Measuring free-living physical activity in adults with and without neurologic dysfunction with a triaxial accelerometer.

OBJECTIVE: To investigate the reliability, validity, and utility of a triaxial accelerometer to measure physical activity in the free-living environment in adults with and without neurologic dysfunction.
DESIGN: Repeated-measures design.
SETTING: General community. PARTICIPANTS: Volunteer sample of 17 men and 30 women (age range, 28-91y) living in the community with stroke of greater than 6 months in duration (n=20), Parkinson disease (n=7), or multiple sclerosis (n=11), and healthy but sedentary controls (n=9).
INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Physical activity measured with the TriTrac RT3 accelerometer, 7-day recall questionnaire, and activity diary.
RESULTS: The accelerometer reliably measured free-living physical activity (intraclass correlation coefficient, .85; 95% confidence interval, .74-.91; P=.000). The standard error of measurement indicated that a second test would differ from a baseline test by +/-23%. Mean daily RT3 data collected in the first 3 days differed significantly from that of the mean daily RT3 data collected over 7 days. The RT3 appeared to distinguish level of mobility better than the 7-day recall questionnaire, and participants found the RT3 to be a user-friendly and acceptable measure of physical activity.
CONCLUSIONS: The triaxial accelerometer provided a stable measure of free-living physical activity, was found to distinguish between people with varying levels of mobility, and was well tolerated by participants. The results indicate that collecting data for 3 days was not reflective of data collected over 7 days.