CHAPTER L. 



EFFECT OF MUSCULAR WORK AND TEMPERATURE ON 



BODY METABOLISM HEAT ENERGY OF 



FOODS DIETETICS. 



The Effect of Muscular Work. It is a matter of common 

 knowledge that muscular exercise increases the food consumed, 

 and scientific experiments have shown that it greatly augments 

 the consumption of material in the body. Physiologists have 

 attempted to determine which of our energy-yielding foodstuffs 

 is directly affected by muscular activity. A brief statement of 

 the development of our knowledge upon this point will make clear 

 our present theories. According to Liebig, our foods fulfill two 

 general purposes in the body : they are burnt to supply heat, respira- 

 tory foods fats, and carbohydrates, or they are used to construct 

 tissue, plastic foods proteins. It seemed to follow, from this 

 generalization, that muscular tissue in activity should use protein 

 material, and it was believed at that time that the metabolism of 

 protein furnished the source of muscular energy. That it is not 

 the sole source was demonstrated by the interesting experiments 

 of Fick and Wislicenus. These physiologists ascended the Faul- 

 horn to a height of 1956 meters. Knowing the weight of his body, 

 each could estimate how much work was done in ascending such 

 a height. Fick's weight, for example, was 66 kilograms; therefore 

 in climbing the mountain he performed 66X1956=129,096 kilo- 

 grammeters of work. In addition, the work of the heart and the 

 respiratory muscles, which could not be determined accurately, 

 was estimated at 30,000 kilogrammeters. There was, moreover, 

 a certain amount of muscular work performed in the move- 

 ments of the arms and in walking upon level ground that was 

 omitted entirely from their calculations. For seventeen hours 

 before the ascent, during the climb of eight hours, and for six 

 hours afterward their food was entirely non-nitrogenous, so that 

 the urea eliminated came entirely from the protein of the body. 

 Nevertheless, when the urine was collected and the urea estimated, 

 it was found that the energy contained in the protein destroyed, 

 reckoned as heat energy, was entirely insufficient to account for 

 the work done. Although later estimates would modify somewhat 

 the actual figures of their calculation, the margin was so great that 



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