For decades, people have been donning sweaters after heavy exercise. The name sweater, in fact, has obvious origins. The sweater began as a means of keeping the body warm and covered once it had become hot and sweaty.

Unless exposure to inclement weather is a problem, or the individual has particular reasons for putting on a sweater at the end of a hot workout, the sweater myth is just that. Under normal temperature, weather, and other conditions, the sweater simply prolongs the body’s hot state. That helps not at all.

Some stiffness can, of course, result from exercise. But wearing a sweater is not the way to prevent that. Stiff ness usually has its sources in the body’s condition—or lack of it.

The advice that counsels moderation in launching a fitness program or in starting new phases of it has a sound basis in physiology. The purpose is to avoid excessive fatigue. Muscular fatigue is defined as stimulation of a muscle or group of muscles beyond their ability to recover. A second type of fatigue affects the entire body. Known as physical fatigue, this form can be regarded as normal after physical exercise if it does not suggest undue stress.

Keep in mind that a flexible plan may call for adjustments under different circumstances. It may indicate sometimes that it is best to terminate the day’s activities. On other occasions, it may require elimination of some exercises and continuation with others.

-Your knee begins to bother you. You drop the exercises calling for knee exertion and retain those that don’t.

-You get a “stitch” in your side. Because it hurts continually, you decide to downplay those exercises—for that day—that produce or exacerbate the discomfort.

-While running in place, you find yourself troubled by shin splints, those pains along the sides of the shin bones. You stop running and turn to something else.

-Flexibility can exist alongside dedication to a program. As common sense dictates, the individual should sometimes slow down or blow the whistle completely on some exercises. Even Napoleon retreated now and then.

Another important principle should be noted: the individual will build and take to a fitness program most readily if he believes it will do him some good. And if he has faith and confidence in it, he is likely to stay with the program over the long run.

Three stages of fitness have been identified. The individual who stays with an intelligently devised program moves through beginning, intermediate, and advanced stages. These have been termed by some authorities the low, medium, and excellent stages or phases. Some experts add a fourth level: the elite stage at which a person finds himself able to take part in highly competitive and demanding athletic activities.