The doctor switches on an electric motor, and a treadmill starts to move. A patient, stripped to running clothes, gets on and starts to jog, while a videotape machine records shin bones rotating inward, thigh bones rotating outward. And knock-knees.

Later, in another room, patient and doctor watch the slow-motion tape on a small TV set. The doctor adds his own observations: slight scoliosis (curvature of the spine), severe pronation (flat feet).

"I'd say you have a good potential for tendinitis, knee, hip and back problems," he says. And there's always greater trochanteric bursitis" - pain in the hip.

The patient gulps.

"Does that mean I can't run? Should I just cut my feet off?"

"Of course not," says the "running doctor," David Brody. "Just get some arch support pads, do straight-leg lifts with ankle weights and plenty of stretching."

For a runner there's nothing worse than the prescription: no more running for a while.

For some damaged souls who must go "cold turkey," Brody has recommended wearing a flotation jacket and running in the deep end of a swimming pool. The pressure on the injury is relieved while aerobic conditioning is sustained.

The George Washington University Runner's Clinic is a diagnostic center that opened this past summer to treat the many of running injuries springing from the latest fad. Though marathoners have dominated the examining room, it's available to runners of all levels. The one-room clinic, operating out of the the basement of GW's Smith Athletic Center, has become the last chance for a growing number of runners whose chronic problems threaten to make them hang up their shoes.

Brody, an orthopedic surgeon, got the idea for the clinic when he noticed a dramatic increase in running-related injuries. He has been treating runners and football players for 12 years. A marathoner himself (he averages nearly 70 miles a week), Brody found that he was more likely to hurt himself when he tried to increase his speed or distance.

"Most injuries occur when people make transitions from one level of running to another," he explains.

The lack of proper conditioning - tight or weak muscles - can cause trouble, and congenital problems and earlier injuries that never heeled properly can be aggravated by strenuous exercise. The results often are stress fractures, tendon inflammation, knee and back problems, shin splints, heel pain and ligament strain around the knees and hips.

The videotaping, a common part of a routine examination at the clinic, helps Brody analyze the patient's gait and discern weaknesses, stiffness or tension in the back, legs and feet. He also measures each patient's leg lengths (from navel to base of the foot), and wiggles the legs to determine the amount of hip rotation (if any) while running.

Many problems can be easily solved, by changing shoes or inserting orthotic devices or by doing stretching and strengthening exercises. In other cases X-rays are needed to see if there has been skeleted damage. One patient discovered he had been working out with fractures in both feet. The cost of a basic examination is $20, but X-ray can push it higher.

Brody says many runners actually force injuries by trying to keep up with someone who has a stronger stride and pace. A beginner frequently tries to play "catch-up ball" and feels frustrated with his or her mere two miles a day when a friend or spouse (who's been at it much longer) can cover twice the distance in the same time. Brody estimates that two-thirds of the 25 million Americans who run are doing it wrong - and quite a few of them would be better off swimming or riding a bicycle. Their physical makeup is just no geared for even light jogging.

Worst of all, many runners keep right on cranking out the laps in spite of intense pain.

"Frequently the patients erroneously believe they can run through the problem, and end up with worse damage than before," says Brody. "With a pulled muscle this can be done, but not something more serious like a compression fracture."

Lance Cole is a 17-year-old cross-country runner. His time is good: a 4 1/2-minute mile. Ten or 15 seconds faster and he will qualify for a college athletic scholarship. But the persistent ankle-to-knee pain in his right leg (which started when he upped his mileage from 50 to 70 miles a week) became unbearable. Diagnosed as a severe case of shin splints (which meant no running), he tried to negotiate with Brody. Just these next few races, he pleaded, and he would lay off until it's better.

They compromised: Skip one race, compete in the next, then lay off for two to six weeks.

Trudy Papp's feet hurt so that she could barely walk, let alone train for the next race. The Marine Corps marathon was out of the question.

"I shouldn't have driven myself so hard, but I couldn't stop." Tears welled up.

"There, there," soothed the doctor. He prescribed straight-leg lifts with weights, no running on land - only in water.

Another patient, a 37-year-old racer, is feeling the vulnerability of his body. For 17 months, since last year's Boston Marathon he had pain in his back, thigh and groin. Periodically he would feel it inside his leg (near the bone) when seated at his office desk. Brody suspected a past compression fracture in the spine that never got a chance to heal. He winced and smiled tersely when the doctor told him to hang up the shoes for a bit.

"Most runners are compulsive about it," says Ed Ayres, editor of Running Times magazine. He believes that once runners witness the sharp change in themselves (improved muscle tone, increased energy and peace of mind), they get a sense of self-determination over their bodies. When they sustain an injury or unsuccessfully ignore the pain from an old one, they feel an enormous sense of frustration at losing control.

"There's a similarity between a competitive runner's inability to stop when he's getting hurt and a compulsive eater's inability to stop eating when he knows he's on the verge of terminal obesity." Ayres says.

He also attributes the growth of running injuries to the use of inadequate shoes. A lot of shoes on the market look good but actually aren't. He faults chain drugstores and supermarkets that put out cheap imitations that don't provide the proper shock absorption and protection runners need.

"Each time a runner lands on his heels, a great deal of shock is transmitted up the legs," he says. "In a good shoe the force is about three Gs [triple the person's own body weight] coming through the heel. In poor-quality shoes, it's as much as 10 Gs - hazardous enough to cause injury."

The way to test your own shoes is simple. Hold the toe in one hand and heel in the other, and press your hands together. The shoe should bend in half easily. If it's stiff, it doesn't provide adequate protection.

Because of the extensive research and testing done by podiatrists and experts in the field and top-quality materials used, good running shoes are expensive - $30 to $40 a pair.