Vertical loading in the underbody blast (UBB) condition generates high accelerative loading at the contact points between the occupant and vehicle, particularly the lower extremity. The objective of this study is to use the Global Human Body Models Consortium (GHBMC) average male lower extremity to quantify loads experienced in representative UBB conditions. A secondary aim is to evaluate the stability and robustness of the model in these conditions. A design of experiments (DOE) was conducted using the GHBMC M50-O v. 4.5 leg (proximal tibia through foot). The DOE consisted of forty-nine simulations in which the time-to-peak (TTP), acceleration, jerk, and pulse duration were varied, matching previously published data of UBB events. Peak kinematics were extracted from virtual load cells at the knee, tibia, and calcaneus. Fracture risk for the lower extremity was assessed using published risk curves for the UBB environment. All 49 simulations normal terminated. Accelerations ranged from 45 G’s to 1665 G’s. The peak knee, tibia, and calcaneus forces were 11.3, 13.6 and 14.9 kN respectively. Twenty- six of the 49 simulations resulted in a fracture risk greater than 0.5, thus the majority of the simulated trials indicated the presence of injury. The GHBMC M50-O lower extremity model was stable and robust in the simulated UBB environments.