If you want to burn fat, it's better to hit the treadmill than the weight room, a new study suggests.

The results show aerobic workouts are better than resistance training for reducing fat mass.

And a workout that combines the two activities — lifting weights in addition to running — is no better at burning fat than running alone, the researchers said. The findings contradict the idea that resistance training can help with weight and fat loss by improving metabolism, the researchers said.

But the findings don't mean that resistance training is not useful. The study found that resistance training was better at increasing lean body mass than aerobic training alone. And for older adults who are experiencing muscle loss, resistance training is beneficial, the researchers said.

But for young, healthy adults who want to lose weight, aerobic training may be the way to go.

"Balancing time commitments against health benefits, our study suggests that aerobic exercise is the best option for reducing fat mass and body mass," said study researcher Cris Slentz, an exercise physiologist at Duke University in Durham, North Carolina. "It's not that resistance training isn't good for you; it's just not very good at burning fat," Slentz said.

The study involved 234 overweight and obese adults who did not have diabetes, and did not exercise regularly before the study. Participants were randomly assigned to one of three workouts: a resistance training workout (consisting of three days of weight lifting per week); an aerobic workout (running 12 miles a week); or a combination workout (three days of weight lifting plus 12 miles of running a week). The workout regimens lasted eight months.

The aerobic training group and the combination group lost more weight and fat mass than the resistance-training group.

Despite requiring double the exercise time, the combination workout did not reduce body mass and fat mass beyond what was seen in the aerobic training group, the researchers said.

While some studies suggest resistance training can improve metabolic rate, and thus allow people to burn more calories, the new results do not suggest this. Regardless of participants' metabolic rate, they did not lose more weight or fat mass with resistance training.

"No one type of exercise will be best for every health benefit," said study researcher Leslie Willis, an exercise physiologist at Duke. "However, it might be time to reconsider the conventional wisdom that resistance training alone can induce changes in body mass or fat mass due to an increase in metabolism, as our study found no change."

Although a focus on weight loss is understandable, "when considering the big picture, I like to encourage individuals to pursue a complete exercise program — including both aerobic exercise and resistance training," said Barbara Bushman, a professor at Missouri State University's Department of Kinesiology who was not involved in the study. "If time is limited and it comes down to one or the other, this study, as well as [statements from the American College of Sports Medicine] would seem to be in agreement that aerobic exercise along with dietary restriction are of the greatest benefit," Bushman said.

The study is published in the Dec. 15 issue of the Journal of Applied Physiology.

Pass it on: Aerobic workouts are best for fat loss.



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