EFFECT OF MUSCULAR WORK ON METABOLISM 715 



man. The total energy output of a man was reckoned as heat by 

 means of the calorimeter. The heat equivalent of the external 

 muscular work performed by the man was also reckoned as heat. 

 In the following Table we give the total output of energy per day 

 during rest and work, the latter being also expressed in calories* : 



ENERGY PER 



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 respira- 

 tory 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 

 exchanges 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 performance of muscular work. Thus during 

 a period of rest and starvation the average output of carbon dioxide 



* One large calorie, or ' kilo-calorie,' is equivalent to 425 kilogramme! res. 



