LOCOMOTION 337 



selves so that the knees straighten themselves to resist the pres- 

 sure and are not bent by the weight. In the " easy " attitude 

 the joint between hip and knee lies 1 cm. behind the frontal plane. 

 The tension caused by the weight of the bust is such that the 

 knees lose their stiffness. If the bone of the patella is touched 

 it will be found to be absolutely slack, while, on the other hand, 

 the muscles of the calf and the ligaments of the knee are firmly 

 stretched. ( l ) 



In the same way the joint of the foot, which receives the thrust 

 of the leg, supports at its upper extremity the weight of the 

 bust and the thigh. In the " easy " attitude the joint between 

 the tibia and the foot lies 5 cm. behind the frontal plane, that 

 is 4 cm. behind the plane of the knee-joint. The muscles of the 

 sole of the foot have therefore to balance the moment of 

 rotation of the weights under consideration. 



We have, for a lower member, the following : 



WEIGHT IN KG. PERCENTAGE OF TOTAL 



WEIGHT OF BODY. 



Thigh ... 6-800 11-64 



Leg and foot ... 3-990 6-83 



Total for lower member 10'790 18'47% 



Therefore the combined weight of both lower members is 

 21-580 kg., 36-94% of the total weight of the body. 



The muscles of the soles of the feet have therefore to balance 

 a moment of rotation produced by a weight of : 

 36-820 + 2 x 6-800 - 50-420 kg. 



The arm of the lever is about 4 cm. in length. On the other 

 hand, the Achilles Tendon draws up the heel, which causes, in 

 effect, pressure by the front of the foot on the ground, by which 

 the total weight of the body is transmitted, the reaction of the 

 ground on the foot being equal and opposite. As long as the 

 line of gravity of the complete body falls within the base of sup- 

 port constituted by the feet, equilibrium is maintained and the 

 standing position is possible. 



261. Economical Attitudes of the Human Body. In the 



standing attitude the base of support depends on the position of 

 the feet whether the heels are together or separated. The 

 body is in equilibrium if the line of gravity falls within the 

 base of support. The nearer that line is to the centre of the 

 polygon of support, the more stable is the equilibrium. 



When the feet are in the position shown in fig. 237, with 

 the heels touching, the base of support has a greater dimension 



( x ) Haycraft Animal Mechanics in Schafer's Text-book of Physiology, 

 Vol. 2, p. 228, 1900. 



