The effect of ball characteristics on head impact magnitude during purposeful heading in adolescent male and female football players

Introduction: Purposeful heading is a unique footballing skill where the head is deliberately used to re-direct the ball. In Australia, there are approximately 2 million football participants with a total growth rate of 6% (11% in females) from 2018 to 2019. Considering the continued popularity and concerns that frequent heading could have long-term detrimental effects on brain function, player injury prevention has never been more important. Mathematical and head-form models have demonstrated that head impact magnitude (including peak linear acceleration and angular velocity of the head) during heading can be influenced by ball characteristics (mass and pressure), however, few human trials exist. The aim of this cross-sectional study was to explore the effects of different ball types and characteristics on head acceleration during purposeful heading in adolescent football players. Methods: Experienced male and female players (n=61) aged between 12-17 years completed heading trials with 4 different balls (Ball 1, mass 192 grams(g), pressure 5.0 pounds per square inch(psi); Ball 2, 432g, 5.0psi; Ball 3, 255g, 5.0psi; Ball 4 430g, 10.5psi) whilst wearing a head-mounted inertia measurement unit. Balls 1, 2 and 4 were size 5 balls; Ball 3 was a size 4 ball. Results: Multivariate analysis of variance and post-hoc univariate analyses revealed a statistically significant difference between ball type and head acceleration during heading for both linear acceleration (adjusted R2=0.68; F=140.90; p=<0.001) and angular velocity (adjusted R2=0.28; F=26.52; p=<0.001). Ball 1 (lightest size 5 ball) and Ball 3 (size 4 ball) demonstrated linear head accelerations up to 59% lower (p=<0.01) when compared with Ball 4 (size 5 regulated match ball). Discussion: Given the conflicting evidence whether frequent heading of the ball is associated with long term issues with brain health, it is prudent to explore strategies which can minimise the potential harm to players. This study provides evidence that reducing ball pressure, ball size and/or ball mass can reduce head impact magnitude in adolescent players. Changing ball characteristics, particularly in training when heading is practiced, is an easy strategy to implement but may require top down support from football organisations to increase buy-in from players and coaches.