366 



A A D V = work diagram, in reality the hypothenose is not straight but has a 

 concave curve. The A has the same area as the rectangle A M M' V. 



A M = the average tension. 



Work = A M X A V kilogrammeters if the size of the ordinate as expressed in 

 kilograms and the abscissa in meters. 



FIG. 386 



Although the muscle works with a changing tension, yet the accomplishment is 

 the same as if it were contracting with the tension of the midposition. 



In reality the amount of work is somewhat greater since even in extreme con- 

 traction the muscle still retains a certain amount of tension so that the maximum 

 amount of work is more nearly like AD X. We know that a muscle may have 

 an extreme actual shortening of about 80 per cent, of its length when the tendon 

 of insertion is cut. 



The trapezoid A D S V represents more nearly the amount c.f work, but since 

 there are only approximate values and A D S V is not much larger than A M M' V, 

 we may use the latter. 



Only the tension and amount of shortening are needed to determine the amount 

 of work of the muscle. Neither the lever arm nor the fiber angle in pinnate muscles 

 need be considered.' 



The diagram Fig. 367 shows that the lever arm is of no importance for deter- 

 mining the amount of work the muscle performs. 



J B and J B 1 = two bones jointed at J. CD and E F = the direction of the pull 

 of two muscles of equal cross-section, each having a muscle tension of 1000 gms. 



The centers of the attachments are such that perpendiculars J c and J e to 

 C D and E F are equal to 40 and 23 mm. respectively, J c = 40 mm. and J e = 

 23 mm. The static moments are equal to 1000 X 40 and 1000 X 23, therefore the 

 first muscle can hold a much larger load (L) on the bone J B 1 at H l (100 mm. from 

 J) than the second muscle whose load can be designated as L 1 . 



Equilibrium exists for the first muscle if 



L X 100 = 1000 X 40 or L = 



1000 X 40 

 100 



= 400 gms. 



For the second muscle L 1 X 100 = 1000 X 23. 



71 1000 X 23 



L 1 = -JQQ = 230 gms. 



If we suppose J B to be fixed and J B 1 to move in the plane of the paper about 

 J and the muscle C D to shorten 5 mm. C d = C D 5 mm. and with the tension 

 of 1000 gms., J B 1 will take the position J B z and the load (L) will be lifted from 

 H l to H\ 



