Muscle and Muscular Exercise

After violent exertion, recovery may take a considerable time, up to 8o minutes for the case when exercise was prolonged as well as strenuous. Even 'co yards run at top speed may require 5o minutes for complete recovery. Fitter individuals tend to have a higher recovery rate.

The Effect of Breathing High and Low Pressures of Oxy gen.—During prolonged and strenuous exertion unpleasant sub jective feelings may be much relieved by breathing oxygen instead of air, and measurement shows that under such conditions a con siderable rise in the oxygen intake may .take place. The blood, rushing at high speed through the lung capillaries, apparently does not collect its full quota of oxygen unless diffusion through the lung membranes is quickened up. Conversely, by low oxygen pressures the unpleasant subjective feelings may be aggravated and the rate of oxygen intake diminished. This is of great im portance at high altitudes; no amount of "acclimatisation" will compensate completely for the lower pressure of oxygen in the lung alveoli. At high altitudes dyspnoea more rapidly sets in, the tendency to work by incurring an oxygen debt is more insistent, while at extreme heights the rests for recovery become more fre quent since the oxygen income is so largely diminished. The ad ministration of oxygen brings immediate relief, by quickening the passage of oxygen into the blood, as well as by supplying the brain and heart with oxygen at a higher partial pressure.

Muscular Training.

Very little physiological knowledge ex ists as to the nature of the changes that come over the body during muscular training. There are many possibilities: (I) Better muscular co-ordination, involving more economical and better di rected movement ; (2) an improvement in those chemical relation ships of the tissues which determine the speed of recovery; (3) greater mechanical strength in the connective tissue of the muscles and in the sarcolemma of the fibres; (4) an increased oxygen carrying power of the blood; (5) a more complete capillary circu lation, and a better lymph supply; (6) an increase in the alkali reserve of the blood and muscle fibres, resulting in a greater lactic acid tolerance; (7) an increase in muscle glycogen, and possibly in the phosphate intermediaries of the lactic acid break down; (8) a more powerful heart beat, perhaps due to improve ments in the coronary circulation.

The list might be extended considerably, but to little purpose. To illustrate the inadequacy of present knowledge the case of muscular stiffness may be cited. Some individuals readily become stiff, others do not. A fit and healthy man may be reduced to the extremity of stiffness by a few seconds of unaccustomed exercise: yet, on another occasion, having been "trained" by a few previous bouts of the same exertion, he is completely unaffected. This case is mentioned specifically because the layman, discussing muscular exercise with a physiologist, often tends to ask the cause of muscular stiffness, to which, at present, if he be honest, the physiologist must reply that he does not know.

BIBLIOCRAPHY.-Publications

of the Industrial Fatigue Research Board, H.M. Stationery Office, London ; Publications of the Nutri tion Laboratory, Carnegie Institution, Washington ; F. A. Bainbridge, The Physiology of Muscular Exercise (2nd ed. rev. 1923) ; Sir W. M. Bayliss, Principles of General Physiology (1924) ; J. Barcroft, The Respiratory Function of the Blood; Part I. "Lessons from High Altitudes" (1925) ; J. F. Fulton, Muscular Contraction and the Reflex Control Movement (1926) ; J. J. R. Macleod, Physiology and Biochemistry in Modern Medicine (1926) ; E. H. Starling, Principles of Human Physiology (1926) ; A. V. Hill, Muscular Activity; Lec tures on the Herter Foundation, 1924 (1926), Muscular Movement in Man; George Fisher Baker Lectures in Chemistry, Vol. III. (1927), Living Machinery : Lectures before a "juvenile auditory" at the Royal Institution (1927). (A. V. H.)