The experimental procedures have made it possible to analyze the basal metabolism under different conditions of nutritional level with the normal and with the low diet. Furthermore, as was seen in a preceding section, the metabolism with both normal and reduced diet was studied for the standing position, this representing a somewhat greater expenditure of energy than that for the lying position, and the influence of the restricted diet was found to be of practically the same magnitude as that affecting the lying metabolism. The treadmill experiments make it possible to study the influence of the lower nutritional level upon a moderately active form of muscular exercise. While in the lying experiments there is no voluntary muscular effort and in the standing experiments the muscular effort is only slight, walking approximates, to a certain extent, a great deal of the activity incidental to the ordinary life of most individuals not engaged in severe manual labor. The walking experiments, therefore, are of particular value in determining the influence of the low nutritional state upon the probable metabolism during periods of time other than quiescent, i. e., periods with a moderate amount of activity.

In the walking experiments here discussed it was possible to measure quantitatively a condition of metabolic activity involving an increase in metabolism of over 200 per cent above the basal standing metabolism. The treadmill experiments may be looked upon, therefore, from two standpoints, first, as to the capacity of the organism to carry out a simple physical operation, such as that of walking a given distance, and second, as to the efficiency with which the operation may be done. Knowing from the earlier researches of Durig and his associates that when weight is added in the form of a.load on the back, the energy required for the transportation of this material is, up to a certain limit, essentially constant per kilogram of body-weight, we could assume a priori that when these men had lost a certain amount of weight they would be able to walk a given distance with a lower metabolism. It should be borne in mind, however, that the experiments of Durig deal with a basal metabolism of a constant intensity and with an organism living at a normal nutritional level. Although it has been shown in the foregoing sections that the basal metabolism was very greatly lowered as a result of the restricted diet, it is not logical to assume, without supporting experimental evidence, that the walking would be accomplished necessarily with essentially the same degree or a less expenditure of energy.

In addition to considering the capacity of the organism to transport itself a given distance, one may very properly consider whether the energy required to transport 1 kg. of body-weight 1 meter in a horizontal direction has been materially affected by the change in diet. With a relatively large number of individuals, at least, the average figures have shown approximately uniform constancy for this factor. This is more of an abstract physiological phase of the problem and of somewhat less practical importance. In the following analysis of our walking experiments, therefore, we will first consider the capacity of the organism as a whole to transport itself or to walk a given distance, in the belief that walking makes up a not inconsiderable amount of the activity of each individual during the day, and likewise, as has been pointed out earlier, walking is one of the most practiced and commonest muscular performances of mankind.

The technique described in an earlier section, employing the treadmill and the closed chamber with gas analyses for both carbon-dioxide increment and oxygen deficit, was utilized to determine the total heat production during the process of walking. It has been the custom of investigators, however, to recognize that a certain proportion of this heat is required for the ordinary maintenance activity. In the calculation of the heat required for walking, this maintenance energy is usually deducted from the total heat during the walking period. The time available for these experiments was not sufficient for us to determine both the total heat production of walking and the heat of maintenance in the treadmill chamber. Use was therefore made of experiments with the portable apparatus, in which the subject was in the standing position, it being the consensus of opinion of physiologists that the basal metabolism standing is one of the best base-lines for maintenance activity for deduction from the total gaseous metabolism during walking.

The observations of the gaseous metabolism during walking included two series of experiments with Squad B on January 6 and 28, and one series of experiments with Squad A on February 3. The first series with Squad B was made when the men were on full diet, the second when they had been on a much reduced diet for 20 days. The single series of experiments with Squad A was made at the end of the research, when the men had been on low diet with some intermissions for about 4 months. These walking experiments were preceded in all cases by basal standing experiments.