Effects of Field and Strength Training Load on Injury Risk in Japanese Collegiate American Football Players

OBJECTIVES In this study, we aimed to assess relationships between field and strength training loads and injury occurrence in Japanese Division II collegiate American football players, focusing on both same-day and previous-day effects of strength training load. It was hypothesized that higher strength training load, particularly when combined with high field training load, would increase injury risk.METHODS Twenty male Japanese collegiate American football players were observed over a 21-week training period. Daily training loads were recorded using the session rating of perceived exertion (session-RPE) for both field and strength sessions; strength training volume load was also calculated. Injuries were documented by certified athletic trainers and expressed per 1,000 athlete-exposures (AEs). Logistic regression models were used to assess associations between training load categories (rest, middle, high) and injury risk, considering sameday and previous-day effects and interaction terms between field and strength training loads.RESULTS A total of 26 injuries (10.4 per 1,000 AEs) were recorded. High session-RPE (≥ 875 AU) for field training was significantly associated with increased injury risk in both same-day and previous-day models: odds ratio (OR) = 7.90 (95% confidence interval [CI]: 1.99-31.39, <i>p</i> = 0.003) and OR = 7.78 (95% CI: 1.95-31.08, <i>p</i> = 0.004), respectively. However, neither session-RPE for strength training nor total volume load for strength training was associated with injury risk in any model.CONCLUSIONS Field training load appears to be the primary factor associated with non-contact injury risk in Japanese collegiate American football players, highlighting the importance of careful monitoring and management of field training demands. In contrast, supervised strength training showed no harmful association with injury risk and may support injury prevention when appropriately integrated within a structured training program.