Finally, and most importantly, none of this would have been possible without the love and patience of my family. My immediate family has been a constant source of love, concern, support and strength all these years. I would like to thank my husband, Gary. His support, encouragement, quiet patience and unwavering love were undeniably the foundation upon which the past thirty plus years of my life have been built. His tolerance of my occasional rude, offensive and wretched moods is a testament in itself of his unyielding loyalty and love. I would like to express my heartfelt gratitude to my children, Sarah and Sam, for their faith in me. I hope I have shown them dreams come true with hard work and that one is never too old to learn and grow. My extended family has also aided and encouraged me throughout this endeavor. I have to give a special mention for the support given by Christopher Reyes and Vernie Kuglin. I warmly appreciate their generosity and understanding. v ABSTRACT Purpose. The purposes of this dissertation were to (1) explore the relationships among fitness, heart rate variability (HRV), inflammation and components of the Metabolic Syndrome in obese African American youth participating in a supervised weight management program, (2) examine the effect of change in severity of obesity on these variables, and (3) identify predictors of weight loss. Method. This study consisted of a post-hoc analysis of existing pre and post-intervention data obtained from 50 African-American youth (70% female, aged 7-18 years). Anthropometric assessment of height, weight, waist circumference, systolic blood pressure, body mass index, body mass index percentile ranges, and relative body mass index were conducted. Laboratory measures included high-density lipoprotein cholesterol, triglycerides, fibrinogen, and C-reactive protein levels, and fasting and 2-hr postprandial insulin and glucose levels obtained during a mixed meal tolerance test for determination of impaired glucose tolerance and insulin resistance. Aerobic fitness was assessed by cardiopulmonary maximal treadmill exercise using the Branching Protocol (VO 2max). Heart rate variability was measured with a 24-hour Holter monitor and measures of circadian fluctuation (SDNN), parasympathetic function (HF), and sympathetic/ parasympathetic balance (LF/HF ratio) were calculated. Measures were repeated at 6 months. Data were analyzed using descriptive statistics, Pearson's correlation coefficient, non-parametric t-tests and multiple linear regression. Metabolic Syndrome was defined based on World Health Organization definition with age, gender, and race-specific cut-points. Results. Baseline measures revealed the following means: age 12.9 ± 2.9, weight 92.2 kg ± 28.4, relative body mass index 195.5 ± 42.4, HF 5.9 [ln(ms 2)] ± 0.9, SDNN 128.1(ms) ± 38.2, LF/HF ratio 1.1 ± 0.1, VO 2max 18.8 ± 4.5 mg/kg/min, C-reactive protein 0.75 mg/L ± 1.34, fibrinogen 372.64 mg/dl ± 71.12. The prevalence of the Metabolic Syndrome was 46% based on 39 subjects with complete data sets. Th...