A new match-heading index for male professional football players based on objective and video sources - SoccHealth

Repetitive heading of the ball is a distinctive feature of professional football (soccer) and has been discussed as a potential long-term risk factor for neurodegenerative disease. Epidemiologic investigation is limited by the absence of valid methods to quantify heading exposure across a player's career. To provide a tool for estimating the heading frequency in male professional football players for epidemiological studies where detailed career histories exist but sufficient individual heading exposure data are lacking. Detailed career histories of former male football players were combined with position-specific heading rates derived from two systematic video analyses spanning multiple decades and league levels in Germany. Season-specific heading rates were estimated using natural cubic splines by position, league level, seasons, and combined with playing time to calculate cumulative exposure. Heading rates varied substantially by position and changed markedly over time. In the absence of a gold standard, the plausibility of the match-heading index was evaluated in the SoccHealth project using negative control outcomes. The cumulative heading index showed no association with negative control outcomes (body mass index and handgrip strength), while expected age-related associations remained, which may be interpreted as consistent with the index's plausibility. We present a novel match-heading index that can be combined with objective career-history data to estimate cumulative career-long match-heading exposure in former male football players. By integrating objective video-based data with detailed career histories and accounting for temporal and positional variation, this approach substantially improves exposure assessment for future epidemiologic studies of long-term neurological outcomes in football players.