Daniel Venditto, age 13, of Provindence, R.I., for his question:
WHAT CAUSES FATIGUE?
Fatigue is another name for tiredness. Doctors do not know exactly what causes fatigue. They do not know why a person feels tired after muscular exertion or mental effort. However, they do know that psychological as well as physical factors contribute to fatigue.
The effect of fatigue has been closely studied. Research workers have shown that persons who spend long hours at things that bore them or at tasks they do not want to do soon develop fatigue. If the person's morale or general attitude and incentive or promise of reward are good, it takes longer for fatigue to develop.
But no matter how good morale or incentive might be, a person who works or plays long enough or hard enough will definitely develop a feeling of fatigue.
If we work hard, play hard or go without rest or sleep, we expect to feel fatigued. In such cases, fatigue is normal. We know from experience that this feeling will disappear after we rest.
But sometimes fatigue is a symptom of illness. A physically ill person often feels weak and becomes fatigued after even a slight amount of work or exertion. Such persons need a great deal of rest, often much more than they would need if they were well.
Doctors have found that fatigue occurs frequently in many different kinds of illnesses. Rest in bed has become a part of the treatment for almost every kind of physical illness.
Fatigue may be one of the symptoms of a mental or physical illness. In either case, rest helps a person feel less tired. But no amount of rest will cure the tendency to become tired easily. This tendency will disappear or improve only if the physical or mental illness that causes the fatigue is improved or cured.
Engineers use the term "fatigue" to describe certain changes that occur in substances like metals. This fatigue is usually the result of extensive use of the metal.
Physiologists the people who study the 'action of living tissue use the word "fatigue," in a somewhat different sense than do physicians. These people sometimes study the reaction of muscles to stimuli.
Physiologists make a muscle contract again and again by stimulating it with an electric current. They do not let the muscle rest, but make it contract and relax continually for a long time. As the stimulation continues, the contractions become weaker and weaker.
When the muscle becomes very weak, the researchers allow it to rest for a while. When they stimulate it again after the rest period, it contracts as strongly as ever.
The progressive weakening of the muscle is called fatigue. It differs from the "feeling" of fatigue people have after muscular exertion. But the two conditions are so much alike that they are called by the same name.