428 MOVEMENTS OF THE LIMBS 



The body then falls forwards and towards that side on which the 

 foot has moved. This brings the centre of gravity over that foot, 

 and to prevent undne nuiscnlar action this leg is straightened, 

 bringing the centre of gravity right over the ankle-joint, etc., as 

 already explained. The other foot aids this process of the re- 

 distribution of the incidence of the weight of the body by pushing 

 against the ground with its toes and raising the heel from the 

 ground to do so. The second foot is now raised clear of the ground 

 by flexion at the knee and lifting of the toes. This foot follows a 

 similar path to the first foot, i.e. is swung forward by muscular 

 contraction until it reaches a position where the heel is placed on 

 the ground by the extension of the knee. 



The leg thus acts, in walking, like a compound pendulum, and, 

 therefore, the amplitude of its swing, i.e the length of the stride, 

 will be determined by the length of the pendulum, i.e. by the 

 distance between the centre of gravity of the limb and the hip- 

 joint. A short leg will, therefore, have a short quick sw'ing, and 

 a long leg a long slow one. By altering the effective length of the 

 pendulum by lowering or raising the centre of gravity of the limb 

 one produces an amplitude of swing to which the leg muscles are 

 not accustomed. Fatigue wdll in these circumstances set in more 

 rapidly than normally. The alteration in the centre of gravity 

 may be accomplished quite simply by wearing extra heavy or 

 extra light-weight shoes. 



As was mentioned above, the hip moves backw^ards to compen- 

 sate the shift forwards of the centre of gravity. One would, 

 therefore, expect to find a compensatory movement of the hips in 

 walking in order to keep the centre of gravity near the inner 

 border of each foot in turn. Not only does this side-to-side 

 movement take ])lace, but two other hip movements occur which 

 together cause the hips to follow the line of a double sigmoid 

 curve with each complete step. (1) When the body is falling 

 forward the hip moves in the arc of a circle, of which the centre is 

 the ankle-joint and the radius is the distance between hip and 

 ankle, (2) During the period when the weight of the body is being 

 shifted to the other leg the hips trace the arc of a circle whose 

 radius is half the distance of foot to ground. 



Owing to the shortness of the ileo-fcmoraJ ligament in the 

 female, her leg cannot swing back as far as that of the male. If 

 she wishes to lengthen her stride to keep ])ace with a male partner, 

 she must twist her pelvis on the vertebral column. Because of the 

 ileo-femoral ligament and the wide pelvis, the adult female has a 

 gait characterised by a greater degree of rotation than that of the 

 male or of the younger female. 



