Walking Experiments With Normal Diet, Squad B

The series of experiments on January 6 was made specially to serve as a base-line for subsequent experiments after diet restriction. Unfortunately, on January 6 an accident to the Sonden gas-analysis apparatus after walking experiments had been made with 5 subjects rendered it impossible to determine the oxygen consumption and to compute the respiratory quotient for the other 7 men on that date. The average quotient obtained with the 5 subjects was therefore used for these 7 men and the heat was calculated from this average figure. Fortunately, the carbon-dioxide measurements in all cases are satisfactory. How, on both January 6 and 28, had difficulty in using the mouthpiece in the standing experiments; consequently the oxygen consumption for this subject in the standing position was not obtained directly, but was calculated from his body-weight, and the average oxygen consumption per kilogram of body-weight of the other members of the squad on these dates. The results of the basal standing experiments have been discussed in a previous section (see p. 527), and find use in the subsequent calculations.

The method of calculation for a typical walking experiment has been given in the technique section (see p. 136). It is unnecessary here to present all the protocols, but it is important to note that the temperature of the air inside the chamber in all series of experiments, with both Squad A and Squad B, was within a narrow range - with Squad B on January 6 ranging from 21.37° C. to 23.45° C. On January 28, with the same squad, the range was from 19.90° C. to 21.67° C. With Squad A, on February 3, the temperatures were slightly higher, the range being from 19.59° C. to 22.86° C. In individual experiments the difference in temperature readings at the beginning and the end rarely exceeded 0.5° C.

The moisture accumulated slowly as the experiment progressed, but at no time became excessive. Expressed in percentages, the increase in humidity was usually from 3 to 10 per cent. The average humidity for the experiments on January 6 with Squad B was not far from 33 per cent and on January 28 approximately 30 per cent; on February 3, with Squad A, it was perceptibly higher, and more nearly 50 per cent.

Obviously in experiments lasting but 20 to 24 minutes, barometric changes are physiologically insignificant.

The more important data from the experiments on January 6 with Squad B have been brought together in table 138. It is specially to be noted that the body-weight used in all of these treadmill experiments is not that appearing in all other tables of this monograph, but includes the weight with clothing, electrodes, and pneumograph, for we are particularly interested here in the actual weight transported in the process of walking. These men had their last meal at 5 p. m. the evening previous, so Van, who was the first subject, had been 12 hours without food and was therefore in the post-absorptive condition. This subject was wakened at 4 a. m. and began his standing experiment at 4h25m a. m.; as the squad had retired at 11 p. m., he had had only 5 hours of sleep that night; but Tho's walking experiment was not made until 12h25m noon; it was therefore 19 1/2 hours since his last meal, but he had had a full night's rest. These differences in the hours of rest and intervening time between the previous meal and the experiment could not be avoided in these individual measurements; though undesirable, they were probably without significant influence.

From table 138 it is seen that the rate of walking is practically uniform at 69.4 meters per minute, even the grossest variation being only 0.5 meter. This is evidence of the careful control of the treadmill speed. The total heat per minute is recorded in column h. As was the case with the standing metabolism, the total heat output is in general agreement with the weight of the subject, the heaviest men having usually the largest heat output. The exceptions to this were no more frequent nor larger than might be expected in general. Although the speed of the treadmill was adjusted to that for moderate walking, it seems best to discuss the total distance walked more in terms of an average day's walking performance for these men. It was found that, in general, Squad A showed pedometer records of not far from 6.5 miles per day.1 Consequently we have used for both squads the round figure of 10 km. to represent the total distance walked daily. The total heat required in walking 10 km. has been computed for Squad B and recorded in the last column of table 138 (column I). The average value of 626 calories as the heat produced while walking 10 km. corresponds approximately to one-seventh of the daily net energy intake of the men in Squad B at this time. The value for the average heat required to walk 10 km. (626 calories) may be assumed to be a basal unit which will be referred to when the experiments made upon the subjects at the lower nutritional level are considered.

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Table 138. - Increase In The Heat Output During Walking In Treadmill Chamber And The Computed Total Heat Required In Walking 10 Kilometers - Squad B Normal, January 6, 1918

1 Equivalent to 4.2 km. (2.6 miles) per hour, at rate of 70 meters per minute. 2 Average of quotients for five subjects. 3Computed; see page 535. 4 Omitted in average. 5 Omitting McM.

It should be emphasized here that this value represents the total heat output of an individual in walking this distance.

We have, furthermore, to consider specifically the increase in the heat output for walking under these conditions. This is shown in column j, in which the heat for standing as measured in the standing experiments is deducted from the total heat. The heat output shown in this column represents the increase in the caloric output per minute for individuals walking a definite distance, for all the subjects walked the same distance on the treadmill. In other words, it represents a difference in calorific value per minute ranging from 2.50 calories with Sne to 3.54 calories with How. These differences in heat output are, it is seen, independent of the body-weight of these two individuals, for both men had essentially the same body-weight, or 74 kg., as compared with 75.5 kg. From an inspection of the values for body-weight and for total heat increase over standing, it is difficult to note any relationship.

A comparison of the values for total heat output per minute (column h) or even for the increase in heat over standing (column j) does not give a definite idea of the efficiency of the man, for owing to differences in body-weight (in these experiments distances remain constant) varying amounts of work were performed. It is therefore desirable, in so far as possible, to secure the caloric data with regard to the performance of unit amounts of work, i. e., the heat required to transport 1 kg. 1 meter in a horizontal direction. We have accordingly (as is customary in reporting experiments of this kind) divided the total heat output above standing by the total horizontal kilogrammeters, namely, the body-weight times the distance walked (column d). By this we find the coefficient for the heat output per horizontal kilogrammeter (column A;).