During evasive manoeuvring, substantial variability is seen in volunteer displacements, with standard deviations typically at 50% of average displacements. Volunteer characteristics such as sex, stature, age and BMI explain some of the variation. In an attempt to identify other sources of the variation, this study replicated a physical experiment with passengers in braking, using Active Human Body Model simulations, by modeling a synthetic experiment to quantify the expected variation in kinematics, to identify the parameters accounting for most of this variation, and to quantify the expected influence on displacements of these parameters. First, a sensitivity study of boundary conditions was conducted to determine which boundary condition parameters were most important to explain the volunteer response variability. Secondly, the synthetic experiments were conducted by randomly sampling influential boundary condition parameters together with influential human characteristics. The parameters, sampled using Latin Hypercube, were seat longitudinal position, vehicle velocity change, belt stiffness, occupant posture and muscle strength. Results indicate that the most important sources of variability among the investigated parameters were seat position and occupant posture, which explain 70–80% of variation in peak displacements and 60% of variation in timing of peak seen in simulations. Together, the six investigated parameters captured 25–30% of variation of forward displacements seen in the physical experiments.