Development of a functional in-vivo head impact testing model would enhance the ability to elucidate mechanisms underlying individual responses to head impact in sports where a helmet is not worn. The objective of this paper is to describe a novel in-vivo method of assessing human head linear impact acceleration during the functional activity of soccer heading, using a repeated-measures design in a university research laboratory. 17 college-aged soccer players (age, 20.93 years (standard deviation (SD), 1.17 years); height, 170.39cm (SD, 10.15cm); mass, 71.50kg (SD, 9.89kg); head—neck mass, 5.90kg (SD, 0.83kg)) participated in this study. All participants read and signed a university Institutional-Review-Board-approved informed consent before participating.

The resultant linear head acceleration (in units of g) was measured for each participant during soccer heading. The head impact model consisted of controlled soccer headers and a triaxial accelerometer affixed to a custom-fitted mouthpiece. A force-sensitive resistor on the forehead assessed impact quality. Standard soccer balls were projected from a JUGS soccer machine travelling at 11.10m/s (25mile/h) and covering a distance of 11m (35ft). The subjects performed standing or simulated headers while aiming at a target positioned 5m in front of them. The intra-class correlation coefficient (ICC2,1) was 0.845 for resultant accelerations.

In this paper, the development and testing of a novel in-vivo functional human head impact testing model are described. Results suggest that this methodology has potential for assessing resultant peak linear head impact accelerations during the functional activity of soccer heading and in other non-helmet-wearing sports.