374 



THE HUMAN MOTOR 



varies from -4 to -9 small calories approximately. It will be seen 

 from the curve in fig. 268 that the minimum expenditure is at a 

 speed of 4-5 km. per hour which is therefore the most economical 

 speed of walking. 



To take a concrete case. If a man, weighing 65 kg., walks at 

 5-4 km. per hour, the expenditure per metre-kilogramme is -56 

 small calories per kg. of the body's weight. 



The expenditure, for a single pace of -78 metres in length, is 

 therefore 



56 X 65 X -78 = 28-392 small calories. 



We have seen (vide 272) that, in the case of the experiments 

 of Braune and Fischer under similar conditions, the muscular 

 work was found to be 6 kilogramme-metres. If, therefore, we 

 convert the above expenditure of 28-392 small calories into kilo- 

 gramme-metres we find that the apparent nett efficiency is : 

 n 



28-392 x -425 = 49% W^^y- 



This efficiency is obviously too high. We cannot therefore 

 have much confidence in the accuracy of values obtained by the 

 above method. Reliable results are only to be obtained by 

 measurements of the consumption of oxygen. On this basis we 

 shall find that, for ordinary speeds of walking (without a load) 



from 4 km. to 6 km. per hour, 

 the consumption is equivalent 

 to from -5 to -6 small calories per 

 metre-kilogramme. We shall 

 also see that the most economi- 

 cal speed is 4-5 km. per hour. 



Fig. 269. Zuntz's portable 

 respiratory apparatus. 



The preceding experi- 

 ments are fairly consistent and 

 reliable. The probable error is 

 not more than 2% plus or minus. 

 Zuntz's experiments were carried 

 out with a portable apparatus 

 for the measurement of the 

 gases mounted on the shoulders 

 of his subject (vide fig. 269). 

 The speed was measured by a 

 tachometer fixed to the head. 

 He caused his subjects to tra- 

 verse various distances for at 

 least 8 or 10 minutes. 



