From tennis elbow to shin splints, Achilles tendonitis to jumper's knee, most exercise-related injuries stem from "unbounded enthusiasm," says orthopedic surgeon James Garrick.

"People go on vacation and play seven straight days of tennis, or ski season starts and they hit the slopes like fanatics," says Garrick, director of the Center for Sports Medicine at St. Francis Hospital in San Francisco and author of "Be Your Own Personal Trainer" (Crown, 1989). "Well over half of these injuries are overuse injuries, and they are almost all preventable."

While prevention is the best treatment for any ailment, most active people will get injured sooner or later. And one of their biggest mistakes, Garrick says, is trying to ignore it. Instead, realize that pain is your body's way of telling you what's going on with your muscles and joints and tendons. It can be a message to change your training schedule, adjust your equipment, alter your performance or seek help.

To keep exercising injury-free, listen to your body and be aware of the factors that put you at risk of getting hurt.

"Injuries are definitely related to how much you do," says Michael Pollock, director of the Center for Exercise Science at the University of Florida in Gainesville. Exercise in moderation -- for example, up to 20 miles per week for runners -- carries less likelihood of injury. But if you're thinking about drastically increasing the frequency, the duration or the intensity of your exercise, Pollock says, "you're flirting with potential problems."

In one study of young runners, injury rates were virtually unchanged when the exercisers went from one weekly, 30-minute exercise session to three weekly, 30-minute exercise sessions. "Yet when they went from three days to five days of exercise per week, there were about triple the amount of injuries," according to Pollock.

In another study, injuries were not significantly greater when new exercisers went from 15-minute sessions to 30-minute sessions. "But when they went from 30 to 45 minutes of activity, the rate of injuries doubled," Pollock says.

High-impact activities such as running and some kinds of aerobic dance also are more associated with injury, Pollock notes. And older people are more prone to injury, he says, particularly if they are just beginning to exercise.

But fear of injury shouldn't keep you from being active, since the benefits of exercise far exceed the risks. Just remember to start slowly and build up progressively and consider these injury-preventing tips:

Never make abrupt changes in your activity or dramatically increase your workload, whether it's the number of hours you play a sport, the amount of weight you lift or the distance you cycle. Always progress gradually.

Pay attention to pain. If you experience a sharp, sustained pain, stop exercise immediately and seek treatment. If you're experiencing a creeping, nagging pain, take a few days off and try to figure out the reason; do you need new equipment, have you been doing something differently? If the pain doesn't go away with self-treatment or if it gets worse, seek professional help.

Get expert advice. Improper form and technique can result in injury. Consider getting professional pointers by taking a class, joining a gym or hiring a personal trainer.

Wear proper shoes. Don't wear running shoes for aerobic dance or tennis, since running shoes are made for moving forward and dance and tennis require side-to-side movement. Even the best shoes lose their cushioning over time, so don't wear a worn-out pair.

Never do a sport to get in shape; get in shape to do a sport. Sports are stressful. Jumping into basketball season or onto the ski slopes without getting into condition first is asking for trouble.

Be sensitive to past injuries. The familiar ache of an old injury may be a signal to slow down or get new shoes or seek medical help. Consult a fitness professional for strategies to minimize re-injury.

Be aware that anatomical factors such as having one leg longer than the other, or flat feet, can result in pain and injury. In-shoe orthotics or lifts can help some people. Consult a good sports podiatrist.

Try cross-training. If you're hooked on daily exercise, but your knees complain if you run every day, alternate your high-impact activity with a low-impact workout like swimming or bicycling. At the very least, alternate hard/easy training days.

Strive for a balanced workout. If you strengthen certain muscles at the expense of others, the resulting imbalance can cause injury. Vary your activities to achieve a more balanced body. Maintain your flexibility by stretching after your warm-up and at the end of your exercise session. Maintain your strength by performing eight to 10 exercises involving all the major muscles groups, two to three times a week. Never stop exercising abruptly. Always cool down.

Consult a physician before beginning any vigorous exercise program if you are over 40 or if you have risk factors of heart disease, including obesity.

Appreciate the recuperative power of rest. Beginners should consider resting one day between vigorous activity. New exercisers who want to stay active on their "off day" can take a leisurely walk or swim. And seasoned athletes need to remember that even God rested on the seventh day.

Bodyworks appears on alternate Tuesdays.