The biofidelity of side impact ATDs is crucial in order to accurately predict injury of human occupants. Although the arm serves as a load path to the thorax, there are currently no biofidelity response requirements for the isolated arm. The purpose of the study was to characterize the compressive stiffness of male and female upper arms in lateral loading and to develop corresponding biofidelity stiffness corridors. This was accomplished by performing a series of pendulum tests on sixteen isolated upper arms, obtained from four male and four female cadavers, at impact velocities of approximately 2 m/s and 4 m/s. The upper arms were oriented vertically with the medial side placed against a rigid wall in order to simulate loading during a side impact automotive collision. The force versus deflection response data was normalized to that of a 50th percentile male or a 5th percentile female and then response corridors were developed. For both impact rates the cadaver arms exhibited a considerable amount of deflection under very low force, i.e. toe region, before the any substantial increase in force. The deflection at which the force began to increase substantially was found to be similar to the average difference in thickness between the initial and compressed volunteer arm thickness measurements for both the 5th percentile female and 50th percentile male. Although the response of the SID-IIs arm was similar in shape to that of the female cadaver arms for both impact rates, the SID-IIs arm did not exhibit a considerable toe region and therefore did not fall within the response corridors for the 5th percentile. The results of the current study could lead to an improvement in the overall biofidelity of side impact ATDs by providing valuable data necessary to validate the compressive response of ATD arm independent of the global response.