Edition: U.S. / Global

Weights Build Muscles, But Not the Manly Kind

Published: June 23, 2002

AS any woman who has ventured into a health club knows, the weight-lifting area is very much a male domain. The rubber-surfaced nonslip floor where the barbells and dumbbells reside is dominated by hefty men, grunting and groaning as they pump iron. Most women steer clear, clustering instead in the group exercise classes, taking yoga or step aerobics.

And that, medical experts say, can be a mistake, at least for women who want to reshape their bodies. While cardiovascular exercise like running can help the heart and burn calories, the best way for women to change their look is to lift weights -- heavy weights.

''To really reshape yourself, you have to hypertrophy muscles,'' said Dr. William J. Kraemer, a professor of kinesiology at the University of Connecticut, referring to the medical term for muscle growth. Dr. Kraemer was the principal author of a new position paper on weight lifting for the American College of Sports Medicine and is the editor of a leading research journal on weight lifting, The Journal of Strength and Conditioning Research.

There are also health benefits, said Dr. Claude Bouchard, the director of the Pennington Biomedical Research Center at Louisiana State University. If men or women work sufficiently hard at weight training, the muscle they build is more efficient, with more mitochondria, which are the cell's energy factories. The muscle is also better at using fat for fuel and better at allowing people to use insulin to clear sugar from the blood, which reduces their susceptibility to diabetes.

Studies also show that weight lifting can help with problems of aging. Investigators at the National Institute of Aging found that older people with osteoarthritis of the knee had less pain and improved mobility when they strengthened their leg muscles, working on those that support the knee. And, researchers say, weight lifting can stave off the sort of muscle wasting that forces older people to grab a chair handle for support when they rise.

One problem that women face, however, is that they are hobbled by myths about weight lifting, expecting the wrong things and, sometimes, expecting too much, exercise physiologists say.

The worst myth, these researchers stress, is that women who lift weights risk growing muscles like a man's.

Dr. Gary A. Dudley, an exercise physiologist at the University of Georgia and an author of the American College of Sports Medicine's statement on weight lifting, says he tries to dispel that notion by telling women to look around the gym at the women who are lifting heavy weights.

''That's the simplest answer -- just look around,'' he said. ''There's a girl who works in my lab who does pull-ups like a yo-yo. She does not have 26-inch arms like Arnold used to have,'' he said, referring to Arnold Schwarzenegger. ''They're just not there.''

Somehow, that message has not reached the general public, Dr. Kraemer said. Even his 22-year-old daughter believed it, asking Dr. Kraemer to help her and her friends by suggesting a program that would help them get fit without getting big.

Even women who are genetically capable of growing big muscles can never grow ones as large as a man's, Dr. Kraemer said. When researchers biopsied the muscles of female bodybuilders, who spend hours each day lifting weights, ''They had smaller muscle fibers than the average male,'' Dr. Kraemer said. ''And these were women who were taking drugs'' to increase their muscle mass, he added.

''A lot of women are just sitting there with a 10-pound weight,'' Dr. Kraemer said. ''It's better than nothing, but they're really taking a second-class program. A lot of them are dramatically undercutting themselves.''

Even building bone requires that muscles be stressed, researchers say. They explain that bones have receptors that respond to demands on muscle, and weights can signal those receptors.

''Studies showed that stair climbing can help your bones -- but the women wore weighted vests,'' Dr. Kraemer said.

If the muscles-like-a-man myth discourages women from starting to lift heavy weights, other myths can discourage women from continuing, physiologists say. These are the myths that lead women to expect too much from resistance training and encourage them to give up when the benefits do not emerge.

One problem is expecting immediate results.

''It takes a lot of time to develop muscle,'' Dr. Kraemer said. ''Most people want to have it happen in the first few months, but it takes three months or longer, usually three to six months,'' before a person looks much different, he added.

Forget the idea of spot reducing, researchers say, like ''toning'' the muscles of the inner thighs, for example, and slimming them. ''Spot reducing is not a real thing,'' Dr. Kraemer said.

Many women also cling to a belief that is almost an act of faith among exercisers: muscle burns more calories than fat. Therefore weight lifting, by building muscle, will noticeably increase the body's metabolism.

Sorry, said Dr. Bouchard, who is directing a national study on the genetic inheritance of an ability to train with aerobic exercises. He said that weight lifting had virtually no effect on resting metabolism. The reason is that any added muscle is minuscule compared with the total amount of skeletal muscle in the body. And muscle actually has a very low metabolic rate when it is at rest, which is most of the time.