Figure 3: Mechanical model of the isolated fiber.

(A) Time evolution of the fiber transverse displacement during deformation. Black dashed lines show the time when the motion of the stage is halted, allowing fiber relaxation. Inset magnification of the viscoelastic relaxation e′ = e − e* in function of t′ = t − t*. e* is the transverse displacement at the end of the stretching phase and t* is the time when the stage is halted. Red dashed line shows fit of the additional deformation with the exponential function , which allows the extraction of the characteristic time τ. (B) Mechanical model of the fiber. The fiber with tension T subjected to elongation δ is approximated by a standard linear solid model (SLS) that has 3 elements in parallel: a primary spring of constant k₁, a secondary spring (k₂) in series with a dashpot (η) and an active element corresponding to pre-tension (T₀). (C) Time evolution of the transverse displacement (left) and the cantilever measured force (right) during deformation of four fibers. Circles indicate experimental values and colored solid lines represent the best fit to the SLS model. (D) Parameters of the SLS model for the curves shown in (C). Corresponding curves are color-coded. (E) Time evolutions of the transverse displacement (left) and the cantilever measured forces (center) during deformation of the same fiber before (red) and after myosin inhibition (cyan). The force-deformation graph (right) illustrates that after myosin inhibition, a lower cantilever force (F_clv) is needed to achieve the same deformation (e). Circles indicate experimental values and colored solid lines represent the best fit to the SLS model. Corresponding graphs for T vs δ are found in Supplementary Figure 2, at t = 0 (control) and t = 51 (Y27632). (F) Parameters of the SLS model for the curved shown in (E). Corresponding curves are color-coded.