This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
The healthy working of the muscles is dependent on a healthy state of the body in general; this is indispensable that they may be sufficiently supplied with proper nourishment, and have their wastes promptly carried away. Hence good food and pure air are necessary for a vigorous muscular system. Muscles also should not be exposed to any considerable continued pressure, since this interferes with the flow of blood and lymph through them which is essential for their nutrition.
Why do short-legged persons tend to take a quicker step than others?
How does running differ from walking? Describe the act of running How is the number of steps taken in a given time increased in running? How is the stride increased?
How does the state of general health influence the muscular system? Why does an athlete need good food and air?
Exercise is necessary for the best development of the muscles. A muscle long left unused diminishes in bulk and degenerates in quality, as is well seen when a muscle is paralyzed and remains permanently inactive because of disease of its nerve ; although at first the muscle itself may be perfectly healthy, it alters in a few weeks, and when the nerve is repaired the muscle may in turn be incapable of activity. The same fact is illustrated by the feeble and wasted state of the muscles of a limb which has been kept motionless in splints for a long time : when the splints are removed it is only after careful and persistent exercise that the long idle muscles regain their former size and power. The great muscles of the "brawny arm" of the blacksmith illustrate the converse fact—the growth of muscles when exercised.
Exercise, to be useful, must be judicious; taken to the point of extreme fatigue, day after day, it does harm. When a muscle is worked its substance is used up; at the same time and afterwards more blood flows to it, and if the exercise is not too violent and the intervals of rest are long enough, the repair and growth will keep pace with or exceed the wasting : but excessive work and too short rest will lead to diminution and enfeeblement of the muscle just as certainly as too little exercise.
Few persons can profitably attempt to work hard daily with both brain and muscle, but all should regularly use both; choosing which to work with, and which to simply exercise. The best earthly life, that of the healthy mind in the healthy body, can only so be attained. For persons of average physique, engaged in study or business pursuits of a sedentary nature, the minimum of daily exercise should be an amount equivalent to a five-mile walk.
Why should muscles not be exposed to continuous pressure?
What happens when a muscle is not used ? Illustrate by examples. Why are the muscles of a blacksmith's arm large?
When does exercise do harm? Why? Can most persons work hard with both brain and muscle at the same time?
Since extra muscular work means extra muscular waste, and should be accompanied by an abundant supply of food materials to the muscles, violent exercise should not be taken after a long fast. Neither should it be taken immediately after a meal; a great deal of blood is then needed in the digestive organs to provide materials for digesting the food, and this blood cannot be sent oft to the muscles without the risk of an attack of indigestion. Strong and hearty young people may take a long walk before breakfast, but others had better wait until after eating something before engaging in any kind of hard work.
In walking and running the muscles chiefly employed are those of the lower limbs and trunk ; these exercises leave the muscles of the chest and arms imperfectly worked. Rowing is better, since in it nearly all the muscles are used. No one exercise employs in proper proportion all the muscles, and gymnasia in which different feats of agility are practiced so as to call different muscles into action have a deserved popularity. It should be borne in mind, however, that the legs especially need strength; while in the arms delicacy of movement is more important to most persons than great strength; and the fact that gymnastics are usually practised indoors is also a great drawback to their value. Out-of-door exercise in good weather is better than any other, and every one can at least take a walk. The daily "constitutional " is very apt to become wearisome, especially to young persons, and exercise loses half its value if unattended with feelings of mental relaxation and pleasure. Active games, for this reason, have a great value for young and healthy persons; lawn-tennis, base-ball, and cricket are all attended with pleasurable excitement, and are excellent also as exercising many muscles.
How can the highest development of man, regarded merely as a thinking and moving machine, be attained?
Why should we not exercise when fasting? Why not soon after eating?
What muscles are chiefly used in walking and running? Which are imperfectly exercised? Why are gymnasia useful?