Transition and formation of the torque pattern of undulatory locomotion in resistive force dominated media

In undulatory locomotion, torques along the body are required to overcome external forces from the environment and bend the body. Using a resistive force theory model, we find that the torque from external resistive forces has a traveling wave pattern with decreasing speed as the wave number (the number of wavelengths on the locomotor's body) increases from 0.5 to 1.8, and the torque transitions into a two-wave-like pattern and complex patterns as the wave number increases to values of 2 and greater values. Using phasor diagrams analysis, we reveal the formation and transitions of the pattern as the consequences of the integration and cancellation of force phasors.