The trajectories emergent of the paws corresponding to different levels of energy provided by the environment, parameterized with the speed of the treadmill. The repetitiveness of the trajectories proves the stability of the locomotion pattern over a variety of environmental conditions. In the passive experiment, the robot still has the synergy-based tendon routings such that the fore- and hindlimbs are connected, but the synergies are not actuated via the motors, instead the energy is input in the system by any forces applied by the treadmill to the robots limbs, which, in turn, can lead to tendon activation.
