This study, published in the Journal of Applied Physiology, is the biggest randomized trial to measure revisions in body composition from three different types of exercise in overweight adults who do not have diabetes.
Aerobic exercise, commonly know as "cardio", including running, walking, and swimming, has historically been established as a good way to lose weight. Recently, however, recommendations have pointed out that resistance training, such as weight lifting to build and perpetuate muscle mass, could also contribute to weight loss via boosting a person's resting metabolic level.
An earlier study conducted by researchers at the University of Minnesota suggested that breast cancer survivors receive more benefits from weight training than from aerobic training. The researchers saw that strength training provided these participants with more help for their physical and emotional state than aerobic training.
Previous studies have shown health advantages for resistance training, such as improving glucose control. However, research on the effects of resistance training on fat mass have not had significant conclusions.
Leslie H. Willis, MS, an exercise physiologist at Duke Medicine and the study's lead author explained, "Given that approximately two-thirds of adults in the United States are overweight due to excess body fat, we want to offer clear, evidence-based exercise recommendations that will truly help people lose weight and body fat."
The current study included 234 obese or overweight adults. Subjects were randomly given one of three exercise groups: aerobic training (nearly 12 miles per week), resistance training (three days per week of weight training, three sets per day, 8-12 repetitions per set), or aerobic and resistance training together (three days a week, three sets per day, 8-12 repetitions per set for resistance training, and around 12 miles per week of cardio).
The exercise trainings were observed in order to accurately calculate how well the programs were followed by participants. From the study, 119 volunteers who finished their programs and had complete body composition data were examined to measure the effectiveness of each training program.
The aerobic training and the aerobic plus resistance training groups collectively lost more weight than those who completed only resistance training. The group doing only resistance training gained weight because of a boost in lean body mass.
Cardio exercise proved to be a more efficient type of exercise for losing body fat. The cardio group underwent an average of 133 minutes per week training and ended up losing weight. The resistance training group, on the other hand, spent around 180 minutes a week exercising without losing a pound.
The group participating in both resistance and aerobic training spent double the time training and ended with a blended outcome. The program aided in weight loss and fat mass loss, however, it did not decrease body mass or fat mass with just cardio exercise alone. The combination group showed the largest reduction in waist circumference, which may be explained by the amount of time the subjects exercised.
Resting metabolic rate, which decides the amount of calories burned while resting, was not directly calculated during this study. Previous hypotheses suggest that weight training can improve metabolic rates, resulting in weight loss. In this specific study, resistance training did not reduce fat mass or body weight significantly, regardless of any differences in resting metabolic rate.
"No one type of exercise will be best for every health benefit. 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."
The investigators said that exercise suggestions are age-specific. For example, older adults with muscle atrophy have been seen to improve with resistance training. Younger, healthy adults who desire to lose weight will benefit more from aerobic training.
Cris A. Slentz, PhD, a Duke exercise physiologist and study co-author concluded:
"Balancing time commitments against health benefits, our study suggests that aerobic exercise is the best option for reducing fat mass and body mass. It's not that resistance training isn't good for you; it's just not very good at burning fat."