Short communicationAnticipatory postural responses prior to protective steps are not different in people with PD who do and do not freeze
Introduction
Anticipatory postural adjustments (APAs) prior to voluntary steps are small in people with Parkinson’s disease (PD), leading to ineffective steps [1]. Protective steps are quick movements in response to a loss of balance, and are critical for fall prevention [2]. Interestingly, unlike voluntary stepping, APAs prior to protective stepping may be larger than normal in people with PD [[3], [4], [5]].
Recent work suggests a potential link between large APAs during protective stepping and “start hesitation”, a form of freezing of gait (FOG) [3,6]; as people with PD who freeze (PD + FOG) exhibit larger APAs compared to healthy controls during protective stepping [3]. These larger APAs may be related to an inability to either trigger a step or effectively couple the APA and the step. However, the relationship between FOG and APAs is incompletely understood. Although people with PD + FOG exhibit larger APAs during protective stepping compared to healthy adults [3,4], it is unknown whether they exhibit larger APAs compared to people with PD who do not freeze (PD-FOG). Therefore, the larger protective-step APAs observed previously may be due to PD progression generally, rather than freezing status. Finally, although postural stability is particularly affected in the backward direction in people with PD [7], APAs during protective backward steps have not been characterized in those with PD.
The purpose of this study was to further characterize the relationship between FOG and APAs during protective stepping by measuring APA size in people with PD + FOG and PD-FOG prior to forward and backward protective steps. Understanding the relationship between APAs and FOG may inform treatment strategies aimed at reducing postural instability and falls in people with PD. Such information is particularly important given the challenges associated with fall prevention in people with PD [8].
Section snippets
Participants
A convenience sample of twenty-eight people with PD participated. Inclusion criteria were: ability to stand without aid for longer than 1 h, currently taking levodopa, and devoid of orthopedic or neurological conditions (other than PD) affecting balance. Thirteen of 28 participants self-reported FOG via the New FOG Questionnaire (NFOG-Q) [9]. To better characterize freezing status, participants who self-reported as PD-FOG were contacted 3.25(SD = 0.43) years later, and asked if they had
Results
For forward and backward stepping, APA size and percent of trials with APA were not significantly larger in the PD + FOG group compared to the PD - FOG group (p > 0.27 for all, Table 2, Fig.1). No direction or group by direction interactions were observed for APA size or percentage of trials with an APA. The relationship between FOG severity and APA size was non-significant for forward (p = 0.21) and backward (p = 0.20) stepping.
APA size became smaller across time for backward stepping, both
Discussion
This study investigated the effect of freezing and perturbation direction on APA size prior to protective steps. APAs prior to protective stepping were not significantly different in people with PD + FOG compared to PD-FOG. This remained true even after removing people who went on to freeze from the PD-FOG group. Further, direction of protective stepping did not impact APA size or frequency.
The neural and behavioral circumstances that lead to a freezing event are incompletely understood. Poorly
Conclusions
APA size and frequency were not statistically different in people who freeze compared to those who do not freeze. Although the freezing group was relatively mild, they did exhibit more frequent self-reported falls. Together, these findings support the hypothesis that, in mild to moderate PD, freezing may not be precipitated by poorly sized APAs.
Funding sources
This work was supported directly by: The United States Department of Veteran’s Affairs Rehabilitation Research and Development Service (Career Development Award-1: #I01BX007080; PI: DSP) and the Medical Research Foundation of Oregon (Early Investigator Award; PI: DSP). Over the past 12 months, authors have also been funded by: the Canadian Institutes of Health Research (PTJ 153330; CoI: KRL), Auburn University Internal Grants Program (IGP Project #: 170,138; PI: KRL), Federal Aviation
Potential conflicts of interest
Drs. Peterson & Lohse have no conflicts of interest to report. Dr. Mancini has served as a consultant for Axovant and Cadent. Dr. Peterson takes responsibility for the integrity of the data and the accuracy of the data analysis.
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