Teens at risk of developing diabetes can prevent or delay its onset through strength training exercise, a University of Southern California study has found.

Research led by Michael Goran, PhD, professor of preventive medicine in the Keck School of Medicine of USC, showed that overweight Latino teenage boys who lifted weights twice per week for 16 weeks significantly reduced their insulin resistance, a condition in which their bodies don't respond to insulin and can't process sugars properly. Insulin resistance is common in obese children and is a precursor of diabetes. The findings were published in the July issue of Medicine and Science of Sports Exercise.

Previous research has demonstrated that aerobic and resistance exercise is effective in improving insulin sensitivity in adults, but no controlled studies of resistance exercise had been done on overweight youth. Goran and colleagues hypothesized that overweight teens would be more likely to stick with a resistance training regimen compared to aerobic exercise because it is less physically taxing and gives visible results quicker.

The researchers chose to focus on Latino teens because they are at particular risk for diabetes. According to the Centers for Disease Control, about half of all Latino children born in 2000 are expected to develop type 2 diabetes in their lifetime.

Twenty-two boys aged 14 to 17 lifted weights two times a week on gym equipment guided by personal trainers. The trainers used increasing resistance and fewer repetitions as the participants improved. While there was no change in their total body fat mass, the percent body fat significantly decreased and lean muscle mass increased in the resistance-training group compared to the control group. Ninety-one percent of the weight-lifting participants also significantly improved their insulin sensitivity.

"This shows that lifting weights is a good form of exercise that overweight teens can excel at and benefit from," says Goran, who is also associate director of the USC Institute for Health Promotion and Disease Prevention Research. "Whether they lose weight or not is not important – they still benefit by increasing muscle mass," he says.