Experimental testing with post mortem human subjects is costly and complex. Test methods that reduce the cost and increase the repeatability are favourable, although they may affect test outcomes. This study aims to improve the understanding of how test conditions affect PMHS responses related to axial compression spine injury. Select inverted head‐first impact experiments from the literature were reconstructed in a simulated environment using a detailed Finite Element model of the human body, the THUMS. Test conditions such as specimen constraints, and test equipment setup and THUMS characteristics, such as mass and position were varied within each test protocol to assess inter‐ and intra‐test effects. Test outcomes were evaluated and compared based on both the kinetic and kinematic response of THUMS. Constraint of T1 resulted in impact forces twice that recorded in otherwise equivalent inverted drop tests without constraints. The results of the simulations indicate that the introduction of unnatural boundary conditions is likely to interfere with the fidelity of injury production and response. These findings can assist in the development of future test methods to ensure that accurate results are obtained in the most repeatable and reproducible manner without unnecessary extraneous effects.