Is there a Sex Difference in Accelerometer Counts During Walking in Older Adults?

Section: Original Research

Authors: Dane R. Van Domelen¹, Paolo Caserotti², Robert J. Brychta³, Tamara B. Harris¹, Kushang V. Patel¹, Chen Y. Kong⁴, Nanna Ýr Arnardóttir⁵, Gudny Eirikdottir⁶, Lenore J. Launer¹, and Annemarie Koster¹

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.

Acceptance Date: September 16, 2012  

Abstract
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