Running may be great exercise, but without the proper precautions it can do more harm than good. When you run, you're putting a tremendous strain on your feet, essentially smashing them over and over again against a hard surface. A number of common sense precautions can make your running program both a safe and healthy activity. Before you begin any exercise program, a doctor's checkup is recommended. A warm-up is always necessary; you want to get your muscles loose and relaxed before putting any strain on them. Be sure to start slow, on a level track or treadmill, and don't try to increase your distance more than 10% per week. If you experience mild pain, try a longer warm-up or shorter runs. If the pain is more intense, you might want to stop running for a while. Swimming or bicycling can keep your muscles in shape for when you resume your running routine. Pain is your body's way of telling you that something's wrong. If you experience severe pain, stop running and see a doctor.