HUMAN MOVEMENTS 137 



At the moment of jumping, the leg in contact with 

 the ground is violently extended, thereby imparting 

 a vertical impetus to the body, at the same moment 

 the arms are thrown up, giving additional energy to 

 the effort. 



The successive images show the jumper after he 

 has left the ground, with the arms elevated in front 

 and the legs separated ; later on, the arms drop, and 

 the legs are brought nearer together as they become 

 more advanced in front of the body, so that finally the 

 heels of both feet touch the ground together, and in 

 front of the centre of gravity of the body. A fall on 

 the face is thus obviated. At the moment of descent 

 the legs are flexed, so as to counteract the impetus 

 of the body. 



The distance cleared is more or less extensive, 

 according as this series of actions is skilfully or 

 clumsily executed, and according as the jumper lands 

 advantageously on the ground or the reverse. If he 

 has miscalculated his speed, and his feet are not 

 sufficiently far advanced in front of him at the 

 moment of landing, he cannot retain his balance, but 

 has to run forward a few steps until the impetus is 

 checked. 



In the case of pole-jumping (Fig. 93), it is equally 

 easy to follow the various stages. The jumper fixes 

 the end of his pole in the ground, and at the same 

 time raises himself by a vigorous extension of the 

 legs. The combined action of the vertical and hori- 

 zontal impulses imparted to the body enables it to 

 describe an arc of a circle. In falling, the body will 

 continue this curve, and will land just as far in advance 

 of the point of the pole as it was behind it at starting. 

 But a skilful jumper can avail himself of an artifice 

 which enables him to augment his jump considerably. 

 It consists in elongating the radius of the circle 



