Head acceleration events in academy rugby players: Impact of playing position on magnitude and incidence

Background Head acceleration events (HAEs) are increasingly recognised for their cumulative impact on brain health in contact sports. While instrumented mouthguards (iMGs) have advanced the monitoring of HAEs in elite rugby, limited data exist for academy-level players. This study investigated positional differences in the magnitude and incidence of HAEs in Under-21 (U21) professional academy rugby union. Methods Seventy U21 rugby players wore iMGs across 51 matches (359.2 h, 368 player matches), capturing 6742 HAEs. Peak linear acceleration (PLA), peak angular acceleration (PAA), and change in peak angular velocity (ΔPAV) were recorded. HAEs were categorised by intensity (low, medium, high). Non-parametric tests assessed magnitude differences. Negative binomial regression, adjusted for playing time, was used to compare positional incidence rates. Results Forwards had significantly higher PLA (p < 0.001), while Backs had higher ΔPAV (p < 0.001). No positional differences were found for PAA (p = 0.38). The Back Row had the highest incidence across all magnitudes. Forwards experienced 25.3 HAEs/hour, while Backs had 11.9/hour. At higher magnitudes, Back Row and Front Row players showed the greatest exposure. Conclusion Positional differences in HAE magnitude and frequency are evident in professional academy rugby. Forwards, especially the Back Row, are exposed to more frequent and higher-magnitude impacts. These findings support the use of iMGs to monitor cumulative exposure and inform position-specific contact load management strategies in academy rugby environments.