Graphical Analysis and Experimental Determination of the Active State in Frog Skeletal Muscle

1) The time course of the active state was calculated bymathematical analysis based on the three-component model and comparedwith the experimental curve determined by quick release or stretchin the small bundle preparation dissected from frog semitendinosusmuscle at 10°C.2) The three-component model contains a contractile component, which consists of a force generator and a viscous-like component, and aseries elastic component. The active state as the force of the force generatoris determined by substituting the tension and velocity curves of thecontractile component for the force-load-velocity relation.3) By this analytical method, the entire active state curve can be determinednot only in the isometric but also in the isotonic contraction.4) The active state of the isometric twitch does not reach its full extentof Po but only 0.7-0.8 Po.5) In the isotonic contraction the duration of the active state decreaseswith decreasing load, and the rate of rise of the active state increasesat the transition from isometric to isotonic contraction.6) The active state curve determined by quick release or quick stretchagrees approximately with the curve determined by the analytical methodwhen the amount of release or stretch is less than 2% of the muscle length, although the experimental curve varies with the amount of release orstretch.