The Character of Energy Metabolism during Work

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Abstract
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. 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. 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. 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. Over 100 experiments were made upon subjects who were subsisting upon a normal (uncontrolled) diet. A few experiments of the running-in-place type instead of the bicycle riding, were introduced for comparison. 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. The work varied in intensity from 0.76 to 1.4 Cals, per minute and continued for from 5 to 20 minutes. 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. 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. 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. 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.

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