The pursuit of an active lifestyle does not end with age. Traditionally, physical activity is measured using devices called accelerometers. We all know someone who uses or has used a Fitbit to keep track of their steps. These devices are particularly important for older women who are at a higher risk of diseases like osteoporosis and heart disease – conditions that can be mitigated by physical activity. However, accurately measuring physical activity has always been a challenge, especially for older individuals. The majority of accelerometers were originally calibrated for younger and middle-aged adults, overlooking the distinct physical behaviors and metabolic characteristics unique to older adults. An enlightening study from the Journal for the Measurement of Physical Behaviour, led by Drs. Chongzhi Di, Kelly R. Evenson, and their colleagues, brings us closer to solving this puzzle.
The researchers from the Women’s Health Initiative set out to recalibrate these devices specifically for women aged 60-91 years. They focused on developing what are known as “accelerometer intensity cutpoints.” These cutpoints are essentially markers that help distinguish time spent in sedentary behavior, such as sitting, from time spent in light physical activity and moderate-to-vigorous physical activity.
Their approach involved 200 healthy women who participated in sedentary activities, such as watching television or putting together a puzzle, light activities such as mopping and washing dishes, and moderate-to-vigorous physical activity like taking a walk, while wearing an accelerometer on their hip. Oxygen used by the body was measured using a portable calorimeter, providing a robust criterion assessment of sedentary behavior and physical activity intensity, since accelerometer counts increase as oxygen use increases.
One of the critical findings of the study was that the cutpoints could be confidently applied to epidemiologic studies to define sedentary behavior and physical activity intensities in older women. This finding is particularly significant as it addresses a gap for older women, ensuring more accurate monitoring and assessment of their physical activity levels.
The study presented compelling visual data through six charts comparing two different methods—vertical counts and vector magnitude (VM)—for recording physical activity levels using accelerometers. The findings revealed that VM was more precise in identifying lower activity levels and sedentary behavior, boasting higher accuracy scores (0.84 and 0.88) compared to vertical counts (0.74 and 0.80). Conversely, for more vigorous activities, vertical counts showed a slight advantage with an accuracy score of 0.89 over VM's 0.87. These insights are integral to the study's goal of recalibrating accelerometer cutpoints for older women, offering a tailored approach to monitoring their activity.
This study provides a novel approach for more accurately measuring activity levels in older women by calibrating accelerometer cutpoints to better match their behavior. It paves the way for future studies assessing the association of physical activity and sedentary behavior with health outcomes, as well as the effect of physical activity interventions to promote healthy aging. The study underscores the importance of age-specific research and personalizing health guidelines. The authors will utilize these new measures to explore whether sedentary behavior and physical activity is associated with cancer incidence and cancer death among women.
This study received support through grants from the National Cancer Institute (NCI) and the National Institutes of Health (NIH).
Fred Hutch/University of Washington/Seattle Children’s Cancer Consortium Members Drs. Chongzhi Di contributed to this study. Kelly Evenson is a Professor at the University of North Carolina – Chapel Hill.
Evenson, K. R., Wen, F., Moore, C. C., LaMonte, M. J., Lee, I. M., LaCroix, A. Z., & Di, C. (2023). Calibrating Physical Activity and Sedentary Behavior for Hip-Worn Accelerometry in Older Women With Two Epoch Lengths: The Women's Health Initiative Objective Physical Activity and Cardiovascular Health Calibration Study. Journal for the Measurement of Physical Behaviour, 6(2), 156–161.