Strain Injury Research Articles

Anthropometry, Neuroergonomics and Immersive Technologies for the Workplace’s Future: Safer, Self-Sustainable and Digital

Objective: The objective of this research is to identify the best ways to organize tasks, design interfaces and optimize work processes while respecting the cognitive limits, body size and know-how of the workforce. Theoretical Framework: It is possible to prevent occupational and work-related diseases. The future of work is being shaped by a convergence of disciplines that seek to optimize the interaction between humans and machines. Method: The method used included publications related to the topic on immersive training, movement programming and respect for anthropometric differences between genders. Results and Discussion: The results indicate a reduction in mental fatigue, a reduction in the cognitive load in tasks with the creation of work routines and greater attention and productivity. Research Implications: This review research shows how neuroergonomics, anthropometry and immersive technologies, considered pillars of transformation, have the potential to create safer, more efficient work environments adapted to the individual needs of workers. Originality/Value: The study of the physical dimensions and physical-mental characteristics of the human body in the design of equipment and workspaces makes it possible to create more comfortable and safe environments, reducing the risk of repetitive strain injuries and occupational diseases.

Correlation between MRI findings and functional outcomes in patients with calf muscle strain injuries: a retrospective study on 78 patients

BackgroundCalf muscle strain injuries (CMSI), also known as “tennis leg,” are frequently observed in middle-aged and physically active people, including non-professional athletes. While magnetic resonance imaging (MRI) is frequently used to assess the extent of these injuries, the relationship between MRI findings and long-term functional outcomes in non-athletic populations remains underexplored. This study aimed to investigate the correlation between MRI-detected injury severity and functional outcomes using the Achilles Tendon Rupture Score (ATRS) and the Tegner Activity Scale (TAS).MethodsA retrospective review was conducted on 78 non-athletic patients diagnosed with CMSI and were followed for an average of 25.6 ± 16.1 months. Injury severity was classified into three grades: Grade 1 (edema without architectural disruption), Grade 2 (partial muscle disruption with hematoma), and Grade 3 (complete muscle disruption or tendon detachment) based on MRI examination. The functional outcomes were assessed using the ATRS and TAS. A simple linear regression analysis was conducted to assess the impact of demographic variables and MRI findings on ATRS.ResultsThe mean ATRS at the final follow-up was 92.9 ± 10.6, with 75.6% of patients achieving an excellent outcome. Despite the excellent ATRS scores, a notable reduction in TAS was evident from the pre-injury assessment (4.4 ± 1.2) to the final follow-up (3.8 ± 1.3; p < 0.001). Moreover, 44.9% of patients did not resume their pre-injury activity levels. The regression analysis demonstrated no statistically significant correlation between MRI-detected injury severity, demographic factors (age, gender, BMI), and ATRS outcomes (R² = 0.094, adjusted R² = -0.011).ConclusionMRI-detected injury severity does not significantly predict long-term functional outcomes in patients with CMSI, even though most patients achieved excellent ATRS scores. However, nearly half of the patients did not return to their pre-injury activity levels. These findings suggest that additional factors might influence recovery, and further research is needed to elucidate these factors in non-athletic patients.Level of evidenceLevel IV, Retrospective case series.

Examining the effect of verbal feedback vs. real-time software feedback on kinetic and kinematic metrics of the Nordic hamstring exercise

Abstract Purpose A wealth of research exists for the Nordic hamstring exercise and several devices provide real-time feedback on torque profiling. However, none currently offer feedback on technique execution. This study investigated the effect of verbal and software feedback on Nordic exercise kinetic and kinematic metrics. Methods 24 recreational participants completed two sets of three bilateral repetitions on a hamstring testing device. In a crossover design, one set was performed with verbal feedback, while the other set used software-based feedback. Hamstring strain injury risk metrics (peak torque, break-torque angle, and bilateral limb percentage difference) and exercise technique metrics (relative trunk-to-thigh angle and angular velocity of the knee) were recorded for analysis. Results The feedback type significantly affected eccentric knee flexor peak torque, by a mean decrease of 7.1 Nm when performed with software feedback (Cohen’s d = 0.238, p &lt; 0.01). Altering feedback had no significant effect on bilateral limb difference percentage (Cohen’s d = 0.068, p = 0.578) or break-torque angle (Cohen’s d = 0.159, p = 0.115). Software feedback significantly decreased the mean of both the relative-trunk-to-thigh angle at peak torque by 5.7° (Cohen’s d = 0.514, p &lt; 0.01) and the angular velocity of the knee at peak torque by 8.7 deg·s−1. Conclusions An integrated software feedback system significantly improves acute Nordic exercise technique, benefitting individuals initially exhibiting poorer technique the most.

