WALKING AND RUNNING. 485 



forward like a pendulum. In starting, one foot is placed behind 

 the other, so that the line of gravity lies between the two, the 

 hindmost limb having the ankle and knee a little bent. By 

 suddenly straightening these joints, it gives a "push off" with 

 the toes and propels the body forward so as to move it around 

 the axis of motion of the fixed or supporting ankle joint. At 

 the end of the swing, the pendulous leg comes to the ground and 

 leaves the other limb in the attitude ready for the push off. 

 Thus on level ground walking is carried on with but small 

 muscular exercise ; but in ascending a steep incline or going up 

 stairs, the supporting limb has to elevate the body at each step 

 by extending the knee and ankle joints by the thigh extensors 

 and the calf muscles. 



Running is distinguished from walking by the fact that, while 

 in the latter both feet rest on the ground for the greater part of 

 each pace, in the former the time that either foot rests on the 

 ground is reduced to a minimum, and, in fact, the supporting limb 

 disappears. The legs are kept in a semi flexed position ready for 

 the push off or spring, which is so forcibly carried out that the 

 body is propelled through the air without any support. Thus an 

 interval of greater or less duration according to the pace exists 

 during which both the feet are off the ground, as the moment 

 either foot comes to the ground it executes a new spring without 

 waiting for the pendulous swing described in walking. 



