S-S motility mode. (A) Kymograph of the instantaneous magnitude of the traction stresses, $|τ→|$ (upper part), and traction tension, T_x (lower part), for a representative wild-type cell. The black arrow indicates pseudopod protrusion, followed by front TA formation (green arrow). The blue arrow shows the transition of the front TA to back and the red arrow points to the TA loss. The inclined red and black lines indicate the instantaneous position of the front and back cell edges. (B) Schematic representation of the time evolution of the magnitude and location of the TAs, illustrating the implementation of the S-S mode. A side view of the cell is shown as a cartoon for four instants of time and refers to the cell shown in A. The vertical axis indicates time and the horizontal axis depicts the cell location in the direction of motion. Front and back TAs are shown as blue and red ovals underneath the cell. Gray ovals represent weak, newly formed TAs or front TAs undergoing a transition in mechanical load and becoming back TAs. Blue and red arrows illustrate the direction of T_x at the cell’s front and back, respectively. Underneath each cartoon the corresponding T_x(x, t) is plotted. The vertical axis of each plot indicates the scale for T_x values [nN/µm]. Red or blue color indicates positive or negative T_x.