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Background Injuries to the hamstring muscles are among the most common in sports and account for significant time loss. Despite being so common, the injury mechanism of hamstring injuries remains to be determined. Purpose To investigate the hamstring injury mechanism by conducting a systematic review. Study design A systematic review following the PRISMA statement. Methods A systematic search was conducted using PubMed, EMBASE and the Cochrane Library. Studies 1) written in English and 2) deciding on the mechanism of hamstring injury were eligible for inclusion. Literature reviews, systematic reviews, meta-analyses, conference abstracts, book chapters and editorials were excluded, as well as studies where the full text could not be obtained. Results Twenty-six of 2372 screened original studies were included and stratified to the mechanism or methods used to determine hamstring injury: stretch-related injuries, kinematic analysis, electromyography-based kinematic analysis and strength-related injuries . All studies that reported the stretch-type injury mechanism concluded that injury occurs due to extensive hip flexion with a hyperextended knee. The vast majority of studies on injuries during running proposed that these injuries occur during the late swing phase of the running gait cycle. Conclusion A stretch-type injury to the hamstrings is caused by extensive hip flexion with an extended knee. Hamstring injuries during sprinting are most likely to occur due to excessive muscle strain caused by eccentric contraction during the late swing phase of the running gait cycle. Level of evidence Level IV

Understanding how injuries occur (inciting circumstances) is useful for developing etiological hypotheses and prevention strategies. The aims of this study were 1) to evaluate the feasibility of a method combining video and Global Positioning System data to estimate the speed and acceleration of activities leading to injuries and 2) to use this method to analyse the inciting circumstances leading to non-contact injuries. Retrospective descriptive study. Injury inciting circumstances from 46 elite players over three seasons were analysed from video recordings and from external load measures collected through Catapult Vector S7 Global Positioning System. In total 34 non-contact injuries were analysed. Sixteen out of the seventeen hamstring injuries occurred when players were running for (median and interquartile range) 16.75 m (8.42–26.65 m) and achieved a peak speed of 29.28 km·h−1 (26.61–31.13 km·h−1) which corresponded to 87.55 % of players' maximal speed (78.5 %–89.75 %). Of the three adductor injuries, one occurred whilst the player was decelerating without the ball, one occurred whilst the player was accelerating and controlling the ball at knee level, and one occurred whilst the player was performing an instep kick. Two quadriceps injuries occurred whilst the players were kicking either whilst walking or running. From the preliminary results reported in this study most hamstring injuries occurred when players ran >25 km·h−1 and above 80 % of their maximal speed. This study suggests that this novel approach can allow a detailed and standardised analysis of injury inciting circumstances.

BackgroundTo evaluate the efficacy of early versus delayed introduction of lengthening (ie, eccentric strengthening) exercises in addition to an established rehabilitation programme on return to sport duration for acute hamstring injuries in a randomised controlled superiority trial.Methods90 male participants (age: 18–36 years, median 26 years) with an MRI-confirmed acute hamstring injury were randomised into an early lengthening (at day 1 of rehabilitation) group or a delayed lengthening (after being able to run at 70% of maximal speed) group. Both groups received an established rehabilitation programme. The primary outcome was time to return to sport (ie, time from injury to full unrestricted training and/or match play). The secondary outcome was reinjury rate within 12 months after return to sport. Other outcomes at return to sport included the Askling H-test, hamstring strength, clinical examination and readiness questions.ResultsThe return to sport in the early lengthening group was 23 (IQR 16–35) days and 33 (IQR 23–40) days in the delayed lengthening group. For return to sport (in days), the adjusted HR for the early lengthening group compared with the delayed lengthening group was 0.95 (95% CI 0.56 to 1.60, p=0.84). There was no significant difference between groups for reinjury rates within 2 months (OR=0.94, 95% CI 0.18 to 5.0, p=0.94), from 2 to 6 months (OR=2.00, 95% CI 0.17 to 23.3, p=0.58), and 6 to 12 months (OR=0.57, 95% CI 0.05 to 6.6, p=0.66).ConclusionAccelerating the introduction of lengthening exercises in the rehabilitation of hamstring injury in male athletes did not improve the time to return to sport nor the risk of reinjury.

