Hamstring strain injuries frequently occur during professional soccer practice. Low hamstring strength represents an intrinsic modifiable risk factor but cut-offs of isokinetic knee strength ratios are controversial to predict hamstring strain in professional soccer players. We aimed to predict hamstring strain in accordance to cut-offs of isokinetic knee strength ratios. Bilateral, conventional and functional isokinetic strength ratios were calculated in 194 professional soccer players at the beginning of 15 consecutive seasons. 36 soccer players presented a moderate hamstring strain and 158 were not injured. The different calculated isokinetic ratios were compared with the right and left limb of the uninjured population. Different usual cut-offs were tested: at 0.85 and 0.90 for the bilateral concentric and eccentric hamstring-to-hamstring ratio, at 0.60 and 0.47 for the conventional hamstring-to-quadriceps ratio and at 0.80 and 1 for the mixed hamstring-to-quadriceps ratio. The specific ratios for the studied population were also determined by the 10th percentile and then tested. Hamstring strain prediction was established in term of odds ratios. No cut-off with bilateral, conventional or functional isokinetic strength ratio was predictive of hamstring strain after univariate analysis. Specific cut-offs determined from the studied population were not more predictive. Very few injured soccer players presented values under the cut-offs at 0.47 for the conventional ratio and at 0.80 for the mixed ratio. Regardless of their values, cut-offs of isokinetic strength ratios were not predictive of hamstring injuries. The use of isokinetic cut-offs is not recommended to predict hamstring muscle strain in professional soccer players.
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