Validation and Application of a Methodology to Calculate Head Accelerations and Neck Loading in Soccer Ball Impacts

Calculating head accelerations and neck loading is essential for understanding and predicting head and neck injury. Most of the desired information cannot be directly measured in experiments with human volunteers. Achieving accurate results after applying the necessary transformations from remote measurements is difficult, particularly in the case of a head impact. The objective of this study was to develop a methodology for accurately calculating the accelerations at the center of gravity of the head and the loads and moments at the occipital condyles. To validate this methodology in a challenging test condition, twenty (20) human volunteers and a Hybrid III dummy were subjected to forehead impacts from a soccer ball traveling horizontally at speeds up to 11.5 m/s. The human subjects and the Hybrid III were instrumented with linear accelerometers and an angular rate sensor inside the mouth. The dummy was also equipped with accelerometers at the center of gravity of the head and load cells in the upper and lower neck. The force applied to the head by the soccer ball was calculated by double differentiating the ball displacement measured from high speed video. Standard mechanics equations were used to transform mouth accelerations to the head center of gravity and to calculate loads and moments at the occipital condyles. Accurate angular acceleration data were obtained by rigidly mounting a small angular rate sensor inside the mouth on a bite block. The neck loads calculated using inverse dynamics required filtering to a cutoff frequency of 50 Hz in order to reduce the noise to an acceptable level and achieve a good match with the neck load cell data. Noise was a particular problem in the calculated occipital condyle sagittal plane bending moment. Although some differences in the results of the human and dummy tests were observed, The Hybrid III dummy head and neck appeared to be reasonably biofidelic in this loading scenario.