The great runners of the past -- Jim Ryun, Roger Bannister -- were as near to biomechanically perfect as possible. Athletics was selective, and participation was excluded for the less than perfect, because there existed no readily available scientific remedies for poorly constructed body parts. If your feet hurt, you didn't run.

The growing ranks of runners in the mid-1970s spawned both new businesses and new medical subspecialties. Sports medicine and orthotics, shoe inserts that balance the foot, proliferated. Long used to help nurses, waitresses and others on their feet for long periods of time, orthotics allowed many people to overcome structural imbalances and to exercise.

"Science created a better environment for the body to accept stress," said Sheldon Konecke, a podiatrist who practices in Chevy Chase. Koncecke and David Brody, an orthopedic surgeon now in practice in Connecticut, opened one of the first clinics in the country to combine both orthopedics and podiatry in treating sports medicine injuries in 1977 at George Washington University Medical Center.

"There are some people with an exceptionally good biomechanical relationship to the body," said Konecke. "They also have excellent musculo-skeletal relationship. One good example is Bill Rodgers. His foot pronates at the right time . . . his muscle function is right, and he is well-coordinated." Pronation is the rolling in of the foot and relaxation of the arch after the heel strikes the ground.

But most people don't have perfect body structure. Konecke estimates that 70 to 75 percent of the people he treats, most of whom exercise for competition or fitness, need orthotics. As recently as 15 years ago, these people would have had to find some other less weight-bearing activity. But when thousands of people of all shapes, sizes and body types discovered the physiological and psychological benefits of exercise in the form of running, lower extremity injuries were no longer the obstacle they once were.

"Mass fitness promoted orthotics use," said James Bates, president of the Pennsylvania College of Podiatric Medicine. The mass fitness movement sent waves of people to doctors, who found that some problems in other parts of the body were caused primarily by imbalances in the foot.

"Once we gave them orthotics, runners found the knee pains and sciatica were better," said Richard Schuster, 73, who taught biomechanics at the New York College of Podiatric Medicine and was one of the first to discover the relationship between foot impact and injuries to the legs, hips and back. "We began to put things together and found that what happened in the foot, happened on up. And we correlated things to the point that we knew what situation in the foot caused problems elsewhere."

Orthotics are inserts, usually made of leather or plastic, molded to control the movement of the foot and worn inside the shoe to prevent pressure from being exerted on bones not equipped for that kind of support. They maintain the foot in an optimum, neutral position, which varies for each individual. Cost usually ranges from $200 to $400 for custom-fitted inserts. Standard-size mail-order inserts are less expensive but are not recommended because each person's feet and their problems differ.

"An orthotic modifies movement and allows the foot to function properly," according to Paul Taylor, podiatric consultant for the Washington Bullets professional basketball team. He said most of the players "wear some sort of custom control and protection." Orthotics have been used for several decades, by those who stood all day on their jobs, and to accommodate foot deformities caused by polio.

But it wasn't until the 1970s that their application to athletics was seen as a way of improving training. For a while, "people thought the orthotic device actually improved athletic performance, but that's never been proven or disproven," said Taylor, author of "Conquering Athletic Injuries."

Injuries to the feet occur primarily because of overuse. Runners and athletes, such as soccer and football players, who put great stress on their feet often worsen that situation. An athlete may experience no ill effects running 40 miles per week, but inherent imbalances may cause problems if weekly mileage is increased to 60.

"A lot of the problems are due to the way the foot functions, not to trauma, and athletes are going to use orthotics when they get to the point where their biomechanical structure needs help, whether it's at 20, 40 or 60 miles per week," said Konecke.

"We realized runners were different people," Schuster said. "The forces in the feet when running are several times that of walking, and runners do it for long periods. Overuse injuries are due to structural imbalances, which some are born with, so the imbalances seem normal to the individual, but not when subjected to abuse. As a rule, the symptoms don't bother you when you first start, they bother you when you reach a certain level of mileage, which is different for each."

Said Taylor, "If a runner's foot isn't functioning correctly, that'll create torque forces in the lower leg and knee, causing gradual inflammation to the knee."

Orthotics do all kinds of things. "They make up for a short leg, for a tilted foot so it doesn't collapse when it reaches the ground, they support the arch when it depresses beyond a certain point," said Schuster. "They rebalance the feet, like balancing tires and aligning the front end of a car," said Konecke.

Schuster developed his theories of biomechanics from watching children. He discovered their feet are different from those of adults, and introduced an 80-factor examination.

From Schuster's 80-point test, biomechanics and podiatry have evolved to include treadmills, video cameras and other diagnostic tools. Bates said the methods used at the university include a computer that processes information such as gait analysis and weight distribution at 4,000 pieces of information per millisecond.

Evaluation of an injured athlete includes measurements for range of motion, leg length, bone alignment, bone torsion, external and internal rotation at the hips, pelvis level and curvatures of the back and posture, said Konecke.

New diagnostic techniques augment what Taylor said are "the basics, the key to any diagnosis. Most important is the {patient's athletic} history; you can get a lot more information from that than from running a lot of tests."

Schuster said one of the most telling pieces of equipment used today is the runner's shoe. "To treat runners, you have to study the shoe," he said. " There's no other way to find that out than by feeling the lumps and bumps and by reducing the situation to find out what causes them."

With today's exacting, cumulative knowledge, orthotics also function as a preventive measure. "With the evaluation procedures, we are making predictions now and preventing problems from manifesting later on," said Bates. "Because even if there is no pain and there is an imbalance, the body is accommodating at a bad angle and causing friction, and at age 50 there will be arthritis."