Evidence for the Utilization of Dynamic Preload in Impact Injury Prevention

Abstract : Dynamic preload is anticipatory acceleration in the same direction as a later impact acceleration. To evaluate the influence of dynamic preload on human impact response, tests with volunteer subjects were conducted on impact facilities. Test data are presented which indicate that the peak forces and body segment accelerations imposed on subjects during impact accelerations are decreased when those impacts are preceded by dynamic preload. The impact response differences were more striking for comparisons between zero and low levels of dynamic preload than for comparisons between low and higher levels of preload. The medical and subjective data support the assertion that dynamic preload is protective when applied prior to -G(x) impact accelerations. Since impacts conducted on decelerator facilities are all influenced by track friction and therefore preceded by dynamic preload, it appears that they are fundamentally different from impacts conducted on accelerator facilities, involving zero dynamic preload. This indicates a need to reassess previous tolerance estimates derived from rocket sled decelerations. Decelerator tests do not appear to predict the more severe results of similar exposures on accelerators. Research efforts are continuing at AFAMRL to further delineate the significance and utility of dynamic preload as a technique in impact injury prevention.