Aim II:A prospective evaluation to determine in a longitudinal cohort study the timing and relationship of mitochondrial dysfunction to the development of insulin resistance in prepubertal/early pubertal obese children compared to prepubertal/early pubertal non-obese children. Determine in a longitudinal cohort study if obese children with mitochondrial dysfunction develop greater insulin resistance and/or impaired glucose tolerance at an earlier time point. Evaluate the relationship of obesity, timing of puberty and related changes in hormone levels to mitochondrial function and the development of insulin resistance and/or impaired glucose tolerance in longitudinal analyses.