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
