Former NFL quarterback Roman Gabriel has flipped for them. William Shatner has gone head over heels for them too. They're called Inversion Boots, and according to their creator, California physician Dr. Robert Martin, some 200,000 people around the world are now using them to help eliminate physical hang-ups ranging from pot bellies to chronic back pain.

Inversion Boots are part of what Martin calls his Gravity Guiding System, a jungle gym of chrome-plated steel bars, clamps and hooks plus an oscillation bed that rotates 180°. With ankles strapped into the thickly padded metal cuffs, subjects hook their boots onto a metal bar, lean back on the bed and, raising their arms, allow their bodies to fall backward toward the floor. Experienced users may disengage from the bed and hang freely.

Some people experience fear and discomfort at first. "My eyeballs felt like they were coming out," reports a first-time dangler, who nevertheless tried it again. "All you have to do is get conditioned a bit at a time," says Martin, "just as you did when you learned to walk or swim." With the system one can either dangle upside down, which, Martin says, improves circulation and stretches the spine, or perform a variety of exercises including body twists and inverted sit-ups. Once people get the hang of hanging, they experience pleasant feelings, as one puts it, of "freedom and weightlessness."

"Eight out of 10 people will suffer from back problems," says Martin, 72, "and billions are spent annually for back-related treatments. Those statistics must mean we are all doing something wrong." The problem, as Martin sees it, is the wear and tear the simple force of gravity exerts on our spines, tissues and organs. Exercising from an upside-down position for seven to 15 minutes twice a day, he believes, helps to alleviate gravity's effects. "If we hang by our feet," says Martin, "we can elongate, separate, extend, bend and flex the body all at the same time."

In addition to easing back pain, Martin says, inversion therapy's beneficial side effects include improved posture, greater lung capacity and toning of sagging muscles. "I can't imagine that hanging upside down could have all those benefits," counters Dr. David Smith, president of the American Osteopathic Academy of Orthopedics, who cautions people to consult a physician before using Inversion Boots. "There might be additional medical problems such as hypertension or stroke which could be aggravated by increased pressure on the brain," he says. Martin, too, cautions people suffering from high blood pressure, severe bone disease or detached retinas against using inversion therapy.

Inversion Boots have been around since 1967, but they didn't take off until Richard Gere used them in American Gigolo. Since then, Martin estimates that more than 5,500 Gravity Guiding Systems have been sold (the stationary model costs $1,295, portable units sell for $495 and $795), and his Duarte, Calif. factory is turning out the boots, which can be bought separately (and used with a chinning bar) for $80, at the rate of 500 a day.

Martin and his staff of 10 see an average of 50 patients daily at their new Pasadena headquarters. At the clinic up to 25 people can dangle at a time. Martin charges $30 for an initial visit, during which a patient is examined, evaluated, diagnosed and given a personalized program. Subsequent use of clinic equipment costs $10 an hour.

Martin grew up in Pella, Iowa, where his father was a chiropractor. He graduated from the Kansas City College of Osteopathic Medicine in 1948 and received his M.D. from the California College of Medicine in 1962. It was earlier, while engaging in chiropractic in Iowa, that Martin realized the benefits of the head-down position on patients disabled by back problems. "Wouldn't it be wonderful if we could walk on ceilings?" he recalls asking a colleague in the 1930s, but it wasn't until 15 years ago that he developed the prototype for his Inversion Boots.

Hanging is a family affair for Martin, Pearl, his wife of 46 years, and their five grown children. Pearl runs the office with help from daughters Sherry and Sheila, while sons Craig and Robert II, both M.D.s, operate the clinic. Their other son, Bryce, an attorney, is overseeing the franchising of Inversion Factor clinics around the country. Of course the entire family hangs half an hour each day. "It's a life-extending therapy," says Martin, and one he believes is far more advantageous than fitness fads like weight training. "The best dumbbell to lift," he advises, "is yourself."