The muscles enable us to move the frame-work of the system. Their chief purpose obviously is to enable us to carry into effect the various resolutions and designs which have been formed by the mind. But, while fulfilling this grand object, their active exercise is, at the same time, highly conducive to the well-being of many other important functions. By muscular contraction, the blood is gently assisted in its course through the smaller vessels to the more distant parts of the body; and by it the important processes of digestion, respiration, secretion, absorption, and nutrition are promoted; and by it the health of the whole body is immediately and greatly influenced. The mind itself is exhilarated or depressed by the proper or improper use of muscular exercise. It thus becomes a point of no slight importance to establish general principles by which that exercise may be regulated.
In every part of the animal economy, the muscles are proportioned in size and structure to the efforts required of them. Whenever a muscle is called into frequent use, its fibers increase in thickness within certain limits, and become capable of acting with greater force and readiness. On the other hand, when a muscle is little used, its volume and power decrease in a corresponding degree.
In order to secure the most beneficial results from exercise, reference should be had to the time at which it is taken. Those who are in perfect health may engage in it at almost any hour except immediately after a meal; but those who are not robust ought to confine their hours of exercise within narrower limits. To a person in full vigor, a good walk, or other brisk exercise before breakfast may be highly beneficial and exhilarating, while to an invalid or delicate person it will be likely to prove detrimental. In order to prove beneficial, exercise must be resorted to only when the system is sufficiently vigorous to be able to meet it. This is usually the case after a lapse of from two to four hours after a moderate meal. The forenoon, then, will generally be found the best time for exercise for persons whose habits are sedentary. If exercise be delayed till the system feels exhaustion from want of food, its tendency will be to dissipate the strength that remains and impair digestion; while, if taken at the proper time, it will invigorate the system and promote digestion. The reasons are obvious; for exercise of every kind causes increased action and waste in the organ, and if there be not materials and vigor enough in the system to keep up that action and supply the waste, nothing but increased debility can reasonably be expected.
Active exercise immediately before meals is injurious. The reasons are apparent, for muscular exercise directs a flow of blood and nervous energy to the surface and extremities; and it is an established law in physiology, that energetic action can not be kept up in two distant parts of the system at the same time. Hence, whenever a meal is taken immediately after vigorous exercise, the stomach is taken at disadvantage, and, from want of the necessary action in its vessels and nerves, is unable to carry on digestion with success. This is very obviously the case where the exercise has been severe or protracted.
Active exercise ought to be equally avoided immediately after a heavy meal, for then the functions of the digestive organs are in the highest state of activity. If the muscular system be called into vigorous action under such circumstances, it will cause a withdrawal of the vital stimuli of the blood and nervous influence from the stomach to the extremities, which can not fail greatly to retard the digestive process. In accordance with this well-established fact, there is a natural and marked aversion to active pursuits after a full meal. A mere stroll, which requires no exertion and does not fatigue, will not be injurious before or after eating; but exercise beyond this limit is at such times hurtful. All, therefore, who would preserve and improve their health, will find it to their advantage to observe faithfully this important law, otherwise they will deprive themselves of most of the benefits that are usually attendant upon judicious exercise. All, then, who are forced to much exertion immediately after eating, should satisfy themselves with partaking of a very moderate meal. These remarks apply to both physical and mental exercise; for if the intellect be intently occupied in profound and absorbing thought, the nervous energy will be concentrated in the brain, and any demands made on it by the stomach or muscles will be very imperfectly attended to. So, also, if the stomach be actively engaged in digesting a full meal, and some subject of thought be presented to the mind, considerable difficulty will be felt in pursuing it, and most probably both thought and digestion will be disturbed.
Another law of the muscular system requires that relaxation and contraction should alternate; or, in other words, that rest should follow exercise. In accordance with this law, it is easier to walk than to stand; and in standing, it is easier to change from one foot to the other than to stand still. To require a child to extend his arm and hold a book in his hand, or even to keep the arm extended but a short time, is a violation of this law which should never be permitted. Akin to this is the very injudicious practice, which is sometimes resorted to in schools, of requiring a boy to stoop over, and, placing his finger upon a nail in the floor, "hold it in." Teachers who are disposed to inflict punishments like these ought first to try the experiment themselves. Such protracted tension of the muscles enfeebles their action, and ultimately destroys their power of contraction.
These remarks sufficiently explain why small children, after sitting a while in school, become restless. Proper regard for this organic law requires that the smaller children in school be allowed a recess as often, at least, as once an hour; and that all be allowed and encouraged frequently to change their position. I fully concur in the opinion expressed by Dr. Caldwell, who says, "It would be infinitely wiser and better to employ suitable persons to superintend the exercises and amusements of children under seven years of age, in the fields, orchards, and meadows, and point out to them the richer beauties of nature, than to have them immured in crowded school-rooms, in a state of inaction, poring over torn books and primers, conning words of whose meaning they are ignorant, and breathing foul air."
A change of position calls into action a different set of muscles, and relieves those that are exhausted. The object of exercise is to employ all the muscles of the body, and especially to strengthen those that are weak. It ought hence to be frequently varied, and always adapted to the peculiarities of individuals. Different kinds of exercise will therefore be found to suit different constitutions. Sedentary persons best enjoy, and will be most profited by, that kind of exercise which brings into action the greatest number of muscles.
To give exercise its greatest value, it should be taken at the same hour every day. This is well-nigh as important as the rule that requires meals to be taken regularly. If exercise be taken irregularly, one day in the morning, another day at noon, and another day at night, if at all, it is possible that good may result from it, but its beneficial effects would be greatly increased if the same amount of exercise were taken every day at the same hours. Give the system an opportunity of establishing good habits in this respect, and it will derive great advantage from them; but it is difficult for it to derive any benefit from a habit of irregularity, if such may be called a habit. Students, teachers, and all persons who lead sedentary lives, should have their regular times for exercise as well as for meals, and if they find it necessary to do without one, they will generally find it advantageous to dispense with the other also.
Walking, it has been said, agrees with every body. But as it brings into play chiefly the lower limbs and muscles of the loins, and affords little scope for the play of the arms and muscles of the chest, it is of itself insufficient to constitute adequate exercise. To render it most beneficial, the shoulders should be drawn back, and the chest should be enlarged by taking deep inspirations of pure air. The muscles of the chest, and of every part of the body, should be free to move and unconfined by tight clothing. Fencing, shuttlecock, and such other useful sports as combine with them free movements of the upper part of the body, are doubly advantageous, for they not only exercise the muscles of the whole body, but possess the additional advantage of animating the mind and increasing the nervous stimulus, by which exercise is rendered easy, pleasant, and invigorating. For the purpose of developing the chest, physiologists generally concur in recommending fencing as a good exercise for boys. Shuttlecock is a very beneficial exercise for females, calling into play, as it does, the muscles of the chest, trunk, and arms. It ought to be practiced in the open air. When played with both hands, as it may be after a little practice, it is very useful in preventing curvature, and in giving vigor to the spine. It is an excellent plan to play with a battledore in each hand, and to strike with them alternately. The graces is another play well adapted for expanding the chest, and giving strength to the muscles of the back, and has the advantage of being practicable in the open air. It is very important that the muscles of the back be strengthened by due exercise, for their proper use contributes to both health and beauty.