The purpose of this study is to evaluate the effects of resistance training, aerobic training, and combined aerobic and resistance training on percent body fat, measured using Magnetic Resonance Imaging (MRI), in sedentary post-pubertal overweight or obese youth aged 14-18 years.

Background: Obesity and inactivity independently increase risks of chronic disease in adolescence and all-cause mortality in adulthood. In clinical trials, changes in exercise and diet can reduce adiposity and risk of diabetes and other chronic diseases in obese adults and youth. In many school systems, physical education is mandatory in elementary school but not high school, and physical activity often declines during adolescence. Because physical activity habits track from adolescence to adulthood, adolescence may represent a critical period for establishing a physically active lifestyle to prevent diseases associated with inactivity in adulthood. Obesity can make adherence to aerobic activity challenging, but would present less of an obstacle to resistance training. Resistance exercise has shown favorable effects on lean body mass, metabolic rate, insulin resistance, and quality of life in adults, but almost no research has examined effects of resistance training in obese adolescents. Our own survey in a sample of obese, primarily sedentary youth found greater overall interest in resistance exercise than aerobic exercise.

Objectives: The primary objective of this study is to evaluate the effects of resistance training, aerobic training, and combined aerobic and resistance training on percent body fat measured using Magnetic Resonance Imaging (MRI) in sedentary post-pubertal overweight or obese youth aged 14-18 years.

Study Design: Randomized controlled trial conducted at a single site. After a 4-week supervised low-intensity exercise run-in period to test compliance, 292 adolescents with BMI ≥ 85th percentile for age and gender will be randomized in equal numbers to one of 4 arms: Diet + aerobic exercise, diet + resistance exercise, diet + combined aerobic and resistance exercise, or diet-only control. The intervention will last 22 weeks, with a follow-up assessment at 6-months post-treatment (11-months post-randomization).

Hypotheses: Reduction in percent body fat will be larger in diet + aerobic exercise and diet + resistance exercise than diet-only controls at post-treatment, and the combined aerobic and resistance training will be superior to either aerobic or resistance training alone in reducing percent body fat at post-treatment. The combined resistance and aerobic group will show greater improvements in percent body fat, body composition, and physiological and psychosocial function at post-treatment and 12-months follow-up. Groups that include resistance training will produce greater psychosocial changes and better adherence than aerobic training alone at post-treatment and follow-up.

Significance: The global burden of obesity in youth is increasing, and more effective intervention is needed. This study may identify that resistance training is an important component in the treatment of overweight adolescents. As such, findings may influence clinical decision making in the management of juvenile obesity, as well as inform public health exercise guidelines and school-based physical education curricula in attempt to reduce the economic, medical, and psychosocial burden of obesity in youth.

Inclusion Criteria:

• Male or female;
• aged 14-18 years,
• Tanner stage IV or above,
• waist circumference ≥75th percentile for age/gender
• body mass index ≥95th percentile for age, and gender
• AND/OR ≥85th percentile for age/gender with any of:
• Fasting glucose ≥6.0 fasting,
• 2-hour plasma glucose 7.8-11 mmol/L after 75 G oral glucose,
• fasting triglycerides > 1.7 mmol/L,
• fasting plasma insulin >105 pmol/L,
• HDL-C<0.9 mmol/L, LDL-C>3.0 mmol/L,
• total cholesterol/HDL-C >90th percentile,
• or first-degree relative with type 2 diabetes

Exclusion Criteria:

• Participation during the previous 4 months in a regular program of exercise or aerobic sports greater than 2 times per week for at least 20 minutes per session.
• Diabetes mellitus.
• Body weight over 159 kg, and/or BMI>45 kg/m2, exceeding capacity of DEXA and CT machines.
• Use of any performance-enhancing medication.
• Use of any medication or herbal supplement that is likely to affect body composition, lipids or glucose metabolism.
• Significant weight change (increase of ≥10%, or decrease≥5% of body weight during the two months before enrollment).
• Uncontrolled hypertension: BP >150 mm Hg systolic or >95 mm Hg diastolic BP in sitting position.
• Activity restrictions due to disease: unstable cardiac or pulmonary disease, significant arthritis.
• Other illness judged by the patient or study physician to make participation in this study inadvisable.
• Unwillingness/lack of availability to attend exercise and/or nutrition sessions at scheduled times and locations.
• Significant cognitive deficit resulting in inability to understand or comply with instructions.
• Pregnancy at the start of the study, or intention to become pregnant in the next year.
• Inability to communicate in English or French.
• Unwillingness of subject and/or parent/guardian to sign informed consent.