Study to Determine the Criterion Validity of the SenseWear Armband as a Measure of Physical Activity in People With Rheumatoid Arthritis MARIE TIERNEY, 1 ALEXANDER FRASER, 2 HELEN PURTILL, 1 AND NORELEE KENNEDY 1 Objective. Measuring physical activity in people with rheumatoid arthritis (RA) is of great importance in light of the increased mortality in this population due to cardiovascular disease. Validation of activity monitors in specific popula- tions is recommended to ensure the accuracy of physical activity measurement. Thus, the purpose of this study was to determine the validity of the SenseWear Pro3 Armband (SWA) as a measure of physical activity during activities of daily living (ADL) in people with RA. Methods. Fourteen subjects (8 men and 6 women) with a diagnosis of RA were recruited from rheumatology clinics at the Mid-Western Regional Hospitals, Limerick, Ireland. Participants undertook a series of ADL of varying intensities. The SWA was compared to the criterion measures of the Oxycon Mobile indirect calorimetry system (energy expenditure in kJ) and of manual video observation (step count). Bland and Altman, intraclass correlation coefficient (ICC), and correlation analyses were done using SPSS, version 19.0. Results. The SWA showed substantial agreement (ICC 0.717, P < 0.001) and a strong relationship (Pearson’s correlation coefficient  0.852) compared with the criterion measure when estimating energy expenditure during ADL. However, it was found that the SWA overestimated energy expenditure, particularly at higher intensity levels. The ability of the SWA to estimate step counts during ADL was poor (ICC 0.304, P  0.038). Conclusion. The SWA can be considered a valid tool to estimate energy expenditure during ADL in the RA population; however, attention should be paid to its tendency to overestimate energy expenditure. INTRODUCTION Rheumatoid arthritis (RA) is a chronic, systemic, autoim- mune disorder affecting 1% of the population. People with RA have increased mortality (50%) compared to the general population (1), mainly attributable to cardiovascu- lar disease (CVD) (2–3). Regular physical activity is associated with improve- ments in health in many populations, in particular in CV health. Recent studies assessing physical activity in the general adult population have shown a decreased inci- dence of CVD in a graded manner for more physically active subjects (4 – 6). Physical activity has been shown to both prevent and help treat many established atheroscle- rotic risk factors (7). While a few studies (8 –11) have objectively measured the physical activity levels of people with RA, whether physical activity is reduced in this pop- ulation has not been definitively determined (12). Before objective measurement to determine if a reduction in physical activity exists, it is imperative that the physical activity measurement tool used is validated in the popu- lation in which it will be used (13,14). Validation should be undertaken to establish criterion validity against a gold standard of physical activity measurement. Because the construct of interest is physical activity in the field setting, the assessment of validity during a range of daily tasks is needed, as opposed to during a treadmill walking protocol, which does not reflect the activities typically occurring in the field setting. Physical activity is defined as “any bodily movement produced by skeletal muscles that results in energy expen- diture” (15) and is typically measured by recording the amount of movement (generally in the form of step counts) or energy expenditure (16). Because both the amount of movement (step count) and intensity (energy expenditure) of physical activity are re- corded by the SenseWear Pro3 Armband (SWA; Body- Dr. Tierney’s work was supported by scholarships from the Irish Research Council for Science, Engineering and Technology; Intel Ireland; and the Central Remedial Clinic. 1 Marie Tierney, BSc, PhD, Helen Purtill, PhD, Norelee Kennedy, PhD: University of Limerick, Limerick, Ireland; 2 Alexander Fraser, MD: Mid-Western Regional Hospital, Limerick, Ireland. Address correspondence to Marie Tierney, BSc, PhD, De- partment of Clinical Therapies, University of Limerick, Lim- erick, Ireland. E-mail: marie.tierney@ul.ie. Submitted for publication May 8, 2012; accepted in re- vised form November 6, 2012. Arthritis Care & Research Vol. 65, No. 6, June 2013, pp 888 – 895 DOI 10.1002/acr.21914 © 2013, American College of Rheumatology ORIGINAL ARTICLE 888