Hamstring injury risk in male professional football: do external training loads play a role?

Objectives: Hamstring strain injury (HSI) is the most common time-loss injury in football and is prone to recurrence. This exploratory study aimed to describe the relationship between short-term external training load (TL) and HSI occurrence in male senior football players at the professional level. Methods: TL data in terms of global positioning system (GPS) variables and HSI incidence were collected over four seasons from 25 senior professional football players. GPS variables included total distance (TD), very intense accelerations (>3.00 m/s²), very intense decelerations (<-3.00 m/s²), high-speed running distance (>19.8 km/hour), maximal sprint distance (>29.8 km/hour) and maximal velocity. For each injury case, TL during the 7 and 14 days preceding the injury was compared with matched control periods from the same player. Results: 25 hamstring injuries were included for analysis. Large interindividual variation in TL patterns was observed, with some players exhibiting higher and others lower TL in the periods preceding injury compared with control periods. No consistent group-level trends were identified between injured and control periods. Conclusion: This exploratory study found considerable individual variability in TL prior to HSI and no clear group-level patterns. These findings suggest that short-term TL metrics alone may have limited utility in predicting HSI risk at the group level in professional football players.