Lower limb injuries occupy a high percentage of the traffic accident injuries among road users. However, the injury outcomes in accident statistics is somehow different from the results in cadaver tests. The purpose of this study is to determine the influence of active muscle function on the kinetics result of lower limb injuries during emergency braking in car frontal collision. Based on a human body numerical model regrading a Chinese 50th percentile male lower extremity with active muscles, frontal collisions under different overlaps were established. Then, by comparing the peak forces and moments of the femur and tibia, the dynamic responses of lower limbs under different load conditions were determined. Furthermore, the distribution of stress indicators was analyzed to determine the influence of active muscle and collision overlaps on the injury outcomes at a micro level. Results show that active muscle has a significant effect on the lower limbs, which are particularly affected by the increase of bending moments. The moment caused by the active muscles in the right tibia is 3.7 times greater than that of the femur. Moreover, the effect of active muscle is more significant in small overlap frontal impact. In the 25% overlap collision, the moment caused by the active muscles of the tibia increase by 1.2 times that of the 40% offset collision. In conclusion, this study can provide an explanation on the differences of lower limb injuries between the cadaveric tests and traffic accidents statistics.