Exercise in education and medicine / by R. Tait McKenzie.

  • R. Tait McKenzie
Date:
1909
Catalogue details

Licence: Public Domain Mark

Credit: Exercise in education and medicine / by R. Tait McKenzie. Source: Wellcome Collection.

    29/418 (page 29)
    CHAPTER II THE PHYSIOLOGY OF EXERCISE Bodily movements affect profoundly the motor apparatus, the vessels which supply it with nourishment in the form of blood and lymph, the storehouses of nutrition in the abdomen, and the controlling and directing mechanism of brain and nerve. The impulse to contract a muscle begins at its motor center in the brain or spinal cord, and is carried to it by a motor nerve. Each muscle-cell shortens and thickens, scattering some of its sub¬ stance into the lymph-space encircling it, and absorbing food con¬ sisting of carbohydrates and oxygen from this surrounding plasma. By repeated contraction the cells increase in size and number, the perimysium is strengthened, the fibrous wall surrounding the bundle of cells is invigorated, and fresh power is imparted to the sheath inclosing the entire muscle. The result is an increase in bulk, in strength, and in elasticity. The tone of a healthy muscle keeps it in slight contraction even when at rest, so that antago¬ nistic groups retain the inactive limb in normal position, but con¬ stant overaction and strengthening of one group of muscles increases this normal tension until the accustomed pose becomes habitual, as in the curved finders or bent arms of the oarsman or weight- O O lifter. During contraction there may be actual rupture of the cell- walls and exudation of blood and lymph. This is one of the two causes of muscle soreness found after severe straining exercise. The other cause is the presence of irritating waste matter imper¬ fectly carried off by the blood-stream. This process of elimination is improved if the muscle be kept warm, but as muscular action generates heat, this usually regulates itself. When the limb is cold or inactive, the heat of the muscles must be enkindled by prelimi¬ nary massage and light exercise before undertaking with safety anv J O O CO j y