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Purpose: Hamstring muscle strain injury is very common in sports involving high-speed running. Hamstring muscles originate from the ischial tuberosity and thus pelvic position may influence hamstring strain during different sports movements like sprinting, but this has only been evaluated by indirect methods. This study tested the hypothesis that a change in anterior pelvic tilt causes elongation of the overall hamstring complex and disproportionately elongates proximal relative to distal muscle regions., Methods: Seven fresh-frozen specimens (full lower limb with pelvis and lumbar spine) were used for this in vitro study. Specimens were dissected to enable visualization of the hamstring muscles and then fixed into a custom-made testing bench that allowed controlled movement of the pelvis over a fixed femur and tibia. Nine markers were inserted into the hamstring muscles to allow intra- and intermuscle difference measurements. Then, six different anterior pelvic angles were used to measure the difference in hamstring muscle lengthening through a three-dimensional reconstruction system based on stereoscopic machine vision technology., Results: An increase in anterior pelvic tilt produced a significant non-uniform increase in tissue elongation in all regions of the three hamstring muscles (semitendinosus, semimembranosus [SMB] and biceps femoris long head), which was greater in the proximal (>1 cm every 5°) compared to the distal region (≈0.4 cm every 5°). At the proximal hamstring region, SMB showed significantly greater length changes compared to conjoint tendons with nonstatistically significant elongation differences between muscles at the distal region., Conclusion: Considering the results of the study, the pelvis segment will likely play a fundamental role as a strain regulator of hamstring muscles. These results will have an impact on injury rehabilitation and prevention processes of hamstring injuries, as well as optimize future musculoskeletal models and avoid potential underestimation of the hamstring muscle-tendon complex lengthening during high-speed running., Level of Evidence: N/A., (© 2024 European Society of Sports Traumatology, Knee Surgery and Arthroscopy.)

An association has been reported between dynamic anterior pelvic tilt (APT) and hamstring injuries; however, no research has examined if a training-based preventive intervention could alter APT. Therefore, the aim of the present study was to examine if a specific 6-week multimodal intervention, based on the theoretical influence of neighbouring joints and biomechanical interactions between muscles that are inserted to the pelvis, induced changes in APT, during walking gait, hamstring flexibility and trunk endurance. Thirty-five active healthy males volunteered for this single-blind controlled trial and were split into two groups based on baseline data: a control group (CG, n = 20, continued their normal physical activities), and an intervention group (IG, n = 15, performed the intervention programme for 18 sessions over 6 weeks). A significant (p = 0.001) decrease in the APT kinematics during gait, significant increase in the Active Knee Extension Test (p = 0.001), and a significant increase in trunk endurance performance for flexion (p = 0.001), extension (p = 0.001) and side bridge (p = 0.001) were observed, in IG after the 6-week programme, compared to CG.

The aim of this study was to investigate the effects of the Nordic hamstring exercise on the biceps femoris long head (BFlh), biceps femoris short head (BFsh), semitendinosus (SMT), and semimembranosus (SMM) muscles. The Nordic hamstring strengthening exercise has been widely used in injury prevention, yet not much is known about the site-specific activation of this exercise on different muscles of the thigh. Eight male national-level referees were assigned to a Nordic hamstring exercise protocol (5 sets of 8 repetitions). Magnetic resonance imaging (MRI) of the subjects' thighs was performed before, within 3 minutes after, and repeated again 72 hours after the exercise intervention. Fifteen axial scans of the thigh interspaced by a distance of 1 of 15 right femur length were obtained from the level of 1 of 15 Lf to 15 of 15 Lf. The MRI data were analyzed for signal intensity changes. After 72 hours, significant changes in transverse (spin-spin) relaxation time signal intensity and cross-sectional area were maintained distally at BFsh cranial portion and concretely at the nondominant limb, whereas no significant changes were observed in transverse (spin-spin) relaxation time signal intensity at BFlh, SMM, or SMT. This study demonstrated that the Nordic hamstring exercise did not result in a uniform response (training stimulus) neither interhamstring (dominant vs. nondominant) nor intrahamstring muscles (same leg) and was better suited for loading proximal BFsh.

Although many different hamstring strengthening exercises exist, the effect on site specific activation of these exercises on different muscles of the leg is unclear. This study investigated the effects of the eccentric leg curl (LC) and lunge (L) exercises on the biceps femoris long head (BFl), biceps femoris short head (BFs), semitendinosus (ST), semimembranosus (SM), and adductor magnus (AM). Each leg of 11 male professional soccer players was randomly assigned to an LC or L exercise protocol (3 sets of 6 repetitions). Functional magnetic resonance imaging (fMRI) of the subjects' thighs were performed before and 48 hours after the intervention. Fifteen axial scans of the thigh interspaced by a distance of 1/15 right femur length (Lf) were obtained. The fMRI data were analyzed for signal intensity changes. No significant changes were observed in absolute short tau inversion recovery values for the SM and BFs. Significant changes for the ST (∼21-45%) from sections 4 to 10, AM (∼2-13%) at section 4, and BFl (∼ -3 vs. 8%) at section 7 were noted. LC exercises load all the regions of the ST muscle. The L exercises load the proximal regions of the BFl and AM. These findings may have relevance when designing protocols for prevention and rehabilitation of hamstring injuries.