A study of the table on p. 327 will show that it requires much less energy for a horse to move 1 kilogram of his weight 1 meter horizontally than for a dog to do the same at the same velocity. It also appears that a man of small weight requires more energy to a unit of substance than a man of large size. This rule has been confirmed in dogs by Slowtzoff,3 who shows that energy amounting to 0.529 kilogrammeter is required for 1 meter horizontal motion by a dog weighing 37 kilograms, and 1.138 kilogrammeters by a dog weighing 5.5 kilograms. Slowtzoff does not find that this variation is proportional to the skin area of the animal.

The table also shows that there is little variation in the dog, horse, and man in the amount of energy necessary to raise 1 kilogram of body substance 1 meter high:

1 Katzenstein: "Pfluger's Archiv," 1891, xlix, 379. 2 Frentzel and Reach: Ibid., 1901, lxxxiii, 494. 3 Slowtzoff: Ibid., 1903, xcv, 190.

Energy Requirements Of Different Animals In Performance Of The Same Amount Of Mechanical Work

It is possible to calculate the food ration for a march if the figures given in the table be employed. If it be assumed that a man weighing 70 kilograms travels 74.4 meters a minute, he will accomplish 4.46 kilometers or 2.7 miles per hour. If it requires the energy equivalent of 0.217 kilogrammeter to move 1 kilogram of his weight 1 meter, it will require 67,747 kilogrammeters (0.217 X 70 X 4460) to move him 4.46 kilometers - 67,747 kilogrammeters being equivalent to 159.205 calories. This is the equivalent of 17.1 grams of fat, which may be added to the maintenance resting dietary requirement to supply the energy necessary for an hour's quiet walk on a level road. If the road be inclined so that the man raises himself 500 meters during the hour's walk, the metabolism will be still further increased. The work of ascent will be his weight multiplied by the height of his climb, or 35,000 kilogrammeters. The expenditure of energy by the body in order to accomplish this work is threefold the work done, or 105,000 kilogrammeters, which equals 246.75 calories, or 26.5 grams of fat. The hour's walk in this case would require the production of an energy equivalent, above the resting metabolism, amounting to that contained in 43.6 grams of fat - that is, 17.1 grams for a forward locomotion of 4.46 kilometers and 26.5 grams to lift the body to an altitude of 500 meters.

In the last-mentioned table it is seen that there is an increase in the metabolism for a unit of horizontal motion when the progress of the individual is very slow. This is explained by the fact that speed of progress was half the normal, was unusual, and forced.

Later work has confirmed the results above enumerated. Thus, Brezina and Reichel1 find that a man walking on a horizontal plane at a rate not exceeding 80 meters in one minute (3 miles per hour), a rate which they denote as the maximal economic velocity, requires 0.5 calorie of energy (= 0.213 kilogrammeter of work) to move 1 kilogram of weight 1 meter, and this rule also applies to weights carried up to about 20 kilograms. This load is about that carried by a soldier. With weights heavier than this there is a slight increase in the quantity of energy required when the individual labors within the limits of the maximal economic velocity. When, however, this velocity is exceeded the expenditure of energy for more rapid walking increases rapidly, and with especial sharpness when heavy loads are carried. A part of the figures is given in the following table:

The Influence Of Velocity And Of Load In Horizontal Walking Upon The Amount Of Energy In Gram-Calories Necessary To Move 1 Kg. Of Weight Through 1 Meter Of Distance

1 Brezina and Reichel: "Biochemische Zeitschrift," 1914, lxiii, 170.

Benedict and Murschhauser1 have arrived at essentially the same results as those given above as regards the energy requirement involved in horizontal walking, and they further note that running at the rate of about 5.3 miles per hour is accomplished more economically than walking at the same rate. Their results may be summarized as follows:

The total heat produced when walking at the higher speed was about 600 calories per hour, or about that of the same individual (M. A. M.) when he rode a bicycle, as already described (p. 321). At the lower speed it was found that the process of walking involved a total lifting of the body weight from the ground, amounting approximately to a height of 4 meters per minute. The energy necessary to do this would account for 25 per cent, of the total energy utilized in the muscular complex thrown into action for the purpose of forward progression.

The generalization of Brezina and Reichel is that within the limit of economic maximal velocity the energy requirement of the organism approximates a constant minimum value, which is 0.5 gram-calorie for the forward movement of 1 kilogram of weight 1 meter horizontally. With each meter of velocity above 80 meters per minute the requirement of energy increases 1 per cent, of the initial minimal value. When medium loads (20 kg.) are carried the metabolism increases 2 per cent., and with heavy loads 3 per cent., of the minimal value, per each added meter of velocity above 80 meters per minute.

The rule is that the metabolism increases with speed in horses (1.03 per cent, per meter increase above 78 meters per minute), but this is not seen in dogs.1

1 Benedict, F. G., and Murschhauser: "Energy Transformations During Horizontal Walking," Carnegie Institution, Publication 231, 1915.

Brezina and Reichel2 continued their reseafches by determining the effect of the gradient of the pathway upon the metabolism of man when walking and carrying different loads. It was found that the maximal work of lifting the body with its load was accomplished at a minimal expenditure of energy when the incline was 20 per cent, and the weight of the load 19 kilograms. However, when walking on inclines with gradients of 10 or 40 per cent., the energy figures were only slightly above the minimal values and the load also made no essential difference. The authors found that to raise 1 kilogram of body substance plus the load carried, required between 9 and 10 calories of energy of metabolism. This represents the conversion of about 25 per cent, of the energy of metabolism into mechanical work. Weights between 3 and 56 kilograms were raised at expenditures of energy directly proportional to the work accomplished.