Using muscle-tendon load limits to assess unphysiological musculoskeletal model deformation and Hill-type muscle parameter choice.

Musculoskeletal simulations are a useful tool for improving our understanding of the human body. However, the physiological validity of predicted kinematics and forces is highly dependent upon the correct calibration of muscle parameters and the structural integrity of a model's internal skeletal structure. In this study, we show how ill-tuned muscle parameters and unphysiological deformations of a model's skeletal structure can be detected by using muscle elements as sensors with which modelling and parameterization inconsistencies can be identified through muscle and tendon strain injury assessment. To illustrate our approach, two modelling issues were recreated. First, a model repositioning simulation using the THUMS AM50 occupant model version 5.03 was performed to show how internal model deformations can occur during a change of model posture. Second, the muscle material parameters of the OpenSim gait2354 model were varied to illustrate how unphysiological muscle forces can arise if material parameters are inadequately calibrated. The simulations were assessed for muscle and tendon strain injuries using previously published injury criteria and a newly developed method to determine tendon strain injury threshold values. Muscle strain injuries in the left and right musculus pronator teres were detected during the model repositioning. This straining was caused by an unphysiologically large gap (12.92 mm) that had formed in the elbow joint. Similarly, muscle and tendon strain injuries were detected in the modified right-hand musculus gastrocnemius medialis of the gait2354 model where an unphysiological reduction of the tendon slack length introduced large pre-strain of the muscle-tendon unit. The results of this work show that the proposed method can quantify the internal distortion behaviour of musculoskeletal human body models and the plausibility of Hill-type muscle parameter choice via strain injury assessment. Furthermore, we highlight possible actions to avoid the presented issues and inconsistencies in literature data concerning the material characteristics of human tendons.

Megaformer as a Rehabilitation Modality for Hamstring Strain Injury in Division I American Football: A Case Study

BACKGROUND: With athletes striving for peak performance, noncontact muscle strain injuries are increasingly common. Hamstring strain injuries (HSIs) make up the largest portion of noncontact injuries and provide further difficulty because of the high reinjury rate. This case study explores the Megaformer as a modality to treat HSIs with the potential to reduce the return to play timetable and recurrence rate. CASE PRESENTATION: A 23-year-old male American football player with a history of hamstring injuries presented with pain in the right proximal hamstring and deficits in strength and mobility testing as a result of sustained hyperflexion of the right hip with full knee extension. Magnetic resonance imaging (MRI) confirmed a recurrent proximal hamstring strain. OUTCOME AND FOLLOW-UP: Subsequent strength and range of motion testing revealed no impactful tenderness or pain during active participation or palpation after 9 days, and complete alleviation of symptoms at 6 weeks. No reinjury occurred during the remaining football season. DISCUSSION: This case study highlights possible advantageous features of the Megaformer as a recovery modality for HSIs. The Megaformer aims to improve flexibility, strengthen primary and secondary muscles, and enhance neuromuscular coordination to attempt to decrease the return to play timetable and reduce injury recurrence.

