204 



PRACTICAL PHYSIOLOGY. 



fxxxvi 



For isometric curves Fick attached a muscle to the short arm of a lever, the 

 other arm being prevented from moving much by the resistance of a strong 

 spring. In this way one obtains a curve, which shows little change of form, 

 but indicates the increase and decrease of tension during the contraction, the 

 length of the muscle remaining nearly constant, and for this reason Fick 

 called it " isometric." Of course an absolutely isometric curve cannot be 

 recorded. 



FIG. i2i. Muscle-Curve of Frog's Gastrocnemius. The lower line indicates time 

 and each double vibration (D. F.)= T j n sec. 



If one compares an isotonic and isometric curve from the same muscle, one 

 finds that the apex of the isometric curve lies nearer the beginning of the 

 contraction than that of the isotonic curve, i.e., the length remaining the 

 same, the isometric curve reaches the maximum of its tension sooner than it, 



the tension being the same, 

 reaches the maximum of its 

 shortening. Moreover, the iso- 

 metric curve is flat-topped, so 

 that it remains for some time in 

 contraction (fig. 122). 



2. Registration of Ten- 

 sion of a Muscle (Fick). 

 When the two ends of a 

 muscle are so fixed that 

 during activity they cannot 

 approximate towards each 

 other, then the muscle does 



not change its length but only its tension. Fick calls this an 



" isometric " method. 



One can record the change in tension by means of a " tension- 



Fia. 122. a. Diagram of isotonic, b, isometric 

 muscle-corves. 



