Frank Starling Law (length-tension relationship) from z-bands storing retractive force

The discovery in the 1950s of the sliding filament mechanism in the sarcomere, and later advances into Huxley’s model of the cross-bridge cycle, is now known to be caused by the thick and thin filament rotating into one another, like a screw in a plug (Jarosch, 2008). This can be easily seen with electron microscope, is self-evident, and models the data perfectly. Knowing this, the z-bands function is clear, they store retractive force for relaxing the muscle, through twisting the thin filaments fibers around one another. And knowing this, stretching the sarcomere will of course have the opposite effect, twisting the z-bands in the opposite direction, and this retractive force adds on the contractile force of the sarcomere, increasing contractility in stretched fibers as per Frank Starling’s Law.