Novel Supine Isometric Hamstring Test: A Reliability Study

Background: Hamstring strain injuries are highly prevalent, particularly when the hamstrings are in a lengthened position; however, monitoring strength deficits and fatigue throughout a season is currently difficult due to a lack of practical, reliable tests that do not cause undue fatigue. Objective: The aim of the current study was to investigate the intersession reliability of a novel 90°hip: 40°knee isometric hamstring test (IHT) in the supine position. Methodology: This was a prospective, observational cohort study conducted on nine male participants (24 ± 3 years, 81.9 ± 6.4kg, 181.8 ± 5.3cm). Each participant completed two testing sessions of the 90°hip: 40°knee IHT using force platforms. Relative and absolute reliability of isometric peak force (IPF) were assessed using intraclass correlation coefficient (ICC) and coefficient of variation (CV%), respectively. Results: Relative reliability of the 90°hip: 40°knee IHT was considered “good” in the dominant limb (ICC = 0.92, Lower bound 95% Confidence Interval (CI) = 0.72) and “poor” in the non-dominant limb (ICC = 0.76, Lower bound 95% CI = 0.28). Absolute reliability was “acceptable” in both legs with 5.81% in the dominant limb and 9.65% in the non-dominant limb. Conclusion: The 90°hip: 40°knee IHT demonstrated moderate reliability overall, further research is required to discover the optimum IHT configuration which can be reliably executed at longer hamstring muscle lengths. This study provides foundational information for practitioners on a novel method of reliably testing hamstring isometric strength at longer muscle lengths.

The effect of age on musculoskeletal injury compensation costs in South Australian professional urban firefighters: A cohort study.

Firefighting is recognised as a physically demanding occupation involving exposure to hazardous environments and activities. An aging workforce combined with the age-related decline in physical fitness may result in increased future workers' compensation expenditure for fire service organisations. The objective of this research was to investigate the costs associated with musculoskeletal sprain and strain injury and the impacts of age and injury location on Workers' Compensation claims submitted by professional urban firefighters. Claim rates, direct costs, and days lost were extracted from a professional Fire Service organisation's workers' compensation claim database for financial years between 2011 to 2018. The mean cost per claim increased with age, with a mean claim cost of the 60-70-year-old group over 10 times more than the 20-29-year-old group. The mean days lost per claim were also higher for claims submitted by firefighters aged over 50. Older firefighters miss more workdays when injured and are associated with increased claims costs, particularly those in the 60-70-year group. With an aging workforce, Fire Service organisations must implement appropriate management and prevention strategies to reduce the potential risks associated with an aging workforce.

Acute Changes in Hamstring Injury Risk Factors After a Session of High-Volume Maximal Sprinting Speed Efforts in Soccer Players.

Maximal sprinting speed (MSS) overexposure is associated with increased risk of injury. This study aimed to describe changes in sprint performance-related factors and hamstring strain injury (HSI) risk factors after a high-volume sprinting session in soccer players. A high-volume sprinting session can induce acute changes in several sprint performance-related factors (sprint time and mechanical properties) and HSI risk factors (posterior chain muscle strength, hamstring range of motion, and dynamic lumbo-pelvic control [LPC], measured as changes in anterior pelvic tilt [APT] during maximal speed sprinting). Prospective observational case series. Level 4. Fifteen active male amateur soccer players participated. Changes in sprint performance-related factors and HSI risk factors were examined for 72 hours after high-volume MSS efforts (H-VMSSE) using a soccer-contextualized multifactorial approach. Muscle damage proxy markers (hamstring perceived soreness and creatine kinase) were also examined. H-VMSSE induced decrements in sprint performance-related factors. Significant reductions in theoretical maximal horizontal velocity (P < 0.01; effect size [ES], -0.71) and performance (P = 0.02; ES, -0.59) were observed for 48 and 72 hours after H-VMSSE. Small but significant reductions in posterior chain muscle force-generating capacity were detected for 48 and 72 hours after H-VMSSE for the nondominant (P < 0.03; ES, -0.60) and dominant (P < 0.04; ES, -0.40) leg. Finally, players exhibited persistent small, albeit nonsignificant (P = 0.06; ES, 0.53), decreases in dynamic LPC (APT increases) for 72 hours after H-VMSSE. H-VMSSE induced declines in both sprint performance-related factors and HSI risk factors. Sprinting can alter a player's anatomic structure by increasing APT during the maximum speed phase of the sprint. A soccer-contextualized multifactorial approach might allow for the regulation of MSS dosage depending on individual HSI risk factor status, thereby serving as a tailored "vaccine" for sprinting needs.

