Figure 19.

Quick releases of a high amplitude simulated by the model of Figure 14.

(a) Isometric state, the torques 1 and 2 are equilibrated. (b) During the release the Z-filament twisting stage increased transiently e.g. to >B, when the zero point of the Hookenian elasticity is passed over and the thin filament becomes slack. But the thin filament torque has started rotation (arrow 3), and drills the thin filament into the myosin cross-bridges (arrow 4), as long as shortening is stopped. (c) When shortening is stopped, e.g. at the Z-filament twisting stage <A, Ca²⁺ was displaced already in stage >B, resulting in feedback oscillations and reversal or reduction of torque (arrow 1), so that the increasing thin filament torque (arrow 2) can again untwist the Z-filaments and produce force redevelopment. (d) A second release, e.g. in a slack test, can further relax to stage A, where a torque equilibrium may be not more possible (comp. Figure 15 b, c). The strong force-deficit or torque-loss is here shown by the decreased pitch of the model thin filament, that does not so occur in real thin filaments.