All eukaryotic cells contain a cytoskeleton (CSK): The cytoskeleton is typically a meshwork of actin filaments (cables) and more rigid microtubules (struts) which gives a cell its rigidity, shape and underlies cell motility. The cytoskeletal filaments are acted upon by molecular motors: these protein machines constantly convert chemical energy into forces which produce contractile stresses within the cytoskeleton. Many cells types (skin, muscle, cartilage) actively adhere to their surroundings extracellular matrix (ECM) and deform this matrix due to their internal contractile stress [2]. These cells probe the mechanical properties of the matrix and respond by remodelling of their cytoskeleton, regulating of cell-matrix-adhesion, and sometimes by modification of gene expression. The present work is dedicated to better understand how cells deform their ECM or generally how internal forces transmit in fibrous biopolymer gels.