The effect of muscular tension on lower leg injuries was investigated in this study. Rigid body simulation was used to examine the kinematics of an occupant making a braking during a frontal crash. Muscular tension was reproduced by constant spring elements defined in the lower leg. Simulation results showed that tibia1 axial load was increased by the muscular tension. A series of cadaver tests was conducted to study the effect of muscular tension in detail. Dynamic axial loading was applied to human specimens with a pendulum hitting at approximately 3 m/s. The test condition represented loading to a driver’s right foot stepping on a brake pedal and struck by a toe board. The metatarsal heads were placed on the brake pedal and an initial tensile force was applied on the Achilles tendon. Sixteen tests were performed on eight pairs of cadeveric lower legs. There was a significant increase in the tibia1 axial load in comparison with the impact load because of preloading by muscular tension. Tibia1 pylon fracture, which is one of the severest forms of injury of the lower leg. was frequently observed in these tests. Although the fracture load level in the tibia was almost the same as that reported in previous studies, this study shows that less external force is required to cause tibia1 pylon fractures with muscular tension.