Walking, running or other forms of aerobic exercises can be a better way of reducing weight that lifting weights during resistance training, a new study says. Researchers challenge the idea that resistance training burns more calories when the person rests after training.

Recent guidelines said that building muscles through resistance exercise might be effective in helping people cut down weight by increasing a person's resting metabolic rate.

"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," said Leslie H. Willis, MS, an exercise physiologist at Duke Medicine and the study's lead author.

The study included 234 overweight or obese adults. Participants were randomly assigned to three types of exercise routine. They either had to do aerobic exercise, resistance exercise or a combination of both. Exercise sessions were supervised. 119 people completed the study and researchers analyzed the body composition data of these people to see how the exercise affected their body.

Study results showed that people in the aerobic and the combination group lost weight while people in the resistance training actually gained weight due to increase in muscle mass.

In addition, people in the aerobic group, who spent 133 minutes a week on exercise, reduced weight more efficiently than people in the resistance training group who spent nearly 180 minutes a week.

The combination exercise group had mixed results as the weight decreased slightly but they also had a decrease in waist circumference. Researchers say that these kinds of exercises require more time and this may be the reason that people in this group lost more inches around waist than other groups.

The study didn't directly find if resistance training increased resting metabolic rate which determines the number of calories burned while at rest. There are theories that resistance training improves resting metabolic rate. However, people in the resistance exercise group saw no change in either body mass or fat mass.

Researchers add that no one type of exercise is better. "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," said Cris A. Slentz, PhD, a Duke exercise physiologist and study co-author.

The study is published in the Journal of Applied Physiology.