There is a paucity of recent data quantifying the injury risk of forces and accelerations that act on the whole body in a back-to-front direction. The purpose of this study was to quantify the level of back-to-front accelerations that volunteers felt were tolerable and non-injurious. Instrumented volunteers were dropped supine onto a mattress, and their accelerations during the impact with the mattress were measured. Accelerometers were located on the head, upper thoracic and lower lumbar regions. Drop heights started at 0.6 m (2 ft) and progressed upward as high as 1.8 m (6 ft) based on the test subjects' consent. The test panel was comprised of male and female subjects whose ages ranged from 25 to 63 years of age and whose masses ranged from 62 to 130 kg (136 to 286 lb). Peak head, upper thoracic and lower lumbar accelerations of 25.9 g, 29.4 g and 39.6 g were measured. There was considerable restitution in the impacts with the mattress and the test subjects experienced changes in velocity (ΔVs) of 5.2-11.4 m/s (11.6-25.5 mph). There were no permanent injuries although some subjects complained of minor symptoms that resolved within six days. This research showed that volunteer subjects can withstand peak back-to-front accelerations in the 20-30 g range without serious injury.