Previous studies of human thoracic injury tolerance and mechanical response to blunt, midsternal, anteroposterior impact loading were reported by the authors at the 1970 SAE International Automobile Safety Conference and at the Fifteenth Stapp Car Crash Conference. The present paper documents additional studies from this continuing research program and provides an expansion and refinement of the data base established by the earlier work.Twenty-three additional unembalmed cadavers were tested using basically the same equipment and procedures reported previously, but for which new combinations of impactor mass and velocity were used in addition to supplementing other data already presented. Specifically, the 43 lb/11 mph (19.5 kg/4.9m/s) and 51 lb/16 mph (23.1 kg/7.2 m/s) conditions were intercrossed and data obtained at 43 lb/16 mph (19.5 kg/7.2 m/s) and 51 lb/11 mph (23.1 kg/4.9 m/s). Several additional tests were run at 22 mph (9.8 m/s) and confirm a strong velocity sensitivity of the force response throughout the velocity range investigated. Also included are several tests in which the cadaver subjects were rigidly supported midsagittally along the spine to preclude whole body motion. Finally, the kinematics of thoracic compression under blunt, A-P impact have been demonstrated by high-speed cinematography of a thorax unilaterally denuded of skin and superficial tissues to enable visualization of the rib surfaces and intercostal musculature during loading.Response in terms of force-time and deflection-time histories and force versus deflection crossplots, and tolerance in terms of associated necropsy findings and AIS ratings, are presented for all tests. Correlations of the AIS rating with both maximum force and normalized chest deflection, several composite summary plots, and a general data tabulation are also included.