The value of a continuous ambulatory activity monitor to quantify the amount and intensity of daily activity in patients with rheumatoid arthritis

Objective. To examine the reliability, validity, and responsiveness of a co ntinuous ambulatory activity monitor in patients with rheumatoid arthritis (RA). Methods, Ferry-one patients with RA, participating in a randomized controll ed trial examining the effect of an intensive exercise program, were assess ed by means of the Dynaport(R) ADL (activities of daily living) monitor(R) (AM). The time spent on activities (locomotion. standing, and active sittin g) during 24 hours and the intensity of trunk movement during these activit ies were recorded. To determine test-retest reliability 20 patients were re assessed with the AM one week after the first assessment. Construct validit y of the AM was determined by comparing the AM results with physical fitnes s measures (muscle strength, endurance, joint mobility), disease activity, and functional status. As well, 37 patients were assessed 18 months after t he first assessment to determine responsiveness. Results, All AM measurements showed satisfactory test-retest reliability (I CC 0.63-0.76). AM measures were significantly associated with physical fitn ess, functional status, and disease activity, indicating construct validity of the AM. The AM could discriminate between patients with improvement and deterioration in physical fitness. indicating sufficient responsiveness of AM variables. Conclusion, This study shows the value of an ambulatory activity monitor to quantify both the amount and intensity of physical activity of patients wi th RA during a day in their own environment. The ambulatory activity monito r seems to be a promising instrument for research into rehabilitation of pa tients with RA.