The kinetic constants of steps 4 and 5, and T₅₆, deduced from the effect of Pi on 2πb and tension. (A) K ₄ is the equilibrium constant of the force generation step 4. (B) K₅ is Pi association constant (step 5). (C) T₅₆ is fiber tension when all CBs are either at AM*DP or AM*D states, and scales with force/CB. (D) k₄ is the forward rate constant of the force generation step 4. (E) k₋₄ is its backward rate constant. n = 7 for Neb⁺ fibers, and n = 8 for Neb⁻ fibers. Assoc, Association; Equilib, Equilibrium; const, constant.