Relationship between Peak Eccentric Force during the Nordic Hamstring Exercise and One Repetition Maximum Deadlift Performance.

The Nordic hamstring exercise (NHE) is useful for preventing hamstring strain injuries. However, its adoption rates in the sports field are currently low, necessitating a safe and efficient introduction. The purpose was to examine the relationship between the eccentric force during the NHE and the one repetition maximum of deadlift. It was hypothesized that the eccentric force during the NHE would be correlated with the one repetition maximum (1RM) of the deadlift. Cross-sectional study. Healthy student rugby players with no history of hamstring tears were recruited to participate. The peak eccentric forces during the NHE, which is the vertical peak force on the part holding the leg, were measured in both legs, while gradually leaning forward to a prone position over three seconds. The 1RM of deadlift was calculated from the weight that could be raised three times during a deadlift (x kg) using the estimated formula (x kg / 0.93). The correlation between the left and right peak eccentric forces during the NHE, the total left and right forces, and the 1RM of the deadlift was examined using Spearman's rank correlation coefficient, with all values corrected for body mass. During the NHE, the peak eccentric force of the right and left legs and the total peak eccentric force of both legs were 3.8 ± 1.1 N/BM, 3.8 ± 1.2 N/BM, and 7.6 ± 2.1 N/BM, respectively. The 1RM of deadlift was 1.9 ± 0.3 kg/BM. Weak correlations (r = 0.34-0.37) were found between the 1RM of the deadlift and the peak eccentric force in the right and left legs and the total peak eccentric force of both legs. The present study revealed a weak correlation between the peak eccentric force during the NHE and 1RM of deadlift. 2c.

Epidemiology of Hamstring Strain Injuries in Elite Male Australian Football Players: An Analysis of 773 Injuries Over 7 Seasons

OBJECTIVE: To describe the incidence, recurrence, and time loss until achievement of recovery milestones of hamstring strain injuries (HSIs) across 7 playing seasons using data from the Soft Tissue Injury Registry of the Australian Football League (STRAFL). STUDY DESIGN: Descriptive epidemiology study. METHODS: Eighteen AFL teams participated in the STRAFL in at least 1 season between 2014 and 2020 (average 15.7 teams per season). Details of each clinically diagnosed HSI were recorded on a standardized injury surveillance form by medical staff. RESULTS: 773 HSIs from 424 different players were reported, with each team averaging 7 HSIs per season. Of all in-season injuries, 72% occurred during competitive games. The biceps femoris was most commonly injured (84%) followed by the semimembranosus (11%). Recurrent HSIs accounted for 26% of all injuries, with 52% occurring within 2 months of the index injury. The majority (93%) of recurrent injuries were to the biceps femoris. Return to play was 30 ± 19 days for index injuries and 36 ± 22 days for recurrent injuries. CONCLUSIONS: An average of 7 HSIs per season per club were sustained, including a recurrence of 26%, with most injuries occurring within in-season competitive games. The biceps femoris took longer than the medial hamstrings to reach recovery milestones of running at &gt;90% top speed, return to full training, and return to play. JOSPT Open 2024;2(4):289-296. Epub 15 July 2024. doi:10.2519/josptopen.2024.0359

Imaging And Clinical Factors Associated with Return to Play Following Quadriceps Muscle Strain Injury

Imaging And Clinical Factors Associated with Return to Play Following Quadriceps Muscle Strain Injury

Alterations in hamstring properties of athletes with hamstring strain injuries can impact jump-landing performance.

Hamstring strains may alter the contractile properties of the muscle and affect functional movement. Thus, this study evaluated the association between the hamstring properties and the jump-landing performance in athletes with hamstring strains. Sixteen hamstring-injured athletes and 16 healthy controls were recruited. The mechanical properties and contractile function of the hamstring were assessed in both the injured and non-injured legs. The control group was tested only in the matched injured leg. The kinetic outcomes during squat jump (SJ) and countermovement jump (CMJ) tasks were analyzed to evaluate the jump-landing performance. The injured limb exhibited higher muscle tone (P=0.042) and stiffness (P=0.010), but lower flexibility (P=0.002) and strength (P=0.040) than the control limb. The injured limb showed a poorer jumping performance (P=0.037 for jump height) and landing performance (P=0.011 for landing force and P=0.004 for loading rate) during the CMJ task compared to the control limb. All the hamstring properties showed mild-to-moderate correlations with the jump-landing performance. Impairments in the muscle properties following hamstring strain impact the jumping and landing performance, leading to degraded sports outcomes in athletes with hamstring injuries. Thus, more attention should be paid to tissue property changes following hamstring strain injuries to develop effective strategies for restoring muscle function and improving sports performance.

