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The functional role of the biceps femoris short head (BFsh) remains unclear. Clarifying the functional role of each biceps femoris head may provide useful insights into the reduction of biceps femoris long head (BFlh) injuries. This study aimed to clarify whether the passive tension in the BFlh would change with BFsh detachment using cadavers. The shear modulus of the BFlh and BFsh was measured using ultrasonic shear wave elastography as an index of passive tension in three tissue processing conditions (intact, removal of all tissues from skin to deep fascia, and BFsh detachment) in four limb positions, with hip [H0°, H90°] and knee [K0°, K90°] joint angles under each tissue processing condition. The measurement site was the distal 30 % of the line connecting the sciatic tuberosity (100 %) and fibular head (0 %). Three-way analysis of variance was conducted with muscles, tissue processing, and positions as factors, which revealed a significant interaction (P < 0.01). The post-test results indicated that the BFlh was significantly higher than the BFsh at H90° and K0° before tissue processing; however, no difference was observed between the muscles after skin and deep fascia removal. After BFsh detachment, the shear modulus of the BFsh decreased, whereas that of the BFlh significantly increased (P < 0.01), suggesting that the BFsh might be involved in the passive tension reduction of the BFlh in a lengthened position, as the shear modulus of the BFlh increased after detachment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Background and Objective: Enhancing joint range of motion is regarded as one of the most long-term goals in the management of cerebral palsy (CP). With CP, there are well-documented changes in the neurological drive to skeletal muscle, which leads to modifications in the architecture of the muscles. Whole-body vibration (WBV) is one intervention to modify muscle and joint. However, its efficacy needs to be accurately studied. This study investigates the effects of WBV on fascicle length, knee joint angle and function in children with spastic hemiplegic CP., Methods: Eighty children with hemiplegic CP aged 4-6 years were enrolled. Participants were randomly divided into experimental and control groups. The control group received a designated physical therapy program and the experimental group received a designated physical therapy program in addition to WBV. Program was performed 3 times a week for 12 weeks. Goniometry, ultrasonography and gross motor function measurements were used to measure knee extension joint angle, fascicle length of hamstrings and function, respectively., Results: The results of this study indicated that, designed physical therapy program with WBV could increase the active range of motion in knee extension (p = 0.001) and fascicle length of hamstring (p = 0.001) muscles as well as improve function in children with hemiplegic CP (p = 0.001)., Implication for Physiotherapy Practice: According to the findings, the use of WBV can be considered as an effective treatment in increasing the range of motion of knee extension and fascicle length and finally improving function in children with CP., (© 2024 John Wiley & Sons Ltd.)

Biceps femoris long head (BF LH ) aponeurosis size was compared between legs with and without prior hamstring strain injury (HSI) using two approaches: within-group (injured vs. uninjured legs of previous unilateral HSI athletes) and between-group (previously injured legs of HSI athletes vs. legs of No Prior HSI athletes). MRI scans were performed on currently healthy, competitive male athletes with Prior HSI history ( n =23;≥1 verified BF LH injury; including a sub-group with unilateral HSI history; most recent HSI 1.6±1.2 years ago) and pair-matched athletes with No Prior HSI history ( n =23). Anonymized axial images were manually segmented to quantify BF LH aponeurosis and muscle size. Prior unilateral HSI athletes' BF LH aponeurosis maximum width, aponeurosis area, and aponeurosis:muscle area ratio were 14.0-19.6% smaller in previously injured vs. contralateral uninjured legs (paired t-test, 0.008≤P≤0.044). BF LH aponeurosis maximum width and area were also 9.4-16.5% smaller in previously injured legs ( n =28) from Prior HSI athletes vs. legs ( n =46) of No Prior HSI athletes (unpaired t-test, 0.001≤P≤0.044). BF LH aponeurosis size was smaller in legs with prior HSI vs. those without prior HSI. These findings suggest BF LH aponeurosis size, especially maximum width, could be a potential cause or consequence of HSI, with prospective evidence needed to support or refute these possibilities., Competing Interests: The authors declare that there is no conflict of interest and that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation., (Thieme. All rights reserved.)

Magnetic resonance imaging (MRI) is the gold standard for measuring muscle size. However, postural conditions for thigh musculature have not been standardized across studies, with some employing supine or prone positions and the thigh either placed on the examination table or suspended to avoid contact. In either case, the thigh is compressed or sagged by gravity, potentially affecting muscle size. This study aimed to examine the effects of postural conditions on thigh muscle size. Twenty Olympic-style weightlifters and 20 untrained controls (10 men and 10 women in each group) underwent 3-Tesla MRI in the supine and prone positions, with the thigh in compressed and suspended conditions to determine the maximal anatomical cross-sectional area (ACSAmax) and muscle volume of 15 thigh muscle groups/individual muscles. Postural conditions changed the ACSAmax of the quadriceps (range of postural-related changes: 1.0%-7.9%), hamstrings (0.8%-19.1%), and adductors (2.4%-19.2%). Regardless of measurement position, the total volume of thigh muscles decreased under compressed conditions (0.6%-3.8%). Quadriceps and adductors decreased in muscle volume under compressed conditions (0.9%-4.0% and 0.8%-6.6%), while hamstrings increased (1.4%-9.3%). Male weightlifters, who possessed the largest thigh muscle volume, showed greater postural-related changes in the muscle volume of quadriceps, hamstrings, and adductors than the other subgroups. Therefore, postural conditions during MRI substantially change thigh muscle size, and the magnitude of the change depends on muscle size. Our results provide in vivo evidence of the compressive behavior of thigh muscles and a new technical perspective for assessing thigh muscle size., (© 2024 The Author(s). Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Objective: This study examines the correlation between MRI findings and difficult dissection during proximal primary hamstring repair and postoperative sciatica., Materials and Methods: A total of 32 cases of surgically repaired hamstring tendon tears that underwent preoperative and postoperative MRI were divided into sciatica (n = 12) and control (n = 20) groups based on the presence or absence of postoperative sciatica. Cases were scored by two blinded musculoskeletal radiologists for imaging features associated with difficult surgical dissection and the development of subsequent sciatica. Intra- and interrater agreements, as well as correlation of MRI findings with symptoms (odds ratio, OR), were calculated., Results: On preoperative MRI, diffuse hamstring muscle edema pattern suggestive of active denervation (OR 9.4-13.6), and greater sciatic perineural scar circumference (OR 1.9-2) and length (OR 1.2-1.3) were significantly correlated with both difficult dissection and postoperative sciatica. Preoperatively, a greater number of tendons torn (OR 3.3), greater tear cross-sectional area (CSA, OR 1.03), and increased nerve T2-weighted signal (OR 3.2) and greater perineural scar thickness (OR 1.7) were also associated with difficult dissection, but not postoperative sciatica. On postoperative MRI, hamstring denervation, sciatic nerve tethering to the hamstring tendon, and development of perineural scar and greater perineural scar extent were all significantly correlated with postoperative sciatica., Conclusion: Preoperative hamstring MRI demonstrates findings predictive of difficult sciatic nerve dissection; careful MRI evaluation of the nerve and for the presence and extent of perineural scar is important for preoperative planning. Preoperative and postoperative MRI both depict findings that correlate with postoperative sciatica., (© 2024. The Author(s), under exclusive licence to International Skeletal Society (ISS).)

