Purpose: To evaluate secular trends in recreational sedentary behavior among high school students in the United States between 2003 and 2015. Design: A series of cross-sectional assessments over a 12-year period. Setting: Data from the 2003 to 2015 Youth Risk Behavior Surveillance System was used. Participants: Samples of 10 978 to 14 894 adolescents, drawn every 2 years: 2003 to 2015. Measures: The evaluated recreational self-reported sedentary behaviors included TV hours and computer hours that are not schoolwork. Results: For the entire sample, and using polynomial orthogonal coefficients via regression modeling, there was an upward linear trend for total sedentary behavior hours (β = 0.03; p = .001), a downward linear trend in TV watching (β = −0.06; p < .001), and an upward linear trend in computer use (β = 0.08; p < .001) from 2003 to 2015. Similar linear trends ( p < .001) were observed across several subpopulations, including the groups by gender, race/ethnicity, and body mass index. However, various subpopulations differed in TV watching, with black or African American, and obese adolescents having the highest TV watching hours, respectively (eg, 3.82 h/d vs 3.13 h/d in 2015; blacks vs whites; p < .05). Various subpopulations also differed in computer use, with obese adolescents (4.26 h/d in 2015) having the highest computer use. Conclusion: There were significant changes from 2003 to 2015 in sedentary behavior patterns in the US adolescent population. Total recreational sedentary behavior increased in this period. Specifically, TV viewing decreased while computer use increased. Continued monitoring of sedentary behavior trends is needed to better understand the changing behaviors of American adolescents and how they relate to changes chronic disease risk.

The purpose of this study was to assess trends in physical education and physical activity among U.S. high school students from 2011 to 2017, respectively, and to evaluate temporal trends in the relationship between physical education class participation and physical activity levels. Data from a total of 51,616 high school students who participated in the Youth Risk Behavior Surveillance System (YRBSS) from 2011 to 2017 were analyzed for this study. Physical education was measured as follows: In an average week when you are in school, on how many days do you go to physical education classes? Physical activity was measured as follows: During the past 7 days, on how many days were you physically active for a total of at least 60 min per day? Meeting physical activity guideline was defined as engaging in 7 days per week of at least 60 min per day. Across the 2011–2017 YRBSS, there were no linear (p = 0.44)/quadratic trends (p = 0.37) in physical education and linear (p = 0.27)/quadratic trends (p = 0.25) in physical activity, respectively. Regarding the trends in the association between physical education and physical activity, there were no statistically significant linear (unstandardized regression coefficient (b) = 0.013, p = 0.43) or quadratic (p = 0.75) trends; however, at the sample level, there was a slight increase in the odds ratio effect sizes from 2011 to 2017 (ES = 1.80–1.98). The pooled association between physical education participation and physical activity was statistically significant, OR = 1.88, 95% CI = 1.75–2.03, p < 0.001. That is, on average across the four YRBSS cycles, students who participated in physical education had 1.88 times higher odds of meeting physical activity guideline when compared to students who did not participate in physical education. The trends of physical education and physical activity did not change between 2011 and 2017. Overall, we observed a significant relationship between participation in physical education and physical activity. There was a non-significant yet stable trend of association between participation in physical education and physical activity over time.

Dedication This work is dedicated to those who have supported me outside of my graduate studies over the last few years. My family deserves as much credit as anyone for the work generated as part of this study. Namely, Kristin Bagby, Christine Lassiter, Mechelle Lassiter, Bette Rose Ryan, and Michele Poague deserve recognition; without them I would not have been able to work as tirelessly as I have on this project. v Acknowledgements Many individuals contributed significantly to the completion of this project. Though the thesis is my own, the project is a result of a team effort. First and foremost Lynne Kammer helped me every step of the research process, from study design, to data collection, and proofreading. Zhenping Ding played another critical role in training and overseeing the completion of the biochemistry techniques used as part of this work. Assays were completed is listed last, his help on this and other projects that I have been a part of is understated and I commend him for being such a hard-working and loyal individual. My graduate studies have been made possible through the concerted efforts of the entire kinesiology staff at the University of Texas and I would like to recognize the contributions to my education made by Ivy have served as readers for my thesis and for this I owe them recognition. Lastly I would like to thank the sponsor of my research, SWSS law, and the participants who were willing to ride their bikes in the lab for the sake of expanding our scientific understanding. vi Abstract Effect of an Energy Drink on Physical and Cognitive Performance in Trained Cyclists David Gray Lassiter, MS KIN The University of Texas at Austin, 2012 Supervisor: John Ivy This study investigated the effectiveness of an energy drink (ED) in enhancing cycling time-trial performance, and cognitive performance at rest, during moderate-intensity exercise, and after exercise. The protocol was double-blind, randomized, placebo-controlled, two-period, and within-subjects. The treatments were ED containing caffeine and carbohydrate, and a caffeine-free non-caloric flavored placebo beverage (PLA). Exercise performance was measured by time to finish a simulated 35 km time-trial course. Cognitive performance was measured by a Stroop task, a tapping task, a reaction time task, and an executive function task consisting of both tapping and reaction time. The effects of ED on blood markers were also assessed. Race performance was enhanced by an average of 3% when participants had ED compared to PLA without a difference in rating of perceived exertion (RPE). Performance was improved by ED even in participants that arrived to the lab with elevated blood caffeine concentrations. Both before and after the exercise, ED resulted in more taps per second in the tapping task. After receiving ED, plasma insulin spiked, there was a fall in free fatty acids (FFA) and vii blood glucose remained unchanged. Exercise onset caused a drop in blood glucose when participants consumed ED, though glucose returned to a level that was not di...

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The purpose of this study is to establish evidence of validity for wearable activity monitors providing realtime cadence against a criterion measure. Thirty-six healthy adults, aged 18-65 years, participated in the study. Four activity monitors including 2 watch-based monitors and 2 cadence sensors attaching to shoelaces were tested. Each participant completed the study protocol consisting of 2 distinct components: (1) treadmill protocol and (2) overground protocol. Lin's concordance correlation and mean absolute percentage error (MAPE) were calculated for the comparisons between the criterion and measures of the monitors. Bland-Altman analysis was performed to determine the mean bias and 95% limits of agreement. All activity monitors showed high correlations with the criterion measures (p < .01). Lower correlations were observed at slow walking speeds in the watch-based monitors. In contrast, consistent and strong correlations were found with both cadence sensors regardless of walking speeds (p < .01). Similar patterns were observed in the MAPE scores. Greater than 90% of the participants were able to maintain prescribed walking intensity using real-time cadence. The results suggest that the wearable activity monitors are an acceptable measure of real-time cadence and provide the potential to improve intensity-based prescription of physical activity using the monitors.