158 



MOVEMENT 



B. Horizontal work. 



C. Work expended on keeping up the oscillations 

 of the legs^Luring their period of suspension. 



A. Muscular Work done in a Vertical Direction. — 

 The movements of the head are practically the same 

 as those of the centre of gravity. Now, the trajectory 

 of the head-movements is an undulating curve (Fig. 

 107), which periodically reaches its maximum as the 

 foot arrives at the mid phase of contact, and similarly 

 reaches its minimum at the mid phase of suspension.* 



The parallel and dotted lines (Fig. 107), which are 

 tangents to the upper and lower limbs of this curve, 

 afford a measure, by the distance which separates 



rrr 



:t- 



Fig. 107.— Vertical oscillations of tlie head when walking. 



them, of the extent of the vertical oscillations of 

 the body. 



To measure the absolute extent of these discursions, 

 a transparency of Fig. 107 is thrown on the screen, 

 and enlarged by means of an optical arrangement to 

 its actual dimensions, so that the extent of a vertical 

 oscillation corresponds to the length of half a step 

 measured on the ground. The work done each time 

 the body is elevated or depressed can be estimated 

 by multiplying the weight of the pedestrian by the 

 vertical height which separates the dotted lines in the 



* On the other hand, in running, the maximum corresponds to 

 the period of suspension, and the minimum to the period ol contact. 



