(A) FA structural model consists of two parallel layers of proteins, which can be conceptualized as either ‘sensor’ (blue) or ‘linker’ (orange) elements. (B) Mimicking what was done in experiments (Figure 4), simulations involved three sensor elements with distinct stiffnesses (, , ), arranged in a stratified fashion with a single linker element (stiffness ), loaded by a bulk extension (or force) input. The forces and the extensions experienced by each sensor element were calculated, and a relating the relative variation in forces to the variation in extensions was calculated (see Appendix 2 for details). (C) Schematic depiction of parameter space examined using this simple structural model of FAs, wherein the relative number of the sensor and linker element is varied (x-axis) along with their relative stiffness (y-axis); thicker springs indicate stiffer mechanics. (D) Summary of results from simulations quantifying force-controlled versus extension-controlled loading of the sensor element. describes the ratio of variation in forces to the variation in extensions experienced by the sensor elements and will be positive for extension-controlled situations and negative for force-controlled situations. Following a bulk extension input, force-controlled loading of the sensor element occurs when the sensor element is stiff and in relatively high abundance, while extension-controlled loading of the sensor element occurs when the sensor element is soft and/or in relatively low abundance. Dashed contour lines are depicted that correspond to the measured for VinTS, VinTS + Y-27632, VinTS-A50I, and VinTS on 10 kPa gels (, respectively). (E-F) FA structural model predictions of the relationship between sensor element stiffness (spring constant) and force (E) or extension (F). Dashed contour lines in panel (D) correspond to force-stiffness relationships in (E) and extension-stiffness relationships in (F).