INCLUSION CRITERIA:
Volunteers will qualify if they meet the following criteria:
1. Good general health. Individuals taking medications for any serious medical condition will be excluded.
2. Age 7 to 11 years.
3. Body Mass Index 15th to 85th percentile for lean children or greater than or equal to 95% for age for overweight children.
4. Pre-pubertal (breast Tanner I - III for girls, testes size less than or equal to 10 mL for boys).
EXCLUSION CRITERIA:
Volunteers will be excluded for the following reasons:
1. Presence of major illnesses: renal, hepatic, gastrointestinal, most endocrinologic (e.g., Cushing syndrome, untreated hyper- or hypothyroidism), hematological problems or pulmonary disorders.
2. Taking any medications that might interfere with weight or growth such as oral steroids, or psychotropic agents.
3. Presence of movement or tic disorders, since conditions increasing involuntary movements may interfere with the measurement of NEAT.
4. Individuals who are taking and/or have taken stimulant or weight loss medications in the last 6 months.
5. Individuals who cannot commit to living in a similar environment with similar levels of activity during the two weeks they wear the activity monitors and timer (i.e. cannot have one week wearing the activity monitors in school and the other week wearing the activity monitors on a ski vacation).
6. Intentional weight loss of more than 3 percent of body weight in the past two months.
7. Weight in excess of 300 lbs, because of the weight limits of the dual energy x-ray absorptiometry (DXA) scanners available at the NIH Clinical Center.
8. Inability to undergo MRI (e.g., volunteers with metal within their bodies including cardiac pacemakers, neural pacemakers, aneurysmal clips, shrapnel, ocular foreign bodies, cochlear implants, non-detachable electronic or electromechanical devices such as infusion pumps, nerve stimulators, bone growth stimulators, etc. that are contraindications).
9. Inability to tolerate study procedures at the screening visit.