Injury knowledge and beliefs influence uptake of prevention programmes, but the relationship between knowledge, beliefs and adherence remains unclear. To describe injury knowledge and beliefs among youth female soccer coaches and players, and to identify the relationship between these factors, different delivery strategies of the FIFA 11+ programme and adherence. A subcohort analysis from a cluster-randomised controlled trial of 31 female soccer teams (coaches n=29, players (ages 13-18) n=258). Preseason and postseason questionnaires were used to assess knowledge and beliefs. Teams recorded FIFA 11+ adherence during the season. At baseline, 62.8% (95% CI 48.4% to 77.3%) of coaches and 75.8% (95% CI 71.5% to 80.1%) of players considered 'inadequate warm-up' a risk factor for injury. There was no effect of delivery method (OR=1.1; 95% CI 0.8 to 1.5) or adherence (OR=1.0; 95% CI 0.9 to 1.1) on this belief. At baseline, 13.8% (95% CI 1.3% to 26.4%) of coaches believed a warm-up could prevent muscle injuries, but none believed it could prevent knee and ankle injuries. For players, 9.7% (95% CI 6.1% to 13.3%), 4.7% (95% CI 2.1% to 7.3%) and 4.7% (95% CI 2.1% to 7.3%) believed a warm-up would prevent muscle, knee and ankle injuries, respectively. Years of playing experience were negatively associated with high adherence for coaches (OR=0.93; 0.88 to 0.99) and players (OR=0.92; 0.85 to 0.98). There were gaps in injury knowledge and beliefs, which differed for coaches and players. Beliefs did not significantly affect adherence to the FIFA 11+, suggesting additional motivational factors should be considered.

Background Owing to the complexity and heterogeneity of muscle injuries, a generally accepted classification system is still lacking. Aims To prospectively implement and validate a novel muscle injury classification and to evaluate its predictive value for return to professional football. Methods The recently described Munich muscle injury classification was prospectively evaluated in 31 European professional male football teams during the 2011/2012 season. Thigh muscle injury types were recorded by team medical staff and correlated to individual player exposure and resultant time-loss. Results In total, 393 thigh muscle injuries occurred. The muscle classification system was well received with a 100% response rate. Two-thirds of thigh muscle injuries were classified as structural and were associated with longer lay-off times compared to functional muscle disorders (p<0.001). Significant differences were observed between structural injury subgroups (minor partial, moderate partial and complete injuries) with increasing lay-off time associated with more severe structural injury. Median lay-off time of functional disorders was 5–8 days without significant differences between subgroups. There was no significant difference in the absence time between anterior and posterior thigh injuries. Conclusions The Munich muscle classification demonstrates a positive prognostic validity for return to play after thigh muscle injury in professional male football players. Structural injuries are associated with longer average lay-off times than functional muscle disorders. Subclassification of structural injuries correlates with return to play, while subgrouping of functional disorders shows less prognostic relevance. Functional disorders are often underestimated clinically and require further systematic study.

Purpose Hamstring injuries are a major cause of time-loss in athletes, often leading to prolonged recovery and high recurrence rates. This randomized controlled trial evaluated the efficacy of ultrasound-guided platelet-rich plasma (PRP) injections in accelerating return to play (RTP) and enhancing radiological healing in grade 2 hamstring injuries. Methods Sixty athletes with MRI-confirmed grade 2 hamstring injuries were randomized into two groups: PRP plus standard therapy (n = 30) and standard therapy alone (n = 30). All followed a standardized rehabilitation protocol. Primary outcome was time to return to play (TTRTP). Secondary outcomes included MRI healing at 21 days, re-injury rates, and adverse events, with a 2-year follow-up. Results The PRP group showed significantly faster RTP (26.4 ± 4.5 vs. 34.2 ± 5.7 days; p  < 0.001) and greater MRI healing at 21 days (70% vs. 36.7%; p  = 0.003). Re-injury rates were lower in the PRP group (3.3% vs. 16.7%), though not statistically significant ( p  = 0.09). No adverse events were reported. Conclusion Ultrasound-guided PRP injection with standard rehabilitation accelerates return to play and improves radiological healing in acute grade 2 hamstring injuries, representing a safe and promising adjunct in sports injury management.

RationaleHamstring injuries are common in elite sports. Muscle injury classification systems aim to provide a framework for diagnosis. The British Athletics Muscle Injury Classification (BAMIC) describes an MRI classification system with clearly defined, anatomically focused classes based on the site of injury: (a) myofascial, (b) muscle–tendon junction or (c) intratendinous; and the extent of the injury, graded from 0 to 4. However, there are no clinical guidelines that link the specific diagnosis (as above) with a focused rehabilitation plan.ObjectiveWe present an overview of the general principles of, and rationale for, exercise-based hamstring injury rehabilitation in British Athletics. We describe how British Athletics clinicians use the BAMIC to help manage elite track and field athletes with hamstring injury. Within each class of injury, we discuss four topics: clinical presentation, healing physiology, how we prescribe and progress rehabilitation and how we make the shared decision to return to full training. We recommend a structured and targeted diagnostic and rehabilitation approach to improve outcomes after hamstring injury.

