Previous Hamstring Strain Injury Research Articles

Fatigue effects on the knee flexors neuromuscular parameters during repeated sprinting.

To identify at which point fatigue on neuromuscular parameters occurs in the knee flexors during a repeated sprint protocol. Physical active males without previous hamstring strain injury were recruited. Neuromuscular parameters such as peak torque (PT) and rate of torque development (RTD) were assessed after every two sprints in a 5 × (2 x 30m) repeated sprint protocol. Twenty physical active males participated in the study. A significant effect of sprint number was found (p < 0.001; η2p = 0.643) with a decreased sprint speed by 6.9% from fastest to slowest sprint. No significant differences were observed in the time between finishing the sprint and performing the first MVIC (46.3 ± 4.7s; p = 0.423), nor in the time between finishing a set and starting the next set (121.2 ± 7.6s; p = 0.503). Regarding neuromuscular parameters, the only significant difference found was in PT between before and after two sprints (117.95 ± 5.61N⋅m vs. 110.64 ± 5.71N⋅m; p = 0.048, d = 0.289) and on RTD 0-50ms before and after ten sprints (465.78 ± 223.76N⋅m/s vs. 382.30 ± 189.56N⋅m/s; p = 0.008; η2p = 0.149). A recovery time of 46s between sprints and testing neuromuscular parameters (due to experimental design) seems sufficient to restore the neuromuscular system. Therefore, it can be suggested that time recovery is the principal factor in detecting fatigue on neuromuscular parameters.

Hamstring Strain Injury Prevention: Current Beliefs and Practices of Practitioners Working in Major League Baseball.

Hamstring strain injury (HSI) is the most frequently sustained injury in Major League Baseball (MLB). However, the beliefs and practices of practitioners working in MLB regarding HSI risk factors and prevention strategies in baseball athletes have not been documented. To document the current beliefs and practices of practitioners working in MLB regarding HSI prevention. Cross-sectional study. Major League Baseball via an online survey. Athletic trainers, physical therapists, and strength and conditioning coaches working in MLB during the 2021 season. An online survey was conducted, with participants completing the survey once. Questions pertained to risk factor identification, the use and perceived effectiveness of prevention strategies, and barriers to implementation. Descriptive statistics were calculated for each question. A total of 91 responses were received featuring respondents from 28 of 30 MLB organizations. The perceived most important intrinsic risk factors were tolerance to high-speed running for first-time HSI and previous HSI for recurrent injury. The perceived most important extrinsic risk factor for both first-time and recurrent HSI was internal communication between staff. The perceived most effective prevention strategies were managing overall workload, regular exposure to high-speed running, and periodization. The most used prevention strategies were core or lumbopelvic strengthening, traditional resistance-training exercises, and managing overall workload. Approximately half (53%) of respondents reported barriers to effective implementation of HSI prevention strategies, including player and coach buy-in, compliance, workload management, and scheduling. This was the first survey to investigate MLB practitioner beliefs and practices regarding HSI prevention. Responses from practitioners regarding their beliefs about risk factors and appropriate prevention strategies varied, and discrepancies existed between the perceived most effective strategies and those most frequently used.

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

The aim of the present study is to compare the effects of a (i) repeated sprint protocol on the sprint performance, hamstrings shear modulus pattern, and neuromuscular parameters between players with and without previous hamstring strain injury (HSI); and (ii) between limbs with HSI and their healthy contralateral limbs on the hamstrings shear modulus pattern and neuromuscular parameters. One-hundred-and-five professional and semiprofessional football field players were invited to participate in this study during the pre-season 2021/2022 (June–July), resulting in a sample size of 210 limbs with 46 sustaining HSI in the previous 2 years. No differences were seen between previously injured and healthy control players regarding their sprint performance, hamstrings shear modulus pattern, and neuromuscular parameters, except for the early rate of torque development (0–50 ms) with previously injured limbs in the biceps femoris long head (BFlh) displaying higher rates than their contralateral muscle (injured: 496.93 ± 234.22 Nm/s; contralateral 422.72 ± 208.29 Nm/s; p = 0.005; η2p = 0.469). Overall, the present study provides evidence for no differences regarding sprint performance, hamstrings load sharing pattern, and major neuromuscular parameters between players with previous HSI in the last 2 years and healthy control players. Therefore, the results can possibly suggest that the duration between injury and screening could recover the differences between injured-control and injured-contralateral groups.