Purpose: Most athletes experience short-term training cessation because of illness, injury, post-season vacation, or other reasons. Passive muscle stiffness is a potential risk factor for a sprint-type hamstring strain injury, but limited information is available about the effect of short-term training cessation on passive muscle stiffness. The present study aimed to identify whether and how passive muscle stiffness of the biceps femoris long head (BFlh) would vary due to 2 weeks of training cessation in sprinters., Methods: Passive BFlh shear-wave speed (a proxy for stiffness) was measured using ultrasound shear-wave elastography in 28 male sprinters, before and after 2 weeks of intervention. During the 2 weeks, the participants in the training-cessation group (n = 14) were allowed to maintain their normal daily activities but not to perform any physical training, including stretching and resistance exercises. The participants in the training continuation group (n = 14) performed the training (including maximum speed sprint, plyometric, and weight training) prescribed by their coaches 5 days per week., Results: In the training-cessation group, passive BFlh shear-wave speed increased after the 2 weeks of training cessation (4.75 ± 0.77 to 5.00 ± 0.88 m/s, P < 0.001). In contrast, there was no significant difference before and after the 2 weeks of training continuation (4.90 ± 0.85 to 4.93 ± 0.85 m/s, P = 0.521)., Conclusions: The present findings indicate that muscles stiffen by training cessation in sprinting athletes., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Purpose: Muscle quality is explained by the ratio between muscle size and strength. Conventionally, muscle size is evaluated without considering the composition of contractile and non-contractile tissues in muscle, hence the influence of non-contractile tissues on muscle quality is not fully understood, especially within aging muscle. This study investigated the differences in intramuscular non-contractile tissues between different age and sex groups, and investigated their influence on muscle quality., Methods: Eighty-two older and 64 young females and males participated. Muscle cross-sectional area (quadriceps and hamstrings), separating contractile and non-contractile areas, was calculated from the magnetic resonance image of the right mid-thigh. Maximal voluntary isometric knee extension and flexion torque was measured. Torque/muscle area and torque/contractile area were calculated for each age and sex group., Results: Non-contractile/muscle area was higher in older than in young individuals in both muscle groups (p < 0.05), and it was greater in the hamstrings than in the quadriceps. For the hamstrings, torque/muscle area was lower in older than in young individuals in both sexes (p < 0.05). However, torque/contractile area did not show the differences between age groups, only between sexes (males>females) (p < 0.05)., Conclusions: The results indicate that 1) the presence of non-contractile tissues varies by age and muscle groups, 2) the extensive presence of non-contractile tissues can contribute to the underestimation of its muscle quality, and 3) the sex differences in muscle quality are influenced by factors other than muscle composition., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Introduction: Age-induced inflexibility may lead to significant mobility impairments and declines in well-being. However, the relationship between the structural and mechanical properties of soft tissue and joint extensibility remains unclear. This study aimed to investigate the correlation between flexibility, muscle tendon unit (MTU) stiffness, muscle ultrasound characteristics, muscle strength, and hamstring flexibility prediction in older males with hamstring inflexibility., Methods: A hundred retired old males (mean age: 67.2 ± 4.9 years) participated in this investigation. Muscle ultrasound, flexibility, MTU stiffness, and knee flexors strength were measured in a single visit., Results: The results revealed a modest correlation between straight leg raise (SLR) and biceps femoris fascicle length (FL) elongation (r = 0.222), MTU stiffness (r = -0.401), and eccentric strength (r = 0.219) (all p < 0.05). MTU stiffness, eccentric strength, and FL elongation collectively explained 24.8% of the variance in SLR prediction, while deep fascia thickness predicted MTU stiffness with a variance of 6.4%., Conclusion: In summary, increased SLR was associated with lower MTU stiffness, lengthened FL, and higher eccentric strength. SLR was primarily predicted by MTU stiffness, with lesser contributions from FL elongation and knee flexor eccentric strength in older males experiencing hamstring tightness., Competing Interests: Declaration of competing interest The authors declare that they have no conflict of interest., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Introduction: The hamstring muscles play a crucial role in sprint running but are also highly susceptible to strain injuries, particularly within the biceps femoris long head (BFlh). This study compared the adaptations in muscle size and strength of the knee flexors, as well as BFlh muscle and aponeurosis size, after two eccentrically focused knee flexion training regimes: Nordic hamstring training (NHT) vs lengthened state eccentric training (LSET, isoinertial weight stack resistance in an accentuated hip-flexed position) vs habitual activity (no training controls: CON)., Methods: Forty-two healthy young males completed 34 sessions of NHT or LSET over 12 wk or served as CON ( n = 14/group). Magnetic resonance imaging-measured muscle volume of seven individual knee flexors and BFlh aponeurosis area, and maximum knee flexion torque during eccentric, concentric, and isometric contractions were assessed pre- and post-training., Results: LSET induced greater increases in hamstrings (+18% vs +11%) and BFlh (+19% vs +5%) muscle volumes and BFlh aponeurosis area (+9% vs +3%) than NHT (all P ≤ 0.001), with no changes after CON. There were distinctly different patterns of hypertrophy between the two training regimes, largely due to the functional role of the muscles; LSET was more effective for increasing the size of knee flexors that also extend the hip (2.2-fold vs NHT), whereas NHT increased the size of knee flexors that do not extend the hip (1.9-fold vs LSET; both P ≤ 0.001). Changes in maximum eccentric torque differed only between LSET and CON (+17% vs +4%; P = 0.009), with NHT (+11%) inbetween., Conclusions: These results suggest that LSET is superior to NHT in inducing overall hamstrings and BFlh hypertrophy, potentially contributing to better sprint performance improvements and protection against hamstring strain injuries than NHT., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

Purpose: Previous evidence indicated that the tibiofemoral bone configuration might elevate the risk of an anterior cruciate ligament (ACL) injury. Furthermore, a low hamstring-to-quadriceps muscle ratio predisposes especially females to unfavourable knee kinematics. The primary objective of the present study was to investigate sex-specific associations between tibiofemoral bone geometry and isokinetic knee flexion torque in patients with primary ACL injury followed by ACL reconstruction., Methods: N = 100 patients (72 = male, 28 = female, age = 31.3 ± 10.2, body mass index = 25.3 ± 3.6) with primary ACL rupture with isokinetic knee flexion torque assessments before and 6 months after ACL reconstruction surgery were analysed. Magnetic resonance imaging scans were analysed for medial posterior tibial slope (MPTS) and lateral posterior tibial slope, notch width index (NWI) and lateral femoral condyle index (LFCI). Additionally, isokinetic knee flexion torque (60°/s) and hamstring-quadriceps ratios were evaluated. Subsequently, functional parameters were correlated with imaging data for gender subgroups., Results: The findings showed that presurgical isokinetic knee flexion torque was not associated with any marker of femoral or tibial bone geometry. Further, while significant differences were observed between female (0.883 ± 0.31 Nm/kg) and male (1.18 ± 0.35 Nm/kg) patients regarding preoperative normalized knee flexion torque (p < 0.001), no significant sex differences were found for percentage increases in normalized knee flexion torque from presurgery to postsurgery. Generally, female patients demonstrated significantly higher MPTS magnitudes (p < 0.05) and lower LFCI values (p < 0.05) compared to men., Conclusion: The present results demonstrated no association between tibial or femoral bone geometry and muscle strength of the hamstrings in patients with ACL reconstruction, indicating an important mismatch of muscular compensation to deviations in bone geometry. There were no sex-specific differences in tibiofemoral bone parameters., Level of Evidence: Level III., (© 2024 European Society of Sports Traumatology, Knee Surgery and Arthroscopy.)

Targeted resistance training stimulates hamstring muscle hypertrophy, but its effect on tendon-aponeurosis geometry is unknown. This study examined changes in hamstring muscle, free tendon, and aponeurosis geometry following a 10 week Nordic or hip extension exercise intervention. Thirty recreationally active males were randomly allocated (n = 10 per group) to a Nordic, hip extension, or control group. Magnetic resonance imaging of both thighs was acquired pre- and post-intervention. Changes in free tendon and aponeurosis volume for each hamstring muscle, biceps femoris long head (BFlh) aponeurosis interface area and muscle volume-to-interface area ratio were compared between groups. Regional changes in muscle CSA were examined via statistical parametric mapping. The change in semimembranosus free tendon volume was greater for the Nordic than control group (mean difference = 0.06 cm 3 , 95% CI = 0.02-0.11 cm 3 ). No significant between-group differences existed for other hamstring free tendons or aponeuroses. There were no between-group differences in change in BFlh interface area. Change in BFlh muscle volume-to-interface area ratio was greater in the hip extension than Nordic (mean difference = 0.10, 95% CI = 0.007-0.19, p = 0.03) and control (mean difference = 0.12, 95% CI = 0.03-0.22, p = 0.009) groups. Change in muscle CSA following training was greatest in the mid-portion of semitendinosus for both intervention groups, and the mid-portion of BFlh for the hip extension group. There was limited evidence for tendon-aponeurosis hypertrophy after 10 weeks of training with the Nordic or hip extension exercises. For the BFlh, neither intervention altered the interface area although hip extension training stimulated an increase in the muscle volume-to-interface area ratio, which may have implications for localized tissue strains. Alternative muscle-tendon loading strategies appear necessary to stimulate hamstring tendon adaptations., (© 2024 The Author(s). Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Objective: Identify key flexibility and point-of-care musculoskeletal ultrasound (POCUS) measures for prognosticating return-to-play (RTP) following a first hamstring strain injury (HSI) and informing the clinical decision-making process., Design: Exploratory prospective cohort study., Setting: Sport medicine and rehabilitation clinic of a Canadian university., Participants: One hundred and sixty-seven elite Canadian university football athletes followed over 5 seasons., Interventions: Clinical and POCUS measures collected within 7 days after HSI and preseason clinical measures., Main Outcome Measures: Active knee extension (AKE) and Straight Leg Raise (SLR) to quantify hamstring flexibility, POCUS-related outcomes to characterize tissue alteration, and RTP until full sport resumption were documented (categorized as Early [1-40 days] or Late [>40 days] RTP)., Results: A total of 19 and 14 athletes were included in the Early RTP (mean RTP = 28.84 ± 8.62 days) and Late RTP groups (mean 51.93 ± 10.54 days), respectively, after having been diagnosed with a first HSI. For the clinical results, height and a greater flexibility asymmetry measure with the AKE or SLR when compared with both ipsilateral preseason and acute contralateral values significantly increases the chance of facing a long delay before returning to play (ie, RTP). For the POCUS-related results, the Peetrons severity score, extent of the longitudinal fibrillary alteration, and novel score lead to similar results., Conclusions: Early hamstring flexibility asymmetry following acute HSI, particularly the AKE, along with some POCUS-related measures are valuable in prognosticating late RTP following among Canadian university football athletes., Competing Interests: The authors report no conflicts of interest., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Hamstring strain injuries (HSIs) are prevalent in sports involving high-speed running and most of the HSIs are biceps femoris long head (BFlh) injuries. The primary cause for HSIs during high-speed running remains controversial due to the lack of in vivo measurement of the BFlh muscle behavior during running. Therefore, the purpose of this study was to quantify the muscle-tendon unit (MTU) and fascicle behavior of BFlh during running. Seven college male sprinters (22.14 ± 1.8 years; 177.7 ± 2.5 cm; 70.57 ± 5.1 kg; personal bests in 100m: 11.1 ± 0.2 s) were tested on a motorized treadmill instrumented with two force plate for running at 4, 5, 6m/s. The ground reaction force (GRF), 3D lower limb kinematics, EMG, and ultrasound images of biceps femoris long head (BFlh) in the middle region were recorded simultaneously. BFlh fascicles undergo little length change (about 1 cm) in the late swing phase during running at three submaximal speeds. BFlh fascicle lengthening accounted for about 30% of MTU length change during the late swing phase. BFlh was most active during the late swing and early stance phases, ranging from 83%MVC at a running speed of 4 m/s to 116%MVC at 6 m/s. Muscle fascicles in the middle region of BFlh undergo relatively little lengthening relative to the MTU in the late swing phase during running in comparison to results from simulation studies. These results suggest that there is a decoupling between the fascicle in the middle region and MTU length changes during the late swing phase of running., (© Journal of Sports Science and Medicine.)

