LOCOMOTION 



363 



It is obvious that the effort required for propulsion increases 

 in proportion to the resistance. The intensity of the effort can 

 be gauged by the prominence of the quadriceps and sural muscles. 



In this case no certain computation can be made of the work 

 done, as it is dependent, amongst other factors, on the inclination 

 of the body, the manner in which the arms are used, and the parts 

 sustained by various groups of muscles in the operations. 

 Furthermore, familiarity with the work done may result in a 

 reduction in the static effort and an elimination of unnecessary 

 motions which may considerably modify the results. Neverthe- 

 less, the variations in the work done can be measured by the cor- 

 responding consumptions of oxygen. 



277. The Ascending Walk. We will now consider the operation 

 of walking up a staircase or an inclined plane. 



In walking upstairs one of the legs is raised by flexion at the 

 knee, and its foot is placed flat upon the next step of the stair. 

 A contraction of the quadriceps muscle permits this elevation and 

 also the previous flexion in regard to the trunk (vide fig. 258). 

 The " carrying " leg is now in extension. Next the body is 

 inclined forward and the Centre of Gravity is, thereby, brought 



over the bent leg. This leg 

 now is gradually straightened, 

 sustaining, the while, the whole 

 weight of the body and the 

 rear leg, by a movement com- 

 bining oscillation and slight 

 flexion, is brought to the upper 

 step. Generally it does not 

 remain here, but by an increased 

 flexion it is taken on to the next 

 step, the other member be- 

 coming in its turn the carrying 

 leg. 



If the horizontal distance be- 

 tween the steps is reduced, the 

 oscillation is, likewise, dimin- 

 ished, but the period of "double 

 support " is lengthened. 



The work done is equal to the 

 weight of the body multiplied 

 by the height ascended. An 

 examination of the curve of 



W///////////M 



FIG. 258. 



Mounting a staircase. 



ascent will show that the ver- 

 tical oscillation of the Centre of 

 Gravity, which take place on the level, disappears in this case. 