Post-game recovery of isometric hamstring strength in a high-risk hamstring strain injury group throughout an Australian Football League season

ABSTRACT This study sought to investigate post-game hamstring strength recovery of 26 Australian Football League (AFL) players with a previous hamstring strain injury (HSI) across an AFL season. Maximal unilateral isometric knee flexion strength was assessed using an externally fixed dynamometer, and inter-session reliability was measured during the pre-season period. Linear mixed effects models investigated the influence of numerous variables on post-game hamstring strength decrement (relative change between initial weekly test and individual baseline) and individual within-week strength change following gameplay. The test demonstrated good inter-tester reliability (ICC = 0.81–0.88; CV = 6.73–7.33), and an acceptable level of error (MAE = 5.77–7.14%). Player as a random effect strongly influenced post-game strength decrement and within-week strength change (marginal R2 = 0.185–0.407; conditional R2 = 0.455–0.654). Within-week hamstring strength change was strongly determined by post-game strength decrement alone (estimate = 0.51, 95% CI = -0.66- -0.36 ; η2 = 0.32; P=<0.001) and in interaction with number of days post-game (estimate = 0.43, 95% CI = 0.20–0.66; η2 = 0.096; P=<0.001). This study shows the importance of early individual assessment of post-game hamstring strength in players with prior hamstring injury and could be valuable to inform post-game hamstring recovery in future applications.

Impact of an isometric or eccentric hip extension exercise intervention on hamstring strength, architecture, and morphology: a randomised intervention trial

Introduction: Hamstring strain injury (HSI) is the leading cause of time lost from competition in running-based sports. Following return to sport, individuals with previous HSI often have persistent deficits in hamstring muscle strength, architecture and morphology. Considerable research effort has gone into identifying ways to address these variables, as they have been associated with future HSI risk. Eccentric knee flexion exercises have been shown to modify these variables, although implementation of these interventions in injury prevention programs is not widespread.

Knee Flexor Eccentric Strength, Hamstring Muscle Volume and Sprinting in Elite Professional Soccer Players with a Prior Strained Hamstring.

Simple SummaryGiven the link between a prior hamstring injury and the increased risk of suffering a subsequent injury in professional soccer, an understanding of the features displayed by previously injured players is important. The aim of the present study was to investigate if players with a history of hamstring injury exhibit bilateral deficits in knee flexor eccentric strength, hamstring muscle volume, and sprinting performance. The eccentric knee flexor strength was greater in the previously injured limbs compared to both the contralateral uninjured limbs in the previously injured group and the uninjured limbs in the previously uninjured players. Previously injured limbs showed possibly larger short heads of the biceps femoris and likely semitendinosus muscle volumes. Sprinting performances in the 5-m were possibly worse in players with a history of hamstring muscle strain injury compared to the previously uninjured players.The aim was to determine if players with a prior hamstring strain injury (HSI) exhibit bilateral deficits in knee flexor eccentric strength and hamstring muscle volume and differences in sprinting performance compared with players without a history of HSIs. Forty-six male professional soccer players participated in this study. Eccentric knee flexor strength, hamstring muscle volume (MRI), and a 20-m running sprint test (5- and 10-m split time) were assessed at the start of the preseason. Eccentric knee strength of the previously injured limbs of injured players was greater (ES: 1.18–1.36) than the uninjured limbs in uninjured players. Previously injured limbs showed possibly larger biceps femoris short heads (BFSh) and likely semitendinosus (ST) muscle volumes than the contralateral uninjured limbs among the injured players (ES: 0.36) and the limbs of the uninjured players (ES: 0.56), respectively. Players who had experienced a previous HSI were possibly slower in the 5-m (small ES: 0.46), while unclear differences were found in both the 10-m and 20-m times. Players with a prior HSI displayed greater eccentric knee flexor strength, possibly relatively hypertrophied ST and BFSh muscles, and possibly reduced 5-m sprinting performances than previously uninjured players. This can have implication for the design of secondary hamstring muscle injury prevention strategies.

