The sun is high; the road, flat; the spring breeze, playfull. Too nice to come in, so you run on -- maybe two or three miles more than usual. The next day, every day you take is a reminder: you went a little too far.

Aches and pains can visit anyone, but 85 percent of the sport-related injuries that physicians see happen to runners, according to a recent British study. Gabe Mirkin, a sports medicine author and physician who treats running and other sport injury problems, thinks he knows why. "After you set over the first six weeks, you start feeling good when you run. There's an emotional high that lasts 16 to 18 hours. But soon you have to run farther and farther to get the high. So you increase your distance and that often leads to an injury."

These injuries are sometimes complicated by the what-goes-up-must-come-down nature of running. "If something happens to a runner when he's five miles out, he still has to come back," Mirkin says.

The figure of 50 percent sticks in David Brody's mind. Brody, medical director of Washington's Marine Marathon and an assistant professor of orthopedic surgery at George Washington University School of Medicine, reports that 50 percent of the running injuries he sees are caused by overtraining. "If you increase your mileage injudiciously, you're taking a Kamikaze approach to training. The biggest problem among runners is too much, too soon."

The other non-traumatic causes (traumatic would be twisting your ankle in a pothole in the road) are muscle imbalance, structural abnormalities and lack of flexiblity. Problems from these causes, however, might never show up if mileage weren't being increased.

Meanwhile, there you are with a sore knee, aching heel or stiff back. Where do you go if it hurts, and when?

"It depends on the character of the pain," says Robert Nirshl, Chairman of the Committee on Sports Medicine of the Medical Society of Virginia and an assistant professor of orthopedic surgery at Georgetown University School of Medicine.

Nirschl divides pain into four categories. Phase one is when you experience discomfort, soreness and pain after an activity. The pain last 6 to 24 hours, then is gone. Phase two is an increase in pain in termns of stiffness and soreness before the activity. The pain goes away when you warm up, and you're comfortable while you're participating in the activity, but afterwards, you're stiff and sore again.

"Neither phase one or two indicate a serious problem," Nirschl says. You would probably do well to play or run a little less hard, take a hot bath, two asprin and call a running friend in the morning. You might also check your equipment (are your running shoes wearing thin?), the sports medicine and running books to see if you can figure out what happened and why you hurt. You could also call the Foot Fact Tape, 354-1171 (tape 6 is "Running and Sports Injuries.")

Phase three is when you have persistent pain while you're participating in your activity. Phase four is constant pain. Whether or not you're participating, you hurt. The pain may even wake you up at night.

"The last two phases are clues that you should be checked," Nirschl says, adding that there's one more factor to consider. "If the part of your body that hurts is swollen or if there's an anatomical change (such as decreased motion), if you palpate or touch the part and it's pretty sore, that would be an indication to check it out."

You don't want to wait too long to see if the pain will disappear by itself. "When an injury isn't getting better, you should come in and have it checked," says Mirkin who doesn't believe you should dash to a doctor's office everytime you ache. "Some people don't come in when they should, though. They wait six or eight weeks, somtimes months, thinking they will run through it. They end up bumping into walls because tears are in the way -- they can't see where they're going.It only makes matters works to keep running on a painful injury."

Physicians like Nirschl, Mirkin and Brody specialize in sports medicine and sport-related injuries as they apply to any athlete, whether professional, collegiate or recreational. They deal with the physical and psychological fallout of runner's knee, tennis elbow, karate elbow, fencer's ankle, gymnast's back, dancer's toes and skiers' thumb. It's rare, but some sport injuries are so severe and threatening to life and limb that the athlete must give up the sport and find another. The overall mind set of the sport medicine physician, however, is to find the cause of the injury, suggest a rehabilitation routine to restore full strength and get the runner or other athlete back on the track.

"If you tell an injured runner to rest and be patient, he's not going to come back. You have to offer a program that will keep him in shape and get him back to his sport," Mirkin says, adding that from the patient's point of view, "If you go to a doctor with an athletic injury and all he does is give you pain medicine or an injection, go and find another doctor. That's like treating body odor with perfume. He should be able to work out the cause of the injury."

Whether the injury is severe (as in Nirshl's phase three or four) or just something that annoys or worries, you can seek help from a sports medicine physician (usually an orthopedist or podiatrist, for running problems) or from a runner's clinic. There are two clinics in the Washington area. One is at George Washington Univeristy's Smith Center, 600 22nd Street NW; 676-6253. The hours are 1 to 5 Wednesday afternoons. The other is at the Sports Medicine Center, 5454 Wisconsin Avenue, Bethesda; 986-9252. The hours are 1 to 5, Tuesday afternoons and 9 to 12, Thursday mornings. The fee is $40 and is usually covered by insurance. Both clinics were designed and developed by Brody. He and Sheldon Konecke, a podiatrist who specializes in sport injuries, are the physicians in charge. Visits are by appointment only. For non-emergency visits, expect to wait three or four weeks for an appointment.

Clinic routine is similar to that of a regular visit to a sports medicine physician, but with one or two variations. The visit lasts about half an hour. It starts with a recounting of how the injury happened and a detailing of previous injuries. After a physical examiniation, Brody goes over your training regime. (Bring all logs). Then you don your running shorts and shoes, hop on a treadmill and run. Brody videotapes your efforts and goes over the tape with you to see whether your running style contributed to the injury. Then he comes up with a diagnosis and plan.

"Treatment may involve rest to some degree, some other type of atletic activity while you're getting better," he says. "Often, treatment involves exercises to strenghten and stretch muscles. Occasionally, it may involve medication. Some of the problems have to do with alignment and the way a person is built. That may mean an orthotic device for the shoe to correct an imbalance between foot and knee. We also discuss training -- how many miles, what type of interval training to do or not to do." t

The results, Brody says, are usually good. "Runners are so tuned in to running they will do almost anything to get better. They follow instructions to the letter. There are no malingerers."