# Popular Science Monthly/Volume 53/June 1898/The Physiology of Strength and Endurance

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* THE PHYSIOLOGY OF STRENGTH AND ENDURANCE.
By WILLIAM LEE HOWARD, M. D.
WHEN we read in the daily newspapers of the collapse of a celebrated athlete, or the breaking down during training of a young aspirant for arenic honors, we naturally surmise that fundamental knowledge of the physiology of the muscular mechanism of the human body is either submerged by the overpowering desire to make a record, or totally absent, among certain trainers and their pupils. The want of such knowledge is the cause of many sad conditions existing to-day among former strong and healthy individuals. A comprehensive idea of the physiology of growth, of the physiologic and chemic relations of strength and endurance to age and condition, would be of great value to the present horde of senile individuals—not senile in years, but senile in vessels and tissues—who strive to make their century runs, as well as to the adolescent whose central nervous system is often permanently injured by overexertion in attempting to make the records placed by carefully trained and intelligent athletes.
The human body is a wonderful piece of mechanism, which not only renews itself constantly, but whose strength and endurance and capacity for more work increase with increased use up to the point at which use becomes abuse. At what time and under what pressure this danger line is reached depends upon the individual. However, the approach to this danger line is governed in all cases by fixed and immutable physiologic laws. The athlete must always bear in mind that the length of time that the muscle cell can continue to work will depend upon the rapidity with which the energy holding explosive compounds are formed by the cell protoplasm and the waste products are excreted (Howell). In other words, the ​capital must not be expended at a greater rate than it can be replaced; if it is expended at a greater rate, fatigue commences, and a continuance of this expenditure results in physical bankruptcy. The muscle is continually undergoing change of material. The minute substances which make up the muscle, and whose very actions keep it alive, are being continually cast off, fresh substances taking their place. The cast-off material is the fatigue poison. Without muscle rest this dead, poisonous detritus can not be replaced fast enough by the new products, and the result is an impoverished capital of potential elements. This does not apply only to the muscle in active use up to this point, but to all muscles of the body.
The energy products of food are delivered up to the muscle by the blood, and this fluid picks up and carries away the cast-off dead substances of the muscle. "If the working muscle has taken material from the blood, this material is lost to all the rest; and if the working muscle has given off to the blood poisonous material, this is added to the other parts" (Lombard; Howell's Physiology). These latter, the fatigue products, are only gradually eliminated from the blood. It will now be recognized that to keep on the right side of the danger line in exercise the muscle must have short intervals of rest. Nature so well understood the proneness of man not to heed advice that she placed the action of one muscle beyond his control. This muscle is so internally constructed and adjusted that it has its regular periods of rest, and only in disorder of the body can its expenditure be raised beyond its means. This muscle, the heart, though making contractions at the rate of seventy-two times a minute, is able to continue its work without fatigue throughout the life of the individual. Each contraction of this muscle is followed by an interval of rest, during which the cells recuperate. Push continually the heart beats to a very rapid rate and we approach the danger point at which the fatigue products can not be replaced by fresh cells; the intervals of rest are not sufficient. The same condition exists in every muscle. It is in the extreme rapid exercise, such as sprinting and certain phases of bicycle racing, that we often see either immediate or ultimate collapse followed by irremediable loss of health.
It should be impressed upon all young persons that during life each member of the body, in the very act of living, produces poison to itself. When this poison accumulates faster than it can be eliminated, which always occurs unless the muscle has an interval of rest, then will come fatigue, which is only another expression for toxic infection. If the muscle is given an interval of rest, so that the cell can give off its waste product to keep pace with the new ​productions, the muscle will then liberate energy for a long time. This latter condition is what we call endurance.
The power and endurance of the human machine is limited according to our understanding of the above facts, and also our recognition of its slowness in getting started. Like any other ponderous and intricate machine, the body requires time to get in harmonious working order. The brain, nerves, heart, and skeletal muscles must be given some warning of the work they are expected collectively to perform. Ignorance of this fact has broken down many a young man who aspired to honors on the cinder path. The necessity of getting all the parts of the body slowly in working order is well understood by trainers and jockeys on the race track, as is evidenced by the preliminary "warming up" they give their horses, although it is doubtful if the trainers could give any physiologic reason for this custom.
Of the substances supplied to the muscle by the blood, oxygen is one the want of which is soonest felt. The muscle contains within itself a certain store of oxygen, but one which is by no means equal to the oxidizable substances. The muscle's activity is dependent to a great extent on the character and force of the blood flow through the muscle. It must be clear of the waste products, as well as containing sufficient oxygen to continually keep up a renewal of energy. From what has been said it will readily be seen that the result of a muscular task which an athlete wishes to perform will depend primarily on his muscular bulk and on the condition of these muscles, and the rate at which he expends his capital; the test of his endurance will depend upon the condition of the other parts of his body, and how thoroughly and rapidly they will carry off the quickly formed poisonous products and supply fresh ones.
