LOCOMOTION 



365 



the oscillation of the body, plus the inclination corresponding to 

 the step. 



Thus walking up an inclined plane is equivalent to walking on 

 a level and up a stair. The period of " double support " is pro- 

 longed, the quadriceps, and posterior muscles of the thigh are 

 contracted in the case of the " carrying " leg, and the muscles of 

 the calf cause displacement of the rear leg. But in ascending an 

 inclined plane the inclination of the body calls for a greater static 

 effort than would be needed in the ascent of a stair of a height 

 equal to that of the inclined plane. It might therefore be ex- 

 pected that the expenditure of energy in mounting to a given 

 height by an inclined plane would be greater than that required 

 to traverse the corresponding horizontal distance, and then to 

 reach the given height by means of a stair. 



279. The Descending Walk. In descending a stair slowly the 

 body is held upright, 

 the " carrying " leg 

 is bent, while the 

 other leg is moved, 

 fully extended, to 

 the lower step (vide 

 fig. 261) ; the latter, 

 then, in its turn, be- 

 comes the " carry- 

 ing " leg. The legs 

 always bend alter- 

 nately, while the 

 arms swing but 

 slightly. The force 

 of Gravity is coun- 

 teracted, and the 

 rate of descent main- 

 tained uniform by 

 the action of the 



triceps and solar 

 muscles. 



In a rapid descent 

 of a stair the body 

 bends so as to bring 

 forward the centre 

 of Gravity, the 

 flexion of the " carry- 

 ing " leg is reduced 



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-. ... Fio.2Gl. *> 



Descent of a staircase. 



also the work done by it, the oscillation of the arms, is almost 

 nil. The carrying leg will, however, be somewhat bent when the 

 lower step is reached so that the shock is reduced, while the tee 

 of the foot alone touches the ground at the first contact, and is 



