Effects of Repeated Sprints on Hamstring Active Shear Modulus Pattern and Neuromuscular Parameters in Football Players with and without Hamstring Strain Injury History-A Retrospective Study

Featured Application Hamstring strain injuries occur particularly in the later stages of a football match, suggesting that fatigue may play an important role. Moreover, sprinting is the principal mechanism to sustain a hamstring strain injury since it demands the hamstrings muscle group. After the injury, sprint performance and strength might be reduced, and muscle tissue properties can be altered even after the player returns to competition. Therefore, the aim of the present study is to compare the effects of (i) a repeated sprint protocol on the sprint performance, hamstrings shear modulus pattern, and neuromuscular parameters between players with and without previous hamstring strain injury; and (ii) between limbs with hamstring strain injury and their healthy contralateral limbs on the hamstrings shear modulus pattern and neuromuscular parameters. It should be noted that the biceps femoris long head muscle is the most affected muscle, and it has been reported that a higher contribution of the biceps femoris long head could possibly explain the greater injury rate on this muscle. The aim of the present study is to compare the effects of a (i) repeated sprint protocol on the sprint performance, hamstrings shear modulus pattern, and neuromuscular parameters between players with and without previous hamstring strain injury (HSI); and (ii) between limbs with HSI and their healthy contralateral limbs on the hamstrings shear modulus pattern and neuromuscular parameters. 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. No differences were seen between previously injured and healthy control players regarding their sprint performance, hamstrings shear modulus pattern, and neuromuscular parameters, except for the early rate of torque development (0-50 ms) with previously injured limbs in the biceps femoris long head (BFlh) displaying higher rates than their contralateral muscle (injured: 496.93 +/- 234.22 Nm/s; contralateral 422.72 +/- 208.29 Nm/s; p = 0.005; eta(2)(p) = 0.469). Overall, the present study provides evidence for no differences regarding sprint performance, hamstrings load sharing pattern, and major neuromuscular parameters between players with previous HSI in the last 2 years and healthy control players. Therefore, the results can possibly suggest that the duration between injury and screening could recover the differences between injured-control and injured-contralateral groups.