Don't Muscle Your Way to Weight Loss

Aerobic activity sheds more pounds than resistance training or combining the two

December 29, 2012 / Author:  / Reviewed by: Robert Carlson, M.D

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(dailyRx News) A new year is on the horizon, along with those pledges to lose weight. Aerobic activity is key to doing just that.

A recently published study found that heart pumping exercises like running, walking or swimming is better at burning fat than lifting weights only or doing aerobics and weights together.

Knowing your fitness goals helps determine what kind of exercise program to start engaging in, according to researchers.

"Burn more calories than what you consume."

The study, led by Leslie Willis, MS, an exercise physiologist at Duke University Medical Center, included 119 adults who were classified as overweight or obese with a body mass index between 25 and 35 kilograms per square meter.

Participants, who were between 18 and 70 years of age and did not have diabetes, were randomly divided into one of three groups assigned a different exercise program.

Under the researchers' supervision, the first group lifted weights, three sets a day, three days a week for eight to 10 weeks. The second group did aerobic activity equal to about 12 miles per week, and the third group did both exercises together.

Researchers tracked each of the participants' body mass composition of how much fat, muscle and bone they have.

To track what participants ate, each person kept a food diary for three days at the start of the study and at the end of the training period, accompanied by a 24-hour recall interview.

Researchers found that the two groups with aerobic training lost more weight and inches around the waist than the group who only lifted weights.

The aerobic group lost weight after spending a little more than two hours a week training on average. The weight lifters spent three hours a week exercising without dropping any pounds.

Because the weight lifters gained more muscle mass, that group actually gained more weight.

"Balancing time commitments against health benefits, our study suggests that aerobic exercise is the best option for reducing fat mass and body mass," said Cris Slentz, PhD, an exercise physiologist at Duke and co-author of the study, in a press release.

"It's not that resistance training isn't good for you; it's just not very good at burning fat."

Participants in the group with both aerobic exercise and weight lifting combined lost fat mass and weight, though not as much as the aerobics-only group.

However, they lost the greatest number of inches around the waist, which may be due to the amount of time they spent exercising.

"No one type of exercise will be best for every health benefit," Willis said in a press release.

"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."

Researchers said that exercise recommendations are specific by age. Younger adults or those looking to lose weight benefit from aerobic training, while older adults who may be losing muscle mass would be better off with resistance training.

The authors report no conflicts of interest. They note that their study did not intend to treat the participants, who were all motivated to exercise. Their willingness may skew results, which wouldn’t apply to larger populations.

"When performing aerobic exercise, fat becomes the primary fuel source and therefore, leads to greater fat loss," said Rusty Gregory, a certified personal trainer and dailyRx Contributing Expert.

"Additionally, the intensity of aerobic exercise is not great enough to stimulate muscle hypertrophy; hence, no increase in muscle mass or weight gain."

The study was published online December 15 in the Journal of Applied Physiology. The National Heart, Lung, and Blood Institute from the National Institutes of Health funded the study.