With the advent of alternative seating positions in Highly Automated Vehicles, vehicle manufactures must take care to ensure the safety of new seating positions. The use of Human Body Models (HBMs) can aid in the use of analyzing these new concepts, as they closely represent a human being. HBMs are constructed with Finite Element (FE) modelled bones, muscles, and organs; whereas crash test dummies are made of foams, rubbers, and metallic structures. Due to these differences. HBMs show a different response compared to traditional crash test dummies. A sensitivity study on spinal posture using the THUMS v5 was performed using a BMW prototype reclined concept seat. By changing the initial of the posture of the lumbar spine, changes in spinal kinematics as well as varying force responses were observed during a frontal load case. This type of study could not be conducted with a crash test dummy as the spine of standard front crash dummies does not easily allow for postural changes. These variations suggest that initial spinal posture plays a role in the overall spinal kinematic response as well as the amount of force seen transmitted through the spine.