NORMAL PROCESSES OF ENERGY METABOLISM 589 



the heaviest loads there were definite indications of decreased efficiency. 

 Figure 32 exhibits the relationship of total metabolism to effective work 

 at varying speeds but with a constant load. In computing the net effi- 

 ciency the basal metabolism obtained with the subject lying quietly on 

 a couch was used and since this 

 is practically constant, the net 

 efficiency would be effected by 

 speed in the same way as the 

 gross efficiency (total heat out- 

 put). The figure shows that 

 in order to produce 1.565 cal- 

 ories of effective muscular 

 work at 70 revolutions per 

 minute it is necessary for the 

 subject to produce a total of 

 7.61 calories (gross efficiency 

 20.6 per cent) ; while to pro- 

 duce 2.425 calories of work at 

 130 revolutions required 15.04 

 calories of heat (gross effi- 

 ciency 16.1 per cent). "From 

 the upper curve it is seen that 

 the output of heat is constant 

 per 10 revolutions; on the 

 other hand, the increase in 

 effective muscular work per- 

 formed is not constant for each 

 ten revolutions, but there is a 

 distinct falling off. If, there- 

 fore, we divide the increase in 

 the external muscular work 

 between any two points on the 

 curve by the increase in the 

 total heat output correspond- 

 ing to the same two points, we 

 get an efficiency based upon 

 increasing speed, the load 



6Q 70 60 90 100 110 120 130 140 



Fig. 32. Curves showing the total heat 

 output per minute and corresponding external 

 muscular work per minute, expressed in cal- 

 ories, for subject riding with constant load 

 1.5 amperes at varying speeds. (Benedict and 

 Cathcart.) 

 being the same. For instance, 



in changing from 70 to 80 revolutions per minute, there is an increase in 

 the effective muscular work equivalent to 0.205 calorie. Under these con- 

 ditions there is an increase in the total heat output of 1.24 calories. Divid- 

 ing the increase in heat output due to the muscular work (0.204 calorie 

 by the increase in the total heat output (1.24 calories) we find an efficiency 

 for the increased amount of work performed of 16.53 per cent." Compu- 



