To examine the reliability, validity, and responsiveness of a continuous ambulatory activity monitor in patients with rheumatoid arthritis (RA).
Forty-one patients with RA, participating in a randomized controlled trial examining the effect of an intensive exercise program, were assessed by means of the Dynaport ADL (activities of daily living) monitor (AM). The time spent on activities (locomotion, standing, and active sitting) during 24 hours and the intensity of trunk movement during these activities were recorded. To determine test-retest reliability 20 patients were reassessed with the AM one week after the first assessment. Construct validity of the AM was determined by comparing the AM results with physical fitness measures (muscle strength, endurance, joint mobility), disease activity, and functional status. As well, 37 patients were assessed 18 months after the first assessment to determine responsiveness.
All AM measurements showed satisfactory test-retest reliability (ICC 0.63-0.76). AM measures were significantly associated with physical fitness, 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.
This study shows the value of an ambulatory activity monitor to quantify both the amount and intensity of physical activity of patients with RA during a day in their own environment. The ambulatory activity monitor seems to be a promising instrument for research into rehabilitation of patients with RA.