adults showed increased trunk sway in both pitch and roll directions while older adults demonstrated decreased trunk sway but only in the roll direction when standing and expecting a threat to posture compared to standing without this threat. Individuals with PD showed no significant changes in trunk pitch or roll sway when anticipating a threat to posture compared to standing without this threat. Our findings suggest that the effects of postural anxiety on postural control are dependent on the context associated with the postural threat, and age and disease status.