The 5th percentile (American) female version of the newly-developed Thor-Lx dummy lower extremity, denoted Thor-FLx, was fitted to a 5th percentile female Hybrid III dummy for a series of frontal sled tests with toepan intrusion. The objectives of the study were to compare the Thor- FLx response with that of the Hybrid III/Denton leg, evaluate the effects, if any, on upper-body responses, and evaluate the repeatability and durability of the new leg design. The 56 km/h tests replicated a 40% offset deformable barrier test producing 16 cm of toepan intrusion with peak toepan accelerations of 80 g’s. Tests were performed with a standard threepoint belt, depowered driver’s airbag and a simulated knee bolster. Identical test configurations were used for tests with Thor-FLx limbs and Hybrid III/Denton limbs attached to the same above-knee Hybrid III dummy. Important Thor-FLx design aspects found to influence the response include the tibia axial compliance, ankle joint-stops, Achilles tendon, and anterior tibia shape. An evaluation of test severity based on each designs’ injury criteria produced similar outcomes, with both leg types exceeding injury thresholds. There were no significant differences in any of the upper body responses, and incorporation of the new Thor-FLx did not compromise upper body response repeatability.