CHAPTER III.

LOCAL EFFECTS OF EXERCISE.

Effects on neighbouring parts. Useful Effects: Compression of Vessels by the Contracting Muscles; Quickening of the Circulation as a result-Disappearance of Edema during ExerciseInjurious Effects of Muscular_Contraction: Excessive Compression of Internal Organs-Dangers of Effort—Effects of Work on Muscle-Useful Effects: Increase in Size-Injurious Effects; Wasting of the Organ through Excessive Work—The Accidents of Work. Muscular Ruptures-Tendency of Muscular Fibre to Shorten through Excessive Work-Semi-flexion of the Fore-arm in Gymnasts-Dangers of Muscular ContracturesHow Deviations of the Spine are produced by Ill-planned Exercise.

MUSCULAR work produces local effects of two kinds. The first kind occurs in the muscles themselves, in the bones which are moved, and in the joints which are the centres of movement. The second occurs throughout the region in which the movement takes place, and concerns organs which take no direct part in the exercise. We shall study separately the direct effects of muscular contraction, and its effects on neighbouring parts.

I.

The chief effects observed in the regions which are. the seat of repeated muscular movement are due to the compression which the muscle, in becoming shorter and thicker, exercises on neighbouring parts. This compression may either affect vessels containing fluids, such as the lymph and the blood, or more solid materials, as the intestinal contents, and the pressure may thus be transmitted to remote points. Hence result effects which are not strictly localised, and which serve as a connecting link between the local and the general effects of exercise.

In this manner the contraction of the abdominal muscles during exercise may influence the digestive functions by driving onwards the intestinal contents. An exercise which brings the abdominal muscles into action is thus favourable to defæcation, and can cause the disappearance of digestive disorders due to constipation.

Similarly, the compression which the muscles exercise on the capillary vessels gives a more active impulse to the blood-current, which is transmitted even to the heart, just as pressure on an india-rubber tube filled

with water is transmitted to the elastic reservoir with which this tube communicates. In this manner the local contraction of a muscle can influence the general circulation. We know that stagnation of blood, in motionless limbs, can produce oedematous swelling, and we also know that such limbs can regain their normal size under the influence of exercise which causes contraction of the muscles, and mechanical acceleration of the blood-current in the capillaries.

The effects of muscular compression on the neighbouring parts are not always useful: exaggerated contraction. can lead to accidents. Thus, too powerful contraction of the abdominal muscles can make the intestines, by great pressure, distend a natural orifice and become engaged there. It is thus that herniæ are produced in the inguinal or crural canal through the passage of an intestinal coil subjected to too great pressure. This accident is most commonly produced during the act of effort, which demands, as we have explained, a very energetic contraction of the abdominal muscles.

Still more serious accidents may happen during very powerful contraction. An essential condition of effort is the compression of the distended lungs, which serve to support the ribs. An energetic compression, proportionate to the intensity of the muscular work, is exercised during the effort on the great thoracic vessels, and even on the heart. It may happen that the pressure exercised on the vessels is sufficiently strong to cause a back tide of blood in the capillaries of the lungs or

brain, and to bring about laceration of these vessels, and pulmonary or cerebral hæmorrhage.

Rupture of the great veins of the spine has been observed from the effect of too violent an effort. In this case there occurs a hæmorrhage in the spinal cord which causes paraplegia, that is to say, paralysis of the parts of the body below the lesion. We may frequently see a horse, harnessed to too heavy a cart, give an energetic pull, and fall with its hindquarters paralysed. Through too violent an effort the animal has broken-not its back, as is commonly said-but a vessel in the spinal cord, and paraplegia has ensued.

Ruptures of the heart have even been recorded in consequence of very violent efforts. violent efforts. A porter at Bordeaux had made a wager that he would lift a full hogshead. In the superhuman effort he made to raise this enormous burthen, his heart was ruptured and he dropped down dead.

