Semester

Spring

Date of Graduation

2013

Document Type

Dissertation

Degree Type

PhD

College

School of Public Health

Department

Social and Behavioral Sciences

Committee Chair

George Kelley

Committee Co-Chair

Andrew Bradlyn

Committee Member

Matthew Gurka

Committee Member

Carole Harris

Committee Member

Kevin Larkin

Committee Member

Keith Zullig.

Abstract

Weight gain among United States' children, adolescents and adults has become a pandemic problem, and is of great public health concern, given the increased risk for myriad chronic health problems and associated medical expenditures. It is well established that increased energy expenditure through physical activity may reduce weight and improve health. However, the predominant focus of this research has been with moderate to vigorous levels of activity (MVPA). A growing body of evidence suggests that activity levels below this (i.e., light levels), may also be beneficial. Specific to light activity, a recent area of focus has been on non-exercise activity thermogenesis (NEAT), which includes non-volitional activities and activities of daily living, as well as fidgeting. Correlations exist between higher levels of NEAT and lower body weight across a variety of individuals. The main objective of this project was to increase the understanding of NEAT, utilizing objectively measured light physical activity as a proxy, among a group of rural children and adolescents during the school day. The light activity portion of the accelerometry data was used as a proxy or surrogate for NEAT because it provides an indication of the amount of NEAT in which these youth engage during the school day. In the first study, the relationship between age and NEAT during one physical education (PE) class was examined using linear regression. Accelerometry data from elementary and high school students were utilized. Results indicated that there is an inverse relationship between age and NEAT levels, such that the elementary aged children engaged in higher levels of NEAT during their PE class than did the high school students. Studies 2 and 3 utilized accelerometry data from the high school students only, across a 1-week time period, during the beginning of their semester. Study 2 examined the relative stability of NEAT both during PE class, and during the non-PE class school day. Utilizing two mixed models, performed for males and females, and including gender as a fixed effect, study 2 examined both between-person variation estimates and within-person estimates. Results from this study revealed that the between-person variation during PE class was higher among males than females, yet similar during non-PE classes. Regarding males only, more between-person variation was present during PE class than non-PE classes. Similar results occurred for the females, where more between-person variation was present during PE class than non-PE classes. Finally, within-person effects during PE class were more variable than during the non-PE class school day. Lastly, study 3 examined activity compensation. Specifically, this study sought to determine whether adolescents differentially engage in NEAT activities during the non-PE class school day, as a result of their MVPA and NEAT activity during PE class. Two generalized linear mixed models were performed. The first model was a logistic model of the odds of an individual engaging in ≥10% of NEAT during non-PE classes versus <10% NEAT during non-PE classes. The second model was a traditional linear mixed model to examine whether activity compensation occurred among individuals who engaged in any NEAT. Results from both models found that there was a positive relationship between percent of time spent in NEAT during PE class and the amount of time spent in NEAT during non-PE classes. This result indicates that, among this sample, activity compensation does not occur. In fact, it appears that individuals who engage in higher levels of NEAT, do so across a variety of environments, and the amount of imposed physical activity does not appear to have an effect on this. One of the major strengths of these studies is that objectively measured physical activity via accelerometers was utilized. In addition, these studies were among the first to examine NEAT in a relatively large sample of rural children and adolescents. Although the utilization of light physical activity as a proxy for NEAT may have underestimated NEAT, as triaxial accelerometers and posture position measurements capture >80% of NEAT activities, these studies provided a necessary first step for the characterization of NEAT in rural youth. Future work is needed to examine NEAT in rural youth outside of the school day, as well as whether sport or activity type during PE has an influence on NEAT.

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