EFFECT OF MUSCULAR WORK ON METABOLISM 



ENERGY PER DAY 



639 



If we compare the energy- value of the work done with the excess of the 

 total expenditure of the body over that found during the rest experiments, 

 we find that the performance of muscular work involves an increase in the 

 total energy- expenditure of the body by an amount equal to about five times 

 that of the work done. Of course a certain proportion of this excess of 

 energy over work done is accounted for by the increase in the work which 

 must be performed by the respiratory muscles and heart in the state of 

 greater activity which is imposed upon them by the external work, and is 

 necessary for the proper provision of the active muscles with increased food- 

 supply and oxygen. Even if we neglect these factors altogether, we see that 

 .the efficiency of the body as a machine corresponds to between 16 and 20 per 

 cent., an efficiency which exceeds that of the best of our steam-engines and 

 is only equalled by certain internal- combustion engines. 



A comparison of the excreta of the same individual whose energy ex- 

 changes are given in the above Table during rest and activity will give us 

 information as to the source of the increased energy put out during the per- 

 formance of muscular work. Thus during a period of rest and starvation 

 the average output of carbon dioxide during six hours amounted to 189-6 

 grm. ; during a rest experiment with food the average output for a period 

 of six hours was 2304 grm. of carbon dioxide. During work the average 

 output in the same individual during six hours rose to 705 grm. of carbon 

 dioxide on a carbohydrate diet, and to 634*8 grm. on a diet containing a large 

 amount of fat. The oxidation of carbon was therefore increased more than 

 threefold as a result of muscular work. If we compare in the same way 

 the protein metabolism of the same individul during these experiments no 

 such alteration is observed. Thus the average output per day during rest 

 and starvation corresponded to 82 grm. of protein. During rest and with 

 an approximately sufficient amount of food the average amount of protein 

 consumed was 98-8 grm. During a work day in which he received practically 



