The main body is constructed as a set of three rigid bodies: head, thorax and abdomen, connected by two joints (head-thorax and thorax-abdomen). Each leg is actuated with three selected DOF: trunk-coxa, trochanter-femur and femur-tibia. Movement about the single joints and the resulting stepping patterns are generated by the activity of antagonistic muscle pairs. In the stick insect, the three major muscle pairs of a leg are the protractor and retractor coxae, the levator and depressor trochanteris, and the flexor and extensor tibiae. The protractor and retractor move the coxa, and thereby the leg, forward and backward. The levator and depressor move the femur up and down. The flexor flexes, and the extensor extends the tibia about the femur-tibia joint.