Muscle tension

“ It has been stated, that the excessive use of the muscles, as much as their inactivity, tends to weaken them. Nothing is more painful, than the keeping a muscle constantly on the stretch, without any relaxation [Pg 133] or change. This can be realized, by holding out an arm, perpendicularly to the body, for ten or fifteen minutes, if any one can so long bear the pain. Of course, confinement to one position, for a great length of time, tends to weaken the muscles thus strained. ”

“ That is to say, in the average constitution, no superfluous strength is possessed by any of the appliances for circulating the blood. Take, again, a set of motor organs. Great strain here causes the fibres of a muscle to tear. There the muscle does not yield but the tendon snaps. ”

“ He should make frequent attempts by stretching the rigid groups to overcome the spasm, which in large muscle-masses may be done by grasping with both hands, taking care not to pinch, and pulling the hands apart in the line of the muscle's long axis, thus stretching the muscles. Pressure will sometimes accomplish the same end, and it will be found in certain cases that by kneading during action,—that is, while the patient endeavors to produce voluntary contraction,—the result will be better. ”

“ A contracted muscle, according to this view, is like a strong band of india-rubber pulling on two pieces of wood and drawing them together. In like manner, when a muscle contracts, a similar elastic power is developed that pulls upon the bones and causes movement. When the contraction ceases, the muscle returns to its original length, again by elasticity, but acting in the opposite way.
What is this property of irritability by virtue of which the muscle responds to a stimulus and contracts? ”

“ Action of a nerve—Rapidity of nerve-current—Nature of nerve-current—Analogy with electric current—Nerveless animals—Heat in muscle—Muscles liberate mechanical energy and heat—Chemical changes in muscle.
We have now seen that the living matter forming a muscle is irritable or excitable, that is to say, it responds or reacts to a stimulus. We have also learned that the muscle shows its response or reaction by a contraction. Lastly, we have found that the natural stimulus that sets the muscle into action is something that happens in a nerve. ”

“ To a gradually increasing extent, the contracting force, instead of being withdrawn when the muscle is inactive, remains; and, as we have already seen, an arm or leg that should be passive is lifted, and the muscles are found to be contracted as if for severe action. ”

“ But don’t think for a moment that physiology lends itself to the cult of muscle. Here is a youth whose biceps are his better part: like most of us, he gets what he aims at—some local renown as an athlete. But what does he pay for the whistle? His violent ‘sports’ do not materially increase the measure of blood which sustains him: if the muscles get more than their share, their gain implies loss elsewhere, to the brain, commonly, and, indeed, to all the vital organs. ”

“ We have now seen how nerves and muscles may be irritated in a definite and precise way, and we have found that the irritation of its nerve causes a contraction of a muscle. In the case of a single twitch, however, the movement is too rapid to be appreciated, and still less analysed, by the unaided eye. We cannot tell, for example, whether the contraction occurs in a shorter time than the relaxation, and still less whether the contraction is at a uniform rate in time, or whether it contracts faster at the beginning and more slowly towards the end, or the reverse. ”

“ When the nerve discharges its influence into the muscles, a very rapid molecular change takes place in the substance contained in the cartouches or muscular boxes, which contract, pressing their ends close together. Scarcely has the action of the nerves ceased than they relax and resume their previous form. It is well known, that when a muscle contracts, it becomes thicker and shorter; it suffices to take hold of the arm a little above the elbow and then to bend it in order to feel how the biceps muscle swells and hardens. ”

“ Indeed, all that I want to bring about muscular contraction is, not a metamorphosis of muscle which issues in the development of muscular force, nor a transformation of heat into muscular force, but simply a supply of electricity during the state of muscular inaction which will counteract the tendency which the muscle always has to contract as an elastic body. ”

“ If I move my arm slowly and attend to my feelings, I am conscious of a peculiar impulse immediately preceding each muscular contraction, which I feel to be the cause of the latter. If I temporarily paralyze my arm by compression of the nerve and repeat the experiment, no muscle contracts, but I distinctly feel the impulse referred to. ”

“ The fourth state of muscular contraction is when the muscle is doing negative work, i.e. when work is being done on it, as for instance when we go downstairs, or when a descending weight forces down the opposing arm which attempts to support it. ”

“ The greater the displacement of the line of gravity, the greater the muscular effort required to maintain the equilibrium of the body. Up to a certain extent, exercising the muscle develops the strength and size of the muscle. On the other hand, when a muscle within the body is unused, it wastes; when used within certain limits, it grows. But when the corset splint is applied to the body of the young girl, it supplants the functions of the abdominal and back muscles, which is to hold the trunk erect, and these muscles gradually grow weak and waste. ”

“ We can now go a step further and ask the question, What is there in the blood that thus gives to the muscle the power of contracting, that in other words keeps the muscle alive? The answer is very easily found. What is the name commonly given to this power of a muscle to contract? We generally call it strength. Lay your arm straight out on the table, put a heavy weight in your hand, and try to bend your arm. If you could do it, one would say you were strong; if you could not, one would say you were weak—all the stronger or weaker, the heavier or lighter the weight. ”

“ How the Muscles do their Work.—A tiny nerve [Pg 143] thread runs from the spinal cord or brain to every muscle thread. Messages sent through the nerve threads to the muscles make them act. A muscle can act in only two ways (Fig. 84) . It can become shorter or longer. When it gets shorter, we say it contracts. When it stretches out, it is said to relax.
A muscle cannot contract more than one fourth of its length. To pull the forearm up, the brain sends a message to the muscle fixed by one end at the shoulder and by the other end to a bone at the elbow. ”