Background: Hamstring strain injuries (HSIs) are prevalent in US National Football League (NFL) players, but there is a paucity of information regarding imaging characteristics, injury severity, and player factors associated with time missed and risk of recurrent injury., Purpose: To describe player, football activity, clinical, and imaging characteristics of NFL players with HSIs, as well as determine player characteristics, clinical examination results, and magnetic resonance imaging (MRI) findings associated with injury occurrence, severity, and missed time., Study Design: Cross-sectional study; Level of evidence, 3., Methods: A retrospective cohort of NFL players with acute HSI (n = 180) during the 2018-2019 season was identified. Injury data were collected prospectively through a league-wide electronic health record system. Three musculoskeletal radiologists graded MRI muscle injury parameters using the British Athletics Muscle Injury Classification (BAMIC) system. Player, football, clinical, and imaging characteristics were correlated with HSI incidence and severity and with missed time from sport., Results: Of the 1098 HSIs identified during the 2018-2019 season, 416 (37.9%) were randomly sampled, and 180 (43.3%) had diagnostic imaging available. Game activity, preseason period, and wide receiver and defensive secondary positions disproportionately contributed to HSI. The biceps femoris was the most commonly injured muscle (n = 132, 73.3%), followed by the semimembranosus (n = 24, 13.3%) and semitendinosus (n = 17, 9.4%) muscles. The most common injury site was the distal third of the biceps femoris and semitendinosus muscles (n = 60, 45.5% and n = 10, 58.8%, respectively) and central part of the semimembranosus muscle (n = 17, 70.8%). Nearly half of the injuries (n = 83, 46.1%) were BAMIC grade 2; 25.6% (n = 46), grade 3; and 17.8% (n = 32), grade 4. MRI showed sciatic nerve abnormality in 30.6% (n = 55) of all HSIs and 81.3% (n = 26) of complete tendon injuries. BAMIC grade correlated with both median days and games missed. Combined biceps femoris and semitendinosus injuries resulted in the highest median days missed (27 days)., Conclusion: Among NFL players with acute HSIs, the most common injury was a moderate-severity injury of the distal biceps femoris. BAMIC grade was associated with missed time., Competing Interests: One or more of the authors has declared the following potential conflict of interest or source of funding: M.A.D. has received support for education from Great Lakes Orthopedics, Smith & Nephew, and Arthrex; grant from Arthrex; and hospitality payments from Stryker and Encore Medical. V.K. has received consulting fees from Hyalex Orthopaedics. A.B. has received royalties from Arthrex; consulting fees from Arthrex; and speaking fees from Synthes GmbH. S.A.R. is an associate editor for AJSM and has received consulting fees from Teladoc, DJO, and Novartis Pharmaceuticals Corporation; speaking fees from Terumo BCT and Smith & Nephew; and holds stock or stock options in Ortho RTI. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Muscle functional MRI identifies changes in metabolic activity in each muscle and provides a quantitative index of muscle activation and damage. No previous studies have analyzed the hamstrings activation over a football match. This study aimed at detecting different patterns of hamstring muscles activation after a football game, and to examine inter- and intramuscular differences (proximal-middle-distal) in hamstring muscles activation using transverse relaxation time (T2)-weighted magnetic resonance images. Eleven healthy football players were recruited for this study. T2 relaxation time mapping-MRI was performed before (2 hours) and immediately after a match (on average 13 min). The T2 values of each hamstring muscle at the distal, middle, and proximal portions were measured. The primary outcome measure was the increase in T2 relaxation time value after a match. Linear mixed models were used to detect differences pre and postmatch. MRI examination showed that there was no obvious abnormality in the shape and the conventional T2 weighted signal of the hamstring muscles after a match. On the other hand, muscle functional MRI T2 analysis revealed that T2 relaxation time significantly increased at distal and middle portions of the semitendinosus muscle (p = 0.0003 in both cases). By employing T2 relaxation time mapping, we have identified alterations within the hamstring muscles being the semitendinosus as the most engaged muscle, particularly within its middle and distal thirds. This investigation underscores the utility of T2 relaxation time mapping in evaluating muscle activation patterns during football matches, facilitating the detection of anomalous activation patterns that may warrant injury reduction interventions., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Mechó et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Hamstring strain injuries (HSI) are a common occurrence in athletics and complicated by high rates of reinjury. Evidence of remaining injury observed on magnetic resonance imaging (MRI) at the time of return to sport (RTS) may be associated with strength deficits and prognostic for reinjury, however, conventional imaging has failed to establish a relationship. Quantitative measure of muscle microstructure using diffusion tensor imaging (DTI) may hold potential for assessing a possible association between injury-related structural changes and clinical outcomes. The purpose of this study was to determine the association of RTS MRI-based quantitative measures, such as edema volume, muscle volume, and DTI metrics, with clinical outcomes (i.e., strength and reinjury) following HSI. Spearman's correlations and Firth logistic regressions were used to determine relationships in between-limb imaging measures and between-limb eccentric strength and reinjury status, respectively. Twenty injuries were observed, with four reinjuries. At the time of RTS, between-limb differences in eccentric hamstring strength were significantly associated with principal effective diffusivity eigenvalue λ 1 (r = -0.64, p = 0.003) and marginally associated with mean diffusivity (r = -0.46, p = 0.056). Significant relationships between other MRI-based measures of morphology and eccentric strength were not detected, as well as between any MRI-based measure and reinjury status. In conclusion, this preliminary evidence indicates DTI may track differences in hamstring muscle microstructure, not captured by conventional imaging at the whole muscle level, that relate to eccentric strength., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Select authors of this manuscript declare relationships with the following companies: Dr. Bryan Heiderscheit declares a potential conflict of interest directly related to this work (research support to institution from NBA and GE HealthCare). The other authors (CMW, SAH, MRJ, KL, RK) of this manuscript declare no direct relationships with any companies, whose products or services may be related to the subject matter of the article]., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Context: The incidence and recurrence rate of hamstring strain injuries remain persistently high, with recurrent injuries leading to increased time lost during play and extended recovery periods compared with initial injury. Ultrasound imaging assesses important factors such as hamstring fascicle length (FL), pennation angle (PA), cross-sectional area (CSA), muscle thickness (MT), echo intensity (EI), and shear wave elastography (SWE), all impacting athletic performance. However, its reliability must be established before employing any measurement tool in research or clinical settings., Objectives: To determine the reliability and measurement error of ultrasound for assessing hamstring FL, PA, CSA, MT, EI, and SWE among healthy adults and athletes; to synthesize the information regarding the operationalization of ultrasound., Evidence Acquisition: A systematic literature search was done from January 1990 to February 5, 2023, to identify reliability and validity studies of hamstring ultrasound assessment published in peer-reviewed journals with identifiable methodology of outcome measures., Evidence Synthesis: Intraclass correlation coefficient measurement of 14 included studies reported moderate to excellent intrarater, interrater, and test-retest reliabilities of FL, PA, and MT regardless of the site of muscle testing, probe size, and setting, state of muscle, and use of different techniques in the extrapolation of FL. Good to excellent test-retest reliability rates for all hamstring anatomic CSA along midmuscle and different percentages of thigh length using panoramic imaging. Good intrarater reliability of EI regardless of gender and orientation of the probe but with excellent intrarater reliability in transverse scan using maximum region of interest. Good intrarater, interrater, and interday repeatability on SWE with the muscle in a stretched position., Conclusion: Evidence from studies with a predominantly low risk of bias shows that ultrasound is a reliable tool to measure hamstring FL, PA, CSA, MT, EI, and SWE in healthy adults and athletes under various experimental conditions.

Purpose: The purpose of the study was to evaluate how the initial diagnostic tool used-specifically ultrasound (US) or magnetic resonance imaging (MRI)-for diagnosing proximal hamstring avulsion injury affects the delay before surgery and, secondarily, the outcomes of these injuries., Methods: This was a retrospective analysis of prospectively collected data (2012-2020). It targeted patients primarily treated for proximal hamstring avulsion injury. It included all patients with a preoperative US and/or MRI. Patients were divided into two groups based on the initial diagnostic tool used (US-first vs. MRI-first groups). The primary outcomes measure was the time from initial injury to surgical intervention (surgical delay). The secondary outcomes were the Parisien Hamstring Avulsion Score, as well as the activity level as measured by the University of California, Los Angeles (UCLA) Activity Scale and Tegner Activity Scale., Results: The analysis included 392 patients with a mean age of 43.8 ± 13.6 years for the MRI-first group and 47.6 ± 12.0 years for US-first group. Patients in the MRI-first group had a significantly shorter median time from injury to surgery of 20.0 days (interquartile range [IQR]: 11.0-61.0) compared to 30 days (IQR: 18-74) in the US-first group. At the final follow-up (4.2 ± 2.2 years for the MRI-first group and 5.1 ± 1.9 years for the US-first group), the MRI-first group had significantly higher mean Tegner Activity Scale and UCLA scores than the US-first group: The Tegner Activity Scale was median 5 (IQR: 3-7) for the MRI-first group versus median 4 (IQR: 2-6) for the US-first group (p < 0.05). The UCLA scores were 7.9 ± 2.4 for the MRI-first group compared to 7.3 ± 2.4 for the US-first group (p < 0.05). This difference was more pronounced when comparing the MRI-first group with the patient-false negative initial ultrasound. No difference was found regarding the Parisien Hamstring Avulsion Score., Conclusion: MRI as the initial diagnostic tool for proximal hamstring avulsion injury is associated with a shorter time to surgery and better postoperative outcomes in Tegner Activity Scale and UCLA scores, compared to US., Level of Evidence: Level III., (© 2024 The Authors. Knee Surgery, Sports Traumatology, Arthroscopy published by John Wiley & Sons Ltd on behalf of European Society of Sports Traumatology, Knee Surgery and Arthroscopy.)

