Anticipatory postural responses prior to protective steps are not different in people with PD who do and do not freeze

•How freezing and anticipatory postural responses (APAs) are related is not understood.•APAs prior to protective steps were assessed in PD who do and do not freeze.•APA size & frequency were not statistically different in those who did and did not freeze.•APA size, alone, may not precipitate freezing events. Protective stepping after a loss of balance is related to falls. Anticipatory postural responses (APAs) prior to protective stepping can impact step performance, may be larger in people with PD, and have been suggested to be related to freezing of gait (FOG). However, whether people with PD and FOG (PD + FOG) exhibit larger APAs than people with PD and no FOG (PD-FOG) is unknown. Research Question: Determine the impact of freezing status on APAs prior to protective steps, thus providing a better understanding of the link between FOG and APAs. Twenty-eight people with PD (13 PD + FOG) were exposed to 50 support surface translations (25 forward, 25 backward, random order) resulting in protective steps. The size of medio-lateral weight shifts prior to the protective step (i.e. APAs), and the percentage of trials with an APA were calculated via force-plates. FOG status was assessed at the time of testing as well as 3.25(+/-0.43) years later. Participants without FOG at testing, but with FOG at follow-up were identified as “converters”. For both forward and backward protective stepping, size and percentage trials with an APA were not statistically different between PD + FOG and PD-FOG, even after excluding converters from the PD-FOG group (p > 0.27 for all). No group by direction interactions were observed. These data suggest that, in mild to moderate PD, an inability to couple APAs with stepping, rather than an inappropriately sized APA, may be most related to freezing of gait.