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The response of the human head and neck to impact acceleration has been previously reported for the -X (chest to back) and +Y (right to left) directions. Wide ranges of sled peak acceleration, rate of onset of acceleration and duration of acceleration have been investigated and reported. A major mechanical effect on the dynamic response due to initial position for the -X direction has been reported. The purpose of this study is to report the initial position effect on the human head and neck response for +Y direction experiments. Four initial positions of the head relative to the first thoracic vertebral body (T1) have been investigated over a range of sled acceleration peaks from 2 to 7G. The data from six young adult male volunteers representative of a wide range of anthropometry will be presented. There are 18 experiments for each volunteer for a total of 108 experiments.

A series of human volunteer experiments has been conducted to measure the inertial response of the head and the first thoracic vertebra (T1) to +Gy whole body impact acceleration; that is, acceleration applied to the subject from right to left. The 12-inch HYGE ® accelerator, instrumentation system and procedures were identical to those used for measuring the response to -Gx impact acceleration, previously reported. Three categories of sled acceleration profile were used: high onset, long duration from 2G to 7.5G with end stroke sled velocity limit of 6.5 meters/sec; low onset, long duration with the same peak acceleration and velocity limits; and high onset, short duration from 5G to 11G. Comparison time profiles of angular acceleration, angular velocity and linear resultant acceleration at the head anatomical origin and horizontal linear acceleration at the T1 origin are presented at selected peak sled acceleration levels for 5 subjects of various anthropometric dimensions.

The parameters of duration, rate of onset and peak acceleration of the sled have been identified by other investigators as determinants of the dynamic and injury response of man. A series of human experiments have been conducted to measure the response of the head and the first thoracic vertebrae to these parameters. Each subject was run at three conditions defined as high rate of onset-long duration (HOLD), high rate of onset-short duration (HOSD) and low rate of onset-long duration (LOLD) at peak accelerations of 6, 10 and 15G. Comparison time profiles of angular acceleration, angular velocity and linear resultant acceleration at the head anatomical origin and horizontal linear acceleration at the T1 origin are presented for 5 to 8 subjects at each of the three peak sled acceleration levels.

In preparation of an analog of human head and neck, the reports by R. G. Snyder and others were noted which stated that initial position of the head and neck had a definite effect upon resulting response. An investigation was undertaken to attempt to quantitate this effect, as a part of a much larger study underway for several years. Thirteen human volunteer subjects ranging from the 5th to the 97th percentile in sitting height were exposed to -Gx impact acceleration at peak sled accelerations of 6G and 10G. Two angles of the neck relative to chair and two angles of the head relative to the neck for a total of four conditions were tested for each subject for the 2 peak acceleration levels giving a total of 104 experiments. Instrumentation consisted of 6 accelerometers and two-axis rate gyro at the posterior spinous process of the first thoracic vertebral body, 6 accelerometers at the mouth, and a two-axis rate gyro at the top of the head.