Figure 14. Hill-type muscle model and its properties.

A) Three-element Hill-type model. CE, contractile element; PE, parallel elastic element; T, tendon; m, mass of muscle fascicles. B) Normalized force-length relationship of the contractile element fully activated and producing force isometrically, i.e. without length change. Force is normalized to the maximum muscle force developed by the fully activated muscle at its optimal length. Length is normalized to the optimal muscle fascicle length. C) Normalized force-velocity relationship of the contractile element. Velocity is normalized to the maximum shortening velocity. Positive velocity corresponds to shortening. D) Normalized tendon force-length relationship. Parameters F_Tnl, L_Tnl and $L_T^{Max}$ are empirical constants; L_To is the resting (slack) tendon length. Adapted from (686).