Isometric force development and unloaded isotonic shortening by the Huxley kinetic models. (A) Force development and cross-bridge distributions predicted by MUSICO (black lines and histogram bars), Huxley 1957 (green line), and Huxley PL (dashed red line) models. Maximum isometric tension To = 270 kPa from mass action models is scaled to maximum force per myosin filament (MUSICO) Fo = 530 pN. Comparison of cross-bridge distributions at 5, 20, 80, and 700 ms are shown as insets, where black bars represent bound cross-bridges (MUSICO), Huxley-bound cross-bridge distributions are shown as solid green lines, and Huxley PL as dashed red lines. Cyan diamonds denote the force at which the distributions are taken. The comparison of displacements after a quick release and unloaded shortening are also shown in the inset. (B) The evolution of velocities during isotonic shortening after quick release to zero tension. The cross-bridge distributions at times tQRel = 0+, 10, 20, and 80 ms after the quick release are shown as insets.
