HEAT GIVEN OFF BY BODY, INCLUDING FOR WORK EXPERIMENTS THE HEAT EQUIVALENT OF THE EXTERNAL MUSCULAR WORK.

Kind of Experiment.

Total
Amount
of Heat
in 24
Hours.

Rates per Hour.

Average
for
24 Hours.

Day Periods.

Night Periods.

7 A. M. to
1 P. M.

1 P. M. to
7 P. M.

7 P. M. to
1 A. M.

1 A. M. to
7 A. M.

calories

calories

calories

calories

calories

calories

Rest experiments

2262

106.3

104.4

 98.3

67.9

 94.3

Work experiments
Heat eliminated

4225

231.7

235.6

118.1

78.4

166.6

Heat equivalent of
external muscular
work

451

 58.5

 56.8

. . .

. . .

. . .

Total

4676

290.2

292.4

118.1

78.4

194.8

The work done in these experiments was on a stationary bicycle in the calorimeter, and the heat equivalent was calculated from measurements made by an ergometer attached to the bicycle. We are not concerned here with details, but simply with the general question of the influence of muscular work upon the energy exchange of the body. We note that the work of the day periods, 7 A. M. to 7 P. M., resulted, in the several cases brought together under the average figures, in an increased heat production amounting to more than 100 per cent. Further, we observe that in the body, as in all machines, only a fraction of the energy liberated by the accelerated chemical decomposition, or oxidation, was manifested as mechanical work, the larger part by far being heat eliminated and lost. Thus, Zuntz has found that, in man, about 35 per cent of the extra energy of the food used in connection with external muscular work is available for that work. This, however, shows a noticeably higher degree of efficiency than is generally obtainable by the best steam or oil engines. Lastly, attention may be called to the fact that after the work of the day was finished at 7 P. M., the next period of six hours still showed an accelerated metabolism, as contrasted with what took place during absolute rest.

As bearing upon the exchange of matter in the body in connection with muscular work, and as showing the relationship which exists here between energy exchange and exchange of matter, we may quote a few data relating to the elimination of carbon dioxide; remembering that this substance represents particularly the final oxidation product in the body of carbonaceous materials, such as fat and carbohydrate. The following data, taken from Atwater and Benedict,[38] being results of experiments upon the subject “J. C. W.,” are of value as showing the variations in output of carbon dioxide that may be expected under the conditions described:

Period.Rest
Experiments
without
Food.		Rest
Experiments
with
Food.		Work
Experiments
with
Diet.		Work
Experiments
with
Fat Diet.		Extra Se-
vere Work
Experiment
with
Fat Diet.
gramsgramsgramsgramsgrams
7 A. M. to 1 P. M.189.6230.4 694.0 642.3 907.0
1 P. M. to 7 P. M.172.6232.0 705.6 634.8 821.3
7 P. M. to 1 A. M.167.2196.6 260.1 230.3 842.7
1 A. M. to 7 A. M.146.7153.1 161.1 157.6 502.6
Total for 24 hours676.1812.11820.81665.03073.6

In considering these figures bearing on the output of carbon dioxide under the conditions specified, we note at once a correspondence with the total energy exchange, as indicated in the preceding table. As previously stated, we are at present dealing simply with generalities, and the important point to be observed here is that muscular work—7 A. M. to 7 P. M.—in the work experiments, increases enormously the output of carbon dioxide. We see clearly emphasized a connection between the total energy exchange of the body, as expressed in calories or heat units, and the oxidation of carbonaceous material, of which carbon dioxide is the natural oxidation product. We note that on the cessation of work—7 P. M. to 7 A. M.—the output of carbon dioxide tends to drop back to the level characteristic of the corresponding period in rest, with or without food. In the experiment with “extra severe muscular work,” the results are different simply because here the subject worked sixteen hours, necessitating a portion of the work being done at night-time. Finally, it should be mentioned that the differences in output of carbon dioxide in these experiments are somewhat greater than in many experiments of this type, although all show the same general characteristics. This may be explained, as stated by the authors from whom the data are taken, “by the fact that J. C. W. was a larger and heavier man than any of the others; that the differences in diet were wider, and that the amounts of external muscular work were larger in these experiments than in those with the other subjects.”

If we pass from experiments of this type, conducted in a calorimeter, to those cases where competitive trials of endurance are held by trained athletes, i. e., where external muscular activity is pushed to the extreme limit, we then see even more strikingly displayed the effect of work in increasing the energy exchange of the body. One of the best illustrations of this type of experiment is to be found in the observations made in connection with the six-day bicycle race held in New York City, at the Madison Square Garden, in December, 1898.[39] The observations in question were made upon three of the athletes, one of whom withdrew early in the fourth day, while the others continued until the close of the race—142 consecutive hours—winning the first and fourth places, respectively. The following table gives the computation of energy of the material metabolized, exclusive of body-fat lost:

Subject.Duration of
Experiment.		Total Energy
Metabolized.		Average per
Day.
dayscaloriescalories
Miller6289174820
Albert6364416074
Pilkington3133014464

Miller, the winner of the race, who averaged a daily energy exchange of 4820 calories, rode 2007 miles during the week, and finished the race without physical or mental weakness resulting from the fatigue and strain. During the first five days, he rode about 21 hours a day and slept only 1 hour. Albert, who weighed a few pounds less than Miller, covered 1822 miles in 109 hours, with an average daily exchange of 6074 calories. We may add a table (on the following page) showing the balance of income and outgo of nitrogen in these three subjects, as being of general interest in this connection. The figures given are averages per day.

Subject.

Duration
of Exp.

Income in Food.

Nitrogen.

Proteid.

Fat.

Carbo-
hydrate.

Fuel
Value.

In
Food.

In
Urine.

In
Excre-
ment.

Loss.

days

grams

grams

grams

calories

grams

grams

grams

grams

Miller

6

169

181

585

4770

29.4

36.2

1.8

8.6

Albert

6

179

198

559

6095

29.1

33.7

2.5

7.1

Pilkington

3

211

178

509

4610

36.0

38.9

2.2

5.1