A 12 wk aerobic exercise program will reduce visceral, hepatic and intramyocellular fat accumulation and improve insulin sensitivity and glucose metabolism in obese sedentary Hispanic adolescents.

Lean and Obese post pubertal adolescents perform an aerobic exercise program 30 minx4/week at a heart rate corresponding to at least 70% of that obtained at VO2 peak. The exercise program is preceded and followed by a 7 d diet delivered by the metabolic research kitchen (identical on both study occasions); metabolic studies (identical on both study occasions) including 24h calorimetry, measurements of glucose and lipid metabolism and insulin sensitivity and secretion using compounds labelled with stable i.e. non radioactive isotopes and gas chromatography-mass spectrometry.Fat mass and lean body mass are measured by DXA and visceral/subcutaneous, hepatic and intramyocellular fat by MRI/MRS. Since we want to specifically determine the effects of exercise, there is no intent of weight loss. The subjects are weighed twice a week to assure weight stability.

Inclusion Criteria:

• Healthy
• No medication
• Sedentary
• No first degree relative with diabetes,
• Hispanic
• BMI >30 or <25 kg/m2.

Exclusion Criteria:

• Any medication including birth control pills
• Performing more than >45 min of moderate to light physical activity/week
• Chronic illness

Sedentary, post pubertal, Hispanic lean and obese adolescents