Mental barriers keep obese women from exercising, according to a new study.

Very fat women feel self conscious exercising in the presence of people who are more fit, say researchers from the Center for Obesity Research and Education at Temple University in Philadelphia.

Some obese women won't start an exercise program because they fear they will fail, the researchers said. And very overweight women are more likely to fear injury, or to put off exercising because of minor aches and pains, than are people of near-normal weight.

The study was based on responses to a questionnaire from 278 women enrolled in a yearlong physical activity encouragement study.

"This is the first time we've been able to systematically look at what stops obese women from getting the activity they need," said Dr. Melissa Napolitano, associate professor of kinesiology and a clinical psychologist at the Center for Obesity Research and Education.

Dr. Sam Akhavan, a sports medicine physician at West Penn Allegheny Health System, said the study should remind doctors they should do more than just tell their overweight patients that they should get more exercise.

"A lot of people try to get into an exercise program," he said. "But it can be intimidating for people who haven't been exercising. You can't just tell a person to go to the gym and exercise. The physician needs to fish a little bit more, to see if our patients need more support than just going to the gym.

"The physician needs to be involved in setting up a support program," Dr. Akhavan said. "We can get them involved with a nutritionist. We can get them involved with a therapist. If they require personal training, we can set them up with that."