“ Upon this subject I have made a remark, it is that the quickness and the force of the contractions are not commonly greater if we irritate at the same time all the nerves that go to a muscle, than if we irritate but one. ”

“ We ought to look also to exercise for local effects; in order, in the first place, to keep the joints supple and counterbalance the tendency to incrustation of the cartilages, which is one of the consequences of age; and, in the second place, to keep the muscles as a whole in sufficient strength and volume. The muscle, as we have read, is "the furnace of vital combustion," and in developing the muscular tissue we favor the activity of combustion and the destruction of the refuse of nutrition. ”

“ This relative decrease in the power of bearing stress does not imply a relative decrease in the power of generating energy and moving the body; for in the case supposed the muscles have not only increased four times in their transverse sections but have become twice as long, and will therefore generate an amount of energy proportionate to their bulk. The implication is simply that each muscle has only half the power to withstand those shocks and strains which the creature's movements entail ”

“ Fig. 112—Muscle cells from the heart, highly magnified (after Schäfer) . The Muscular Stimulus.—The inactive, or resting, condition of a muscle is that of relaxation. It does work through contracting. It becomes active, or contracts, only when it is being acted upon by some force outside of itself, and it relaxes again when this force is withdrawn. Any kind of force which, by acting on muscles, causes them to contract, is called a muscular stimulus. Electricity, chemicals of different kinds, and mechanical force may be so applied to the muscles as to cause them to contract. ”

“ A muscle can only remain in a state of contraction for a few seconds, because the force of the muscular fibers is more or less exhausted during contraction. The more rapid the contractions, the sooner does fatigue manifest itself.
Like the steam engine, the muscles of the body, in performing their work, produce heat and motion. The fuel which supplies this force is taken into the body in the shape of food; it is prepared for use in the intestinal tract, and from there carried by the blood, to be stored up in the muscles and various tissues as latent force. ”

“ In this view of the matter the normal condition of the muscle is one of charge, of elongation. Contraction results from the simple elasticity of the muscle itself, the function of the nerve being only that of a discharger. Whether this theory represents the actual fact or not, in all its details, it is supported by the existence of rigor mortis, by the continued relaxation of muscle during the flow of the current, by the cessation of contraction on the free access of blood, and by many other phenomena otherwise difficult to explain. ”

“ Exercising a muscle develops it up to its physiologic capacity, but if a muscle is habitually overworked, pathologic results occur, and instead of a quick, sharp contraction of the muscle, the contractions will be weak and uncertain, and, if carried too far, the muscle may eventually atrophy from overwork. ”

“ From these facts, as well as from the great force with which the muscle contracts, one must conclude that the muscle is a transformer of energy—that within its protoplasm, chemical changes take place whereby the potential energy of oxygen and food is converted into the kinetic energy of motion.
Fig. 113—Capillaries of muscles. Plan of Using Muscular Force.—Two difficulties have to be overcome in the using of muscular force in the body. The first of these is due to the fact that the muscles exert their force only when they contract. They can pull but not push. ”

“ There can be no doubt that when we firmly contract a muscle and maintain the contraction, the muscle is in a state of tetanus, in which the quivers of the partial contractions can be seen. We all know how difficult it is to keep the hand or arm quite steady. They tremble, and we can feel the vibration. ”

“ If the injury be really to the nerves which control the muscles, as is generally the case, the matter is more difficult. The muscle swells, but this is primarily due to the overstrain of the nerves in the sudden effort they make to bear a crushing load on the muscle. The pain is from pressure in the swelling, and also from inflammatory action. ”

“ The duration of the contraction of the voluntary muscles, in some measure, is in an inverse ratio to its force. If a muscle has contracted with violence, as when great effort is made to raise a heavy weight, relaxation will follow sooner than when the contraction has been less powerful, as in raising light bodies. ”

“ There are almost no motions performed by single muscles. Most activity results from the contraction of a group of muscles and these are usually in delicate balance with other groups of muscles which either assist or prevent overaction. The delicate adjustment of muscle groups, which is normally present, results in co-ordinated movements. Following nerve disease or, for that matter, the immobilization of joints and muscles, co-ordination is usually lost to more or less degree. Muscles must be re-trained to work together. ”

“ Most of the muscles act upon the bones, so as to produce the effects of a lever of the third kind, as it is termed by mechanics, where the power acts between the centre of motion and the weight; hence it has a mechanical disadvantage; as an instance of this, the muscle which bends the forearm, is inserted about one eighth or one tenth of the distance from the centre of motion that the hand is, where the weight or resistance is applied; hence the muscle must exert a force eight or ten times greater than the weight to be raised. ”

“ The muscle-engine, in like manner, deteriorates if it is allowed to stand idle. Sometimes this occurs in disease. In paralysis the limb cannot move, and the inactive muscles waste, become thin and flaccid, and undergo curious molecular changes, converting the muscular matter into fatty-like particles. ”

“ First, we have from the muscles the sensation of physical fatigue. If the skin over a muscle is rendered anæsthetic, and the muscle is thrown into forced contraction by an electric current, we have, to begin with, a dull dead pressure; as time goes on, or if the strength of the current is increased, this pressure becomes dragging, the sensation of fatigue; and finally it becomes sore and achy, and passes over into dull pain. From the tendons we get a sensation which, when we are actively pushing or pulling, we call effort, and when we are passively holding or resisting we call strain ”

“ There is a disturbance of the normal smooth-running, indeed almost frictionless, mechanism by which muscles glide over one another. There are practically a series of joints in all muscular groups so as to permit just as free a play as possible of muscles over one another. Each muscle is covered with a glistening membrane so familiar {392} from our dissecting room days, which secretes a substance resembling a synovial fluid, to enable muscles to move upon each other without friction. ”