Transient velocities and cross-bridge distributions after quick release to isotonic force at F/F_o = T/T_o. (A) Evolution of velocities after quick release to isotonic force of F/F_o = T/T_o = 0.4 predicted by MUSICO (black line), Huxley 1957 (green line), and Huxley PL (red line). The displacements after release are the same because the SE components of Huxley 1957 and Huxley PL models match the effect of the myosin and actin filament compliances from MUSICO (inset). (B) Velocity evolution after release to F/F_o = T/T_o values at which all models have the same steady-state shortening velocity of 215.5 nm/s (i.e., 0.133 of v_max). (C) Cross-bridge distributions and state probability density distribution functions at time t_QRel = 20 ms after release to predicted (left column) and to F/F_o values that have the same steady-state velocity of 215.5 nm/s (right column). The arrows on the right signify net binding fluxes and on the left signify net unbinding fluxes, and the horizontal open arrows represent current shortening velocity.