16 METABOLISM DURING WALKING. 



direction, inasmuch as the load is almost imperceptible. Unfortu- 

 nately, relatively few experiments have as yet been carried out with 

 this method, and many of these have been hastily made and without 

 the careful attention to technical detail given in experiments with other 

 types of apparatus. 



Our own justification for making a study of the respiratory exchange 

 in grade walking was, as stated earlier, the fact that it should serve in 

 large part as a preliminary to a research upon grade walking in which 

 direct calorimetry would be employed. The pronounced alterations 

 in the respiratory quotient with severe labor, resulting in quotients 

 at times appreciably over 1.00, make it a fair question as to whether 

 or not the methods of indirect calorimetry give true indices of the 

 actual heat-production under these conditions. Admittedly, the 

 technical details to be overcome in making a study by direct calori- 

 metry of the energy output of a man walking nearly to the limit of 

 human endurance are very great, but it is believed that they may be 

 overcome. In an effort to improve much of this technique, prior 

 to inclosing the man in a hermetically sealed chamber, the treadmill 

 experiments reported in the following pages were carried out at the 

 Nutrition Laboratory. 



PLAN OF STUDY. 



The primary object of the experiments in this research was the 

 determination of the energy expended by the human body in perform- 

 ing the work of lifting itself to a definite elevation by walking up-grade. 

 With a treadmill of unusual design and accuracy, a respiration appa- 

 ratus capable of measuring an oxygen consumption of 3,000 c. c. per 

 minute and over with great rapidity and exactness, much accessory 

 apparatus for studying physiological factors, such as respiratory 

 volume, respiration-rate, pulse-rate, step-lift, etc., it was believed that 

 opportunity was afforded for a contribution to the general physiology 

 of horizontal walking, also, which would amply justify the additional 

 labor. As previously stated, it was at the outset considered that this 

 whole research was preliminary to a subsequent study in which 

 direct calorimetry would be employed. 



The total energy that is expended by the human body during 

 grade walking is the sum of several factors, among which are (1) the 

 energy required to maintain the vital functions, such as respiration and 

 circulation, while the body is at rest, which may be termed basal 

 energy; (2) the energy required for the muscular movements of the 

 simple act of walking on a level; (3) the energy required to lift the 

 body through a vertical distance corresponding to the elevation 

 attained in the grade walking. Since the measurements of the metab- 



