The same technology used by NASA to measure the equilibrium of space shuttle crews when they return from flight is hard at work at Arlington Hospital, where it's being used to help patients, particularly the elderly, prevent falls and bone breaks.

Looking more like an arcade video game than one of the most advanced pieces of balance and mobility rehabilitation equipment on the market, the Balance Master uses interactive technology to guide patients through treatment, which increases their balance and helps prevent falls--the leading cause of injury for older adults.

With the goal of curbing the injury rate, Arlington's Physical Medicine and Rehabilitation Department has developed a comprehensive Fall Prevention Program, which was formally begun about two months ago.

Every year, hospital officials said, one-third to one-half of the population age 65 and over experience falls. Half of the elderly people who fall are likely to do so repeatedly, and falls cause about 300,000 hip fractures each year.

Consider Kelly Carey, who has severe arthritis in his knees and hips and has a weak left leg. Last winter, the gregarious 87-year-old Arlington resident fell five times after losing his balance. To his surprise, he walked away from each mishap without serious injury. But Kelly said he was done taking risks. One more fall, he worried, and he could wind up in the hospital. That's when his doctor recommended he begin fall prevention therapy at Arlington Hospital.

Last week, Kelly clocked in for his second session on the Balance Master, which is built around a six-foot platform that uses sensors to measure the patient's movements.

By standing or sitting on the plank, patients are made to lean or step. Those actions move an icon on an adjacent computer screen. Their goal is to control their movements, and by doing so, move the icon where they want it to go.

The result is similar to a child's Etch-a-Sketch. As the icon moves across the computer screen, it draws a line. If the patient's movements are erratic or out of control, the line appears squiggly and bounces from one side of the computer screen to the other. When he or she learns to control the movements, the line becomes smoother. The computer images are then studied by therapists to diagnose weaknesses and are later used to chart the patient's progress.

Standing on the platform, his therapist Dana Edwards behind him--gripping his belt--Cary shifted his weight from left to right. He seemed pleased with his progress as he watched the icon move slowly from side to side. It was shifting his weight backward that caused Kelly to flail his arms and lean into Edwards for support.

"Try not to arch your back," Edwards said. "Can you feel your weight shifting?"

"This is a tough one," Kelly said as he struggled to make his aging body cooperate.

The idea, Edwards said, is to increase the patient's limit of stability. The larger the limit--the farther a person can lean without needing to rise on their toes or take a step--the less likely he is to fall.

Patients in the program are scheduled for balance therapy as often as three times a week. The sessions can last up to 45 minutes and include work going up and down stairs, curbs, even standing on uneven surfaces such as grass. Kelly is not fond of that exercise, which involves standing on an unstable foam cushion. In fact, it wears him out.

"When I go home from here, I usually take a little nap," said Kelly, who has a heart condition and fatigues easily. "I baby myself, much to my wife's displeasure."

NASA uses a similar but much more elaborate balance system called EquiTest to monitor astronauts, who are tested before they go into space. The goal is to establish a baseline measure of their equilibrium. They are tested again when they return to Earth to determine the effects of space on the human body and to give their doctors a sense of how long their recovery will take.

Officials with NeuroCom International, which manufactures the machines used by NASA, Arlington Hospital and research and medical facilities across the country, said the equipment was particularly useful for NASA when astronaut John Glenn--who in 1962 made the first U.S. orbital space flight--returned to space late last year. Glenn was 77 years old, and researchers used the machine to measure the effects of space flight on an elderly person.

"Some of the things NASA is doing has an impact for studies on the elderly, like falling," said Elizabeth Hatcher, marketing manager for NeuroCom. "It's a big concern because we're an aging population."

The program at Arlington targets the elderly and people with balance and mobility problems as a result of neuromuscular, orthopedic, inner ear and other dysfunctions. Patients who want to undergo balance therapy at Arlington Hospital must be referred by a doctor.

The Balance Master's equipment also has specific applications for patients recovering from stroke, head and sports injuries and, officials said, has proven useful in helping people with the destabilizing effects of multiple sclerosis and Parkinson's disease.

"The whole idea is to keep them here in therapy and not upstairs" in a hospital bed, said hospital spokeswoman Stephanie McNeill.

Georgiana Gordon, 64, of Clarendon, suffers from Guillain-Barre syndrome, which has caused loss of muscle strength and has altered her sense of sensation. As a result, Gordon walks with a cane and has trouble maintaining her balance. Using the Balance Master, Edwards was able to evaluate Gordon's specific weaknesses and develop exercises to strengthen her mobility.

"I'm already at risk because of my disability," Gordon said. "So I need to be as strong as I can to avoid a fall."

CAPTION: "When I go home from here I usually take a little nap," said Kelly Carey, 87, after a session on the Balance Master at Arlington Hospital.

CAPTION: Above, therapist Dana Edwards grips Carey's belt to steady him as he works on the Balance Master. The machine helps Arlington Hospital staff diagnose weakness that could lead to a fall. At left, Carey works on the apparatus, as if stepping up and down stairs.

CAPTION: The display guides Kelly Carey and shows his balance control as he walks on the equilibrium machine.