Definition - Exercise in Relation to Health and Development - Rest - Fatigue - Nature and Duration of Healthy Exercise.

Definition

EXERCISE may be defined as "exertion or labour of the body for purposes of health or development of the natural powers" (Lloyd's Encyclopoedic Dictionary); and work, as exercise undertaken for purposes extraneous to the horse. In training, the term "work" is often used for "exercise."

Exercise In Relation To Health And Development

In writing of exercise under this heading, I assume that the bodily exertion is not carried to an extent which would produce fatigue.

As the animal body has been evolved under conditions of frequent movement, exercise is necessary for maintaining it in health, that is to say, in its ordinary condition. In other words, as "the function makes the organ," the existence of an organ is dependent on the exercise of its function, as we may see in cases of paralysis. For instance, when certain muscles of the larynx suffer from the form of paralysis which causes "roaring," they gradually waste away, and at last become converted into fibrous tissue. Exercise is therefore needed for maintaining the balance between bodily waste and bodily repair. The effect of the exercise of the limbs is not confined to the muscles of movement and their adjuncts (tendons, ligaments, and bones), but extends to the entire system. Exercise quickens the circulation of the blood, by which means development of tissue is promoted, and secretion and excretion are stimulated. By stimulating the circulation of blood in the surface of the body and by quickening the action of the lungs, exercise entails a loss of water from the system proportionate to its severity, as we may see from the following results obtained from experiments made by Grandeau : -

These amounts would of course be greatly influenced by differences in temperature. Under ordinary conditions, the quantity of water removed from the system by the kidneys (in the form of urine) is on an average about double that given off by the lungs and skin; a difference which exercise tends to reverse. For instance, during severe exertion, the skin of a man may give off two and a half times the quantity of water which is discharged in the urine. The increased activity of the skin and lungs during exercise is essential to health, for removing the extra heat and carbonic acid caused by work. Exercise increases the bodily temperature, which may experience a rise even up to 50 F. from severe work in hot weather; such an increase of heat being naturally accompanied by more or less exhaustion. As the drinking of water promotes perspiration; we may conclude, especially as theory in this case is backed up by practical experience, that horses during labour should not be deprived of water for a long time. We all no doubt have enjoyed the refreshing effect of a drink of water or of a fluid largely consisting of water, when we have been hot and tired after severe exercise, and have felt that the skin, which had been previously hot and dry, became moist and cool from perspiration almost immediately after the fluid had been swallowed. The rapidity of this effect, and the fact that after a copious sweat, the drinking of a large quantity of water will be followed by a comparatively small increase in the amount of urine discharged, show that a considerable portion of the water lost during exercise, is a necessary part of the solids and fluids of the body, and consequently no avoidable delay should occur in its replacement. A full supply of water is not only necessary for removing heat by evaporation, but also for keeping the bowels, kidneys, and other organs in good working order. As the necessity for the cooling effect of evaporation from the skin is proportionate to the exercise taken, other things being equal, the severer and more prolonged the exercise, the cleaner should be the skin and the shorter should be the coat, so that as little impediment as possible may be offered to the escape of perspiration into the air.

As long as exercise is continued, there is practically no danger of chill. But if a horse is pulled up when hot from work and is kept standing in a cold atmosphere without anything being done to protect him from its bad effects, he will be specially liable to catch cold; because the cooling process of evaporation will continue to remain unduly active for a longer or shorter period, during which, the supply of extra heat to the skin from the action of the muscles will be cut off.

Exercise improves the quality of the structures affected by it, and disuse has the opposite effect. Thus we find that a horse out of training is peculiarly liable to injury from unwonted exertion; not only because the muscles, tendons, ligaments and bones of his limbs are wanting in strength and resistance, but also because he will suffer far more severely from fatigue, than a horse in hard condition would do; on account of the comparative inactivity of his powers of excretion. Lymphangitis and azoturia are diseases which are closely connected with want of exercise.

Muscular development "is due in part to the growth of the pre-existing fibres, and in part to the formation of new fibres" (Halliburton).

Owing to the fact that horses when in a state of nature spend a considerable, if not the greater, part of the twenty-four hours in movement, their limbs cannot bear long enforced idleness without becoming more or less unsound. Hence we find that stabled horses which have too little exercise are liable to get swelled legs, especially behind; because the hind legs being farther from the heart than the fore ones, the circulation of blood in them is more torpid. Also, from want of pressure, the growth of the frog becomes diminished, and consequently its secreting membrane becomes liable to inflammation, which is made manifest by thrush. The habit of standing on cold stones appears to be a not un-frequent predisposing cause of navicular disease. Long continued standing, as on board ship (p. 371), is a fertile exciter of laminitis (fever of the feet). It seems probable that this variety of laminitis is set up by waste nitrogenous material (pp. 56, 122 and 123), the deposition of which would be favoured by the slowness of the circulation in the feet of an unexercised horse, and by their coldness.

As the tissues can utilise the nutritive materials which they receive from the blood only at a slow rate; exercise for both health and development should be long continued during the day, and from day to day.

Rest

As the energy (p. 10) expended by the body, even during slow walking, is greater than that obtained from the blood in the same time, the system requires rest proportionate in length to the effect which the exertion has had on it, so as to allow time for the assimilation of the necessary potential energy and for the removal of poisonous products (p. 56). Although the heart, which is a hollow muscle, appears to be in constant work, it has a succession of brief periods of rest and of labour, the former being about twice as long as the latter.