Figure 4.

Force transmission on rigid substrates ($\mathrm{K}\to \infty$) exhibits a biphasic dependence on motor activity. Time-averaged dimensionless traction force, fraction of bound clutches, and clutch strain rate as a function of the myosin activity parameter $\mathrm{F}$ for five different values of the clutch kinetic parameter $\tau$, and two different values of the parameter $\omega$ ((A) First row, $\omega =100$; (B) second row, $\omega =1000$). Traction force and fraction of bound clutches monotonically increase with $\tau$, whereas clutch strain rate decreases with $\tau$. Traction force exhibits a maximum at an intermediate value of the myosin activity parameter ${\mathrm{F}}^{\mathrm{o}\mathrm{p}\mathrm{t}}$ (see Fig. 5A for further analysis). Clutch extension rate also exhibits a maximum at an intermediate value of the myosin activity parameter $\mathrm{F}>{\mathrm{F}}^{\mathrm{o}\mathrm{p}\mathrm{t}}$. Curves reach $\mathrm{F}$-independent asymptotic values at high myosin activity (large $\mathrm{F}$) (see Fig. 5B and C for additional details). Solid lines correspond to the numerical solution of the mean-field model (Eqs. S31–S36) and symbols correspond to the numerical solution of the stochastic model. Dashed lines correspond to our low-$\mathrm{F}$ asymptotic solutions (Eqs. S51, S46, and S49). To see this figure in color, go online.