PART III. 
DISCUSSION OF RESULTS. 
The mass of experimental data accumulated in connection with this 
research permits of the adequate discussion of several major and innumerable 
minor problems in the relationship between muscular work and metabolism. 
We shall lay our greatest stress upon a consideration of the character of the 
katabolism and the mechanical efficiency of the body, and finally devote a 
portion of the discussion to a presentation of our evidence bearing upon a 
number of the physiological effects of muscular work. 
THE CHARACTER OF THE KATABOLISM AS AFFECTED BY MUSCULAR WORK. 
When muscular work is performed by the human body, the consumption 
of fuel either from food or from body-material is greatly increased. When 
food is not given, the energy must be supplied from body-material. If we 
consider to what extent, under these conditions, the constituents of the body- 
material are available for the production of energy, we find that the amount of 
protein present in the normal human body is amply sufficient to provide for 
all drains upon nitrogenous material during rest or a short period of work. 
Similarly, with a well-nourished man there is a practically unlimited supply 
of fat. On the other hand the supply of carbohydrates is found to be very 
limited; thus, with dogs and with other animals, it is possible to rid the body 
of all but traces of glycogen by starvation, by strychnine convulsions, and 
by the shivering induced by prolonged exposure to severe cold, while under 
the same conditions there is no material draft upon the body-protein and but 
a small part of the large amount of body-fat is used. Apparently the storage 
of carbohydrates is also somewhat easily depleted by excessive muscular 
work. It is believed, therefore, that the ideal conditions for a study of the 
question as to whether or not there is a selective combustion of carbohy- 
drate material during severe muscular work would obtain after the subject 
had abstained from food for twelve to fifteen hours, i.e., when there was a 
relatively large supply of body-protein, and a relatively small supply of body- 
glycogen. If, under these conditions, a selective combustion took place, the 
supply of body-glycogen would be rapidly depleted and this would be indicated 
by the respiratory quotient. Nearly all of our experiments, therefore, includ- 
ing both the rest and the work experiments, were made in the morning, the 
subject having taken no food since the previous evening. 
We have found it difficult to select a word to express this condition of 
abstinence from food for 12 hours. As is well known, the stimulating action 
of the substances absorbed from recently-introduced foodstuffs produces an 
increase in total katabolism which frequently obscures the effect to be 
studied. A German word, "niichtern," has been freely used in the past but 
in our opinion it is not explanatory. English words, such as fasting, break- 
fastless, etc., have been considered but owing to difficulties in connection 
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