Lower knee flexion and hip extension rate of torque development in athletes with previous hamstring strain injury

ABSTRACT Persistent deficits in strength and voluntary activation have been observed in athletes with a history of hamstring strain injury. The mechanisms contributing to these deficits are poorly understood and consequently may not be appropriately addressed during rehabilitation. This study aimed to investigate the impact of intended knee flexor contraction mode (concentric, eccentric or isometric) on the rate of torque development and surface electromyography (sEMG) rise in athletes with and without a history of unilateral hamstring strain injury. The impact of the previous injury on hip extensor rate of torque development was also investigated. Previously injured limbs exhibited a slower rate of torque development (mean difference = −31%, p = 0.02, Cohen’s d = 0.62) and biceps femoris rate of sEMG rise (mean difference = −181% · s−1, p = 0.003, Cohen’s d = 1.10) during intended eccentric knee flexor contractions compared with control limbs. Previously injured (mean difference = −29%, p = 0.01, Cohen’s d = 0.85) and contralateral uninjured limbs (mean difference = −31%, p = 0.007, Cohen’s d = 0.73) exhibited a slower rate of torque development during isometric hip extensor contractions compared with control limbs. These findings may highlight lower levels of descending input to hamstring motoneurons in previously injured athletes.

Increased short interval intracortical inhibition in participants with previous hamstring strain injury.

Cortical mechanisms may contribute to weakness in participants with previous hamstring strain injury. This study aims to examine intra-cortical inhibition (SICI) and corticospinal excitability in previously injured participants. In this cross-sectional study, TMS was used to examine SICI, silent period, silent period: MEP ratios and area under the stimulus response curve in the biceps femoris and medial hamstrings. Comparisons were made between participants with (n = 10) and without (n = 10) previous hamstring strain injury. Motor threshold and isometric knee flexor strength were also compared between participants and the relationship between strength and SICI in control and previously injured participants was examined. Isometric knee flexor strength was lower in previously injured limbs compared with control limbs (mean difference = -41 Nm (-26%) [95% CI = -80 to -2 Nm], p = 0.04, Cohen's d = -1.27) and contralateral uninjured limbs (mean difference = -23 Nm (-17%), [95% CI = -40 to -6 Nm], p = 0.01, Cohen's d = -0.57). Previously injured limbs exhibited smaller responses to paired pulse stimulation (i.e. greater levels of SICI) in the biceps femoris compared with control limbs (mean difference = -19%, [95% CI = -34 to -5%], p = 0.007, Cohen's d = -1.33). Isometric knee flexor strength was associated with the level of SICI recorded in the biceps femoris in previously injured participants (coefficient = 23 Nm [95% CI = 7-40 Nm], adjusted R2 = 0.31, p = 0.01). There were no differences in markers of corticospinal excitability between previously injured and control limbs (all p > 0.24, all Cohen's d < 0.40). Athletes with previous injury in the biceps femoris exhibit increased SICI in this muscle compared with control participants. Increased SICI is related to lower levels of hamstring strength, and rehabilitation programs targeting the removal of intra-cortical inhibition should be considered.

Predictors of time to return to play and re-injury following hamstring injury with and without intramuscular tendon involvement in adult professional footballers: A retrospective cohort study

