PHYSIOLOGY: H. M. SMITH 
157 
EFFECTS OF A PROLONGED REDUCTION IN DIET ON 25 MEN 
III. INFLUENCE ON EFFICIENCY DURING MUSCULAR WORK 
By H. Monmouth Smith 
Nutrition Laboratory, Carnegie Institution of Washington, Boston 
Communicated by F. G. Benedict. Read before the Academy, April 22, 1918 
Of the various forms of muscular activity which might have been chosen 
for a quantitative study of the efficiency of the human machine under a pro- 
longed period of reduced diet, that of walking was selected since it is the most 
common and necessary exercise, the element of training is practically negli- 
gible, and the results can be expressed in common and well understood terms. 
The principle employed in this study consisted of the measurement of the 
gaseous exchange during the period of walking, and from the oxygen consumed 
and its known heat value for the determined respiratory quotient the energy 
requirement was calculated by indirect calorimetry. 
The heat requirements thus found may be considered in two ways: (1) as the 
total cost to the individual to walk a given distance including that fraction 
of heat which is necessary to maintain the body organs at their normal func- 
tions and irrespective of the differences in the amount of body weight trans- 
ported, or (2) it may be considered on the basis of the cost to the individual 
to move a unit mass of body weight a unit distance, over and above the cost 
for the maintenance of the body at some selected basal condition, such as lying 
or standing quietly. In other words it would be the cost of the superim- 
posed work of walking. In reporting the energy requirement by the latter 
method it is necessary to know this resting or basal metabolism as well as 
that of walking. 
The problem then was to determine the gaseous exchange of the subjects, at 
rest and walking, both before and after reduction of diet, and from the differ- 
ences in the heat developed compute the average energy expended for each 
man under the different conditions. 
Of the various methods of determining the gaseous exchange, the closed 
chamber principle with gas analyses for carbon dioxide and oxygen at the 
beginning and end of the experiment was selected for the walking experiments. 
Accordingly an air-tight sheet-iron chamber was built large enough to 
enclose a power-driven treadmill with a man walking on it. The chamber was 
irregular in shape with a total volume of approximately 2400 liters. Suitable 
arrangements were installed for controlling the speed of the mill and record- 
ing the distance traveled and the number of steps taken. 
The temperature of the chamber was determined by six resistance ther- 
mometers suitably placed and connected in series with a Wheatstone bridge 
and galvanometer placed in an adjoining room. Two electric fans stirred the 
air within the chamber while a blower capable of moving 1000 liters of air a 
