Fig. S1.

Schematic showing two interacting fiber strands $f_i$ (blue) and $f_j$ (red) as well as other strands (gray). Circles denote points of mechanical constraints in the form of cross-links or branch points. Relaxation of $f_i$ along its backbone tugs $f_j$ inducing a transverse displacement $\delta {\ell }_{\perp }$ (blue arrow) and longitudinal displacements $\delta {\ell }_{\parallel }$ (red arrows). In a similar manner, $f_i$ experiences both displacements from its interaction with other strands. The zoom-in shows a simple first-approximation geometric relation between these displacements.