ObjectivesIn one English Premier League football club over four seasons, 1) describe the number of hamstring strain injuries (HSI) sustained using the British Athletics Muscle Injury Classification (BAMIC); 2) determine if intramuscular tendon HSI influenced the time to return to play (TTRTP) and reinjury rate; 3) determine the predictors of TTRTP and reinjury. DesignRetrospective cohort design. MethodsAll first team players who sustained a HSI between 2014 and 2018 were included. Players underwent an MRI scan that was graded by a Radiologist using the BAMIC (0a-4) criteria. TTRTP, reinjury rate and information on suspected predictors were recorded. ResultsThirty-five HSI experienced by 24 players (age = 26 ± 4 years) were recorded over the 4 seasons. There was a difference in TTRTP between grades 1a and 2c (P = 0.007), but not between 2b and 2c (P = 0.845). Grade of HSI (P ≤ 0.001) and removal of the player (P < 0.001) were predictors of TTRTP, with each increase in grade resulting in an additional 3 days of TTRTP, and being removed, an additional 11 days. Grade and all other predictors did not influence reinjury rate, albeit higher odds were evident for previous HSI, experiencing the HSI during sprinting, passing a ball or stretching, and reported increase days of pain during walking. ConclusionsHSIs extending into the intramuscular tendon (2b cf. 2c) did not influence TTRTP or re-injury, albeit TTRTP was affected by the BAMIC grade and if the player was removed from activity.

Previous hamstring muscle strain injury alters passive tissue stiffness and vibration sense

BackgroundHamstring strain is one of the most common among sports injuries. A previous history of this injury is considered a strong predictor of recurrent hamstring strain injury. It has been suggested that fascial tissue alters after muscle strain injury. However, the association between previous hamstring strain injury and tissue stiffness and vibration sense detection has not been investigated. ObjectivesWe aimed to determine whether a previous history of hamstring strain injury affects tissue stiffness and vibration sense in professional soccer players. MethodThe stiffness (MyotonPRO®) and vibration disappearance threshold (tuning fork) were measured in eight professional soccer players with previous history of hamstring strain and eight uninjured players. The differences between two groups’ means were analyzed. Side-to-side differences between injured and uninjured legs were also analyzed. Results: The tissue stiffness was higher, and the vibration disappearance threshold was lower, in previously injured players when compared to uninjured players. Similar differences were found between injured and uninjured legs. No significant relationship was detected between the age or body mass index (BMI) for both tissue stiffness and vibration disappearance threshold (all P < 0.05). ConclusionsSoccer players with a previous history of hamstring strain injury exhibited higher tissue stiffness and lower vibration sensitivity in the injured leg, regardless of the age and BMI. The results that players who have a previous hamstring strain injury with altered tissue stiffness and vibration sense will be useful and feasible evaluation for chronic muscle strain condition.

Hamstring strains in professional rugby players result in increased fascial stiffness without muscle quality changes as assessed using shear wave elastography

IntroductionHamstring strain injury is common among sports injuries. A previous history of this injury is considered a strong predictor of recurrent hamstring strain injury. Fascial tissue reportedly becomes stiffer after hamstring strain injury. However, the association between fascial stiffness and previous hamstring strain injury has not been investigated in clinical studies. We aimed to determine whether a previous history of hamstring strain injury affects fascial tissue and muscle tissues using shear wave elastography. MethodIn eleven male professional rugby players, the stiffness as a shear modulus (kPa) of fascial tissue and muscle was measured on the specific injured area measured by magnetic resonance imaging (MRI) at resting position by using shear wave elastography. The side-to-side differences between the injured and the uninjured side were analyzed. The length and area of the muscle scar tissue were evaluated by MRI in relation to fascial stiffness. ResultsThe shear elastic modulus of fascia was stiffer in the injured vs. the uninjured side; however, no difference was observed in the muscle. No significant relationship was detected between the length and area of the muscle scar tissue (all P > 0.05). DiscussionRugby players with a previous history of hamstring strain injury exhibited passive stiffness of fascial tissues in the injured leg, regardless of the length or area of the muscle scar tissue. However, the passive stiffness of muscles was same between the injured and the uninjured leg. ConclusionThe results can be beneficial to consider future risk for hamstring strain injuries.

SPRINT PERFORMANCE IN FOOTBALL (SOCCER) PLAYERS WITH AND WITHOUT A PREVIOUS HAMSTRING STRAIN INJURY: AN EXPLORATIVE CROSS-SECTIONAL STUDY.

