(The New York Times) -- As any woman who has ventured into a
  health club knows, the weight-lifting area is very much a male
  domain. 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.

  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, Kraemer
  said. Even his 22-year-old daughter believed it, asking 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, 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," 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,"
  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," 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," 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," 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 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.

  Skeletal muscle, Bouchard said, burns about 13 calories per kilogram
  of body weight over 24 hours when a person is at rest. A typical man
  who weighs 70 kilograms, or 154 pounds, has about 28 kilograms of
  skeletal muscle. His muscles, when he is at rest, burn about 22
  percent of the calories his body uses. The brain would use about the
  same number of calories, as would the liver, Bouchard said. If the
  man lifts weights and gains 2 kilograms, or 4.4 pounds of muscle, his
  metabolic rate would increase by 24 calories a day.

  Dr. Jack Wilmore, an exercise physiologist at Texas A&M University,
  said that the average amount of muscle that men gained after lifting
  weights for 12 weeks was 2 kilograms, or about 4.4 pounds. Women,
  of course, will gain much less.

  A corollary to the hypothesis that you burn more calories simply by
  adding muscle is the belief that muscle can noticeably change your
  body weight. The idea is that when you do resistance training you
  may actually be thinner yet weigh the same or a little more, because
  muscle is heavier than fat.

  That holds a grain of truth, because muscle is more dense than fat.
  But, Bouchard said, the problem is that few people put on enough
  muscle in proportion to their total body mass to make a noticeable
  difference in their weight. The idea that you will weigh the same or
  more but you really are thinner may be true if you work hard at
  weight lifting for many months, but otherwise it is another myth.

  But when it comes to weight lifting, researchers also confess that they
  have not answered some age-old questions. Why, for example, do
  muscles feel sore a day or two after they are stressed?

  One possibility is that they get damaged, with tiny tears ensuing from
  the work of lifting weights. But, said Prof. Stanley Salmons, a muscle
  researcher at the University of Liverpool, "damage and pain have
  different time courses, and they respond differently to repeated bouts
  of exercise." He added that delayed muscle soreness remained a
  mystery. "At this moment I do not know why muscles get sore, and
  no one else does either."

  It is also unclear how to prevent soreness. "You hear trainers say it's
  very important to stretch before exercise," Salmons said. "But there
  were experiments in which people did exercise with or without
  stretching, and it didn't seem to make much difference."

  As for the techniques of weight lifting - how often, machines or free
  weights, in what order to do the exercises, how quickly to lift a
  weight, how long to wait between sets - the research is equivocal.

  But, Kraemer said, those are details that should not concern most
  people. Despite the fervent marketing of programs and the magical
  properties attributed to various regimens, there is little difference in
  the results of varying resistance-training systems, he said. What
  matters is keeping the weights heavy enough to stress the muscles,
  exercising consistently and working every major muscle group.

  "Think of yourself as being on a continuum," Kraemer said. "At the
  beginning, when you are out of shape, just about anything can work."

  Copyright 2002 The New York Times. All rights reserved.