A Study of the Effects of Exercise Intensity on Insulin Sensitivity in Overweight Youth

Background:

The investigators know that exercise helps children develop strong bones and muscles and generally stay healthy. What is unclear however, is how much exercise a child needs to lower their risk of developing type 2 diabetes.

Objective:

The investigators will try to find out whether high-intensity exercise for a short-period of time is better than moderately intense exercise for improving the diabetes risk profile in teens who are at risk for type 2 diabetes.

The working hypothesis is that exercise-mediated improvements in insulin sensitivity (a risk factor for diabetes) will be greater following vigorous intermittent physical activity than following low intensity physical activity in overweight adolescents 13-18 yrs at risk for T2DM.

Brief Description of Research Project: Teenagers between the ages of 13 and 18 yrs, who are at risk for type 2 diabetes (either by their family history or an abnormal response to sugar) will be randomly assigned to one of two activity groups or a control group. The activity groups will have supervised exercise sessions 3 to 5 days per week for 6 months. One group will do high-intensity exercise, and the other will do lower-intensity exercise. We will measure how sensitive their body is to insulin and the amount of fat in their muscle and liver tissue at the beginning and end of the exercise intervention.

The Physical activity for OverWEight youth at Risk for type 2 diabetes (POWER) Trial is a randomized controlled clinical trial designed to study the effects of aerobic exercise training regimens differing in intensity (relative to peak fitness) on insulin sensitivity in overweight youth. Additionally, this trial will explore the biologic mechanisms through which chronic physical activity alters lipid metabolism to result in improvements in insulin sensitivity.

We will recruit 90 eligible adolescents and randomly assign them to one of two six-month intervention arms that differ by intensity but elicit similar amounts of energy expenditure: (1) a low intensity continuous activity arm (40-55% of peak oxygen uptake for 60 min); (2) vigorous intensity intermittent activity arm (70-85% of peak oxygen uptake for 30 min) or a sedentary control group. The primary outcome measure of this trial will be insulin sensitivity, measured directly from Bergman's frequently sampled intravenous glucose tolerance test.

Eligibility Criteria:
Inclusion criteria:

* Ethnic minority considered at risk for T2DM
* In utero exposure to hyperglycemia (i.e. mother with gestational or frank diabetes during pregnancy) and/or evidence of hepatic steatosis (serum ALT \> 60U/L, ultrasound or MRI-based evidence of steatosis).

Exclusion criteria:

* The investigators will exclude any patients that may have altered insulin sensitivity or tissue lipid content that would confound (mask) the effects of the intervention.
* These include overweight adolescents who:

  * are diagnosed with impaired glucose tolerance or type 2 diabetes
  * are currently being treated with corticosteroids or atypical antipsychotics, as these agents significantly influence carbohydrate metabolism
  * are undergoing puberty (Tanner Stage 2-4) at the time of the investigation, as it is associated with transient changes in insulin sensitivity
  * have an orthopaedic injury that would prevent them from performing the intervention
  * have experienced weight loss or enrolled in weight loss program in the six months prior to the study
  * have a history of alcoholism or drug abuse.