Comparison of model predictions for steady-state contractile properties assuming either one or three myosin-binding sites per actin target zone. (A) Simulations of force–velocity relationships using parameter values in Tables S1 and S2 for linear cross-bridge elasticity. Data plotted as half-sarcomere shortening velocity versus absolute force averaged over all myosin heads for either the one-site model (black) or the three-site model (blue). (B) Same data as in A but normalized to maximum velocity and maximum isometric force. Simulation results compared with experimental data (purple) from living muscle (Månsson et al., 1989) at 30°C (purple squares) and a small ensemble of myosin molecules in vitro (Pertici et al., 2018) at 23°C (purple dashed line). (C) Simulated force–velocity data using parameter values in Tables S1 and S2 but for nonlinear cross-bridge elasticity. Data plotted as in A for either the one-site model (red, filled symbols) or the three-site model (open red symbols). (D) Plots of the data in C after normalization to the maximum values. Simulation results compared with experimental data (purple) as in B. (E) Simulated [MgATP]–velocity data assuming one site per target zone and linear (black) or nonlinear (red) cross-bridge elasticity. (F) Simulated [MgATP]–velocity relationships assuming three sites per target zone and linear (blue) or nonlinear (red) cross-bridge elasticity. The purple data points in both E and F are experimental data from Persson et al. (2013). Note, in E and F, the quantitatively similar difference between linear and nonlinear cross-bridge elasticity in the prediction of the experimental data for one-site and three-site models. Nonlinearity in cross-bridge elasticity is based on that in Kaya and Higuchi (2010); see also Månsson et al. (2019).