INFLUENCE OF EXERCISE (a) On burns up carbonaceous ma terial but does not increase the nitrogen consumption. The chief carbonaceous fuel is dextrose, which is stored up as a reserve fuel in the liver in the form of glycogen. During exercise the dextrose is oxidized to lactic acid, and if sufficient oxygen is present, to carbon dioxid. Not only does exercise bring into activity the muscular tissues, but all the other organs of the body as well. These activities involve both anabolism and kata bolism. If exercise is so great that anabolism cannot build up what katabolism destroys, the individual loses weight.
(b) On the Flow of Blood and Lymph.--This is at a maximum during work, due to an automatic dilation of the blood vessels in the muscles. This is assisted by the pumping effect which the rhythmic heart action has on the veins.
(c) On the heart readily adapts itself to exer cise. This is accomplished by the metabolites, and by cerebral impulses to the skeletal muscles which inhibit the vagus tone.
(d) On the Arterial Pressure.—This is increased, a constriction of the splanchnic vessels to compensate for the dilation of the cutaneous and mucular vessels, thus increasing the pressure. The amount of the pressure varies with the exercise. Its function is probably to supply a head of pressure, so that if there is a demand on one part of the body the blood may flow there without leaving the rest unsupplied. A blood pressure of about no mm. of mercury will produce a decreased
muscular efficiency. In a healthy person exercise will im mediately cause the pressure to rise, it then soon falls some what to a constant level which is maintained during the period of exercise, then falls below normal with rest and gradually is restored.
(e) On carbon dioxid produced causes a deepening and quickening of respiration.
(j) On Heat Production and increased fuel consumption of exercise results in the production of con siderable heat. This requires the action of the heat regulating mechanism, so that the body temperature will not ascend too high. Exercise may cause a rise of as much as four degrees Fahrenheit above normal.
(g) On stimulation of the sweat glands causes an increase in the amount of perspiration. By this means water and salts, chiefly the former, are eliminated.
(h) On Digestive and absorption go on equally well with rest and muscular exercise. On the other hand, exercise increases the appetite and decreases constipation by stimulating the activity of the colon.
(i) On is promoted by the development of a healthy fatigue.
(j) On Muscular tissues not involved in exercise undergo an atrophy. On the other hand, exercise increases the size of muscle fibers but not their number. If the muscular fibers are overworked, permanent shortening results and the individual is said to be "muscle bound."