The Effects of Training and Subject Reproducibility during Vertical Impact Acceleration

摘要

Several studies have been conducted to collect and analyze the biodynamic responseduring vertical impact acceleration. There is little data, however, describing the effects ofsubject training on human response. There are also questions regarding the effect ofsubject reproducibility and how it might affect data variability. Research is required todetermine the effect of training and to properly describe the human response to a verticalimpact. This could potentially reduce musculoskeletal risks by providing proper bracingtechniques for training implementation. A series of impact tests were conducted on theVertical Deceleration Tower (VDT) at AFRL/HEPA. Ten male and seven femalesubjects volunteered and were exposed to a combination of varying helmet weights and+Gz impact levels: 6, 8, and 10 g. Each combination was reproduced up to three times.The tests were first conducted in a sequential manner, with the lowest exposureexperienced first for safety reasons. The last two replications were randomized so thatthe biodynamic response was not dependent on the last test configuration. Seat pan, seatcushion, sternum, and head accelerations were collected using an on-board dataacquisition system, and neck loads were calculated to compare the biodynamic responsesusing the varying weight. Electromyography was used to collect neck muscle responseduring bracing and on impact. Subjects were evaluated for reproducibility at 6, 8, and 10+Gz with varying helmet weights. The head and sternum accelerations in the z-directionwere used to analyze the biodynamic response along with neck loads generated at theoccipital condyles (OC). These neck forces were calculated using the helmet inertialproperties, subject anthropometry, and the recorded head accelerations. The results fromthe study revealed no effect of training on the subjects' biodynamic response. Areproducibility limit was calculated for all subjects and all test conditions to beapproximately 30% for the dependent variables. Results also showed a significantdifference for gender on neck force and a significant difference for both gender andexperience for sternum Z acceleration. There was no meaningful correlation per testcondition as a function of gender, experience, and reproduced exposures.