Katzenstein3 finds that the metabolism during the descent of a mountain is less by 10 per cent, than the increase caused by walking on a level surface. The muscles which act to inhibit a too rapid descent are not required to be so active as those which give forward impetus to the body on a level road.

This idea has been still further investigated by mountaineers,4 who compared the actual heat production with the energy of metabolism during one minute for horizontal motion and for ascent and descent of a mountain path which had a 25 per cent, incline. The results were as follows:

1Zuntz: "Pfluger's Archiv," 1903, xcv, 192. 2 Brezina and Reichel: "Biochemische Zeitschrift," 1914, lxv, 35. 3 Katzenstein: Loc. cit., p. 376.

4 Zuntz, Loewy, Muller, and Caspari: "Hohenklima und Bergwanderungen in ihrer Wirkung auf den Menschen," 1906.

The smallest liberation of heat occurred during the ascent of the mountain at the time when the energy of metabolism was being converted into energy of position.

The largest heat production occurred during the descent of the mountain. The metabolism was the least, but energy of position was converted into heat through the vibration of the body at each footfall.

Zuntz and Schumburg1 find an increase in the metabolism of a marching soldier if the knapsack be badly placed, or if the body be sore and weary.

Lavonius2 finds the maximum amount of work attainable by a trained wrestler of great reputation to be the equivalent of 30 kilogrammeters per second.

Details of the effect of position upon the metabolism of individuals have been repeatedly published by Benedict and his pupils. Perhaps the most interesting of these studies may be taken from the work of Benedict and Murschhauser3 upon the basal metabolism of the professional bicycle rider, M. A. M. The results may thus be summarized:

* As in rapid walking.

A subject of very great interest is the result of training. It is well known that if a cobbler, for example, be removed from his trade and be compelled to climb a mountain, he will at first be of little use as compared with a Swiss guide. But after continued practice the blood-vessels dilate at once in response to the needs of the muscles and the heart expends less energy; unnecessary motions with the arms and legs are diminished in number; the strain for the accomplishment of a given piece of work diminishes; the thorax enlarges to promote readier respiration; the man becomes "trained," and there is a lessened metabolism for the fulfilment of a definite amount of work.

1 Zuntz and Schumburg: "Studien zu einer Physiologie des Marsches," Berlin, 1901.

2 Lavonius: "Skan. Archiv fur Physiologie," 1905, xvii, 196. 3 Benedict and Murschhauser: Loc. cit.

The experimental measurements of the efficacy of the working organism as described above were made on well-trained men, a difference on account of training having been early recognized by Zuntz.

Burgi1 made some investigations upon an individual before and after training for mountain climbing. The ascents were made at different altitudes on the roadbed of mountain railways, and the carbon dioxid elimination was measured. The results are shown in the following table:

Effect Of Training On Metabolism

It is evident from this that a trained mountaineer accomplishes his work at the expense of less metabolism than does the untrained. Also that at a moderately high altitude (3000 meters = 522 mm. of mercury, barometric pressure) the trained organism is as efficient for mechanical work as at the sea-level, whereas the untrained man required a much greater metabolism to accomplish a unit of work at the higher altitude than at the lower.

Another fact of importance is that the effect of training especially affects the muscles involved in the particular movement, and not those which do not contract. Thus Zuntz2 found that a dog trained for horizontal motion on a level street required 1179 small calories to move 1 kilogram body weight 1000 meters and 7.668 small calories to raise 1 kilogram body weight 1 meter high. The dog was then gradually trained to ascend an incline. After two years he required only 5.868 small calories to lift 1 kilogram 1 meter, but he required 1343 small calories per kilogram for horizontal locomotion through 1000 meters. Therefore the specifically trained muscles work more economically than those which are at the time but little used.

1 Burgi: "Archiv fur Physiologie," 1900, p. 509. * Zuntz: "Pfluger's Archiv," 1903, xcv, 200.

A man trained for mountaineering will often find himself uncomfortable when walking on a level road. The mountaineer will not find the bicycle an easy means of locomotion,1 nor will the bicylist unscathed essay the mountain.

A benefit derived from riding a horse is the shaking of the internal organs, which is also achieved by descending a steep pathway. This may be beneficial to the life processes in such a comparatively immobile organ as the liver for example. It also appears to promote a freer evacuation of the bowels.

In swimming there is considerable respiration gymnastics.2 The water pressure upon the thorax is the equivalent of the weight of an 8-kilogram sand-bag, which the swimmer seeks to counterbalance by increasing the pressure in his lungs through puffing with his lips. By turning over on the back the swimmer removes this respiratory influence. Cold water stimulates metabolism (p. 144), but the effect of the salt in ordinary sea water is certainly negligible.

There can be little doubt that exercise, especially in the open air, strengthens the organism and therefore tends to prolong life. Sometimes muscular exercise is mistakenly considered as favoring intellectual activity. Yet college presidents are not selected from the ranks of prize-fighters.

1 Concerning energy expended in bicycle riding see Berg, Du Bois-Reymond, and L. Zuntz: "Archiv fur Physiologie," Supplement, 1904, p. 20. 2 R. Du Bois-Reymond: Ibid., 1905, p. 253.