BackgroundIndividuals with rheumatoid arthritis (RA) often are sedentary and have an increased risk of developing comorbid conditions. Women with RA are more likely to experience challenges in maintaining an active lifestyle over their life span than men with RA or people who are healthy. As the benefits of physical activity (PA) are well known, measuring PA accurately in this population is important. ObjectivesThe purposes of this study were: (1) to characterize PA as measured with the SenseWear Armband (SWA) in women with RA and (2) to determine the measurement time frame to obtain consistent estimates of PA and daily energy expenditure (EE) in women with RA. DesignThis was a cross-sectional study. MethodsParticipants wore the SWA for 7 days. Measurements of daily total energy expenditure (TEE), physical activity energy expenditure (PAEE) during activities at or above 1 metabolic equivalent (MET) level (PAEE[≥]1MET), PAEE during activities at or above 2 METs (PAEE[≥]2METs), PAEE during activities at or above 3 METs (PAEE[≥]3METs), and number of steps were obtained. ResultsFifty-three women participated. Complete data were obtained for 47 participants (89%). Daily usage of the SWA was 98% of the time (23:31 hours/24 hours). Means (SD) were 2,099 (340) kcal/d for TEE, 1,050 (331) kcal/d for PAEE[≥]1MET, 642 (309) kcal/d for PAEE[≥]2METs, 239 (178) kcal/d for PAEE[≥]3METs, and 7,260 (2,710) for number of steps. Results of intraclass correlation coefficient analyses and multiple linear regressions indicated that 2 days were needed to reliably estimate TEE; 3 days for PAEE[≥]1MET, PAEE[≥]2METs, and number of steps; and 4 days for PAEE[≥]3METs. LimitationsThe sample was composed of well-educated women with RA who had mild to moderate difficulty performing daily activities. ConclusionThe SWA may be useful to quantify PA in women with RA and to monitor effectiveness of interventions aiming to increase PA levels. Minimizing the number of days necessary for data collection will reduce the individual’s burden and may improve adherence in studies of PA behaviors.