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 greatly augments the physio- 

 logical oxidations as measured by the CO2 ehminated and the heat 

 produced in and given off from the body. This general fact is well 

 illustrated in the following table:* 



Average Normal Output of Carbon Dioxid and Heat from the Body 



Average Quantities 



PER Hour. 

 Carbon 



Dioxid, Heat, 



Conditions of Muscular Activity. Gm. Cals. 



Man at rest, sleeping 25 65 



Man at rest, awake, sitting up 35 100 



Man at light muscular exercise 55 170 



Man at moderately active muscular exercise 100 290 



Man at severe muscular exercise 150 450 



Man at very severe muscular exercise 210 600 



Physiologists have attempted to determine which of our energy- 

 yielding foodstuffs is directl}^ 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, oui 

 foods fulfil two general purposes in the body : they are burnt to sup- 

 ply heat, respiratory foods — fats, and carbohydrates, or they are 

 used to construct tissue, plastic foods — proteins. It seemed to fol- 

 low, from this generahzation, that muscular tissue in activity should 

 use protein material, and it was believed at that time that the metab- 

 oHsm of protein furnished the source of muscular energy. That it \i 

 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 climbing to such 

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

 in chmbing 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, 

 * Benedict, "Science," July 16, 1915. 

 933 



