110 THE HUMAN BODY 



ally leaving the ground, and its toes only are at that moment 

 upon it: from these a push is given, as before, with the right foot, 

 and the knee being bent so as to raise the foot, the left leg swings 

 forwards at the hip-joint to make a fresh step. 



During each step the whole Body sways up and down and also 

 from side to side. It is highest at the moment when the advanc- 

 ing trunk is vertically over the foot supporting it, and then sinks 

 until the moment when the advancing foot touches the ground, 

 when it is lowest. From this moment it rises as it swings forward 

 on this foot, until it is vertically over it, and then sinks again 

 until the other touches the ground ; and so on. At the same time, 

 as its weight is alternately transferred from the right to the left 

 foot and vice versa, there is a slight lateral sway, commonly more 

 marked in women than in men, and which when excessive pro- 

 duces an ugly " waddling" gait. 



The length of each step is primarily dependent on the length 

 of the legs; but can be controlled within wide limits by special 

 muscular effort. In easy walking little muscular work is em- 

 ployed to carry the rear leg forwards after it has given its push. 

 When its foot is raised from the ground it swings on, like a pendu- 

 lum ; but in fast walking the muscles, passing in front of the hip- 

 joint, from the pelvis to the limb, by their contraction forcibly 

 carry the leg forwards. The easiest step, that in which there is 

 most economy of labor, is that in which the limb is let swing 

 freely, and since a short pendulum swings faster than a longer, 

 the natural step of short-legged people is quicker than that of 

 long-legged ones. 



In fast walking the advanced or supporting leg also aids in 

 propulsion; the muscles passing in front of the ankle-joint con- 

 tracting so as to pull the Body forwards over that foot and aid 

 the push from the rear foot. Hence the fatigue and pain in front 

 of the shin which is felt in prolonged, very fast walking. From 

 the fact that each foot reaches the ground heel first, but leaves 

 it toe last, the length of each stride is increased by the length of 

 the foot. 



Running. In this mode of progression there is a moment in 

 each step when both feet are off the ground, the Body being un- 

 supported in the air. The toes alone come in contact with the 

 ground at each step, and the knee-joint is not straight when the 



