Continued development of computational models and biofidelic anthropomorphic test devices (ATDs) necessitates further analysis of the effects of muscle activation on the biomechanical response of human occupants in automotive collisions. The purpose of this study was to investigate the effects of pre-impact bracing on human occupant chest compression during low-speed frontal sled tests. In this study, a total of 10 low-speed frontal sled tests (5.0g, 􀇻v=9.7kph) were performed with 5 male human volunteers. The height and weight of the human volunteers were approximately that of the 50th percentile male. Each volunteer was exposed to 2 impulses, one relaxed and the other braced prior to the impulse. A 59 channel chestband, aligned at the nipple line, was used to measure anteriorposterior sternum deflection for all test subjects. Subject head accelerations, spine accelerations, and forces at each interface between the subject and test buck were recorded for all tests. A Vicon motion analysis system, consisting of 12 MX-T20 2 megapixel cameras, was used to quantify subject 3D kinematics (±1 mm) at a sampling rate of 1 kHz. The chestband data showed that bracing prior to the initiation of the sled pulse essentially eliminated thoracic compression due to belt loading for all subjects except one. The load cell data indicate that forces were distributed through the feet, seatpan, and steering column as opposed to the seatbelt for the bracing condition. In addition, the forward excursion of the elbows and shoulders were significantly reduced during the braced condition compared to the relaxed condition. The data from this study illustrates that muscle activation has a significant effect on the biomechanical response of human occupants in frontal impacts and can be used to refine and validate computational models and ATDs used to assess injury risk in automotive collisions.