Head Acceleration Event Exposure during Pre-Season Training in Elite Men’s Rugby Union

BACKGROUND: Head acceleration event (HAE) outcomes in elite men's rugby union have been well described during matches and in-season training but have not been investigated during pre-season training. OBJECTIVES: Describe HAE incidence and magnitude during elite men's pre-season rugby union training. METHOD: Data was collected from three English PREM Rugby clubs (44 training sessions and 53 players) during field-based training sessions using instrumented mouthguards (iMGs) throughout the pre-season training period before the 2025-26 season. Training drills were recorded using routinely tagged GPS data. The incidence of HAEs was calculated per player minute, for forwards and backs, and during training sessions during the first, middle, and final three-week phases of pre-season. A negative binomial generalised linear mixed model compared playing position, and phases of pre-season, expressed as incidence rate ratios (IRR). RESULTS: for forwards was 0.10/min [0.08-0.11] and equated to 5.87 ± 5.51 HAEs per player-training-session exposure, compared to 0.05/min [0.04-0.07] and 3.22 ± 3.39 HAEs per player-training-session exposure for backs (IRR = 1.84 [1.02-3.31], p = 0.041). The mean HAE incidence for forwards during the first three weeks of pre-season was lower (0.05/min [0.03-0.08]) than the middle (0.09/min [0.07-0.11]) and final (0.13/min [0.11-0.15]) three weeks. The incidence of HAEs for backs was similar in the first (0.04/min [0.02-0.06]), middle (0.06/min [0.04-0.08] and final (0.06/min [0.04-0.08]) three weeks. The incidence of HAEs during the middle (IRR = 1.55 [1.14-2.11], p = 0.005) and final (IRR = 2.82 [2.06-3.85], p < 0.001) phases of pre-season was statistically significant. CONCLUSION: The incidence and magnitude of HAEs during pre-season is very low compared to matches and similar to in-season training. Future work should identify players who accumulate more HAEs in matches and training compared to the rest of the population, and why. This study completes a holistic understanding of HAE exposure throughout a season, which can be used to benchmark individual's exposure against.