LOCOMOTION 367 



not subject to any great fatigue. In the second case it is subject 

 to greater fatigue owing to being bent. The tendency is, there- 

 fore, to increase the rate of the change of the weight from one leg 

 to the other. The steps, therefore, become less in length, but 

 more in number, and the descent is carried out with more speed, "f 1 ) 



281. Running.- T*he most salient characteristic of the move- 

 ments of the act of running is not so much its speed, but the fact 

 that the period of " double support " disappears. The legs are, 

 indeed, alternately in single support, but during their alternation 

 there is a moment when the body is completely off the ground, 

 in suspension. All the phases of the act of walking are to be 

 found in the act of running, except that the period of " double 

 support " in the former is replaced by the above-mentioned 

 period of "suspension." The lower members, however, remain 

 bent, the degree of flexion depending on the speed of running. 



Generally the leg which is on the ground rests on the entire 

 sole of the foot. (In very fast running the toes alone may touch 

 the ground.) Before it is developed by the full extension of the 

 lower limb the flexor 

 muscles - - gastrocne- \f ^ 



mius and soleus con- 

 tract and thrust the 

 limb from the ground 

 sharply. The result is Fio 2 



a s U C C e s S i O n of "pres'sures of the feet in running. 



bounds from one 



leg to the other. As the speed increases the period of the sus- 

 pension also increases, while the period of support grows less 

 being sometimes no more than a mere touch of the foot on the 

 ground. The resultant impact increases with the speed. Its 

 vertical component V (vide fig. 263) is always positive. The tan- 

 gential component H is first negative and then positive. 



The greatest speed which is reached in racing is about 10 metres 

 per second, i e., three or four paces, varying from 2-5 m. to 3 m. 

 in the second. The time of a pace varies from -20 to -35 seconds 

 as the length varies from 1-5 m. to 3-4 m. The period of the 

 suspension also increases with increased length of pace. The 

 total period of suspension first for the single leg and then for 

 both together aggregates approximately -25 seconds, the latter, 

 the " double " suspension lasting for 8 or 9 hundred ths of a 

 second (vide the curved line in fig. 264) . 



( x ) Histoire A cad. Roy. des Sciences, 1721, p. 24. 



