CERTAIN MOVEMENTS IN MAN 159 



enlarged figure. So that, if the weight is 75 kilo- 

 grams, and the amplitude of the oscillations 0*04 

 of a metre, each elevation of the body wi^l represent 

 3 kilogrammetres of positive work, and each depres- 

 sion the same amount of negative work. As there are 

 two double oscillations of this kind in a completed 

 step, the muscular work corresponding to the verti- 

 cal oscillation will be 12 kilogrammetres for each 

 step.* 



B. Muscular Wtrk expended on Movement in a 

 Horizontal Direction in Walking. — The velocity of the 

 horizontal movement of the body is subject to periodic 

 variations, and hence there must be periodic variations 

 in the energy required, in proportion to the work 

 executed in the different phases of foot-contact, whether 

 this work be represented by movement or by resistance. 

 These variations in speed are deduced from the degree 

 of separation of the points on the trajectory, because 

 these points are photographed at equal intervals of 

 time, lor instance, at intervals of -^ of a second. The 

 horizontal projection of these intervals allows one to 

 construct the velocity curve of the horizontal move- 

 ment by taking as ordinates lengths which correspond 

 to the distances which separate the points, that is to 

 say, which correspond to the velocity. 



From the maximum and minimum velocities of the 

 body mass, the corresponding measure of the energy 

 expended can be deduced. The energy developed 

 by muscles both in producing movement and in 

 offering resistance is equal in each case to half the 

 variation of the vital force. So that the total sum 

 of these two forms of energy can never exceed the 



* This estimate, namely, the body weight multiplied by twice the 

 height of the vertical oscillation, is an inexact valuation, which does 

 not really give the expenditure of muscular force : a certain portion of 

 the energy seems to store itself up in the muscles during each period 

 of descent, and to be liberated in the next phase of ascent. 



