ii MECHANICS OF LOCOMOTOE APPAKATUS 123 



as was said above, the duration of the contact diminishes with 

 increased speed. 



In order to form a true conception of the mechanism of 

 running it is very instructive to ascertain the exact moment at 

 which the vertical oscillations of the body reach their maximum 

 upward excursion. The Webers held that this occurred as the 

 body is projected upward and forward by the force of the impulse 

 given by the rapid extension of the limb in contact with the 

 ground. Marey's tracings show, on the contrary, that the body 

 attains the maximum of its vertical ascents as one foot comes to 



Fio. 82. Instantaneous photograph of running on a fixed plate. (Marey.) 



the ground. As shown by curve 0, Fig. 81, the head begins to 

 rise at the moment at which the foot touches the ground, and 

 reaches its maximum height midway through the period of 

 contact, after which it descends and reaches its minimum at the 

 moment when the foot leaves the ground, and before the other 

 foot comes into contact with it, i.e. during the phase of suspension. 

 This proves that the suspension is due essentially not to the 

 sudden extension of the leg but to its subsequent flexion, which 

 suddenly withdraws it from the ground after giving the upward 

 and forward thrust to the body. 



Both the leg on the ground and also the swinging leg are 

 much more active in running than in walking. The muscles of 

 the upper limbs also contribute to the forward thrust of the body, 

 since they oscillate alternately with the homologous lower limbs. 



The torsion of the trunk round a vertical axis and inclination 