The muscle-tendon properties of the semitendinosus (ST) and gracilis (GR) are substantially altered following tendon harvest for the purpose of anterior cruciate ligament reconstruction (ACLR). This study adopted a musculoskeletal modelling approach to determine how the changes to the ST and GR muscle-tendon properties alter their contribution to medial compartment contact loading within the tibiofemoral joint in post ACLR patients, and the extent to which other muscles compensate under the same external loading conditions during walking, running and sidestep cutting. Motion capture and electromyography (EMG) data from 16 lower extremity muscles were acquired during walking, running and cutting in 25 participants that had undergone an ACLR using a quadruple (ST+GR) hamstring auto-graft. An EMG-driven musculoskeletal model was used to estimate the medial compartment contact loads during the stance phase of each gait task. An adjusted model was then created by altering muscle-tendon properties for the ST and GR to reflect their reported changes following ACLR. Parameters for the other muscles in the model were calibrated to match the experimental joint moments. The medial compartment contact loads for the standard and adjusted models were similar. The combined contributions of ST and GR to medial compartment contact load in the adjusted model were reduced by 26%, 17% and 17% during walking, running and cutting, respectively. These deficits were balanced by increases in the contribution made by the semimembranosus muscle of 33% and 22% during running and cutting, respectively. Alterations to the ST and GR muscle-tendon properties in ACLR patients resulted in reduced contribution to medial compartment contact loads during gait tasks, for which the semimembranosus muscle can compensate.

Purpose The aim of this study is to report the effects of autologous PRP injections on time to return to play and recurrence rate after acute grade 2 muscle injuries in recreational and competitive athletes. Methods Seventy-five patients diagnosed with acute muscle injuries were randomly allocated to autologous PRP therapy combined with a rehabilitation programme or a rehabilitation programme only. The primary outcome of this study was time to return to play. In addition, changes in pain severity and recurrence rates were evaluated. Results Patients in the PRP group achieved full recovery significantly earlier than controls ( P  = 0.001). The mean time to return to play was 21.1 ± 3.1 days and 25 ± 2.8 days for the PRP and control groups, respectively ( P  = 0.001). Significantly lower pain severity scores were observed in the PRP group throughout the study. The difference in the recurrence rate after 2-year-follow-up was not statistically significant between groups. Conclusions A single PRP injection combined with a rehabilitation programme significantly shortened time to return to sports compared to a rehabilitation programme only. Recurrence rate was not significantly different between groups. Level of evidence I.

This study investigated the effect of five consecutive days of cold‐water immersion (CWI) on recovery from exercise‐induced muscle damage (EIMD) in the hamstrings following maximal eccentric contraction (EC) exercise. Eighteen healthy adult women were randomly assigned to a CWI group and a control group (CG) (n = 9/group). Participants performed 10 sets of 10 repetitions of isokinetic EC at 30°/second and underwent maximum voluntary isometric contraction (MVC), delayed onset muscle soreness (DOMS) assessment, straight leg raise (SLR) test, and plasma myoglobin (Mb) measurement. The CWI group received one 14‐min session of CWI treatment (14°C) at 1, 25, 49, 73, and 97 h after the EC test, whereas the CG rested in a seated position at the same five time points without receiving treatment. (1) All the dependent variables in the CWI group and CG exhibited significant changes after the EC test (p < 0.05). (2) The recovery effect in the CWI group was significantly greater than in the CG in terms of the MVC, DOMS, SLR, and plasma Mb concentration results. MVC increased by 89.3 ± 2.0% on the fourth day (p < 0.013), DOMS decreased by 15.4 ± 1.5 mm on the second day (p < 0.000), SLR increased by 86.3 ± 1.1% on the second day (p < 0.014), and plasma Mb decreased by 436.3 ± 60.8% on the third day (p < 0.014). The study indicates that five consecutive days of CWI at 14°C significantly enhance recovery from exercise‐induced muscle damage in the hamstrings. Highlights CWI treatment was beneficial for recovery from EIMD after high‐intensity exercise. All the participants exhibited similar and significant responses in their MVC, DOMS, SLR, and plasma Mb concentration results after the EC test. The CWI group demonstrated mostly superior recovery responses compared with the CG after receiving the CWI treatment on 5 consecutive days after the EC test.