94 ENERGY TRANSFORMATIONS DURING HORIZONTAL WALKING. 

 INFLUENCE OF FATIGUE UPON THE HEAT-OUTPUT PER UNIT OF WORK. 



Many of our experiments were made with a sufficient number of con- 

 secutive walking periods to permit a study of the heat per unit of work 

 done under conditions of accumulated work. The average length of 

 the walking period was 14 minutes. The distance traveled in a period 

 in the prolonged walking experiments varied from 800 to 1,200 meters, 

 and the subject walked not only during the experimental periods, when 

 the gaseous metabolism was being measured, but also between these 

 periods. When, therefore, the experiment consisted of four or more 

 experimental periods, it will be seen that the continuous walking would 

 amount frequently to several kilometers, thus providing conditions for 

 studying the effect of fatigue. In relatively few of these experiments, 

 however, was there substantial evidence of extreme fatigue. 



The results of the observations in which there were four or more 

 periods of continuous walking are brought together in table 18. The 

 data given show the total distance walked by the subject prior to the 

 beginning of each experimental period 1 and both the distance walked 

 per minute and the heat-output per unit of work performed during the 

 period. On two days, April 28 and 29, 1914, there were eight walking 

 periods; the total distance traversed each day in continuous walking 

 was approximately 23 kilometers. Throughout both experiments the 

 distance per minute remained essentially constant at about 80 meters; 

 we thus have ideal conditions for studying the influence of fatigue 

 resulting from continuous walking. On April 28, when the subject was 

 without food, there was no essential difference in the unit of work done 

 as the experiment progressed, although there were variations from 

 period to period. On the next day, a similar experiment was made 

 after food had been taken. The average heat per unit of work done 

 on this day was considerably less than that on April 28 and a general 

 tendency was also shown for the heat per unit of work done to decrease 

 as the work progressed. Inspection of the values found for another 

 experiment of 6 periods on May 13, when the subject was without food, 

 shows more or less fluctuation in the values obtained for the heat per 

 unit of work done, but there is no uniformity in the changes and, 

 indeed, the values are somewhat greater in the last periods than in the 

 earlier periods. With the experiments having only four periods, in 

 which the total distance walked prior to the last period ranged from 

 8 to 12 kilometers, we find that on certain days there was a tendency 

 for the heat per unit of work to decrease as the walking progressed and 

 on other days to increase, but in the majority of the experiments there 

 was no regularity in the variations. 



From the data given in table 18, we may conclude that there may be 

 noticeable differences in the absolute heat per unit of work done on 

 different days, a point particularly brought out in the experiments of 



'For total distance walked, see table 4, pp. 56 to 60. 



