The six-state CB model that was used in the present study. A, actin; M, myosin; D, MgADP; S, MgATP; and P, Pi, phosphate. Upper-case letters K indicate equilibrium constants (including association constants), and lower-case letters k indicate rate constants of the elementary steps of the CB cycle. These are as a whole called “kinetic constants.” z, direction of the Z-line; +, direction of the + end; −, direction of the − end.