Translational and rotational accelerations from blunt head impact can induce excessive brain strain and cause traumatic brain injuries. However, it is not clear which acceleration plays a major role in the mechanism. The current study used the SIMon human finite element head model (FEHM) and delineated the contributions of these accelerations using post mortem human subject (PMHS) lateral head impact experimental data. Results indicated that rotational acceleration contributes more than 90% of total strain, and translational acceleration produces minimal strain. Therefore, the rotational component is a more important biomechanical metric in this study.