Author(s): NAKAGAWA, Y., SOMEYA, Y., SHIOTA, Y., KOMATSU, T., IZAWA, H., AOYAGI, M., TOGASHI, I., HAMAI, A., AI, R., YAMADA, M., TAKAZAWA, Y., Institution: JUNTENDO UNIVERSITY, Country: JAPAN, Abstract-ID: 1183

INTRODUCTION:
Head acceleration events (HAE) occur frequently in contact sports, particularly rugby union. Repetitive HAEs are associated with an increased risk of injury (World Rugby, 2023) and concussion (Stemper et al., 2022). Therefore, World Rugby recommends individualized monitoring of HAEs using instrumented mouthguards (iMG). However, existing iMG-based studies have focused mainly on elite athletes. Even in studies of high school rugby players abroad, HAEs have typically been reported at the group level, with limited longitudinal individual-level data. High school rugby players are in a developmental stage and may be more susceptible to neurological effects compared with adult athletes (Patricios et al., 2023). This study aimed to use instrumented mouthguards (iMG) to describe HAEs over a three-month period in Japanese high school rugby players and to calculate individual HAE rates normalized to training and match playing time.
METHODS:
This study was conducted over a three-month period (from November 2025 to February 2026). Six high school male rugby players (age: 16.0 ± 0.0 years; height: 172.2 ± 4.9 cm; weight: 70.3 ± 4.8 kg) were prospectively monitored using iMG. A HAE was defined as a head impact exceeding 8 g of peak linear acceleration and was identified using a proprietary algorithm designed to exclude non-impact noise. Although peak angular acceleration was recorded by the device, it was treated as a reference value and was not included in the analyses. Athlete exposure (AE) was quantified as athlete-exposure minutes, where one AE was defined as one athlete participating in one minute of training or match play. HAE rates were calculated as the number of events per 100 AEs, representing the incidence of HAEs per 100 minutes of player participation.
RESULTS:
The mean total training participation time was 2220 ± 805 minutes, and the mean total match playing time was 98.3 ± 61.5 minutes. During training, the mean HAE rate was 6.1 ± 1.9 per 100 AEs. In contrast, match play demonstrated a higher mean HAE rate of 23.9 ± 9.3 per 100 AEs. No clinically diagnosed concussions occurred. However, one high-magnitude HAE occurring during training (90 g peak linear acceleration, 4514 rad/s² peak angular acceleration) exceeded thresholds used for Head Injury Assessment in professional rugby. This event occurred during a breakdown, with suspected contact between the player’s jaw and an opponent’s shoulder.
CONCLUSION:
This study provides preliminary data describing individual HAE rates in Japanese high school rugby players. HAE rates differed markedly between training and matches, with greater inter-individual variability observed during match play.