Authors: Dane R. Van Domelen1, Paolo Caserotti2, Robert J. Brychta3, Tamara B. Harris1, Kushang V. Patel1, Kong Y. Chen4, Nanna Ýr Arnardóttir5, Gudny Eirikdottir6, Lenore J. Launer1, Vilmundur Gudnason5,6, Thórarinn Sveinsson4, Erlingur Jóhannsson7, and Annemarie Koster1,8
Affiliations: 1Laboratory of Epidemiology, Demography, and Biometry, National Institute on Aging, Bethesda, MD. 2Institute of Sports Science and Clinical Biomechanics, University of Southern Denmark, Odense M, Denmark. 3Clinical Endocrinology Branch of the National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD. 4Metabolic Research Core, NIH/National Institute of Diabetes and Digestive and Kidney (NIDDK) Diseases, Bethesda, MD. 5Research Centre of Movement Science, University of Iceland, Reykjavik, Iceland. 6Icelandic Heart Association, Reykjavik, Iceland. 7Research Centre for Sport and Health Sciences, University of Iceland School of Education, Reykjavik, Iceland. 8School for Public Health and Primary Care, Department of Social Medicine, Maastricht University Medical Centre, Maastricht, The Netherlands.
Acceptance Date: September 16, 2012
Background: 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-min walk test.
Methods: The study population was older adults (78.6 ± 4.1 years) from the AGES-Reykjavik Study (N = 319). Participants performed a 6-min 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.
Results: On average, males walked 7.2% faster than females (1.31 vs. 1.22 m·s-1, p < 0.001) and had 32.3% greater vertical axis counts·s-1 (54.6 vs. 39.4 counts·s-1, p < 0.001). Accounting for walking speed reduced the sex difference to 19.2% and accounting for step length further reduced the difference to 13.4% (p < 0.001).
Conclusion: Vertical axis counts·s-1 were disproportionally greater in males even after adjustment for walking speed. This difference could confound free-living activity estimates.
Key Words: Physical activity, 6-minute walk test, accelerometry, AGES-Reykjavik Study