Hamstring strain injuries are common in many sports. Following a hamstring injury, deficits in peak and explosive strength may persist after return to sport potentially affecting sprint performance. Assessment of repeated-sprint ability is recognized as an important part of the return to sport evaluation after a hamstring injury.Purpose: This purpose of this exploratory cross-sectional study was to compare sprinting performance obtained during a repeated-sprint test between football players with and without a previous hamstring strain injury. Forty-four fully active sub-elite football players, 11 with a previous hamstring strain injury during the preceding 12 months (cases; mean age, SD: 25.6 ± 4.4) and 33 demographically similar controls (mean age, SD: 23.2 ± 3.7), were included from six clubs. All players underwent a repeated-sprint test, consisting of six 30-meter maximal sprints with 90 seconds of recovery between sprints. Sprint performance was captured using high-speed video-recording and subsequently assessed by a blinded tester to calculate maximal sprint velocity, maximal horizontal force, maximal horizontal power, and mechanical effectiveness. A significant between-group difference was seen in favor of players having a previous hamstring injury over 6 sprints for maximal velocity (mean difference: 0.457 m/s, 95% CI: 0.059-0.849, p = 0.025) and mechanical effectiveness (mean difference: 0.009, 95% CI: 0.001-0.016, p = 0.020). Repeated-sprint performance was not impaired in football players with a previous hamstring strain injury; in fact, higher mean maximal sprinting velocity and better mechanical effectiveness were found in players with compared to without a previous hamstring injury. The higher sprinting velocity, which likely increases biomechanical load on the hamstring muscles, in previously injured players may increase the risk of recurrent injuries. 3b.

Rapid hamstrings to quadriceps ratio at long muscle lengths in professional football players with previous hamstring strain injury

Hamstring strain injuries (HSI) are the most common injury in male professional football and are potentially a primary risk factor to re-injury. Although the isokinetic strength ratios have often been used to identify strength imbalances that can augment the risk of injury in football players, the rate of torque development hamstring to quadriceps ratio (RTD H/Q) has rarely been considered in previous reports. Furthermore, little consideration has been given to selective hamstring lengths (30° of knee flexion) and its influence on torque production. The aim of this study was to investigate the RTD H/Q at long hamstring lengths, conventional (concentric/concentric) and functional (eccentric/concentric) H/Q ratios in football players with and without previous HSI. Twenty-four professional male football players (12 and 12 without previous HSI) performed maximal voluntary isometric contractions at long hamstring lengths (knee and hip flexed at 30° and 85°, respectively) and isokinetic concentric and eccentric contractions at 180°.s−1 and 60°.s−1. Conventional and functional H/Q ratios based on peak torque throughout the entire isokinetic range of motion and at long hamstring lengths were calculated. The RTD H/Q was extracted at long hamstring lengths in incrementing time periods of 50 milliseconds (ms) from the onset of contraction (50–250 ms). No significant differences were found between groups in any H/Q ratios studied. However, small effects (d = 0.4) were found in previously injured hamstrings to lower RTD H/Q at 50 ms and flexor eccentric torque. Previous HSI group showed small to moderate (0.4 > d < 0.6) higher RTD H/Q in late time intervals (>100 ms).

Predictive Modeling of Hamstring Strain Injuries in Elite Australian Footballers.

Three of the most commonly identified hamstring strain injury (HSI) risk factors are age, previous HSI, and low levels of eccentric hamstring strength. However, no study has investigated the ability of these risk factors to predict the incidence of HSI in elite Australian footballers. Accordingly, the purpose of this prospective cohort study was to investigate the predictive ability of HSI risk factors using machine learning techniques. Eccentric hamstring strength, demographic and injury history data were collected at the start of preseason for 186 and 176 elite Australian footballers in 2013 and 2015, respectively. Any prospectively occurring HSI were reported to the research team. Using various machine learning techniques, predictive models were built for 2013 and 2015 within-year HSI prediction and between-year HSI prediction (2013 to 2015). The calculated probabilities of HSI were compared with the injury outcomes and area under the curve (AUC) was determined and used to assess the predictive performance of each model. The minimum, maximum, and median AUC values for the 2013 models were 0.26, 0.91, and 0.58, respectively. For the 2015 models, the minimum, maximum and median AUC values were, correspondingly, 0.24, 0.92, and 0.57. For the between-year predictive models the minimum, maximum, and median AUC values were 0.37, 0.73, and 0.52, respectively. Although some iterations of the models achieved near perfect prediction, the large ranges in AUC highlight the fragility of the data. The 2013 models performed slightly better than the 2015 models. The predictive performance of between-year HSI models was poor however. In conclusion, risk factor data cannot be used to identify athletes at an increased risk of HSI with any consistency.

