93 How to identify fallers and non-fallers in people with HSP Discussion This exploratory cohort study provides insight in the potential of various constructs - i.e., subjective balance confidence, objective clinical balance and gait capacity tests, and several promising biomechanical measures of gait stability - to discriminate between fallers and non-fallers among people with HSP. As a first step, we compared outcomes between people with HSP and healthy age-matched controls. We found that subjective balance confidence (ABC-6), objective clinical balance and gait capacity (Mini-BEST and 10mWT), and multiple biomechanical measures (spatiotemporal variability of step length and step time, FPD, and LDEs of the trunk) were significantly poorer in people with HSP compared to healthy controls. Subsequently, we compared the outcomes between fallers and non-fallers in HSP. Subjective balance confidence (ABC-6) showed excellent discriminative ability and objective clinical balance capacity (Mini-BEST) showed acceptable discriminative ability, whereas none of the biomechanical measures of gait stability were able to differentiate between fallers and non-fallers in HSP. It is not surprising that people with HSP showed decreased balance confidence (ABC6), balance capacity (Mini-BEST), and gait capacity (10mWT) compared to healthy controls, as these findings are in line with the literature. 2, 3, 31-33 The observed greater variability of spatiotemporal gait parameters in people with HSP compared to agematched controls is also in line with the literature. 34 Although no studies have assessed FPD or LDEs in people with HSP, previous studies did report a higher FPD in people with incomplete spinal cord injury23, and higher LDEs in a mixed neurological cohort35 compared to healthy controls. In contrast, a previous study found reduced medio-lateral MoS at midstance in HSP36, whereas we did not find such differences between both groups. These contrasting results might be due to differences in disease severity of the included participants, but unfortunately this assumption cannot be verified as no measure of disease severity was reported in the study by van Vugt et al. 36 It may be argued that differences in biomechanical measures between HSP and controls emerged as a result of differences in gait speed. Indeed, comfortable gait speed was significantly lower in people with HSP, and earlier studies have demonstrated that gait speed affects gait stability. 28, 29, 37, 38 To make a speedcontrolled comparison between HSP and controls, we asked both groups to walk at a similar, fixed gait speed. For these conditions, we still found that people with HSP walked with greater variability of step length and step time. Furthermore, we found greater variability of the mediolateral MoS, and a larger LDE of the trunk in vertical direction) in HSP compared to controls. These findings indicate that the 6
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