Objective:

Background:

Worsening Expanded Disability Status Scale (EDSS) scores and longer Timed 25-Foot Walk (T25FW) times generally correspond to increased MS disability and correlate with lower daily physical activity. Patterns of diurnal physical activity and MS disability progression are understudied.

Design/Methods:

Participants (n=577) in the SPI2 study of MD1003 (high dose biotin) in progressive MS underwent EDSS and T25FW every three months with up to 27 months of follow up. A Fitbit flex (or flex2) continuously monitored step counts per minute. Recorded data was analyzed using the function-on-scalar regression technique where EDSS, T25FW and other patient demographics were used to predict per-patient diurnal step counts.

Results:

From 12pm to 8pm, EDSS (mean R2 = 0.36±0.02) outperformed T25FW (mean R2 = 0.26±0.02) in predicting mean diurnal step count curves per patient after adjusting for sex, age, and BMI. Including EDSS and T25FW increased mean R2 to 0.39±0.02. Men took 5.2% more steps than women from 12am to 7am on average, while women took 5.1% more steps than men from 10:30am to 1:30pm and 4.3% more from 7:30pm to 10pm on average (all p<0.001). The impact of age was strongest from 3pm to 10pm, where each year of age corresponded to 0.44% fewer steps (p<0.0001). From 10am to 11pm, every one-point increase in BMI translated to 1.3% fewer steps (p<0.0001). Mean diurnal step count had midday troughs in summer, evening troughs in winter, and morning peaks in spring (all p<0.001).

Conclusions:

The association between lower physical activity and disability metrics is not uniform throughout the day, and changes with the seasons. These results highlight the need for consistency in timing of clinical evaluation in research, and provide important insight into specific times of day that may be preferable for effective rehabilitation interventions.