The Effects of Training and Subject Reproducibility during Vertical Impact Acceleration

摘要

Several studies have been conducted to collect and analyze the biodynamic response during vertical impact acceleration. There is little data, however, describing the effects of subject training on human response. There are also questions regarding the effect of subject reproducibility and how it might affect data variability. Research is required to determine the effect of training and to properly describe the human response to a vertical impact. This could potentially reduce musculoskeletal risks by providing proper bracing techniques for training implementation. A series of impact tests were conducted on the Vertical Deceleration Tower (VDT) at AFRL/HEPA. Ten male and seven female subjects 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 exposure experienced first for safety reasons. The last two replications were randomized so that the biodynamic response was not dependent on the last test configuration. Seat pan, seat cushion, sternum, and head accelerations were collected using an on-board data acquisition system, and neck loads were calculated to compare the biodynamic responses using the varying weight. Electromyography was used to collect neck muscle response during 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-direction were used to analyze the biodynamic response along with neck loads generated at the occipital condyles (OC). These neck forces were calculated using the helmet inertial properties, subject anthropometry, and the recorded head accelerations. The results from the study revealed no effect of training on the subjects' biodynamic response. A reproducibility limit was calculated for all subjects and all test conditions to be approximately 30% for the dependent variables. Results also showed a significant difference for gender on neck force and a significant difference for both gender and experience for sternum Z acceleration. There was no meaningful correlation per test condition as a function of gender, experience, and reproduced exposures.