Flexibility, strength, and fascicle length of football players with and without history of hamstring strain injury in the prior season

This study aimed to verify the hamstring flexibility, strength, and fascicle length of football (soccer) players with and without history of hamstring strain injury (HSI) in the prior season. Eighty male football players (45 from senior category and 35 from under-20 category) were included in this case–control trial: 20 with history of unilateral HSI in the prior season, and 60 free of HSI in the prior season. Passive straight-leg raise (PSLR) test, isokinetic dynamometry, and biceps femoris long head (BFLH) ultrasonography were performed at preseason to identify risk factors for HSI. No significant differences were found between injured and uninjured limbs of the previously injured players for any outcome (p > 0.05; trivial effect sizes). Uninjured players had higher values than both injured and uninjured limbs of previously injured players for hamstring-to-quadriceps (H/Q) conventional and functional ratios (p < 0.05; medium effect sizes), as well as BFLH fascicle length (p < 0.05; small to medium effect sizes). Football players that had sustained unilateral HSI in the prior season demonstrated lower H/Q strength ratios and shorter BFLH fascicles in both limbs compared to uninjured players.