in stress fibers by applying external

Effect of stretching and bending on the measured tension The method proposed in this study measures the displacement of individual SFs by applying an external force perpendicular to the fiber axis. Although the method enables us to measure tensions, it also generates other undesired forces in the SFs due to phenomena such as stretching and bending. Here, we estimate the stretching and bending forces and analyze the effects of these undesired forces on the measured tensions in SFs. The SFs are assumed to have a cylindrical shape and elastic mechanical properties. The geometrical parameters associated with the tension measurements are shown in Fig. S1. When an external force F is applied perpendicular to the SF axis, the SF becomes stretched as shown in Fig. S2 A, where FS represents the stretching force. Considering the left part of the SF, the strain, L, due to the stretching is expressed as