Muscle Physiology Basis of the Strength Training Exercises for Muscle Development

The nervous system initiates and controls every movement of the body, and the energy required for the carrying out of physical exercises is developed in the muscles themselves, and their power to transform potential into kinetic energy, which appears as work or heat, and to renew their store of energy is the central] bet of muscular exercise. For a long time, physiologists were content to study the causes of the transformation of energy and the conditions which regulate the mechanical efficiency of the muscles. Their investigations, carried out for the most part on isolated muscle, yielded many valuable results, but the tendency to regard muscular exercise as almost exclusively a muscular act led to a narrow and imperfect conception of its true character. It has gradually become clear, however, that the processes taking piece in the muscles, important though they are, constitute only a fraction of the total activities of the body during exercise, and that muscular movement is a very different thing from voluntary exercise. 

Although the setting free of energy, when a muscle contracts, is a non-oxidative process, oxygen is necessary for the restoration of its potential energy, and, in the absence of oxygen, mammalian muscle rapidly loses the power of contraction. Further, since the energy of muscular work is ultimately obtained from the oxidation of the food-stuffs, the enormous increase in the amount of energy developed in the muscles during exercise involves a corresponding rise in the intensity of their metabolic activities and in the extent to which they consume oxygen. Indeed, it is now well known that the amount of oxygen which a man consumes is a criterion of the degree of activity of his muscles during exercise.

A man, who is performing hard physical exercises, may use eight or ten times as much oxygen as during rest, and the burden of meeting this demand for oxygen falls upon the respiratory and circulatory systems, which, for this purpose, are indissolubly linked together. Every increase in the requirements of the body for oxygen is accompanied by adaptive changes in the circulation and the respiration, which enable oxygen to be transferred more rapidly from the lungs to the tissues; and the rapid, deep breathing, the powerfully beating heart, the high blood-pressure, and the frequent pulse, present in the man who is engaged in violent exercise, are just as much a part of the exercise, and just as vital to its effective performance, as the movements of the muscles themselves. Violent exercise taxes the resources of the circulatory and respiratory systems equally with those of the muscles; and, partly because it is called upon to maintain an adequate supply of oxygen to the brain as well as to the muscles, partly, perhaps, owing to the larger number and greater complexity of the adjustments required for this purpose, the heart, as a rule, reaches the limit of its powers earlier than the skeletal muscles, and its functional capacity determines a man's capability for exertion. It is clear, then, that, apart from the changes taking place in the muscles themselves, the activities of the rest of the body are largely directed during exercise to the provision of an adequate supply of oxygen for the muscles, the heart, and the brain; hence any picture of muscular exercise must include the whole range of these activities.

Muscular exercise thus presents three problems. The first is the changes taking place in the skeletal muscles, whereby the transformation of energy, which constitutes muscular movement, is effected; the second is the nature of the adjustments occurring elsewhere in the body in order to provide the muscles with the oxygen and food-stuffs required for this purpose; and the third is the means by which these are interwoven and bound together to produce the fabric of muscular exercise.

If the body is to work efficiently and to develop its physical powers to their fell extent, it is absolutely essential that the movements of the muscles on the one hand, and the activities of the circulatory and respiratory systems on the other hand, should be coordinated and integrated into a harmonious whole. Perfect co-ordination brings about the maximum of work with the minimum of effort. Incomplete co-ordination, on the contrary, inevitably spells inefficiency. An exaggerated response on the part of the respiratory and circulatory systems involves a useless expenditure of energy ; a deficient response rapidly throws out of gear the controlling influence of the nervous system, cripples the energies of the skeletal muscles, and renders exercise ineffective or even impossible. In order to realize the completeness to which this co-ordination can attain, and the effects of even the slightest disturbance of the balance between the activities of the muscles and of the rest of the body, it is only necessary to watch a trained and an untrained man running in a race or engaged in some other form of exercise. In the former, every organ is working smoothly, and is contributing its proper share towards bringing about the perfect harmony of action which is requisite for efficient exercise. In the latter, the leas perfect adjustment of the body is evident, both to the man himself and to others, in the greater sense of effort, in the clumsiness of movement, and in the more severe respiratory and circulatory distress.
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