Does repeated sprinting alter the hamstring shear modulus pattern and mechanical parameters in football players with hamstring strain injury history? - A retrospective study

Abstract Background: Hamstring strain injuries (HSI) occur particularly in the later stages of a football match, suggesting that fatigue may play an important role. Moreover, sprint is the principal mechanism to sustain an HSI since it demands the hamstrings muscle group. It has been reported that a higher contribution of BFlh in the load sharing pattern could possibly explain the greater injury rate in BFlh. Objective: To compare the effects of a (i) repeated sprint protocol on the sprint performance, hamstrings shear modulus pattern and mechanical parameters between players with and without previous HSI; and (ii) between limbs with HSI and their healthy contralateral limbs on the hamstrings shear modulus pattern and mechanical parameters. Methods: One hundred and five professional and semiprofessional football field players were invited to participate in this study during the pre-season 2021/2022 (June-July), resulting in a sample size of 210 limbs with 46 sustaining HSI in the previous 2 years. Results: No differences were seen between injured and non-injured players regarding their sprint performance, hamstrings shear modulus pattern and mechanical parameters, except for the early rate of torque development (0-50ms) with BFlh injured limbs displaying higher rates than their contralateral (injured: 0.48±21 N/ms; contralateral 0.40±0.18 N/ms; p=0.005; η2p=0.469). Conclusion: The present study provides evidence for no differences regarding sprint performance, hamstrings load sharing pattern and mechanical parameters between players with previous HSI in the last 2 years and non-injured players, although an increase in early rate of torque development was seen in BFlh-injured limbs compared to their healthy counterpart. Therefore, the results can possibly suggest that the duration between injury and screening could recover the differences between injured-control and injured-contralateral groups.