MUSCULAR ACTION 389 



In developing strength the muscles and their nutrition are almost 

 solely concerned, although the exercise involved indirectly tends to 

 develop all parts of the body (see below). It is not easy to find any data 

 of a precise histological nature on the effects of long-continued exercise 

 or work on the muscle-fiber itself, either smooth or cross-striated, but 

 the effects on a muscle in general are fairly well known. In the first 

 place, when a muscle by working becomes stronger, it grows somewhat 

 larger, and this notwithstanding that the thin layers of fat within the 

 muscle are oxidized and disappear. The muscle-fibers probably in- 

 crease not only in number but in size as well. A second condition obvious 

 in a strong muscle (and a better strength-index than size) is hardness or 

 tone together with an increase of elasticity. The growth of the fiber 

 distends more fully the sarcolemma and that of the fiber-bundles their 

 coverings of fascia. In an abundantly fed muscle the elasticity is greater 

 than in one poorly fed. A fourth change which takes place as a muscle 

 strengthens is a marked increase in the collagen coverings (sarcolemma, 

 fascia, aponeurosis, etc.) of the muscle-bundles. These membranes 

 are very strong and elastic, for their function is to keep in place the muscle- 

 fibers and muscle-bundles which are more than half liquid, allowing them 

 at the same time to glide with little friction over or within each other. In 

 a poorly nourished man, especially if at the same time his muscle be 

 overworked, these coverings are especially prominent, developing out of 

 proportion to the protein muscle-fibers. This consideration has a 

 bearing on the contention of Chittenden that most men eat far too much 

 protein, being against the supposition as applied to those who do much 

 muscular work. A fifth but accessory change in a hard-worked muscle 

 is a development of the blood-vessels to allow of a freer nutritional supply 

 and excretion. There is a corresponding new-growth of nerve-fibrils 

 which more than replaces those lost by metabolic and mechanical wear- 

 and-tear, especially at the beginning of training. 



In developing skill (delicacy and accuracy of adjustment), a group of 

 muscles develops not only itself and its immediate blood- and nerve- 

 supply, but without a doubt no small part of the nervous system also. 

 A man who is very skilful in one set of muscular movements has acquired 

 much more than adroitness with that one muscular mechanism, for he 

 has learned how to become generally skilled, and his neuro-muscular 

 mechanism has developed to a higher degree of efficiency in every sort 

 of activity. 



In just what this sort of development consists so far as the muscle is 

 concerned is not yet known, nor indeed are certain data at hand as to 

 what then happens in the nervous system. Keeping in mind the nature 

 of the nervous system, especially its fibrillar structure, we may suppose 

 that in the muscles there is a proliferation of afferent and efferent end- 

 organs, and that in the cortex cerebri (on both sides of Rolando's fissure 

 or in the cerebellum) a corresponding increased interlacement between 

 neurones develops. This sort of difference between muscles capable 

 of fine adjustment and those incapable of it is apparent in the number 



