LEAPING. 447 



b. Leaping. 



In the action of leaping, the whole body is raised from the ground ; 

 and, for a short period, suspended in the air. It consists, essentially, 

 in the sudden extension of the limbs, after they have undergone an 

 unusual degree of flexion. Leaping may be effected directly upwards, 

 forwards, backwards, or laterally. 



In the ordinary case of the vertical leap, the head is slightly bent on 

 the neck; the vertebral column curved forwards; the pelvis bent upon 

 the thigh; the thigh upon the leg; and the leg upon the foot; the heel 

 generally pressing lightly on the soil, or not touching it at all. This 

 state of general flexion is suddenly succeeded by a quick extension of 

 all the bent joints; so that the different parts of the body are rapidly 

 elevated, with a force surpassing their own gravity, and to an extent 

 dependent upon the force developed. In this general muscular move- 

 ment, the muscles that form the calf of the leg, and are inserted into 

 the heel, have to develope the greatest force, inasmuch as they have to 

 raise the whole body, and to give it the impulse, which surmounts its 

 gravity. They are, however, favourably circumstanced for the pur- 

 pose; being remarkably strong; inserted perpendicularly into the heel; 

 and having the advantage of a long arm of a lever. Figure 188 will 

 show, that whenever the body is bent in the position it assumes prelimi- 

 nary to a leap, opposite impulses must be communicated by the restora- 

 tion of the different parts to the vertical line B F. The leg B will tend 

 to impel the body backwards, by following the curved line C G. CD, on 

 the other hand, by -describing the curve D I, will tend to impel it forward; 

 whilst the head and trunk, represented by the line D E, will describe 

 the curve E F, and give an impulse backward. Every vertical leap 

 must, therefore, be a mean between these different impulses, or rather 

 the backward and forward impulses must destroy or neutralize each 

 other ; and that which is concerned in the elevation of the trunk be 

 alone effective. 



In the forward leap, the movement of rotation of the thigh predomi- 

 nates over the impulses backward, and the body is projected forward. 

 On the other hand, the impulses of the vertebral column, and of the 

 leg on the foot, prevail in the backward leap. The length of the lower 

 limbs is favourable to the extent of the leap. The forward leap, in 

 particular, is greatly dependent upon the length of the femur, in which 

 the forward impulse is situate. It does not appear, that any kind of 

 impulse is communicated to the body, at the moment of leaping, by 

 the surface on which we rest, unless it be very elastic. In this last 

 case, however, its reaction is added to the effort of the muscles, that 

 occasion the elevation of the body ; hence, the wonderful leaps of the 

 performers in circuses and on the tight-rope. On the other hand, if 

 the soil does not afford the necessary resistance, and yields to the feet, 

 leaping is almost or wholly impracticable. 



The upper extremities are not without their use in leaping. They 

 are brought close to the body, whilst the joints are bent, and are sepa- 

 rated from it at the moment when the body leaves the ground. By 

 being held firmly in this manner, they allow the muscles, that pass from 



