90 Chapter 6 group was 10.1±3.9 points. The mean time since first symptom onset was 16±13 years. Participants with HSP and healthy controls did not differ in age or sex. Clinical assessment Participants with HSP scored significantly worse on the ABC-6, Mini-BEST, and 10mWT compared to healthy controls (Table 1). Biomechanical assessment at comfortable walking speed Participants with HSP showed a slower comfortable treadmill speed than the healthy controls (0.88 ± 0.26ms-1 vs. 1.31 ± 0.11ms-1; p<0.001). Five participants with HSP used the treadmill bars occasionally to restore balance (one participant one time, one participants two times, two participants five times, and one participant eight times). None of the healthy controls used the treadmill bars. They also showed significantly greater variation of step length and step time (Table 1). In line with these results, the foot placement deviation and the LDE of the trunk in mediolateral direction, and the LDEs of the pelvis in anteroposterior and vertical direction were significantly higher in participants with HSP compared to healthy controls (Table 1). The MoS outcomes did not differ between groups. Biomechanical assessment at fixed walking speed A total of 24 participants with HSP were able to perform the additional trials at a slower fixed speed of either 0.6ms-1 (n=16) or 0.8ms-1 (n=8). Nine participants were unable to perform these additional trials: five participants were too fatigued, and four participants already had a self-selected walking speed below 0.6ms-1. To provide insight in whether this imposed a selection bias of this subgroup (i.e., only the best ‘walkers’ remained in the analysis), we included the scores of balance confidence, balance capacity and gait capacity test of the selected participants in Table 2. This shows that the subgroup of 24 participants performed more or less the same on the clinical tests compared to the full cohort of 33 participants (ABC: 59±23 vs. 56±23 points; MiniBEST: 20±4 vs. 20±5 points; 10mWT at comfortable gait speed: 1.3±0.3 vs. 1.3±0.2ms-1, respectively). Of the 24 participants included in this analysis, five patients with HSP used the treadmill bars to restore balance (four participants one time, one participant two times). None of the healthy controls used the treadmill bars. To perform the statistical analysis, we individually matched the slow fixed speed trials performed by the HSP participants with trials from the healthy control group: ten at the fixed speed of 0.6 ms-1 and five at the fixed speed of 0.8 ms-1. The coefficient of variation of step length and step time remained significantly higher among participants with HSP compared to healthy controls. In addition, participants with HSP showed significantly greater LDE of the trunk in vertical direction and MoS variability (Supplementary Table 1).
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