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Accelerometers have emerged as a useful tool for measuring free-living physical activity in epidemiological studies. Validity of activity estimates depends on the assumption that measurements are equivalent for males and females while performing activities of the same intensity. The primary purpose of this study was to compare accelerometer count values in males and females undergoing a standardized 6-minute walk test.


The study population was older adults (78.6 ± 4.1 years) from the AGES-Reykjavik Study (N = 319). Participants performed a 6-minute walk test at a self-selected fast pace while wearing an ActiGraph GT3X at the hip. Vertical axis counts·s−1 was the primary outcome. Covariates included walking speed, height, weight, BMI, waist circumference, femur length, and step length.


On average, males walked 7.2% faster than females (1.31 vs. 1.22 m·s−1, P < .001) and had 32.3% greater vertical axis counts·s−1 (54.6 vs. 39.4 counts·s−1, P < .001). Accounting for walking speed reduced the sex difference to 19.2% and accounting for step length further reduced the difference to 13.4% (P < .001).


Vertical axis counts·s−1 were disproportionally greater in males even after adjustment for walking speed. This difference could confound free-living activity estimates.

Van Domelen is with the Dept of Biostatistics and Bioinformatics, Rollins School of Public Health, Emory University, Atlanta, GA. Caserotti is with the Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense, Denmark. Brychta and Chen are with the National Institute of Diabetes and Digestive and Kidney Diseases, Diabetes, Endocrinology, and Obesity Branch, Bethesda, MD. Harris and Launer are with the Laboratory of Epidemiology and Population Science, National Institute on Aging, Bethesda, MD. Patel is with the Dept of Anesthesiology and Pain Medicine and Center for Pain Research on Impact, Measurement, and Effectiveness, University of Washington, Seattle, WA. Arnardóttir, Eirikdottir, Gudnason, and Sveinsson are with the Icelandic Heart Association, Kopavogur, Iceland. Arnardóttir is also with the Research Centre of Movement Science, University of Iceland, Stapi at Hringbraut, Reykjavik, Iceland. Gudnason is also with the Faculty of Medicine, University of Iceland, Reykjavik, Iceland. Jóhannsson is with the Research Centre for Sport and Health Sciences, University of Iceland School of Education, Reykjavik, Iceland. Koster is with the Dept of Epidemiology, Demography, and Biometry, National Institute on Aging, Bethesda, MD, and the School for Public Health and Primary Care, Dept of Social Medicine, Maastricht University Medical Centre, Maastricht, The Netherlands.