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Abstract
Sleep, sedentary behavior (SED), light physical activity (LPA) and moderate to vigorous physical activity (MVPA) are four behaviors that make up the 24-Hour Activity Cycle (24-HAC) model. Traditional methods to measure the 24-HAC behaviors are based upon different self-report instruments or the application of a single wrist worn accelerometer. However, these current approaches are primarily limited by self-report recall errors or overestimations of total physical activity from a single device. Integrating multiple, valid objective measurements may be needed to a) assess the 24-HAC behaviors with acceptable precision and b) to examine the associations of different 24-HAC profiles with important demographic and health outcomes. The first portion of this dissertation simultaneously used three different research grade monitors (ActiGraph GT3X+=LPA/MVPA, activPAL3=SED, and ActiGraph GT9X=Sleep) to describe the 24-HAC components by demographic, academic, and lifestyle characteristics in university students. Findings from the study concluded that university students spend 34% of their day sleeping, 41% SED, 21% LPA, and 4% MVPA. Mean sleep, SED, and LPA tended to be similar across groups with different demographic and lifestyle characteristics with no significant differences. Mean MVPA significantly differed by sex and race/ethnicity but did not significantly differ by body mass index or academic or lifestyle characteristics.
The second portion of this dissertation explored the associations between smartphone screen time and the 24-HAC in university students. Findings from this study revealed that smartphone screen time had a significant negative association with LPA. After adjusting for confounders and other components of the 24-HAC, smartphone screen time had a significant positive association with SED. Although not significant, smartphone screen time had a positive association with sleep duration and a negative association with MVPA.
Because the measurement of 24-HAC has emerged as a new paradigm, measurement of these components needs additional research. Future studies should examine if using a single objective measurement device can provide similar estimates of the 24-HAC compared to those derived from multiple devices. Future studies should also consider exploring the advantages and disadvantages of simultaneous combined measurement of the 24-HAC in different samples.