In sport, not all pain is bad. Sometimes it is necessary to increase fitness levels and performance. However, some forms of discomfort during exercise are signals that something is wrong. By learning how to distinguish between good and bad pain, it is possible to avoid injuries from overtraining. It is well known that there is some discomfort during exercise and sport. That is because for a muscle to become stronger, it must be stressed at a higher level than it is used to. The phrase 'no pain, no gain', coined in the 1980s, was made in reference to the 'burn' in the muscle that occurs during or immediately after exercise. It is caused when the muscle is fatigued and the feeling should go away within a few minutes or at the most after a few hours of rest. Health and fitness experts agree that this is a good sign, as long as proper rest follows, because it demonstrates that the individual is pushing their physiology. But this fatigue should leave you exhilarated, not exhausted. Another type of soreness that occurs in the muscle is called 'delayed onset muscle soreness' or Doms. Muscles that have not been exercised for long periods of time respond to increases in stress levels by becoming sore. Feeling like a dull ache in the muscle, the sensation usually peaks somewhere between 24 and 48 hours after the workout. Even if someone is really fit, if they go harder or longer than their body is used to they experience Doms. Some athletes plan a workout (for example, lifting weights eccentrically) to produce this type of soreness as they believe it will improve performance. Yet some exercise physiologists feel that Doms is merely a reflection of muscle damage, or microscopic tears, and athletes should not continually try to achieve this soreness. A little bit of pain or discomfort means that the muscle has been stressed, but too much and the muscle may swell. In severe cases, the muscle may be damaged to the point where the cells release their contents, such as enzymes, into the blood plasma, indicating that there is muscle damage. If left unchecked, this can result in permanent damage. And for those individuals who are really out of shape, exercising intensely can cause muscles to release proteins into the blood stream which shut down the kidneys. This is another reason why it is a good idea to start slowly when you begin any exercise programme. Other soft tissues that can be over-stressed in workouts are tendons, bones, and cartilage. These tissues react quite slowly to the stress of exercise. If too much pressure is applied too quickly, these structures can not respond in time and will begin to fail. Tendonitis pain can result from exercising. If severe enough, it can carry on into daily activities that use that particular tendon or muscle. Bone responds to an increase in stress by 'remodelling' or removing bone from areas of less stress and adding bone to areas under high stress. Again, if the stress level is too high and it is reached too fast, the bone can't remodel fast enough. Usually the first signs of this are 'stress fractures', where there's pain along the bone. If left untreated and the activity continues without the necessary time to remodel, the pain will become more localised and tiny hair-like fractures will show up on the affected bone. When cartilage is over-stressed too rapidly, the joint becomes painful and swells. Again, if left untreated and the exercise continues the pain and swelling become worse and can affect simple daily activities. Pain is the body's way of communicating. Slight discomfort during or immediately after exercise followed by adequate rest is the proper way to increase fitness. Swelling, sharp pain or fatigue that lasts for days are indications that something is wrong. One of the first signs of bad pain is when the pain continues beyond the exercise period. If in any doubt about the pain or discomfort you experience, the best thing to do is seek out the advice of someone qualified to deal with sports injuries.