Context: Data are limited on the effects of controlled aerobic exercise programs (without weight loss) on insulin sensitivity and glucose metabolism in children and adolescents.

Objective: To determine whether a controlled aerobic exercise program (without weight loss) improves peripheral and hepatic insulin sensitivity and affects glucose production (GPR), gluconeogenesis and glycogenolysis in sedentary lean and obese Hispanic adolescents.

Patients and Design: Twenty-nine post-pubertal adolescents (14 lean: 15.1 ± 0.3y; 20.6 ± 0.8kg/m²; 18.9±1.5% body fat and 15 obese: 15.6 ± 0.4y; 33.2 ± 0.9kg/m²; 38.4 ± 1.4% body fat) (mean ± SE), completed a 12 wk aerobic exercise program (4 x 30 min/week at 70% of VO₂ peak). Peripheral and hepatic insulin sensitivity and glucose kinetics were quantified using GCMS pre- and post-exercise.

Results: No weight loss occurred. Lean and obese participants complied well with the program (90% of the exercise sessions attended, resulting in 15% increase in fitness in both groups). Peripheral and hepatic insulin sensitivity were higher in lean than obese adolescents but increased in both groups; peripheral insulin sensitivity by 35 ± 14% (lean) (p < 0.05) and 59 ± 19% (obese) (p < 0.01) and hepatic insulin sensitivity by 19 ± 7% (lean) (p < 0.05) and 23 ± 4% (obese) (p < 0.01). GPR, gluconeogenesis and glycogenolysis did not differ between the groups. GPR decreased slightly, 3 ± 1% (lean) (p < 0.05) and 4 ± 1% (obese) (p < 0.01). Gluconeogenesis remained unchanged, while glycogenolysis decreased slightly in the obese group (p < 0.01).

Conclusion: This well accepted aerobic exercise program, without weight loss, is a promising strategy to improve peripheral and hepatic insulin sensitivity in lean and obese sedentary adolescents. The small decrease in GPR is probably of limited clinical relevance.