Date of Award


Document Type

Open Access Dissertation


Exercise Science


Norman J. Arnold School of Public Health

First Advisor

Michael W. Beets


Emerging evidence shows children gain 3-5 times the amount of weight and lose cardiorespiratory fitness (CRF) during summer compared to the 9-months of the school year. Notably, this trend is more pronounced in children who are already overweight or obese going into summer and/or from low-income ethnic minority households. There is little evidence to investigating the underlying mechanisms driving the pronounced occurrence of these negative health outcomes during summer.

The purpose of this dissertation as a whole was to investigate children’s obesogenic behaviors (physical activity, sedentary/ screen time, sleep, and diet) during summer versus school, and compare any differences in relation to changes in health outcomes (body mass index and CRF).

The purpose of study 1 was to provide a scientific hypothesis to explore some of the differences between summer and school months, in absence of a larger literature base to draw from. The Structured Days Hypothesis (SDH) posits that obesogenic behaviors are beneficially regulated when children are exposed to a structured day (i.e., school weekday) compared to what commonly occurs during summer. In this study, the author examined empirical data that compares weekend day (less-structured) versus weekday (structured) obesogenic behaviors in U.S. elementary school-aged children. From 190 studies, 155 demonstrated elementary-aged children’s obesogenic behaviors are more unfavorable during weekend days compared to weekdays. In light of this evidence, the SDH would suggest that structured environments (e.g., weekdays/schooldays) may protect children by regulating obesogenic behaviors, such as exposure to compulsory physical activity opportunities, restricting caloric intake, reducing screen time occasions, and regulating sleep schedules. Summer days may be less-structured thereby allowing negative obesogenic behaviors to occur at a greater rate and for an extended period of time.

The purpose of study 2 was to examine elementary school-aged children’s obesogenic behaviors (physical activity (PA), sedentary/screen-time, diet, and sleep) during school versus summer using a repeated-measures within-subjects design., children (n=55 mean age=8.2 years; 57% female; 37% overweight/obese; 100% African American) wore accelerometers on the non-dominant wrist and parents completed a daily diary for 9 consecutive days. Children spent more time sedentary (69 vs. 67% of wake weartime), less time in light PA (25 vs. 23% of wake weartime), had higher screen-time (242 vs. 123 min/day), slept longer (428 vs. 413 mins/night), and consumed more sugarbased foods (6 days vs. 2.5 days/week) and fruit (7 days vs. 4.7 days/week) during summer compared to school (p<0.05). Initial evidence suggests children are displaying multiple unfavorable obesogenic behaviors during summer compared to school that may contribute to the accelerated weight gain during summer. Longitudinal evidence with larger, more diverse samples of children is necessary to identify specific behavioral targets for interventions during summer.

The purpose of study 3 was to investigate changes in children’s obesogenic behaviors between summer and school in relation to their changes in body mass index (BMI) and CRF during summer. Elementary school-aged children had their BMI and CRF measured before (May) and after (August) summer (2016). A 9-day protocol captured physical activity, sedentary/ screen time, sleep and diet during school (May) and summer (July). There was a small negative association for zBMI change and healthy summer behaviors (r=-0.36; p=0.09), and a positive association for CRF change (r=0.31; p=0.14) and healthy summer behaviors. Children who increased in zBMI and displayed a concurrent loss in CRF over summer presented less favorable obesogenic behaviors during summer. Further research is needed to confirm this relationship.

This dissertation provides preliminary evidence of differences in children’s obesogenic behaviors during summer versus school and how unfavorable obesogenic behaviors occurring during summer could be impacting health outcomes occurring during this time. Summer may be the critical period where future childhood obesity efforts need to be focused, however, longitudinal evidence with larger, more diverse samples of children is necessary to identify specific behavioral targets for interventions during summer.


© 2017, Keith Brazendale