22 MUSCULAR WORK 
has recently been calibrated with especial care, together with the development 
of a new form of respiration apparatus capable of measuring accurately the 
large amounts of carbon dioxide produced and oxygen consumed during severe 
muscular work, it was considered that this laboratory was peculiarly well 
fitted for undertaking an investigation on the influence of severe muscular 
work upon not only the character of the material katabolized, but also upon 
the amounts of material katabolized. Moreover, the striking disagreement 
between the results for the mechanical efficiency of man obtained on the one 
hand by Benedict and Carpenter and on the other by Zuntz and his associates 
made further experiments on this subject necessary. The study reported 
here was intended to amplify the results of the earlier investigations. 
The research was primarily designed to secure evidence with regard to 
the influence of severe muscular work upon the character of the metabolism, 
as well as evidence with regard to the efficiency of the body as a machine. 
The experiments were for the most part carried out with a professional 
bicyclist riding a carefully calibrated ergometer with an electric brake." 
While no calorimetric measurements were made, the carbon dioxide produced 
and the oxygen consumed were determined by means of the new form of 
respiration apparatus, which was especially modified to meet the exacting 
requirements of experiments with severe muscular work. The experimental 
periods were all of such length as to overcome the criticism that has previously 
been made with regard to the short experiments of earlier investigators. 
In order to obtain values for use as a base-line, a large number of experi- 
ments were made in which the resting metabolism of a subject without food 
was determined while he lay quietly upon a couch. Studies were also made of 
the resting metabolism while the subject sat quietly upon the bicycle seat, 
with his feet in position for riding, but without movement. In the muscular- 
work experiments, the work varied from very light to extremely severe, i. e., 
the heat equivalent of external muscular work was 2 calories per minute 
or 850 kilogramme ters per minute; in some experiments the subject rotated 
the pedals without load; in others, he kept his feet upon the pedals while they 
were rotated by a motor; in the majority of the work experiments, the subject 
rode with a load which was varied from light to heavy according to the 
character of the experiment. All of the experiments were made when the 
subject had been at least 12 hours without food. The majority of the work 
experiments were preceded by rest experiments. To carry out successfully a 
series of experiments of this kind it was necessary to have a well-trained sub- 
ject capable of severe and prolonged muscular exertion. We were extremely 
fortunate in securing a subject who cooperated very intelligently with us in 
the conduct of the experiments, and while the muscular work was frequently 
very severe, it was at no time beyond or even equal to the endurance or ability 
of the subject. 
DETERMINATION OF THE BASAL METABOLISM. 
The basal metabolism was established by studying the respiratory ex- 
change when the subject lay quietly at rest on a couch and at least 12 hours 
after the last food. Under these conditions we obtained what may be termed 
the minimum metabolism of the subject when awake. Inasmuch as this 
<* Benedict and Cady, Carnegie Institution of Washington Publication No. 167, 1912. 