Objectives: Studies identifying clinical and MRI reinjury risk factors are limited by relatively small sample sizes. This study aimed to examine the association between baseline clinical and MRI findings with the incidence of hamstring reinjuries using a large multicentre dataset., Methods: We merged data from four prospective studies (three randomised controlled trials and one ongoing prospective case series) from Qatar and the Netherlands. Inclusion criteria included patients with MRI-confirmed acute hamstring injuries (<7 days). We performed multivariable modified Poisson regression analysis to assess the association of baseline clinical and MRI data with hamstring reinjury incidence within 2 months and 12 months of follow-up., Results: 330 and 308 patients were included in 2 months (31 (9%) reinjuries) and 12 months (52 (17%) reinjuries) analyses, respectively. In the 2-month analysis, the presence of discomfort during the active knee extension test was associated with reinjury risk (adjusted risk ratio (ARR) 3.38; 95% CI 1.19 to 9.64). In the 12 months analysis, the time to return to play (RTP) (ARR 0.99; 95% CI 0.97 to 1.00), straight leg raise angle on the injured leg (ARR 0.98; 95% CI 0.96 to 1.00), the presence of discomfort during active knee extension test (ARR 2.52; 95% CI 1.10 to 5.78), the extent of oedema anteroposterior on MRI (ARR 0.74; 95% CI 0.57 to 0.96) and myotendinous junction (MTJ) involvement on MRI (ARR 3.10; 95% CI 1.39 to 6.93) were independently associated with hamstring reinjury., Conclusions: Two clinical findings (the presence of discomfort during active knee extension test, lower straight leg raise angle on the injured leg), two MRI findings (less anteroposterior oedema, MTJ involvement) and shorter time to RTP were independently associated with increased hamstring reinjury risk. These findings may assist the clinician to identify patients at increased reinjury risk following acute hamstring injury., Trial Registration Numbers: NCT01812564; NCT02104258; NL2643; NL55671.018.16., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY. Published by BMJ.)

Objective: To identify the region of interest (ROI) to represent injury and observe between-limb diffusion tensor imaging (DTI) microstructural differences in muscle following hamstring strain injury., Materials and Methods: Participants who sustained a hamstring strain injury prospectively underwent 3T-MRI of bilateral thighs using T1, T2, and diffusion-weighted imaging at time of injury (TOI), return to sport (RTS), and 12 weeks after RTS (12wks). ROIs were using the hyperintense region on a T2-weighted sequence: edema, focused edema, and primary muscle injured excluding edema (no edema). Linear mixed-effects models were used to compare diffusion parameters between ROIs and timepoints and limbs and timepoints., Results: Twenty-four participants (29 injuries) were included. A significant ROI-by-timepoint interaction was detected for all diffusivity measures. The edema and focused edema ROIs demonstrated increased diffusion at TOI compared to RTS for all diffusivity measures (p-values < 0.006), except λ 1 (p-values = 0.058-0.12), and compared to 12wks (p-values < 0.02). In the no edema ROI, differences in diffusivity measures were not observed (p-values > 0.82). At TOI, no edema ROI diffusivity measures were lower than the edema ROI (p-values < 0.001) but not at RTS or 12wks (p-values > 0.69). A significant limb-by-timepoint interaction was detected for all diffusivity measures with increased diffusion in the involved limb at TOI (p-values < 0.001) but not at RTS or 12wks (p-values > 0.42). Significant differences in fractional anisotropy over time or between limbs were not detected., Conclusion: Hyperintensity on T2-weighted imaging used to define the injured region holds promise in describing muscle microstructure following hamstring strain injury by demonstrating between-limb differences at TOI but not at follow-up timepoints., (© 2024. The Author(s), under exclusive licence to International Skeletal Society (ISS).)

Passive hamstring stiffness varies proximo-distally, resulting in inhomogeneous tissue strain during stretching that may affect localized adaptations and risk of muscle injuries. The purpose of the present study was to determine the acute and chronic effects of static stretching (SS) on intramuscular hamstring stiffness. Thirty healthy active participants had acute changes in passive biceps femoris (BF), semimembranosus (SM), and semitendinosus (ST) stiffness measured at 25% (proximal), 50% (middle), and 75% (distal) muscle length, using shear-wave elastography, immediately after SS. Participants then completed 4 weeks of either a SS intervention (n = 15) or no intervention (CON, n = 15) with stiffness measured before and after the interventions. The acute and chronic effects of SS were compared between anatomical regions and between regions on the basis of their relative stiffness pre-intervention. Acutely, SS decreased stiffness throughout the BF and SM (p ≤ 0.05) but not the ST (p = 0.326). However, a regional effect of stretching was observed for SM and ST with greater reduction in stiffness occurring in stiffer muscular regions (p = 0.001-0.013). Chronically, SS increased BF and ST (p < 0.05), but not SM (p = 0.422) stiffness compared with CON, but no regional effect of stretching was observed in any muscle (p = 0.361-0.833). SS resulted in contrasting acute and chronic effects, acutely decreasing stiffness in stiffer regions while chronically increasing stiffness. These results indicate that the acute effects of SS vary along the muscle's length on the basis of the relative stiffness of the muscle and that acute changes in stiffness from SS are unrelated to chronic adaptations., (© 2024 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The purpose of this study was to examine the differences in thoracolumbar fascia (TLF) and lumbar muscle modulus in individuals with and without hamstring injury using shear wave elastography (SWE). Thirteen male soccer players without a previous hamstring injury and eleven players with a history of hamstring injury performed passive and active (submaximal) knee flexion efforts from 0 ° , 45 ° and 90 ° angle of knee flexion as well as an active prone trunk extension test. The elastic modulus of the TLF, the erector spinae (ES) and the multifidus (MF) was measured using ultrasound SWE simultaneously with the surface electromyography (EMG) signal of the ES and MF. The TLF SWE modulus was significantly (p < 0.05) higher in the injured group (range: 29.86 ± 8.58 to 66.57 ± 11.71 kPa) than in the uninjured group (range: 17.47 ± 9.37 to 47.03 ± 16.04 kPa). The ES and MF modulus ranged from 14.97 ± 4.10 to 66.57 ± 11.71 kPa in the injured group and it was significantly (p < .05) greater compared to the uninjured group (range: 11.65 ± 5.99 to 40.49 ± 12.35 kPa). TLF modulus was greater than ES and MF modulus (p < 0.05). Active modulus was greater during the prone trunk extension test compared to the knee flexion tests and it was greater in the knee flexion test at 0° than at 90° (p < 0.05). The muscle EMG was greater in the injured compared to the uninjured group in the passive tests only (p < 0.05). SWE modulus of the TLF and ES and MF was greater in soccer players with previous hamstring injury than uninjured players. Further research could establish whether exercises that target the paraspinal muscles and the lumbar fascia can assist in preventing individuals with a history of hamstring injury from sustaining a new injury., (© Journal of Sports Science and Medicine.)

Objectives: The main purpose of this research study was to compare mean modified straight-leg raise test (mSLR) and hamstring muscle length (HL) between chronic non-specific low back pain (LBP) and healthy subjects to understand the possibility of neuropathic causes in LBP population as it may impact the diagnosis and treatment of LBP. Another purpose was to compare mean mSLR between those with lumbar nerve root impingement and those without as determine by magnetic resonance imaging (MRI)., Methods: The design of the study is cross sectional and included 32 subjects with ages ranging from 18-50 years old. Clinical exam objective measures were collected such as patient questionnaires, somatosensory tests, HL range of motion, and a mSLR test, and were compared to the findings from a structural lumbar spine MRI., Results: There were no significant differences in mean HL angulation and mSLR angulation between LBP and healthy subjects (p>0.05). There was no significant difference in mean HL by impingement by versus no impingement (38.3±15.6 versus 44.8±9.4, p = 0.08, Cohen's d = 0.50). On the other hand, there was a significant difference in mean mSLR angulation by impingement (57.6.3±8.7 versus 63.8±11.6, p = 0.05, Cohen's d = 0.60)., Conclusions: The mSLR test was found to be associated with lumbar nerve root compression, regardless of the existence of radiating leg symptoms, and showed no association solely with the report of LBP. The findings highlight the diagnostic dilemma facing clinicians in patients with chronic nonspecific LBP with uncorrelated neuroanatomical image findings. Clinically, it may be necessary to reevaluate the common practice of exclusively using the mSLR test for patients with leg symptoms. This study may impact the way chronic LBP and neuropathic symptoms are diagnosed, potentially improving treatment methods, reducing persistent symptoms, and ultimately improving disabling effects., Competing Interests: The authors have declared no competing interests exist., (Copyright: © 2024 Hermosura et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Abstract: Tanji, F, Ohnuma, H, Ando, R, Yamanaka, R, Ikeda, T, and Suzuki, Y. Longer ground contact time is related to a superior running economy in highly trained distance runners. J Strength Cond Res 38(5): 985-990, 2024-Running economy is a key component of distance running performance and is associated with gait parameters. However, there is no consensus of the link between the running economy (RE), ground contact time, and footstrike patterns. Thus, this study aimed to clarify the relationship between RE, ground contact time, and thigh muscle cross-sectional area (CSA) in highly trained distance runners and to compare these parameters between 2 habitual footstrike patterns (midfoot vs. rearfoot). Seventeen male distance runners ran on a treadmill to measure RE and gait parameters. We collected the CSAs of the right thigh muscle using a magnetic resonance imaging scanner. The RE had a significant negative relationship with distance running performance ( r = -0.50) and ground contact time ( r = -0.51). The ground contact time had a significant negative relationship with the normalized CSAs of the vastus lateralis muscle ( r = -0.60) and hamstrings ( r = -0.54). No significant differences were found in RE, ground contact time, or normalized CSAs of muscles between midfoot ( n = 10) and rearfoot ( n = 7) strikers. These results suggest that large CSAs of knee extensor muscles results in short ground contact time and worse RE. The effects of the footstrike pattern on the RE appear insignificant, and the preferred footstrike pattern can be recommended for running in highly trained runners., (Copyright © 2024 National Strength and Conditioning Association.)

