THE MUSCULAR MOTOR AND ALIMENTATION 123 



perpendicular to it, which latter would, from a mechanical point 

 01 view, be the most efficient position. The loss of power is com- 

 pensated by the resultant economy in space. 



Numerous measurements 



Fig. 125. Muscular action. 



87. The useful action of a muscle is therefore a function of 

 its mass (active fibres), of its degree of contraction, and of the 

 angle which its direction makes with that of the bone to be moved. 

 The muscle has a definite moment of rotation in relation to 

 the axis, for each of its positions. The moment of rotation is 

 the product of the force F of the muscle by the distance d (fig. 125) . 

 We have: M = F x d. 



The contraction modifies F and d. 

 of the moment of 

 rotation have been 

 made by Braun & 

 Fischer ( l ) on ana- 

 tomical specimens. 

 F being deduced 

 from the size of the 

 muscular section ; it 

 was found that the 

 moment varied with 

 the angle of flexion 

 up to a certain value. 

 When the arm is 

 fully extended the 



product of F and d 

 is not zero, as might 

 be expected. It 







Fir, 



( l ) Braune et Fischer (Abhandl..., vol. xv., n 3, p. 247, 1889). 



