Actigraphy as a measure of physical activity for wheelchair users with spinal cord injury

Background: Research has indicated that actigraphy is valid and reliable for measuring low levels of physical activity among ambulatory individuals, and that it may be a valid indicator of energy expenditure for wheelchair users in laboratory conditions, but there are no reports of its evaluation in free-living conditions. Objective: To assess the suitability and validity of actigraphy as a measure of free-living physical activity for wheelchair users with spinal cord injury. Methods: In a methodologic descriptive correlational study, measures of physical activity by an actigraph and a self-report physical activity record were obtained for six individuals in laboratory conditions and 22 individuals in free-living conditions during a 4-day period. At the completion of the home monitoring trial, all the participants completed a questionnaire about their experience wearing the monitor and maintaining the record. Results: Mean activity counts by actigraphy during active tasks were significantly different from the counts during inactive tasks (p = .003). During home monitoring, the participants wore the monitor, on the average, 95% of the prescribed wearing time, rated it as very comfortable, and were willing to wear it again. Pearson correlation Coefficients of activity counts with self-reported activity intensity varied from .30 to .77 (p <.01) for individual participants, The mean correlation across the sample was .60 (p <.01). Activity counts varied with reported activity, indicating concurrence between the two activity measurement methods. Conclusions: Actigraphy is suitable as a measurement of activity for people with spinal cord injury. This initial investigation suggests that it has concurrent validity with a self-report measure of activity intensity and frequency, as evidenced in this sample of wheelchair users in free-living conditions.