Introduction: Increased time to surgery has been previously associated with poorer clinical outcomes after surgical treatment of proximal hamstring ruptures, though the etiology remains unclear. The purpose of this study was to evaluate whether degree of muscle atrophy, as assessed using the Goutallier classification system, is associated with worse outcomes following surgical treatment of chronic proximal hamstring ruptures., Materials and Methods: This was a retrospective case series of patients who underwent repair of proximal hamstring ruptures from 2012 to 2020 with minimum 2-year follow-up. Patients were included if they underwent primary repair of a proximal hamstring rupture ≥ 6 weeks after the date of injury and had accessible preoperative magnetic resonance imaging (MRI). Exclusion criteria were allograft reconstruction, endoscopic repair, or prior ipsilateral hip surgery. Patients were administered validated surveys: the modified Harris Hip Score (mHHS) and Perth Hamstring Assessment Tool (PHAT). Fatty atrophy on preoperative MRI was independently graded by two musculoskeletal radiologists using the Goutallier classification. Multivariate regression analysis was performed to evaluate associations of preoperative characteristics with muscle atrophy, as well as mHHS and PHAT scores., Results: Complete data sets were obtained for 27 patients. A majority of this cohort was male (63.0%), with a mean age of 51.5 ± 11.8 years and BMI of 26.3 ± 3.8. The mean follow-up time was 62.6 ± 23.1 months, and the mean time from injury-to-surgery was 20.4 ± 15.3 weeks. The Goutallier grading inter-reader weighted kappa coefficient was 0.655. Regression analysis demonstrated that atrophy was not significantly associated with PHAT (p = 0.542) or mHHS (p = 0.574) at latest follow-up. Increased age was significantly predictive of muscle atrophy (β = 0.62, p = 0.005) and was also found to be a significant predictor of poorer mHHS (β = - 0.75; p = 0.037)., Conclusions: The degree of atrophy was not found to be an independent predictor of clinical outcomes following repair of chronic proximal hamstring ruptures. Increasing age was significantly predictive of increased atrophy and poorer patient-reported outcomes., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Objective: To determine if MRI-based radiomics from hamstring muscles are related to injury and if the features could be used to perform a time to return to sport (RTS) classification. We hypothesize that radiomics from hamstring muscles, especially T2-weighted and diffusion tensor imaging-based features, are related to injury and can be used for RTS classification., Subjects and Methods: MRI data from 32 athletes at the University of Wisconsin-Madison that sustained a hamstring strain injury were collected. Diffusion tensor imaging and T1- and T2-weighted images were processed, and diffusion maps were calculated. Radiomics features were extracted from the four hamstring muscles in each limb and for each MRI modality, individually. Feature selection was performed and multiple support vector classifiers were cross-validated to differentiate between involved and uninvolved limbs and perform binary (≤ or > 25 days) and multiclass (< 14 vs. 14-42 vs. > 42 days) classification of RTS., Result: The combination of radiomics features from all diffusion tensor imaging and T2-weighted images provided the most accurate differentiation between involved and uninvolved limbs (AUC ≈ 0.84 ± 0.16). For the binary RTS classification, the combination of all extracted radiomics offered the most accurate classification (AUC ≈ 0.95 ± 0.15). While for the multiclass RTS classification, the combination of features from all the diffusion tensor imaging maps provided the most accurate classification (weighted one vs. rest AUC ≈ 0.81 ± 0.16)., Conclusion: This pilot study demonstrated that radiomics features from hamstring muscles are related to injury and have the potential to predict RTS., (© 2023. The Author(s), under exclusive licence to International Skeletal Society (ISS).)

Background: Ultrasound (US) imaging is used by physical therapists for diagnosis and assessment of musculoskeletal injury and follow-up., Purpose: The aim was to identify long-term effects of graft harvesting on hamstrings muscle mass among athletes who had undergone anterior cruciate ligament reconstruction (ACLR)., Methods: Twenty-eight participants (ages 18-55) were recruited: 18 with history of ACLR using semitendinosus (ST) autograft and 10 healthy controls. Images of the cross-sectional area (CSA) of ST and biceps femoris (BF) were captured at 30% and 70% of the distance from the ischial tuberosity to the popliteal crease. A mixed model ANOVA was used to identify inter-limb differences in the CSA of ST and BF at each location, for each group., Results: Inter-limb differences were found for the CSA of ST but not BF across both locations for the ACLR group, not controls (p < .001). Within the ACLR group, ST atrophy of the injured limb was relatively greater at the distal vs. proximal location (p < .001)., Conclusion: US imaging identified selective atrophy of ST on the injured side with no compensatory hypertrophy of BF. Specific rehabilitation may influence muscle mass of medial vs. lateral hamstrings muscle groups after ACLR using a ST graft, and monitored with US imaging.

Purpose: The aim of this study was to determine whether a 9-week resistance training program based on high load (HL) versus low load combined with blood flow restriction (LL-BFR) induced a similar (i) distribution of muscle hypertrophy among hamstring heads (semimembranosus, SM; semitendinosus, ST; and biceps femoris long head, BF) and (ii) magnitude of tendon hypertrophy of ST, using a parallel randomized controlled trial., Methods: A total of 45 participants were randomly allocated to one of three groups: HL, LL-BFR, and control (CON). Both HL and LL-BFR performed a 9-week resistance training program composed of seated leg curl and stiff-leg deadlift exercises. Freehand 3D ultrasound was used to assess the changes in muscle and tendon volume., Results: The increase in ST volume was greater in HL (26.5 ± 25.5%) compared to CON (p = 0.004). No difference was found between CON and LL-BFR for the ST muscle volume (p = 0.627). The change in SM muscle volume was greater for LL-BFR (21.6 ± 27.8%) compared to CON (p = 0.025). No difference was found between HL and CON for the SM muscle volume (p = 0.178).There was no change in BF muscle volume in LL-BFR (14.0 ± 16.5%; p = 0.436) compared to CON group. No difference was found between HL and CON for the BF muscle volume (p = 1.0). Regarding ST tendon volume, we did not report an effect of training regimens (p = 0.411)., Conclusion: These results provide evidence that the HL program induced a selective hypertrophy of the ST while LL-BFR induced hypertrophy of SM. The magnitude of the selective hypertrophy observed within each group varied greatly between individuals. This finding suggests that it is very difficult to early determine the location of the hypertrophy among a muscle group., (© 2024 The Authors. Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

Background: There is a correlation between the hamstring stiffness and the decrease of anterior tibial translation in athletic patients with healthy knees. This observation could question the clinical reliability of the Lachman-Trillat test to detect complete ACL ruptures in patients with an important hamstring stiffness. This study aims to determine if anterior tibial translation is correlated with hamstring stiffness in patients with complete ACL rupture., Methods: This is a prospective study including patients with unilateral complete ACL rupture confirmed by MRI. The arthrometer GNRB® was used to measure anterior tibial translation on both knees at 134 N and compute the side-to-side difference. The hamstring stiffness was assessed with the eccentric peak torque using the isokinetic dynamometer CON-TREX. Linear regressions were done between these two parameters on two study groups: one included all patients (GR1), and the other included only isolated ACL injuries without associated lesions (GR2)., Results: Fifty-two patients were included (29 men, 23 women) with an average of 34.9 years old. The mean eccentric peak torque of the hamstrings for pathological knees was 94.9Nm for GR1 and 91.7Nm for GR2. The mean side-to-side difference was 2.42 mm for GR1 and 1.99 mm for GR2. No significant correlations were identified for GR1 (p = 0.66) and GR2 (p = 0.105)., Conclusion: No significant linear correlation was found between side-to-side difference measured by GNRB® and hamstring stiffness for pathological knees with complete ACL rupture. These results lead to believe that the Lachman-Trillat clinical test is not influenced by hamstring stiffness., Level of Evidence: Prospective study, level of evidence IV., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier B.V. All rights reserved.)

The purpose of this study was to examine the effect of passive and active knee flexion efforts on the stiffness of the thoracolumbar (TLF), semitendinosus (STF), and semimembranosus fascia (SMF). Fourteen young healthy males participated in this study. Using ultrasound shear-wave elastography, fascia elastic modulus was measured at rest (passive condition) and during submaximal isometric knee flexion efforts (active condition) with the hip at neutral position and the knee flexed at 0°, 45°, and 90°. Analysis of variance designs indicated that when the knee was passively extended from 90° to 0°, shear modulus of the TLF, SMF, and STF increased significantly (p < 0.05). Similarly, active knee flexion contractions caused a significant increase in TLF, SMF, and STF shear modulus (p < 0.001). Compared to hamstring fascia, the TLF showed greater thickness but a lower shear modulus (p < 0.05) while STF modulus was greater compared that to SMF during active contraction (p < 0.05). These results indicate that exercising the hamstring muscles can remotely influence the stiffness of the fascia which surrounds the lumbar area., (© 2023 The Authors. Journal of Anatomy published by John Wiley & Sons Ltd on behalf of Anatomical Society.)

Authors of previous studies of patients with acute hamstring strains have reported injury to the biceps femoris and semitendinosus (ST) in 50% to 100% and 0% to 30%, respectively. This retrospective case series of hamstring injuries in National Collegiate Athletic Association Division I collegiate athletes exhibited an injury pattern on ultrasound imaging that differed from what would be expected based on prior literature. We examined ultrasound images of 38 athletes with acute hamstring strains for injury location (proximal muscle, proximal myotendinous junction, midportion of muscle, distal muscle) and affected muscles (biceps femoris, ST, or semimembranosus). Twenty-six athletes (68.4%) injured the ST, and 9 athletes (23.7%) injured the biceps femoris long head. Most athletes (23, 60.5%) injured the proximal portion of the muscle or myotendinous junction. Though this study had many limitations, we demonstrated more frequent involvement of the ST and less frequent involvement of the biceps femoris than reported in the literature., (© by the National Athletic Trainers’ Association, Inc.)

