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MECHANICS OF LOCOMOTOR APPARATUS 119 



the number of steps exceeds 150 per minute, i.e. when the duration 

 of the step becomes less than 0'4 second, the speed of walking 

 does not increase because the length of step diminishes. 



The force of walking depends on the extensor muscles of the 

 thigh, leg, and foot. 



Fig. 80 gives an exact idea of the position of the principal 

 articulations not only of the lower limbs, but also of the upper 

 limbs and the head at the different moments of the step cycle. 



FIG. 79. Tracings of the pressure applied to the ground in walking. (Carlet.) Pd, right foot ; 

 Ps, left foot; Of, vertical oscillations; Oo, horizontal oscillations. 1, 2, 3 = period of double 

 application; 3, 4, 5 = period of single application; 1-7 = period of application of left foot; 

 5-11 = period of application of right loot ; 1-3 and 5-7 = application of heel of left or right foot ; 

 4-5 and 8-9 = application of point of left or right foot. 



The cycle begins at the instant in which the left leg is raised 

 from the ground and swings forward, while the heel of the right 

 leg rests upon the ground. 



Each step is divided into 10 successive phases of equal duration, 

 and at every 10th phase the right leg is in the position originally 

 occupied by the left, and vice versa. From the 1st to the 5th 

 phase, which include the first half of the step, the left knee 

 becomes flexed, while the right becomes extended, so that the thigh 

 and shoulder joints (represented by the junctions of the black and 

 red lines) and the vertex of the head (represented by the big dots 

 marked on the upper part of the figure) are somewhat raised. 

 From the 6th to the 10th phase, which include the second half of 



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