A Practical Physiology: A Text-Book for Higher Schools. Albert F. Blaisdell
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against their antagonists.
Fig. 40.--The Standard Special Chest Weight.
A convenient machine by means of which all the muscles of the body may be easily and pleasantly exercised with sufficient variations in the movements to relieve it of monotony.
A space 6 ft wide, 6 ft deep, and 7 ft high nearly in front of the machine is required for exercise.]
In time, however, acts which were first done only with effort and by a conscious will, become automatic. The will ceases to concern itself. By what is called reflex action, memory is developed in the spinal cord and the muscular centers (sec. 273). There is thus a great saving of actual brain work, and one important cause of fatigue is removed.
83. Effect of Exercise on Important Organs. The importance of regular exercise is best understood by noting its effects upon the principal organs of the body. As the action of the heart is increased both in force and frequency during exercise, the flow of blood throughout the body is augmented. This results from the force of the muscular contractions which play their part in pressing the blood in the veins onward towards the heart. Exercise also induces a more vigorous respiration, and under increased breathing efforts the lung capacity is increased and the size of the chest is enlarged. The amount of air inspired and expired in a given time is much larger than if the body were at rest. The blood is thus supplied with a much larger amount of oxygen from the air inhaled, and gives off to the air a corresponding excess of carbon dioxid and water.
Again, exercise stimulates and strengthens the organs of digestion. The appetite is improved, as is especially noted after exercise in the open air. The digestion is more complete, absorption becomes more rapid, the peristaltic movements of the bowels are promoted, and the circulation through the liver is more vigorous. More food is taken to supply the force necessary for the maintenance of the mechanical movements. Ample exercise also checks the tendency towards a torpid circulation in the larger digestive organs, as the stomach and the liver, so common with those who eat heartily, but lead sedentary lives. In short, exercise may be regarded as a great regulator of nutrition.
Exercise increases the flow of blood through the small vessels of the skin, and thus increases the radiation of heat from the surface. If the exercise be vigorous and the weather hot, a profuse sweat ensues, the rapid evaporation of which cools the body. The skin is thus a most important regulator of the bodily temperature, and prevents any rise above the normal which would otherwise result from vigorous exercise. (See secs. 226 and 241).
84. Effect of Exercise upon the Personal Appearance. Judicious and systematic exercise, if moderately employed, soon gives a more upright and symmetrical figure, and an easier and more graceful carriage. Rounded shoulders become square, the awkward gait disappears, and there is seen a graceful poise to the head and a bearing of the body which mark those whose muscles have been well trained. A perfectly formed skeleton and well-developed muscles give the graceful contour and perfect outline to the human body. The lean, soft limbs of those who have never had any physical education, often look as if they belonged to persons recovering from sickness. The effects of sound physical exercise are well exhibited in the aspect of the neck, shoulders, and chest of one who has been well trained. This is noticeable in gymnasts and others who practice upon the horizontal bar, with chest weights, dumb-bells, and other apparatus which develop more especially the muscles of the upper half of the trunk.
Fig. 41.--Young Woman practicing at Home with the "Whitely Exerciser." (From a photograph)
Exercise improves the condition of the tissues generally. They become more elastic, and in all respects sounder. The skin becomes firm, clear, and wholesome. Hence, every part of the surface of the body rapidly takes on a change in contour, and soon assumes that appearance of vigor and soundness which marks those of firm physical condition. The delicate, ruddy aspect of the complexion, the swing about the body and the bearing of the head and shoulders, of young women whose physical training has been efficient, are in marked contrast with those characteristics in persons whose education in this respect has been neglected.
85. Effect of Unsuitable or Excessive Exercise. But exercise, like everything else which contributes to our welfare, may be carried to excess. The words excessive and unsuitable, when applied to muscular exertion, are relative terms, and apply to the individual rather than to amount of work done. Thus what may be excessive for one person, might be suitable and beneficial to another. Then the condition of the individual, rather than the character of the muscular work, is always a most important factor.
Breathlessness is, perhaps, the most common effect of undue exertion. Let a middle-aged person, who is out of practice, run a certain distance, and he is soon troubled with his breathing. The respirations become irregular, and there is a sense of oppression in his chest. He pants, and his strength gives out. His chest, and not his legs, has failed him. He is said to be "out of breath." He might have practiced dumb-bells or rowed for some time without inconvenience.
The heart is often overstrained, and at times has been ruptured during violent exertion, as in lifting an immense weight. The various forms of heart-disease are common with those whose occupations involve severe muscular effort, as professional athletes and oarsmen. Hæmorrhages of various kinds, especially from the lungs, or rupture of blood-vessels in the brain, are not uncommon results of over-exertion.
Excessive repetition of muscular movements may lead to permanent contractions of the parts involved. Thus sailors, mechanics, and others frequently develop a rigidity of the tendons of the hand which prevents the full extension of the fingers. So stenographers, telegraphers and writers occasionally suffer from permanent contractions of certain muscles of the arm, known as writer's cramp, due to their excessive use. But the accidents which now and then may result from severe physical exertion, should discourage no one from securing the benefits which accrue from moderate and reasonable exercise.
86. Muscular Fatigue. We all know how tiresome it is to hold the arm outstretched horizontally even for a few moments. A single muscle, the deltoid, in this case does most of the work. Even in a vigorous man, this muscle can act no longer than four to six minutes before the arm drops helpless. We may prolong the period by a strong effort of the will, but a time soon comes when by no possible effort are we able to hold out the arm. The muscle is said to be fatigued. It has by no means lost its contractile power, for if we apply a strong electric stimulus to it, the fatigue seems to disappear. Thus we see the functional power of a muscle has a definite limit, and in fatigue that limit is reached.
Fig. 42.--A Well-Equipped Gymnasium. (From a photograph.)
The strength of the muscle, its physical condition, the work it has done, and the mental condition of the individual, all modify the state of fatigue. In those difficult acts which involve a special effort of the will, the matter of nerve exhaustion is largely concerned. Thus, the incessant movements in St. Vitus' dance result in comparatively little fatigue, because there is no association of the brain with the muscular action. If a strong man should attempt to perform voluntarily the same movements, he would soon have to rest. None of the movements which are performed independently of the will, as the heart-beats and breathing movements, ever involve the sensation of fatigue. As a result of fatigue the normal irritability of muscular tissue becomes weakened, and its force of contraction is lessened. There is, also, often noticed in fatigue a peculiar tremor of the muscles, rendering their movements uncertain. The stiffness of the muscles which comes on during severe exercise, or the day after, are familiar results of fatigue.
This sense of fatigue should put us on guard against danger. It is a kind of regulator which serves in the ordinary actions of life to warn us not to exceed the limits of useful exercise. Fatigue summons us to rest long before all the force of the motor organs has been expended, just as the sensation of hunger warns us that we need food, long before the body has become weak from the lack of nourishment.
We should never forget that it is highly essential to maintain an unused reserve of power, just as a cautious merchant always keeps at the bank an unexpended balance of money. If he overspends his money he is bankrupt, and the person who overspends his strength is for the time physically bankrupt. In each case the process of recovery is slow and painful.
87.