Objectives: Hamstring injuries are the most common muscle injuries in team sports. The aims of this study were to describe the epidemiology of hamstring muscle injuries in the professional and amateur sport sections of a multi-sport club Football Club Barcelona (FCB) and to determine any potential correlation between return-to-play (RTP) and injury location, severity of connective tissue damage, age, sex, and athlete's level of competition., Methods: This descriptive epidemiological study with data collected from September 2007 to September 2017 stored in the FCB database. The study included non-contact hamstring injuries sustained during training or competition., Results: A total of 538 hamstring injuries were reported in the club's database, of which 240 were structurally verified by imaging as hamstring injuries. The overall incidence for the 17 sports studied was 1.29 structurally verified hamstring injuries per 100 athletes per year. The muscle most commonly involved in hamstring injuries was the biceps femoris, and the connective tissue most frequently involved was the myofascial. There was no evidence of a statistically significant association between age and RTP after injury, and no statistically significant difference between sex and RTP. However, the time loss by professionals was shorter than for amateurs, and proximal hamstring injuries took longer RTP than distal ones., Conclusion: In the 17 sports practiced at multi-sport club, the incidence of hamstring injury was 1.29 per 100 athletes per year. Players from sports in which high-speed sprinting and kicking are necessary, and amateurs, were at higher risk of suffering a hamstring injury. In addition, proximally located hamstring injuries involving tendinous connective tissue showed the longest RTP time. Age did not seem to have any influence on RTP. Documenting location and the exact tissue involved in hamstring injuries may be beneficial for determining the prognosis and RTP.

We aimed to determine whether the anatomical location (intramuscular tendon or T-Junction) of hamstring muscle injuries in professional men's rugby union associates with a prolonged time to return to full training and a higher rate of re-injury/subsequent injury. We reviewed the medical records of an Irish professional rugby union club to identify hamstring muscle injuries incurred across five seasons. Clinicians and players were not blinded to MRI results at the time of rehabilitation. A blinded musculoskeletal radiologist re-classified all included injuries (n = 91) according to the British Athletics Muscle Injury Classification framework. Players who sustained an injury with intramuscular tendon involvement required a longer time to return to full training compared to players who sustained an injury without intramuscular tendon involvement (78 days vs. 24 days). Players who sustained a biceps femoris injury with T-junction involvement did not require a longer time to return to full training compared to players who sustained a biceps femoris injury without T-junction involvement (29 days vs. 27 days). Injuries with either intramuscular tendon or T-junction involvement were not associated with an increased rate of re-injury/subsequent injury to the same limb (intramuscular tendon involvement - odds ratio = 0.96, T-junction involvement - odds ratio = 1.03). When a hamstring muscle injury involves the intramuscular tendon, the injured player and stakeholders should be made aware that a longer time to return to full training is likely required. T-junction involvement does not alter the expected clinical course of biceps femoris injuries., (© 2024 The Authors. Scandinavian Journal of Medicine & Science In Sports published by John Wiley & Sons Ltd.)

This study aimed to determine whether changes in hamstrings passive and active shear modulus after a warmup protocol are correlated. Twenty males without a history of hamstring strain injury participated. Muscle shear modulus was assessed using ultrasound-based shear wave elastography at rest and during isometric contractions at 20% of maximal voluntary isometric effort before and immediately after a warmup protocol. Changes in passive shear modulus did not seem to be associated with changes in active shear modulus. The results of this study suggest that changes in passive and active hamstring shear modulus are not associated after a standardized warmup intervention., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The purpose of this study was to investigate the relationship between muscular parameters of quadriceps/hamstrings and knee joint kinetics in gait. Muscle architecture (thickness, pennation angle, and fascicle length), and quality (echo intensity) of individual quadriceps and hamstrings of 30 healthy participants (16 males and 14 females) was measured using ultrasound. Peak knee flexion moment (KFM), KFM impulse, peak knee adduction moment (KAM), and KAM impulse during walking were obtained at preferred speed. Pearson's correlation coefficient and multiple regression analyses were performed at significance level of 0.05, and Cohen's f 2 values were calculated to examine the effect sizes of multiple regression. The hamstring-to-quadriceps muscle thickness ratio (r = 0.373) and semitendinosus echo intensity (r =  - 0.371) were predictors of first peak KFM (R 2  = 0.294, P = 0.009, f 2  = 0.42), whereas only vastus medialis (VM) echo intensity was a significant predictor of second peak KFM (r = 0.517, R 2  = 0.267, P = 0.003, f 2  = 0.36). Only the VM thickness was the predictor of first (r = 0.504, R 2  = 0.254, P = 0.005, f 2  = 0.34) and second peak KAM (r = 0.581, R 2  = 0.337, P = 0.001, f 2  = 0.51), and KAM impulse (r = 0.693, R 2  = 0.480, P < 0.001, f 2  = 0.92). In conclusion, the greater hamstring-to-quadriceps muscle thickness ratio and the muscle architecture and quality of medial quadriceps/hamstring play an important role in KFM and KAM, and may have implications in knee osteoarthritis., (© 2023. The Author(s).)

The purpose of this study was to determine the effect of donor muscle morphology following tendon harvest in anterior cruciate ligament (ACL) reconstruction on muscular support of the tibiofemoral joint during sidestep cutting. Magnetic resonance imaging (MRI) was used to measure peak cross-sectional area (CSA) and volume of the semitendinosus (ST) and gracilis (GR) muscles and tendons (bilaterally) in 18 individuals following ACL reconstruction. Participants performed sidestep cutting tasks in a biomechanics laboratory during which lower-limb electromyography, ground reaction loads, whole-body motions were recorded. An EMG driven neuro-musculoskeletal model was subsequently used to determine force from 34 musculotendinous units of the lower limb and the contribution of the ST and GR to muscular support of the tibiofemoral joint based on a normal muscle-tendon model (Standard model). Then, differences in peak CSA and volume between the ipsilateral/contralateral ST and GR were used to adjust their muscle-tendon parameters in the model followed by a recalibration to determine muscle force for 34 musculotendinous units (Adjusted model). The combined contribution of the donor muscles to muscular support about the medial and lateral compartments were reduced by 52% and 42%, respectively, in the adjusted compared to standard model. While the semimembranosus (SM) increased its contribution to muscular stabilisation about the medial and lateral compartment by 23% and 30%, respectively. This computer simulation study demonstrated the muscles harvested for ACL reconstruction reduced their support of the tibiofemoral joint during sidestep cutting, while the SM may have the potential to partially offset these reductions. This suggests donor muscle impairment could be a factor that contributes to ipsilateral re-injury rates to the ACL following return to sport., Competing Interests: The authors declare that no competing interests exist., (Copyright: © 2023 Konrath et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Objectives: The objectives of this study were to assess the acute effects of static stretching on hamstring passive stiffness in young and older women. A secondary objective was to compare hamstring muscle size and quality measurements (cross-sectional area and echo intensity) between the two groups and to determine if these characteristics are related to passive stiffness at baseline., Methods: Fifteen young (23±4 years) and 15 older (73±5 years) women underwent two randomized conditions that included a control treatment and an experimental treatment of four, 15-s static stretches of the hamstrings. Passive stiffness was calculated before (pre-test) and after (post-test) each treatment using a passive knee extension test. Ultrasound imaging was used to measure hamstring muscle cross-sectional area and echo intensity., Results: Passive stiffness collapsed across group decreased from pre- to post-test for the stretching treatment (P=0.001) but not for the control (P=0.467). The older women had lower cross-sectional area (P=0.033) and greater baseline (pre-test) passive stiffness (P=0.042-0.049) and echo intensity (P=0.022) than the young women. Moreover, baseline passive stiffness was significantly related to echo intensity (r=0.430, P=0.018) but not cross-sectional area (r=-0.014, P=0.943)., Conclusion: An acute bout of static stretching decreased passive stiffness in both young and older women., Competing Interests: The authors have no conflict of interest.

The purpose of the present study was to examine the acute effects of a maximum repeated sprint protocol on (1) hamstring shear modulus and (2) knee flexor neuromuscular parameters such as peak torque (PT) and rate of torque development (RTD). Muscle shear modulus was assessed in 18 healthy males using shear wave elastography at rest and during 30° isometric knee flexion at 20% of maximal voluntary isometric contraction, before and after a 10 × 30 m repeated sprint protocol. There was a 9% decrease in average speed between the fastest and slowest sprint (p < 0.001; d = 2.27). A pre-post decrease was observed in PT (p = 0.004; η 2 p  = 0.399) and in the 0-50 ms (p = 0.042; η 2 p  = 0.222), and 50-100 ms (p = 0.028; η 2 p  = 0.254) RTD periods. For the active shear modulus, the only significant change after the sprint task was in the biceps femoris long head (BFlh) with an increase of 10% (Pre: 26.29 ± 8.89 kPa; Post: 28.93 ± 8.31 kPa; p = 0.015; d = 0.31). The present study provides evidence that repeated sprinting leads to significant decreases in average speed, PT, early RTD (0-50 ms; 50-100 ms), and to an increase in BFlh active shear modulus without changing the shear modulus of the other hamstrings muscles., (© 2023. Springer Nature Limited.)

