Fig. 5. The four frog models on which forward dynamic simulations of jumping were performed. Here, we assume that the hindlimbs are symmetrical with respect to jumping. Hence model 1 had five rotational degrees of freedom (DOFs). These DOFs are flexion—extension at the iliosacral (1), hip (2), knee (3), ankle (4) and tarsometatarsal (5) joints. Model 2 had seven rotational DOFs. The two extra DOFs compared with model 1 (6 and 7, shown in red) are abduction—adduction and external—internal rotation at the hip. These DOFs permitted the plane of the hindlimb to be rotated under the body and at different angles relative to the ground. Model 3 had eight rotational DOFs. The extra DOF compared with model 2 (8, shown in red) is external—internal rotation at the knee. This DOF permitted the distal limb, consisting of the tibiofibula, astragalus segment and foot, to be rotated further under the body. Model 4 had nine rotational DOFs. The extra DOF compared with model 3 (9, shown in red) is flexion—extension at the metatarsophalangeal joint. This DOF permitted the frog to move its center of mass longer distances during the ground-contact phase of the jump and to achieve higher take-off velocities