268 ANIMAL MECHANICS. 



the body, we notice that the trunk oscillates upwards and downwards 

 on a vertical plane. A crest occurs about the middle of the period 

 during which the limb rests upon the ground. There is another crest 

 which occurs while the leg is off the ground, and this coincides with 

 the middle of the period during which the other leg not represented 

 in the figure is in contact with the ground. 



If we study the position of the limb just before it leaves the ground, 

 it will be noted that the limb is fully extended and forms the hypo- 

 tenuse of a right-angled triangle, whose vertical side falls from the hip- 

 joint to the ground. The trunk is now falling, and in order that 

 the leg may be brought forward free of the ground, it is bent by muscular 

 exertion and reaches its maximum of bending. It then extends until 

 the heel reaches the ground and the limb is once more straight. While 

 the foot remains upon the ground, and while the hip is still advancing, 

 the knee is once more bent, but to a slighter extent. The limbs are 

 straight, therefore, at the moment when they reach and leave the 

 ground ; they are bent at all other times. 



Running. In the case of running, the body remains suspended for a 



FIG. 159. Chronograph of the movements of a man's leg in running. 

 Read from right to left. After Marey. 



moment in the air (see Fig. 156, 3 and 4 ), that is to say, one limb leaves 

 the ground a little before the other leg reaches it. On examining 

 Marey 's chronophotographic figure (Fig. 159) representing a running 

 man, it will be noticed that although the limbs are never quite 

 extended, as in walking, yet the greatest extension is at the time the 

 foot reaches, and then again at the time it leaves, the ground. 



In running, the length of the stride may be greater than in walking, and 

 the frequency of stride may also be greater. On this account it is often stated 

 that a man can run three times as fast as lie can walk. This is undoubtedly 

 an error, as the running and walking " records " conclusively show. While the 

 record for the mile run is 4 minutes 18 seconds, the record for the mile walked 

 is 6 minutes 36 seconds 1 . Even if we calculate for running on the running 

 pace for 100 yds. (10 seconds), this gives for the mile run 2 minutes 56 

 seconds. 



Relationship between duration and length of stride. According 

 to the brothers Weber, 2 there is in walking a relationship between the 



1 Amateur records up to 1895. - " Mechanik der Gelnverkzeuge." 