Purpose: This study aimed to determine if hamstring-strain-injury risk factors related to muscle structure and morphology differed between rugby union players and controls., Methods: The biceps femoris long head (BFlh) fascicle length and passive muscle stiffness and relative and absolute muscle volume of knee flexors (KF) and extensors (KE) were measured in 21 male subelite rugby players and 21 male physically active nonathletes., Results: BFlh fascicle length was significantly longer (mean difference [MD] = 1.6 [1.7] cm) and BFlh passive muscle stiffness was significantly higher in rugby players (MD = 7.8 [14.8] kPa). The absolute BFlh (MD = 71.9 [73.3] cm3), KF (MD = 332.3 [337.2] cm3), and KE (MD = 956.3 [557.4] cm3) muscle volumes were also significantly higher in rugby players. There were no significant differences in the relative BFlh and KF muscle volumes. The relative KE muscle volumes were significantly higher in rugby players (MD = 2.3 [3.7] cm3/kg). However, the percentage BFlh fascicle length:KE (MD = -0.1% [0.1%]), BFlh/KE (MD = -0.9% [1.9%]), and KF:KE (MD = -4.9% [5.9%]) muscle volume ratios were significantly lower in the rugby players. BFlh muscle volume significantly correlated with BFlh fascicle length (r = .59, r2 = .35) and passive muscle stiffness (r = .46, r2 = .21)., Conclusion: Future prospective studies should examine whether there are threshold values in BFlh passive muscle stiffness and BFlh fascicle length:KE, BFlh:KE, and KF:KE muscle volume ratios for predicting hamstring strain injuries.

Background: Muscle thickness can influence the joint kinematics and/or kinetics during dynamic activities. The relationship between the muscle thickness of individual quadriceps and hamstrings or medial-to-lateral thigh muscle thickness ratio and the knee kinematics/kinetics with respect to anterior cruciate ligament (ACL) injury risk remains unclear., Hypothesis: Higher medial-to-lateral thigh muscle thickness ratio would be associated with lower knee valgus angle/moment and lower tibial internal rotation angle/moment during single-leg landing., Study Design: Cross-sectional., Level of Evidence: Level 4., Methods: Muscle thickness of the vastus lateralis (VL), vastus medialis (VM), biceps femoris (BF), and semitendinosus (ST) of 30 healthy participants (16 males and 14 females) were measured using ultrasound. Knee joint kinematics and kinetics during single-leg landing were obtained. Stepwise multiple regression analysis, a follow-up Fisher's r to z test to examine the sex as a moderator, and independent t tests to evaluate sex difference were performed., Results: Both knee valgus moment ( R 2 = 0.466, P < 0.001) and tibial external rotation moment ( R 2 = 0.330, P < 0.001) at peak anterior tibial shear force during single-leg landing were negatively correlated with medial-to-lateral (ie, (VM+ST):(VL+BF)) thickness ratio regardless of sex, whereas medial-to-lateral thigh muscle thickness ratio was not correlated with knee valgus and tibial external rotation angles. Male participants exhibited higher (VM+ST):(VL+BF) thickness ratio than female participants ( P = 0.005), and lower knee valgus moment ( P = 0.04) and tibial external rotation moment ( P = 0.05), as well., Conclusion: The knee joint moments in frontal and transverse planes during single-leg landing were associated with the medial-to-lateral thigh muscle thickness ratio; thus, the medial-lateral thigh muscle thickness could be a potential contributor to frontal and transverse plane knee joint loading during dynamic movement., Clinical Relevance: Strength training that aims to selectively strengthen the medial/lateral thigh muscles might be considered in a new ACL injury prevention training program to alter the biomechanical parameters associated with ACL injuries.

MRI examinations are accurate for diagnosing sports-related acute hamstring injuries. However, sensitive imaging methods for assessing recovery of these injuries are lacking. Diffusion tensor imaging (DTI) and quantitative T2 (qT2) mapping have both shown promise for assessing recovery of muscle micro trauma and exercise effects. The purpose of this study was to explore the potential of DTI and qT2 mapping for monitoring the muscle recovery processes after acute hamstring injury. In this prospective study, athletes with an acute hamstring injury underwent a 3-T MRI examination of the injured and contralateral hamstrings including DTI and qT2 measurements at three time points: (1) within 1 week after sustaining the injury, (2) 2 weeks after time point 1, and (3) return to play (RTP). A linear mixed model was used for time-effect analysis and paired t-tests for the detection of differences between injured and uninjured muscles. Forty-one athletes (age 27.8 ± 7 years; two females and 39 males) were included. Mean RTP time was 50 (range 12-169) days. A significant time effect was found for mean diffusivity, radial diffusivity, and the second and third eigenvalues (p ≤ 0.001) in the injured muscles. Fractional anisotropy (p = 0.40), first eigenvalue (p = 0.02), and qT2 (p = 0.61) showed no significant time effect. All DTI indices, except for fractional anisotropy, were significantly elevated compared with control muscles right after the injury (p < 0.001). Values normalized during the recovery period, with no significant differences between control and injured muscles at RTP (p values ranged from 0.08 to 0.51). Mean qT2 relaxation times in injured muscles were not significantly elevated compared with control muscles at any time point (p > 0.04). In conclusion, DTI can be used to monitor recovery after an acute hamstring injury. Future work should explore the potential of DTI indices to predict RTP and recovery times in athletes after an acute strain injury., (© 2023 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.)

Purpose: Assessing muscle flexibility and architecture is important for hamstring strain injury (HSI) prevention. We investigated the relationship between shear modulus and passive force in hamstring muscles at different sites and the effect of muscle architecture on the slope of the shear modulus-passive force using shear wave elastography (SWE)., Methods: The biceps femoris long head (BFlh), semitendinosus (ST), and semimembranosus (SM) muscles were dissected from nine Thiel-embalmed cadavers and fixed to a custom-made mechanical testing machine. Calibrated weights (0-1800 g) were applied gradually in 150-g increments. The shear modulus and anatomical cross-sectional area (ACSA) were measured at proximal, central, and distal points using SWE. The muscle mass and length were measured before the loading test. The shear modulus-passive load relationship of each tested muscle region was analyzed by fitting a least-squares regression line. The increase in shear modulus slope per unit load was calculated and compared between the muscles before and after normalization by the muscle mass, length, and ACSA., Results: The shear modulus and passive force for all hamstring muscles in each region showed a statistically significant linear correlation. Furthermore, the increase in shear modulus slope was greater for BFlh and ST than for SM (P < 0.05), but after normalization by the muscle length and ACSA, there were no significant differences among the muscles., Conclusion: The local mechanical properties of individual hamstring muscles can be indirectly estimated using SWE, and the slope of increase in shear modulus reflects characteristics of the muscle architecture., (© 2023. The Author(s), under exclusive licence to The Japan Society of Ultrasonics in Medicine.)

Objective: The validity and reliability of 3-D ultrasound (US) in estimation of muscle and tendon volume was assessed in a very limited number of muscles that can be easily immersed. The objective of the present study was to assess the validity and reliability of muscle volume measurements for all hamstring muscle heads and gracilis (GR), as well as tendon volume for the semitendinosus (ST) and GR using freehand 3-D US., Methods: Three-dimensional US acquisitions were performed for 13 participants in two distinct sessions on separate days, in addition to one session dedicated to magnetic resonance imaging (MRI). Volumes of ST, semimembranosus (SM), biceps femoris short (BFsh) and long (BFlh) heads, and GR muscles and from the tendon from semitendinosus (STtd) and gracilis (GRtd) were collected., Results: The bias and the 95% confidence intervals of 3-D US compared with MRI ranged from -1.9 mL (-0.8%) to 1.2 mL (1.0%) for muscle volume and from 0.01 mL (0.2%) to -0.03 mL (-2.6%) for tendon volume. For muscle volume assessed using 3-D US, intraclass correlation coefficients (ICCs) ranged from 0.98 (GR) to 1.00, and coefficients of variation (CV) from 1.1% (SM) to 3.4% (BFsh). For tendon volume, ICCs were 0.99, and CVs between 3.2% (STtd) and 3.4% (GRtd)., Conclusion: Three-dimensional US can provide a valid and reliable inter-day measurement of hamstrings and GR for both muscle and tendon volumes. In the future, this technique could be used as an outcome for strengthening interventions and potentially in clinical environments., Competing Interests: Conflict of interest The authors declare no competing interests., (Copyright © 2023 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Purpose: Muscle architecture is associated with motor performance and muscle injury. While muscle architecture and knee-flexor eccentric strength change with growth, the influence of anthropometric measures on these properties is rarely considered. This study aimed to investigate the relationship between hamstring muscle architecture and knee-flexor eccentric strength with anthropometric measurements., Methods: Sixty male footballers (16.6 [1.05] y) from the U16, U17, and U19 teams of an elite soccer club were included in this study. Fascicle length, pennation angle, and muscle thickness of the biceps femoris long head (BFlh) and semimembranosus muscles were measured in both legs using ultrasound. Knee-flexor eccentric strength, height, body mass, leg length, femur length, and peak height velocity (PHV) were measured within 1 week of the ultrasound images. A stepwise regression and 1-way analysis of variance tests were used to evaluate the effects of age, maturity, and anthropometric measurements on muscle properties., Results: Variance within BFlh and semimembranosus muscle thickness (r < .61), semimembranosus pennation angle (r < .58), and knee-flexor eccentric strength (r = .50) were highly related to body mass. We observed no significant correlations between muscle architecture and age (P > .29). However, moderately greater BFlh muscle thickness was shown for the post-PHV compared with the PHV group (effect size ± 90% CI: 0.72 ± 0.49)., Conclusions: In conclusion, weak correlations between muscle architecture and anthropometric measurements suggest that other factors (ie, genetics, training regimen) influence muscle architecture. The moderate effect of maturity on BFlh muscle thickness strongly suggests post-PHV hypertrophy of the BFlh muscle. Our results confirmed previous findings that eccentric knee-flexor strength is influenced by body mass.

