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Objective: To determine: 1) if Fitbit Flex (an activity monitor) is a valid consumer-friendly alternative to research-grade accelerometers (ActiGraph) for recording step count; 2) whether 4-week continuous activity monitoring can enhance the granularity of multiple sclerosis (MS) disability assessments; and 3) if 6-month continuous activity monitoring with Fitbit was a) feasible and b) showed changes in step count that were associated with changes in patient-reported measures.

Methods: Participants with either progressive or relapsing MS were given a Fitbit Flex. Participants were excluded if they had experienced a clinical relapse within the last 30 days, had major cardiovascular or musculoskeletal comorbidities affecting gait or were not able to walk for at least 2 minutes with or without an assistive device. 1) Step count via Fitbit, ActiGraph and manual tallying were compared during a two-minute-walk (2MW) test (n=61), and Fitbit versus ActiGraph during 7 days in 20 participants. 2) Fitbit step count over 4 weeks was compared to Expanded Disability Status Scale (EDSS), 2MW and patient-reported disability (i.e. MS Walking Scale, MSWS-12) at baseline (n =80). 3) Fitbit step count was recorded continuously over 6 months in 50 participants and compared to the same patient-reported outcomes at 1.5, 3 and 6 months.

Summary of Findings: Fitbit Flex activity monitors are potential alternatives to research-grade accelerometers. They were found to be feasible, even for extended epochs (6 months). Fitbit tended to count more steps than ActiGraph, particularly when a greater total number of steps were taken per day. Measures indicating greater MS disability were associated with lower average daily step count but step count captured important variability in natural environment walking activity otherwise masked by EDSS. An increase in average daily step count from month 1 to 6 was associated with an increase in disability (MSWS-12) in people with EDSS≥4 at study entry. However, baseline average daily step count was not associated with MSWS-12 scores at 6 months. Larger studies are needed to determine if results are generalizable, and to assess if monitoring activity for longer durations can provide information on the predictive applications of continuously monitoring disease progression in MS.

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