Kinematic, Neuromuscular and Bicep Femoris In Vivo Mechanics during the Nordic Hamstring Exercise and Variations of the Nordic Hamstring Exercise

The Nordic hamstring exercise (NHE) is effective at decreasing hamstring strain injury risk. Limited information is available on the in vivo mechanics of the bicep femoris long head (BFLH) during the NHE. Therefore, the purpose of this study was to observe kinematic, neuromuscular and in-vivo mechanics of the BFLH during the NHE. Thirteen participants (24.7 ± 3.7 years, 79.56 ± 7.89 kg, 177.40 ± 12.54 cm) performed three repetitions of the NHE at three horizontal planes (0°, 20° and −20°). Dynamic ultrasound of the dominant limb BFLH, surface electromyography (sEMG) of the contralateral hamstrings and sagittal plane motion data were simultaneously collected. Repeated measures analysis of variance with Bonferroni post hoc corrections were used on the in vivo mechanics and the kinematic and sEMG changes in performance of the NHE. Likely differences in ultrasound waveforms for the BFLH were determined. Significant and meaningful differences in kinematics and in vivo mechanics between NHE variations were observed. Non-significant differences were observed in sEMG measures between variations. Changes to the NHE performance angle manipulates the lever arm, increasing or decreasing the amount of force required by the hamstrings at any given muscle length, potentially changing the adaptive response when training at different planes and providing logical progressions ore regressions of the NHE. All NHE variations result in a similar magnitude of fascicle lengthening, which may indicate similar positive adaptations from the utilization of any variation.

Optimizing radiology remote reading: leveraging technology to improve efficiency.

Remote work has been increasingly utilized in the profession of radiology over recent years. Setting up your individual workstation offers an opportunity to tailor it to suit your preferences without the restriction of a universal setup to accommodate multiple users. Important considerations when setting up a home workstation include selecting the optimal work location, choosing the proper desk and chair, and configuring an ideal computer monitor layout. The use of peripheral devices, such as programmable mice and hands-free dictation tools can improve efficiency and reduce repetitive strain injuries. This article also explores the use of smart home devices and programmable scripts using AutoHotKey to further streamline workflow and maximize the benefits of a remote workstation.

Fascicle Behavior and Muscle Activity of The Biceps Femoris Long Head during Running at Increasing Speeds.

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.

Characterizing Muscle Activity in Soccer Players with a History of Hamstring Strain Injuries during Accelerated Sprinting.

This study aimed to characterize muscle activity in male soccer players with a history of hamstring strain injuries (HSI) during accelerated sprinting. Thirteen patients each in the HSI group (history of HSI) and in the healthy group (with no history of HSI) were included. 26 male soccer players of which 13 with and 13 without HSI history were included in this study. Ten muscles were evaluated on electromyography activity during overground sprinting. The testing protocol consisted of a maximal sprint over a distance of 30 meters. One running stride was divided into the early stance phase, late stance phase, early swing phase, mid-swing phase, and late swing phase, and the average muscle activity per phase and the timing of the peak root-mean-square value appearance during each stride were calculated. Statistical analysis was performed using repeated-measures two-way ANOVA (group × phase), and multiple comparison tests were performed using the Bonferroni method when the interaction or main effect was significant. The statistical significance level was set at p < 0.05. Gluteus maximus (Gmax), gluteus medius (Gmed), and external oblique (EO) showed activity differences based on HSI history. Gmax was 30% lower, EO was 20% lower, and Gmed was 40% higher in HSI group. This study suggests that, despite previous findings that HSI is most likely during the late swing phase, the HSI group shows a higher injury risk in the early stance phase. This is due to differences in trunk and gluteal muscle activity between the late swing and early stance phases compared to the healthy group. In summary, HSI group had lower activity in the muscles contributing to trunk instability, especially EO and Gmax, before and after ground impact during accelerated sprinting, compared to Healthy.

