Human locomotion is emerged by the synergy of whole body dynamics: not only of the legs, but also the torso, the arms, and even the head which are compliantly connected with each other by antagonistic muscles. Such compliance provides human locomotion with flexibility, adaptability, and stability.
  A robot driven by antagonistic artificial muscles is able to realize flexible motion like a human. Adaptive and flexible behavior emerges through the interaction between such a robot and the environment, which is difficult for existing rigid robots built with electric motors and gears. The Physio-SI group investigates such adaptive bipedal locomotion emerged through the interaction between the body and the environment, which leads to the design principle of intelligence.