This description of muscular fatigue lays the foundation for an understanding of the problem of nervous fatigue. The nerve cells, like the muscles, get clogged by the products of their own action. They then fail to carry nervous impulses freely, and the individual can do his mental or physical work only with excessive effort. Fatigue of nerve cells means that nature has limits of work in these cells. Fortunately, the limit is reached long before exhaustion or other real dangers set in.
Conditions like Fatigue
Matters are complicated by the fact that physical conditions other than ordinary use produce fatigue-like effects in nerve cells. Excitement of any kind rapidly changes the condition of nerve cells, and sometimes foreign chemical substances get into the blood, as in fever or infection, and produce a condition that is in effect the same as fatigue.
Still further, as a fact of large importance in determining capacity for work, the nerve cells pass each day through a kind of internal cycle of conditions. At certain hours their condition is such that they transmit nervous impulses freely, and work is easy; at other hours work drags because the nerve cells are not prepared to be active; their internal chemical condition is such as to obstruct transmission of impulses. Thus, one is usually very energetic in the middle of the forenoon, but is logy at noon and sleepy at a late hour in the afternoon. Marked individual differences appear, making this statement merely a general statement. Furthermore, personal habits can be changed to some extent through the adoption of new habits of life.
Finally, there are all sorts of pathological conditions which profoundly affect the life and action of nerve cells. Anæmia and malnutrition may render nerve cells utterly incapable of continued action.
Practical Precepts based on Study of Fatigue
Enough has been said to make it clear that no simple formula can be applied to a group of pupils when one tries to determine for purposes of the daily program how long their nerve cells can be kept at work on a single task. The wisest course for the teacher to follow is to be alert, and when a class reaches its limit of profitable work to introduce a change. On the other hand, the teacher should be very discriminating and should understand that fatigue is not a dangerous symptom. For example, suppose that the athlete always stopped his exercise just as soon as he began to feel the necessity of sending stronger nervous impulses down to his muscles. He would lose the best results of training, for these results consist in the acquisition of the power to overcome fatigue. So also with the pupil. The acquisition of the power to overcome fatigue is a most important part of the pupil’s training.
Keeping the principles suggested in the foregoing discussion in mind, it is relatively easy to arrive at certain practical rules of program administration.
First, maturity ought to mean greater power of endurance. The older classes should—and usually do—have longer periods of work.
Second, the period should be long enough to stretch the pupil’s powers. Regulation of work within this period should be left to the teacher, and teachers should train themselves to recognize the symptoms of fatigue and to judge when training has gone as far as it can in overcoming fatigue.