Figure 5.

Coefficient of geometric hysteresis η_geom plotted against m; its geometric construction is shown in the cartoon. In the absence of muscle contribution, the hysteresis loop is entirely controlled by surfactant, and the loop is counterclockwise with positive η_geom. Its value progressively decreases with muscle activation, crossing zero into a regime dominated by muscle, where the loops are clockwise and η_geom is negative. Also shown is the hysteretic behavior in the absence of surfactant, showing the uniformly negative η_geom.