VOL. 12 (1953) 



SERIES ELASTIC COMPONENT IN MUSCLE 



III 



length 100, then this muscle has length 140. F"rom equilibrium length 80 the muscle 

 must be stretched by 75% to reach this length. As the picture shows, the E-band now 

 distinguishes itself sharply by its low density from the A-band proper, having been 

 stretched almost to the limit of its reversible extensibility. The additive width of the 

 two E-bands is 20% of the whole height of the sarcomer. The appearance of the E-band 



Fia;. 3. Explanation in text. 



thus again accounts grossly for half of the gain in length of the muscle fiber. The x\-band 

 proper, if anything, has become narrower. The rest of the gain in length is accounted for 

 by the increase in the distance between the Z membrane and A-band. 



It is easy to predict the changes which can be expected to take place in an isometric 

 contraction : the E-band will appear. This is borne out by Fig. 4 which shows muscle of 

 equilibrium length in isometric contraction and should be compared with Fig.i which 

 shows muscle of the same length at rest. This figure also shows the protofibrils running 



References p. 133. 



