Theses and Dissertations

Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


College of Psychology

First Advisor

David Reitman

Second Advisor

Christian DeLucia

Third Advisor

Stephen A. Russo


Accelerometry, Physical activity, Youth fitness


Prevalence of obesity, low physical activity, and poor physical fitness of youth in the United States are increasingly poor and in need of intervention to prevent later concerns like hypertension. The overall goal of this dissertation was to examine which factors weigh heaviest in predicting cardiovascular fitness in diverse youth, and how we might measure those factors by maximizing clinical utility and psychometric properties. The sample was gathered from a larger study examining physical activity in youth from Miami-Dade county enrolled in out-of-school programs. Participants (N = 58) were aged 6-17 and comprised exclusively of Hispanic and Non-Hispanic Black children and adolescents, the majority of whom were from low-income families. Predictors of fitness were gathered in three primary categories: demographic variables (age, gender, race/ethnic category, family income level), body composition (Body Mass Index [BMI] percentile, Bioelectrical Impedance Analysis [BIA]-measured body fat percentage), and habitual physical activity (accelerometer-measured counts per minute). These factors were entered in a hierarchical regression model to predict cardiorespiratory fitness measured by performance on a 20-meter shuttle run. Physical activity was not found to be significantly associated with fitness, and the effect size of this relationship was small, particularly when considering the impact of demographic and body composition variables. Overall, results reinforced the need for interventions to improve body composition and increase physical activity: the average participant was at the 81st percentile of BMI, had 26% body fat, was sedentary for approximately 84% of awake time, and only spent a few minutes per day engaging in vigorous physical activity. There were significant main effects of gender and race/ethnic category such that males and Non-Hispanic Black participants generally spent a greater proportion of time engaging in physical activity, with less sedentary time. Being female, younger, and having less body fat was associated with performance in the healthy fitness range when considering the impact of other variables, even though boys and older participants had more laps on the shuttle run. Findings presented in this dissertation indicate a continued need to develop technology with high utility, validity, and reliability to measure and improve indicators of health in diverse, low-income youth.

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