A recent in-vivo experiment has shown that force can be transmitted between the gastrocnemius and the hamstring muscles due to a direct tissue continuity. However, it remains unclear if this mechanical interaction is affected by the stiffness of the structural connection. This study therefore aimed to investigate the impact of the knee angle on myofascial force transmission across the dorsal knee. A randomized, cross-over study was performed, including n = 56 healthy participants (25.36 ± 3.9 years, 25 females). On two separate days, they adopted a prone position on an isokinetic dynamometer (knee extended or 60° flexed). In each condition, the device moved the ankle three times from maximal plantarflexion to maximal dorsal extension. Muscle inactivity was ensured using EMG. High-resolution ultrasound videos of the semimembranosus (SM) and the gastrocnemius medialis (GM) soft tissue were recorded. Maximal horizontal tissue displacement, obtained using cross-correlation, was examined as a surrogate of force transmission. SM tissue displacement was higher at extended (4.83 ± 2.04 mm) than at flexed knees (3.81 ± 2.36 mm). Linear regression demonstrated significant associations between (1) SM and GM soft tissue displacement (extended: R 2  = 0.18, p = 0.001; flexed: R 2  = 0.17, p = 0.002) as well as (2) SM soft tissue displacement and ankle range of motion (extended: R 2  = 0.103, p = 0.017; flexed: R 2  = 0.095, p = 0.022). Our results further strengthen the evidence that local stretching induces a force transmission to neighboring muscles. Resulting remote exercise effects such as increased range of motion, seem to depend on the stiffness of the continuity.Trial registration: DRKS (Deutsches Register Klinischer Studien), registration number DRKS00024420, first registered 08/02/2021, https://drks.de/search/de/trial/DRKS00024420 ., (© 2023. The Author(s).)

Background: Proximal hamstring tendon avulsions (PHAs) may be treated nonoperatively or operatively. Little is known about the result of the injury, and its treatment, on the quality and function of the hamstring muscle after healing and rehabilitation. We hypothesized that the injured leg would have greater fatty infiltration and atrophy than the uninjured leg at follow-up and that these findings would correlate to muscle weakness., Methods: In a cross-sectional cohort study, 48 patients treated for PHA, either operatively or nonoperatively, were re-examined 2-11 years post-treatment. We measured muscle strength with isokinetic strength tests, and muscle volume and fatty infiltration with MRI. Primary outcomes were hamstring muscle quality, quantified by outlining the cross-sectional area slice-by-slice, and the degree of fatty infiltration estimated using the Goutallier grading method. Secondary outcome was concentric isokinetic hamstring muscle strength measured using BioDex at 60°/sec and tendon attachment assessed on MRI. Comparisons with the outcomes of the uninjured leg were made., Results: The total hamstring muscle volume was on average reduced by 9% (SD ± 11%, p < 0.001) compared to that of the uninjured leg. Fatty infiltration was significantly more severe in the injured hamstrings than in the uninjured hamstrings (p < 0.001). This was also true when only analyzing operatively treated patients. The reduction in muscle volume and increase in fatty infiltration correlated significantly (r = 0.357, p = 0.013), and there was also a statistically significant correlation with muscle atrophy and reduction in isokinetic strength (r = 494, p < 0.001)., Conclusion: PHA injuries result in fatty infiltration and muscle atrophy and the muscle quality impairment correlates with residual muscle weakness., (© 2023. The Author(s).)

The aim of this study was to examine the intra- and inter-muscular differences of the hamstring muscles using textural analysis of ultrasound (US) images, and the relationship between textural indicators with hamstring torque. Transverse US scans were obtained from 10 young males from four different measurement sites along the thigh of each individual hamstring muscle at rest. Maximum-knee-flexion isometric torque measurements were also obtained. Texture analysis was applied to US images, and five gray-level co-occurrence matrix (GLCM) features were quantified: entropy (ENT), angular second moment (ASM), inverse difference moment (IDM), contrast (CON) and correlation (COR). The intraclass correlation coefficients ranged from 0.77 to 0.99, and the standard error of measurement ranged from 0.06 to 10.05%, indicating high test-retest reliability. Analysis of the variance indicated significant differences between measurement sites and individual muscles, with the proximal measurement sites having greater values for ASM, IDM and COR and lower values for ENT and CON compared with the distal sites. Additionally, only the COR at the proximal measurement site exhibited a significant relationship (r = -0.66) with strength. The present study indicated significant differences among hamstrings and measurement locations with respect to the textural analysis and may provide a novel indicator of hamstring functional properties., Competing Interests: Conflict of interest disclosure The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this article., (Copyright © 2022 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.)

Background: Magnetic resonance imaging (MRI) is an integral component of the treatment algorithm for proximal hamstring avulsion injuries., Objective: The purpose of this study was to survey orthopedic surgeons and musculoskeletal radiologists on the reporting and analysis of proximal hamstring avulsions on MRI., Methods: Two online surveys were developed to evaluate musculoskeletal radiologists' and orthopedic surgeons' perceptions of MRI-reporting for proximal hamstring avulsion injuries. Each survey was designed to provide information on physicians' best practices with respect to four primary questions (1) ischial tuberosity landmark determination (2) difficulties associated with measuring tendon retraction, (3) important ancillary findings, and (4) perceived clinical impact of measured retraction. Descriptive statistics were calculated for all categorical variables, which were reported as frequencies with percentages. Chi-squared test was utilized to compare rates of responses between surgeons and radiologists. Statistically significant differences were analyzed with post-hoc Fisher's exact tests; p < 0.05 considered statistically significant., Results: 218-Musculoskeletal radiologists and 33-orthopedic surgeons responded to their respective surveys. There were statistically significant differences with responses to two of the questions asked in both surveys; (1) in cases of complete hamstring avulsion (avulsion of both the semimembranosus and conjoint tendon), which arrow represents the tendon gap measurement used for planning surgery? p = 0.028; (2) in cases of avulsion of only the conjoint tendon, which arrow represents the tendon gap measurement used for planning surgery? p = 0.013. Post-hoc testing demonstrated that for either partial or complete hamstring avulsions, more surgeons use the conjoint tendon origin to measure tendon retraction than radiologists (p < 0.05 for both). Significantly more radiologists use the semimembranosus origin to measure hamstring retraction for partial or complete hamstring tears (p < 0.05 for both). However, for each of these questions, both radiologists and surgeons most frequently stated that the conjoint tendon landmark should be used for surgical planning., Conclusion: Musculoskeletal radiologists and orthopedists frequently utilize the conjoint tendon origin as an anatomic landmark for measuring complete and partial proximal hamstring avulsion injuries; though, orthopedists are more likely to utilize this landmark. Additionally, the broad surface area of the ischial tuberosity may lead to variability in measurement., Clinical Impact: Standard landmarks at the ischial tuberosity and/or detailed descriptions of tendon retractions would improve communication between radiologists and surgeons for proximal hamstring avulsions., (Copyright © 2022. Published by Elsevier Inc.)

Introduction: Football matches show higher hamstring strain injuries (HSIs) than football training. The occurrence of HSIs increases in the last fifteen minutes of both halves of football matches and shows an incremental trend towards the end of the ninety minutes., Objectives: This study aimed to examine football-specific fatigue-induced alterations in risk factors of the HSIs, including biceps femoris long head fascicle length via ultrasonography (BFlh FL), single-leg hop distance, hamstrings' maximal eccentric strength, and single-leg hamstring bridge test (SLHB) performance., Methodology: During ninety minutes of the TSAFT90 football simulation, the BFlh FL and single-leg hop distance were measured three times (before, at half-time and after 90 minutes of simulated match-play), and maximal hamstrings eccentric strength and SLHB test scores were recorded twice (before and after simulated match-play) for both legs in physically active participants (n = 15)., Results: Maximal eccentric hamstrings' strength (dominant leg (D): p < 0.001, Hedges' (adjusted) g effect size = -0.969; non-dominant leg (ND): p < 0.001, g = -0.929) and the SLHB performance (D: p < 0.001, g = -1.249; ND: p < 0.001, g = -1.108) showed large decrements immediately after the TSAFT90 intervention. There were no significant alterations in the BFlh FL, and the single-leg hop distance., Conclusions: Maximal eccentric strength and the SLHB performance of hamstrings are reduced after 90 minutes of simulated football match-play. Practitioners may consider focusing on improving eccentric strength and the SLHB performance. Future studies should examine alterations in the BFlh fascicles' dynamic lengthening and shortening ability during a football match., Competing Interests: Gokhan Yagiz, Vinay Kumar Dayala, Kevin Williams, Julian Andrew Owen, and Hans-Peter Kubis declare that they have no conflict of interest in this article’s content., (Copyright: © 2022 Yagiz et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Introduction: Biceps femoris long-head fascicle length ( Lf ), fascicle angle (FA), and muscle thickness (MT) estimates obtained across 2 d from extended field-of-view (EFOV) sonographic images were compared with those measured from a collage of single ultrasound images (to visualize entire fascicles) as well as a range of geometric equations and extrapolation methods used on single images. Both test validity and intraday reliability were determined., Methods: Twenty healthy adults (10 men and 10 women) were tested on two occasions (day 1 and day 2), 7 d apart at the same time of day for test-retest measurements. Ultrasound imaging was performed using EFOV and static image acquisition sequences; in the latter, four single images were acquired in-series along the muscle. From these images, Lf was assessed using seven methods: EFOV, collage, manual linear extrapolation, and four different trigonometric equations (termed equations A, B, C, and D), and FA and MT were measured in EFOV, collage, and single images., Results: Lf , FA, and MT measured on days 1 and 2 were not different ( P > 0.05) for any method, reliabilities were very high (intraclass correlation coefficient, 0.91-0.98), and correlations were strong (≥0.84). Significant correlations ( P < 0.05; r = 0.67-0.98) were found between EFOV and the other measurement techniques for Lf , FA, and MT. The collage method had the highest reliability for Lf , and highest rank order and correlation with EFOV., Conclusions: Although the six different techniques used to estimate Lf provided values similar to EFOV, higher between-subject measurement variability was observed with trigonometric equations, and the collage method described herein provided the most accurate and reliable results and is therefore recommended for biceps femoris long-head architectural analysis when EFOV is not available., (Copyright © 2022 by the American College of Sports Medicine.)