18 METABOLISM DURING WALKING. 



to determine this elevation, or "step-lift," and to express it in terms of 

 kilogrammeters of work. The proportion of increase in the energy 

 due to this factor in horizontal walking may thus be obtained. If, in 

 the grade experiments, the work due to the step-lift is added to the 

 work of the vertical lift of the grade, the sum represents what may be 

 called the total "work of ascent." 



In addition to these primary measurements, the experimental con- 

 ditions were favorable for collecting data on other physiological 

 factors, and some results are presented on the changes in the respira- 

 tion-rate and pulse-rate, the pulmonary ventilation, and rectal body- 

 temperature which accompany the changes in the amount of work 

 performed. A few observations on the changes in the blood-pressure 

 between rest and exercise were made for comparison with the changes 

 in the amount of work being done. 



The readiness with which the heart and lungs respond to the chang- 

 ing demand of the body when work was either begun or ceased was also 

 studied. The adaptability of the body to new demands at times, a 

 demand approximating the limit of human endurance, necessitating 

 an oxygen consumption of over 3,000 c. c. per minute is a factor in 

 human economy that has been hitherto too little studied. The 

 rapidity of adjustment after most strenuous exercise is of utmost 

 importance in estimating "fitness" for the work performed. These 

 experiments have been referred to as "transitional" experiments, and 

 by measuring the oxygen consumption, ventilation, pulse-rate, and 

 respiration-rate for successive fractions of a minute until either the 

 normal or an approximately constant rate was obtained, the relation 

 between the response of these physiological processes to the amount of 

 work performed was obtained. 



METHODS OF MEASUREMENT. 



The group of apparatus used in this research was, in principle, that 

 employed and described by Benedict and Murschhauser, 1 but with 

 modifications essential for the increased amount of work to be per- 

 formed. The principal apparatus employed were the universal res- 

 piration apparatus for determining the gaseous metabolism and the 

 treadmill for the measurement of the muscular work. In addition, 

 accessory apparatus were used for securing data on the pulse-rate, 

 pulmonary ventilation, body-temperature, etc., which were not 

 obtained by Benedict and Murschhauser in their study. The general 

 arrangement of the apparatus, with subject in position for an actual 

 experiment, is shown in the frontispiece and, in part, in figure 1. 



Benedict and Murschhauser, Carnegie Inst. Wash. Pub. No. 231, 1915, p. 29. 



