Associations of Total Activity Counts and Physical Activity Intensity Levels with the Metabolic Syndrome: A Structural Equation Modeling Approach

To clarify the protective benefits of physical activity (PA), epidemiologists and public health researchers continue to seek improved methods of assessing PA. In particular, accelerometers have gained acceptance with researchers as they provide reliable estimates of PA and can record both the amount and intensity of ambulatory movement. However, there is concern that accelerometer data reduction techniques may not provide quantitatively accurate measurements of time spent in various PA intensity categories. One way to circumvent these inaccuracies is to use the accelerometer-derived total activity counts (TAC), which is a more direct expression of what the monitor records.

In order to explore the efficacy of TAC as a measure of PA, this dissertation used data from the 2003 - 2006 National Health and Nutrition Examination Survey to: 1) investigate whether TAC was more strongly associated with cardiometabolic biomarkers than minutes of moderate-to-vigorous PA (MVPA), 2) determine population-referenced TAC percentiles for the U.S. population, and 3) determine which accelerometer-derived measure(s) of PA intensity and volume provided the best fit for assessing the association with the metabolic syndrome.

The first study demonstrated that TAC had stronger associations with cardiometabolic biomarkers than time spent in MVPA bouts of ≥ 10 minutes, suggesting TAC is a more robust measure of PA (Part IV). In the second study, age- and gender- specific population-referenced percentiles for TAC, MVPA, and light PA (LPA) were developed (Part V). This is a different approach to accelerometer data reduction that complements the current method of looking at time spent in intensity sub-categories.

The third study used structural equation modeling to examine whether TAC, MVPA, or MVPA plus LPA provided the best fit for assessing the relationship with the metabolic syndrome (Part VI). This study also assessed the relative contribution of LPA, MPA, VPA, and TAC to the reduction in the prevalence of the metabolic syndrome. Results indicated a model with TAC provided the best fit for assessing the relationship between PA and the metabolic syndrome. These findings suggest TAC, may be a better measure of PA when examining the reduction in the metabolic syndrome prevalence.