These mechanical effects of exercise are, as we said above, on the borderland between the general and the local effects of exercise. We are now going to describe those which are strictly local.

II.

Muscular contraction may be the cause of useful effects, and may also occasion accidents and various lesions. Among the disagreeable effects of exercise, some are the inevitable result of muscular contraction; others occur accidentally, either through a vicious method of performing the work, or owing to defective resistance in the organs which perform it.

Numerous cases have been recorded of rupture of muscles during the performance of muscular actions. These ruptures are always produced when a muscular fibre contracts with an energy which exceeds its own power of resistance. They are often the consequence of a badly co-ordinated movement. If, for instance, only one muscle is employed in the performance of an action for which a muscular group is needed, it will break just as a cord breaks when employed to lift a weight which is too

heavy for it. Or the defective co-ordination consists in this, that the part to be moved is solicited by a sudden effort to pass from immobility to motion, instead of doing so gradually. Thus unforeseen movements are a frequent cause of muscular ruptures when they are performed with great energy or speed.

Sometimes an awkward contraction tends to shorten a muscle just when a mechanical cause is tending to stretch its fibres. The muscle, subject to two opposing influences, is torn. We owe to our friend Dr. J. Lemaistre the observation of a man who, in the gymnasium, broke a great part of his pectoral muscle. He was a young soldier performing a circle on the rings, under the dread of the brutal menaces of his drill-sergeant. Impelled by the fear of being punished if his attempt were not bold enough, and restrained by the fear of a movement which was new to him, the gymnast, after violently launching his body so as to make a revolution from before backwards, endeavoured to check himself, at a moment when his body was moving with great speed. His body was at this moment as far as possible from his arms, these being above his head. In this position of forced adduction, the fibres of the pectoral-an adductor musclewere as much stretched as possible. Then an effort at contraction, increasing the already excessive tension, produced their rupture. The inferior two thirds of the muscle were torn through their whole thickness.

These effects of exercise, whatever interest they may have for the surgeon, need not occupy us further, for their mechanism is sufficiently obvious, and their production is quite accidental. We shall pass on at once to other phenomena intimately connected with the physiological process of muscular contraction, and which are the inevitable results of work.

III.

Among the most striking effects of muscular exercise, are the changes undergone by the muscles themselves under the influence of work. The muscles increase in

size, and their structure is at the same time changed; they lose the fat which infiltrates their fibres, and tend to be reduced to their own proper elements, the muscular fibres, the density of which, being greater than that of other tissues, gives a characteristic firmness to the region which works. Further, the surrounding fat is burned up, as well as that which formed a constituent part of the organ. The cellular tissue in the midst of which the muscles were imbedded, is burned to feed the combustions, and the whole region undergoes a change of form characterised by the appearance of prominences and hollows; the muscles stand out. We may thus, merely by inspecting a man given to violent exercise or laborious toil, determine what parts of his body are chiefly concerned in the muscular work.

The increase in size of the muscles under the influence of work is due to the greater activity of the circulation during contraction. When a limb works, the blood flows to it, drawn by a physiological force which is difficult to explain, but the effects of which are felt in all organs which work, and during the performance of all functions. The process in virtue of which there is an increased supply of blood to a muscle during work, has for its object to provide this organ with the materials necessary for combustion. Muscle in fact cannot produce work without producing heat; but when it does this, it is at the expense of certain substances brought to it by the blood, and it only burns up its own materials when the supply from without is deficient. So we only see a muscle diminished in size by work in cases of organic exhaustion, when the impoverished constitution cannot supply blood rich enough in combustible materials.

Thanks to the unceasing supply of materials from the blood, the muscle does not use up its own substance unless the contraction be exaggerated or unduly prolonged. In cases of persistent overwork the muscles end by losing in size and feeding on themselves, as we see in certain professional runners whose legs are extremely small, owing to the manner in which they have been abused. The muscle which performs excessive work