86 Chapter 6 as they were unable to walk on the treadmill. Participants were recruited via the Centre of Expertise for Rare and Genetic Movement Disorders of the Radboudumc - part of the European Reference Network for Rare Neurological Diseases (ERNRND) - and via the HSP patient organization “Spierziekte Nederland”. Participants with HSP were found eligible if they met the following inclusion criteria: (i) diagnosis of pure HSP made by a neurologist specialized in inherited movement disorders, (ii) aged between 18-70 years old, and (iii) being able to walk barefoot on a level ground for 50 meters without a walking aid during the assessment (use of orthotic devices was allowed). Exclusion criteria consisted of (i) any concomitant neurological, orthopedic or psychiatric condition affecting balance or gait performance and (ii), any HSP-related surgical procedure of the lower extremities in the medical history. Additionally, fifteen healthy control participants (i.e., without neurological of orthopedic impairments) of comparable age and sex (age: 49.0 ±11 years, 73% male) were recruited from the community. The study was approved by the ethical committee Oost-Nederland and all participants provided written informed consent. Participants visited the movement laboratory of the Radboudumc (Nijmegen, The Netherlands) once. Fall Assessment Prior to the assessment, participants with HSP logged their falls with a digital fall diary for fifteen weeks. During these fifteen weeks, participants were allowed to use their walking aids and orthotics as usual. For this study, a fall was defined as an event that resulted in a person coming to rest inadvertently on a lower level surface. 17 Falls that occurred while playing sports were excluded. Based on these data, participants with HSP were either classified as ‘fallers’ (if they had logged one or more falls) or as ‘non-fallers’ (if they had not logged any falls). Every other week, participants were contacted via a phone call by the primary investigator (LvdV) to remind them of the fall diary. Clinical assessment Balance confidence was assessed with the six-item version of the Activities-specific Balance Confidence scale (ABC-6). 18 Balance capacity was evaluated with the Mini Balance Evaluation Systems Test (Mini-BEST) 19, and gait capacity with the 10-meter Walk Test (10mWT) performed at both comfortable gait speed and at maximum gait speed. 20 As a clinical descriptor, disease severity in people with HSP was assessed with the Spastic Paraplegia Rating Scale (SPRS), where higher scores indicate greater disease severity (range 0-52). 21 Furthermore, to gain insight in the amount of time that people with HSP spent walking on a daily basis, an activity monitor was placed on their right upper leg (Activ8, Remedy Distribution Ltd., Valkenswaard, the Netherlands) for seven consecutive days following the assessment.
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