Weight training alone is not an effective way to reduce the risk of heart disease or diabetes if you are overweight, but aerobic training might be, according to a new study from the Duke University Medical Center.

Participants in the study were divided into three groups for eight months. One group did only resistance training, working out on eight different weight machines three times per week. The second group did two hours of aerobic training per week, and the third group did both programs.

People in the weight training group gained an average of 1.5 pounds, added to their waistline and failed to reduce their risk for heart disease or diabetes. The aerobic training group lost three pounds and a half-inch from their waists, and participants who did both cardio and weights in the study lost four pounds and an inch from their waists. Both groups also decreased their risk of illness.

Although the combination of weight training and aerobic training produced the best results, the study published in the American Journal of Cardiology says that it is hard to determine whether the difference between the combined group and the aerobic group was due to the combination of training being more effective or simply forcing participants to work out twice as much.

“When weighing the time commitment versus health benefit, the data suggest that AT (aerobic training) alone was the most efficient mode of exercise for improving cardiometabolic health,” says the study, titled “Comparison of Aerobic Versus Resistance Exercise Training Effects on Metabolic Syndrome.”

Exercise also plays a prominent role in reducing the risk of sudden cardiac death, which is the result of a sudden loss of heart function due to problems with the heart's electrical impulses, according to another study published earlier this month in the Journal of the American Medical Association.

By analyzing data on lifestyle factors of more than 80,000 women over the span of 25 years, researchers found that those who worked out regularly and also had a healthy body mass index (under 25), did not smoke and ate a well-balanced diet significantly reduced their chances of sudden cardiac death.