8 ENERGY TRANSFORMATIONS DURING HORIZONTAL WALKING. 



oxygen required in the combustion, there are produced from 4.686 to 

 5.047 calories. When pure carbohydrate is burned, each liter of oxygen 

 utilized in the combustion corresponds to 5.047 calories, but when pure 

 fat is burned each liter of oxygen corresponds to 4.686 calories. Zuntz 

 and his co-workers have prepared a table showing the calorific equivalent 

 of the oxygen consumption when fat and carbohydrate are burned. 1 This 

 has been most ingeniously elaborated by Williams, Riche, and Lusk. 2 



By studying the output of carbon dioxide and the intake of oxygen, 

 not only is information secured regarding the total oxidation of material, 

 but also some idea is gained of the character of the combustion by 

 noting the relationship between the volume of carbon dioxide given off 

 and the oxygen absorbed. With equal volumes of carbon dioxide and 

 oxygen, this relationship or ''respiratory quotient" is 1.0 and indicates 

 that carbohydrate has been exclusively burned. When the respiratory 

 quotient approximates 0.7 the indication is that fat has exclusively 

 been burned. By this means, therefore, it is possible to compute with 

 great accuracy the heat output from the total oxygen consumption and 

 the respiratory quotient. 



In certain earlier researches, and especially prior to the time when 

 methods were devised by which oxygen absorption could be more 

 easily determined than formerly, the measurements of the carbon- 

 dioxide output alone were used, but a much greater error is introduced 

 into the computations by this method. Unfortunately, of the two 

 factors, carbon dioxide and oxygen, that which is of the greater sig- 

 nificance, namely, oxygen, is the more difficult of determination, while 

 the measurement of the carbon-dioxide excretion is relatively a simple 

 matter. 



METHODS OF STUDYING THE GASEOUS EXCHANGE DURING 



WALKING. 



Inasmuch as a study of the problem of the energy transformations 

 during walking demands a careful study of the gaseous exchange, we 

 find all the methods used based upon this principle. The simplest is 

 that in which the subject walks inside a closed chamber by means of 

 which the product of respiration carbon dioxide is easily collected. 

 This method was first employed by Sonden and Tigerstedt 3 in the clas- 

 sical research with their large respiration chamber in the Karolinska 

 Institute in Stockholm. This chamber had a capacity of 100 cubic 

 meters and, unlike any respiration chamber previously used, permitted 

 the subject free movement. When the subject walked back and forth 

 across the room, a considerable distance could be traversed. At that 

 time only the carbon-dioxide output was determined with this method. 



x Zuntz and Schumburg, Physiologic des Marsches, Berlin, 1901, p. 361. 

 2 Williams, Riche, and Lusk, Journ. Biol. Chem., 1912, 12, p. 357. 

 3 Sonden and Tigerstedt, Skand. Archiv f. Physiol., 1895, 6, p. 165. 



