YIELD OF THE HUMAN MACHINE 197 



On the other hand any method of activity (walking, ascending, 

 bicycling, moving the pedals of machines with the feet) which 

 utilises exclusively the muscles of the legs, gives an average 

 net yield of 30%. 



In order to include both resistant and motive work, whose 

 expenditures are so different, it is assumed that the former equals 

 T 5 o 2 n of the latter. 



^ In fact, in his experiments on the quarrier's winch ( 134) 

 Chauveau found the following relation between the expenditures : 



Cal. 

 f Ascent ......... 206-50 245 277 292 380 = 1,400-50 



- 117 131-50143-50144 203 = 738 



hence : 738 52 



1,400-5 ~KK> 



but this ratio only holds good if the speed is the same in the 

 two directions of movement and does not exceed 0-12 metres 

 per second ( 116). Thus, if 152 calories is expended in the 

 work of lifting, followed by a descent, 100 calories would be attri- 

 buted to the motor expenditure and 52 calories to the expenditure 

 during the descent. Finally, in the case of the arms, we have : 



T 



r^ = 0-25 ; whence T = 25 Calories. 

 1UU 



The useful effect is often in these 25 calories alone. In any 

 case the muscular work is : 



25 Cal + (52 x 0-25) = 38 Calories. 

 and the total mechanical work : 



25 X 2 = 50 Calories. 



It goes without saying that the muscles should always be 

 worked under the least onerous conditions, and that the estimate 

 of the work done should be made according to the expenditure 

 of energy, as has been shown since 1909 ; which has an eminently 

 practical value f 1 ). The idea has been revived by Jules Lefeure, 

 under the title of The Motor Equivalent (?) of the resistant work 

 (see also 300). 



There is nothing definite to note on the subject of the industrial 

 yield ; it varies from 4 to 10% in proportion as the quantity of 

 daily work increases, and reaches 16% with difficulty. In a 

 working day of 8 hours, unless there is inefficient use of the 

 muscular forces, a waste of energy, or insufficient work, it should 

 not be less than 10%. Its consideration has no scientific interest, 

 whilst under definite conditions of work, a knowledge of the 



(*) Jules Amar, Le Rendement, p. 73-74. 



