As of toady, statutory crash test dummies take neither bracing nor passive muscular effect into account in the lower limb area. The influence of the lower extremity musculature is however arising as a major concern for the study of front seat occupant protection.The lower extremity prototype of the THOR dummy, including a model of the human plantarflexion actuator passive response, was tested in dynamic dorsiflexion. A dynamic test series was performed on Thor-Lx under test conditions similar to those used by Portier et al., 1996, on cadavers and Hybrid III dummy.The test setup imposed a dynamic dorsiflexion to the foot by means of a load exerted under the ball of the foot with no impact velocity.The Thor-Lx and Hill responses are compared to cadaver responses. It is important to note that as of today there are no data available to demonstrate that the passive resistance of the cadaver is equivalent to resistance of a tensed human.The results clearly show a greater similarity between Thor-Lx and cadaver responses than between cadaver and Hybrid III, which does not simulate muscle resistance applied by the Achilles tendon. The amount of muscle tension that should be incorporated into dummy leg designs to simulate the tensed and relaxed human remains to be identified. It is obvious however that only passive muscle resistance was present in the cadavers used in this study (muscle tone being present only in living subjects).Based on these tests, some minor improvements are suggested in order to make the prototype more reliable and easier to use.