366 THE HUMAN MOTOR 



not as in the case of a slow descent, placed flat on the ground. 

 It will be seen that somewhat more work is done by the 

 " carrying " leg. During the transition from one step to another 

 on a stairway the body has to be balanced on one foot only. 

 This explains the difficulty experienced by young children in 

 going up and downstairs. A similar difficulty is expenenced 

 when carrying a heavy load. In both cases small steps are taken 

 and large oscillations 'of the Centre of Gravity are avoided. 



A stairway suitable for the use of persons carrying loads should 

 have comparatively low steps. The height of the step should 

 be from 7 to 10 cm. instead of the usual height of from 15 to 20 

 cm. Especially is this desirable if the persons carrying the 

 loads are of small stature. If this is not done the excessive 

 flexion of the knees induces rapid fatigue. 



280. The descent of an inclined plane is not exactly analagous 



to the foregoing. The body 

 must be inclined in order to 

 maintain the same, length 

 of the pace AB' instead of 

 AB" = AB (fig. 262). 



The leg OB is in exten- 

 sion, but the leg OA is in 

 flexion and, the steeper the 

 slope of the plane the more 



Descent of an inclined plane. . g ^ bent ^ ^ thereby 



allowed to settle itself, so 



to speak, and to withstand the force of Gravity. The feet rest flat 

 on the ground and the period of " double support " is longer 

 than when walking on the level. Propulsion is assured by the 

 tangential component of the force of Gravity which is propor- 

 tional to the slope of the plane ( 52). 



The muscular work is practically the same as that involved in 

 the descent of a stair of the same height as the plane, followed by 

 progress on the level for the corresponding distance, but owing 

 to the bending of the knees the oscillations of the Centre of Gravity 

 appear to be considerably less than when walking on the level. 

 It is also to be noted that this bending appears to increase as the 

 slope is steeper. 



This ruethod of walking is very complex in spite of the fact that 

 the muscular activity exerted is comparatively small. Most of 

 the work is done by the quadriceps muscle, the important functions 

 of which have been already referred to. 



Reaumur and de Mairan have observed that the length of pace 

 in ascent is greater than in descent. They explain this as follows : 

 " In the first case the ' carrying ' leg remains extended, and is 



