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The Character of Energy Metabolism during Work¹

(From the Department of Vital Economics, University of Rochester, Rochester, N.Y.)

1. Experiments on seventeen subjects while riding the bicycle ergometer are reported. Most of the experiments were made on three subjects, two of them boys 14 and 15 years old respectively at the start and 15 and 16 at the conclusion of the experiments. The third subject was a young athlete 21 years of age, who gave instruction in boxing. He was well muscled and in good training generally but not especially trained for bicycle riding.

2. The ergometers used were of the Prony-brake type and the Krogh magnetic-brake type. Experiments on the same subject under like conditions gave equal efficiencies on the two ergometers.

3. In all the experiments on the athlete and in one series on one of the boys the nitrogen excretion in the urine was determined in a resting period and in a second period which included work and recovery and the post work resting period. Alveolar CO₂ determinations were also made in these same series, after the preliminary rest, just before work, just after work and recovery, and at the end of the post-work resting period.

4. The R.Q. of the excess metabolism was obtained by deducting for the total CO₂ and O₂ of the work and recovery period, the CO₂ and O₂ obtained in the previous resting period.

5. Over 100 experiments were made upon subjects who were subsisting upon a normal (uncontrolled) diet.

6. A few experiments of the running-in-place type instead of the bicycle riding, were introduced for comparison.

7. Much time was spent in securing the proper length of recovery period so that complete recovery on CO₂ as well as on O₂ would be shown.

8. The work varied in intensity from 0.76 to 1.4 Cals, per minute and continued for from 5 to 20 minutes.

9. With one boy the average R.Q. of the excess metabolism occasioned by the work, in forty-one out of forty-nine experiments, was lower than the R.Q. of the previous resting period. With the second boy in 15 out of 18 experiments likewise the excess R.Q. was lowered. The average excess R.Q. with both boys on normal (uncontrolled) diet was 0.78. With the mature athletic subject doing work of the same moderate intensity as the boys the R.Q. of the excess metabolism in 15 out of 16 experiments was higher than the R.Q. in the previous resting period giving an average of 0.95.

10. The athletic subject was placed on special high carbohydrate and high fat diets weighed carefully and consumed quantitively. On high fat recovery to the pre-work level of O₂ absorption and CO₂ elimination was much slower than on high carbohydrate.

11. The average excess R.Q. of work and recovery on both diets was higher than the R.Q. of the previous resting period, but the absolute level of the excess R.Q. very clearly was influenced by the diet. The alveolar values in these experiments on special diets showed: (a) more CO₂ in circulation at the end of work and recovery on high carbohyrate than previous to work; and (b) no change or less Co in circulation at the same time on high fat. Urine tests showed the presence of aceto-acetic acid on the high fat diet. The presence of acidosis explains the higher R.Q. of the work metabolism on this diet.

12. In ten of the seventeen subjects studied the mild piece of work performed did not appreciably alter the metabolism. The body produced the necessary energy for the work by oxidation of the various materials in the same proportion as at rest.

13. In general the evidence from this study lends support to the belief of Zuntz that the body uses for the energy of muscular work both carbohydrate and fat.¹

¹ Since the foregoing was written Rapport and Kalli (21) have published experiments on dogs which were made to run on a treadmill inside a respiration chamber. The dogs were maintained for two days prior to the work experiment on diets containing on the one hand 90% fat and 10% protein, and on the other 90% carbohydrate and 10% protein. They were studied in the post-absorptive state following these diets and the results were compared with those obtained in the same condition following normal diets made up of 55 to 60% carbohydrate, 25 to 30% fat and 15% protein. Due account having been taken of the oxygen recovery following periods of 45 minutes and 15 minutes of work, the excess metabolism of work and recovery over the preexercise basal was found to contain an oxidation of carbohydrate amounting to 61 and 55% respectively of the total on normal diet; 70 and 100% on high carbohydrate and 13 and 15% on high fat. The authors' conclusions coincide with our own.

Manuscript received 1 July 1928.