Nineteen pugilists have died in the ring the last seven years. Not one of these deaths was directly due to the force or severity of the blows struck, but because the fighters were "out of condition" The waste products caused by the rapid muscular work accumulated in their bodies, and, forced to go on with their exertion, they dropped exhausted to death—poisoned by material of their own manufacture. Less attention paid to mere muscular exercise, and more to the condition of the blood and other parts of the human machine, would have brought different results. These facts impressed upon a certain class of athletes would be of great moral and social advantage to the world in general. It means that these individuals must have fresh air to live in, clean skins, good, substantial food, a fixed number of hours for sleeping, and avoidance of stimulants. If it was well understood that no man could go into the exhibition ring, or into any contest requiring physical exertion, unless he could show, ​after a careful examination by a competent physician, that his condition would warrant a prolonged and severe muscular effort, the result on the moral and bodily habits of a certain class of young men would be superior to any persuasive or semireligious method that the world has yet premonstrated.
What has been said concerning poisoning by the non-elimination of effete products refers also to the nerves and the brain. As the muscles work faster, so do the central nerve cells which send the stimulating impulses to these muscles. These latter cells become fatigued sooner than the muscles. This is a grand feature of physiologic economy, for, did not this condition exist, the muscle would be worked to an irreparable point. The muscular differences noted in individuals are in reality the difference in the nerve cells, the action of the muscle indicating the activity of the central nervous system. When the muscles are being exercised the nerve cells are being exercised, and the effect of exercise on the nerve cells indirectly determines the muscular activity.
It is the general impression among athletes that exhaustion and loss of wind is due to the inability to consume sufficient oxygen and exhale rapidly enough carbon dioxide. When the muscle is moving rapidly and forcibly it is true that it demands more oxygen, and gives off to the blood more carbon dioxide than when at rest. When a man is running as fast as he can make his limbs move he is able to keep up the pace but for a short distance unless, like the hunted hare, he runs to his death. On account of the forced, vigorous, and rapid muscular action in this case, the poisonous materials are thrown into the blood, to be carried to all parts of the body—muscles, nerves, brain. The heart is affected by this poison through the nerve cells controlling that organ; the muscles of respiration are similarly disturbed. The panting, distressed efforts of breathing, sidelong tumbling, anhelation, and final semiconsciousness of the hunted stag or hare are a good example of acute auto-intoxication ending in death. This latter deplorable condition is not unknown among the annals of human strife for athletic honors, even with our present advanced knowledge of physiology.
One of the main "clearing houses" of the body, by which the blood is cleared constantly of all its poison, is the liver. The minute cells of this organ each have their own individual work to perform in transforming the toxic material into harmless substances. The cells of this "clearing house" are delicate little organs, and will not stand abuse. All habits having a tendency to cause dyspepsia—eating ​rapidly, eating indigestible food, constant and intemperate use of alcoholic beverages, or excessive use of tobacco—disturb the normal work of the liver. Hence, one of the first aims of the athlete should be to keep this organ in the best possible condition. Any clogging or disturbance of the functional duties of the liver prevents the blood from being in a pure state. All parts of the body will show distressing symptoms of fatigue and exhaustion if the little cells of the liver have become diseased or useless through intemperate living and ignorance of the specific duties belonging to each separate organ of the human body.
The changes which take place in the nerves and brain, the changes in the irritability of the former, and the delicate relations which the latter bears to all forms of muscular work, are of too chemic and technic details to be dealt with in this paper. All forms of violent exercise require that the brain and nervous system should be in assured perfect health; that they possess all their normal attributes.
All neurologists have seen the unfortunate and distressing effects of excessive and violent exercise in persons unfit by training or nature for anything more than moderate exertion. The adolescent, the neurotic, and those who have passed their vigorous days, should exercise only under the advice of a physician. Let those who have entered into the false and foolish idea that "century runs" are an indication of prowess remember the ultimate sad consequences liable to follow in a few years. These misguided individuals should understand that to be an athlete for the time being does not mean that they will be healthy. Athletes are healthy, not because they are athletes, but because healthy individuals are athletes. For the average man past five and forty golf offers the best and safest exercise for the Anglo-Saxon. For those who imagine that this pedestrian and philologic game requires no mental effort, the statement made by a caddie to Professor Sellar will be instructive. When this distinguished Hellenist made his first appearance on the golfing green at St. Andrews, the mature caddie who accompanied him remarked, "Ye may be guid enough, professor, at teaching laddies Greek, but gouf needs a heid" Festina lente is a good rule in most of the concerns of life; it is absolutely indispensable in physical exercise.