208 HUMAN PHYSIOLOGY 



Locomotion. In locomotion, the head, the trunk, and the 

 suspended arms must be regarded as a body balanced upon 

 the legs at the hip-joints. The legs support the body and, 

 by stretching, push it forward. The leg can swing forward 

 and backward without any muscular exertion. In order 

 that the one leg may swing forward, it is somewhat elevated 

 by a slight bending at the hip-, knee-, and ankle-joints; the 

 body is meanwhile supported by the other leg. 



The top part of the body is slightly bent forward during 

 locomotion ; this is the greater the faster the motion. The 

 forward movement of the body is produced by the alternate 

 action of one leg supporting the body and pushing it forward 

 while the other, slightly bent, swings forward. 



In walking, a period during which both feet are on the 

 ground is followed by a period in which only one is placed 

 on the ground while the other swings. In running, a period 

 during which neither foot rests on the ground is followed by 

 a period during which one stands while the other swings. 



The process from the beginning of the swinging of one 

 leg until the beginning of the swinging of the other is called 

 a step. The velocity of locomotion is the greater the 

 longer the step and the greater the number taken in a given 

 time (or the smaller the duration of the step). The velocity 

 of locomotion during walking is limited maximum 2.5 m 

 per second because, on account of the simultaneous resting 

 of both feet on the ground, the length and number of the 

 steps cannot exceed a certain amount. In running, the 

 velocity of motion can be greater than in walking because 

 the length and number of steps can be increased, on account 

 of the simultaneous swinging of both feet. 



In walking, the velocity is the greater the lower the 

 position of the head of the femur. Synchronously with the 

 movements of the legs, a rhythmical pendulation of the arms 

 takes place, in opposite direction to that of the legs. 



The alternate rising and sinking of the body during walk- 

 ing is small (about 32 mm). 



The work done by the body during walking on a hori- 