Rationale and design of RESILIENCE: A prospective randomized clinical trial evaluating remote ischaemic conditioning for the prevention of anthracycline cardiotoxicity.

There is a lack of therapies able to prevent anthracycline cardiotoxicity (AC). Remote ischaemic conditioning (RIC) has shown beneficial effects in preclinical models of AC. REmote iSchemic condItioning in Lymphoma PatIents REceiving ANthraCyclinEs (RESILIENCE) is a multinational, prospective, phase II, double-blind, sham-controlled, randomized clinical trial that evaluates the efficacy and safety of RIC in lymphoma patients receiving anthracyclines. Patients scheduled to undergo ≥5 chemotherapy cycles including anthracyclines and with ≥1 AC-associated risk factors will be randomized to weekly RIC or sham throughout the chemotherapy period. Patients will undergo three multiparametric cardiac magnetic resonance (CMR) studies, at baseline, after the third cycle (intermediate CMR), and 2 months after the end of chemotherapy. Thereafter, patients will be followed up for clinical events over an anticipated median of ≥24 months. The primary endpoint is the absolute change from baseline in CMR-based left ventricular ejection fraction (LVEF). The main secondary outcome is the incidence of AC events, defined as (1) a drop in CMR-based LVEF of ≥10 absolute points, or (2) a drop in CMR-based LVEF of ≥5 and <10 absolute points to a value <50%. Intermediate CMR will test the ability of T2 mapping to predict AC versus classical markers (left ventricular strain and cardiac injury biomarkers). A novel CMR sequence allowing ultrafast cine acquisition will be validated in this vulnerable population. The RESILIENCE trial will test RIC (a novel non-invasive intervention to prevent AC) in a cohort of high-risk patients. The trial will also test candidate markers for their capacity to predict AC and will validate a novel CMR sequence reducing acquisition time in a vulnerable population.

Smaller Biceps Femoris Aponeurosis Size in Legs with a History of Hamstring Strain Injury.

Biceps femoris long head (BFLH) 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 BFLH 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 BFLH aponeurosis and muscle size. Prior unilateral HSI athletes' BFLH 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). BFLH 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). BFLH aponeurosis size was smaller in legs with prior HSI vs. those without prior HSI. These findings suggest BFLH aponeurosis size, especially maximum width, could be a potential cause or consequence of HSI, with prospective evidence needed to support or refute these possibilities.

Correlation of Player and Imaging Characteristics With Severity and Missed Time in National Football League Professional Athletes With Hamstring Strain Injury: A Retrospective Review

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.

The impact of a 10-week Nordic hamstring exercise programme on hamstring muscle stiffness, a randomised controlled trial using shear wave elastography

ABSTRACT Hamstring strain injuries (HSIs) remain a burden with high prevalence rates. The Nordic Hamstring exercise (NHE) has been found to be effective in preventing HSIs. However, the preventive mechanisms are not fully understood. Changes in stiffness are postulated as a possible protective mechanism. Surprisingly, the effect of the NHE on the stiffness of different hamstring muscles has never been investigated before. Therefore, the aim of this Randomised controlled trial was to investigate the impact of a 10-week NHE programme on the eccentric strength and the shear wave velocity (proxy of stiffness) of the hamstrings. Thirty-six soccer players were randomly assigned to either the control or the experimental group. The experimental protocol consisted of the incorporation of a 10-week NHE programme within the normal training routine. The hamstring stiffness and eccentric strength were assessed before and after. Within-group analyses showed a significant increase in strength, only for the experimental group. However, no significant effect of the NHE was found on the stiffness of each hamstring muscle. A 10-week NHE programme does not affect hamstring stiffness, despite an increase in eccentric strength, indicating that the preventive mechanism of the NHE is probably not (co-)explained by alterations in hamstring muscle stiffness.