Predicting hamstring strain injury incidence in elite Australian footballers

Background: Hamstring strain injuries (HSIs) are the most common injury in Australian football. The three most common risk factors identified in Australian footballers are previous HSI, increasing age and low eccentric hamstring strength. No study to date however has explored whether these factors can be used to predict HSI occurrence. Therefore, the purpose of this study was to investigate whether these factors, measured across two seasons, can be used to predict HSI occurrence in elite Australian footballers.

Pain-free vs pain-threshold rehabilitation for acute hamstring strain injury: A randomised controlled trial

Background: Hamstring strain injury (HSI) remains the most prevalent cause of time lost from competition in many sports. Deficits in hamstring muscle structure and function following return to play (RTP) clearance and increased re-injury risk in those with a previous HSI, suggest inadequacies in current rehabilitation practices. Conventional clinical guidelines for acute HSI recommend rehabilitation only continue and progress in the absence of pain, despite a lack of scientific comparisons to alternative approaches. The purpose of this study was to investigate whether allowing rehabilitation up to a pain-threshold compared to remaining pain-free alters time taken to achieve RTP clearance, hamstring muscle structure and function and rates of re-injury following acute HSI.

Higher Drop in Speed during a Repeated Sprint Test in Soccer Players Reporting Former Hamstring Strain Injury.

Aim: Hamstring strain injury is common in soccer. The aim of this study was to evaluate the physical capacity of players who have and have not suffered from hamstring strain injury in a sample of semi-professional and professional Norwegian soccer players in order to evaluate characteristics and to identify possible indications of insufficient rehabilitation.Method: Seventy-five semi-professional and professional soccer players (19 ± 3 years) playing at the second and third level in the Norwegian league participated in the study. All players answered a questionnaire, including one question about hamstring strain injury (yes/no) during the previous 2 years. They also performed a 40 m maximal sprint test, a repeated sprint test (8 × 20 m), a countermovement jump, a maximal oxygen consumption (VO2max) test, strength tests and flexibility tests. Independent sample t-tests were used to evaluate differences in the physical capacity of the players who had suffered from hamstring strain injury and those who had not. Mixed between-within subject's analyses of variance was used to compare changes in speed during the repeated sprint test between groups.Results: Players who reported hamstring strain injury during the previous two years (16%) had a significantly higher drop in speed (0.07 vs. 0.02 s, p = 0.007) during the repeated sprint test, compared to players reporting no previous hamstring strain injury. In addition, there was a significant interaction (groups × time) (F = 3.22, p = 0.002), showing that speed in the two groups changed differently during the repeated sprint test. There were no significant differences in relations to age, weight, height, body fat, linear speed, countermovement jump height, leg strength, VO2max, or hamstring flexibility between the groups.Conclusion: Soccer players who reported hamstring strain injury during the previous 2 years showed significant higher drop in speed during the repeated sprint test compared to players with no hamstring strain injury. The maximal speed, leg strength, ability to produce maximal power, endurance capacity, and hamstring flexibility was similar for both groups. Thus, a repeated sprint test consisting of 8 × 20 m could be used as a field-based diagnostic tool to identify players in need of reconditioning programs to ensure complete post-injury rehabilitation.

Short biceps femoris fascicles and eccentric knee flexor weakness increase the risk of hamstring injury in elite football (soccer): a prospective cohort study

Background/aimTo investigate the role of eccentric knee flexor strength, between-limb imbalance and biceps femoris long head (BFlh) fascicle length on the risk of future hamstring strain injury (HSI).MethodsElite soccer players...

Eccentric Knee Flexor Strength and Risk of Hamstring Injuries in Rugby Union

Background: Hamstring strain injuries (HSIs) represent the most common cause of lost playing time in rugby union. Eccentric knee flexor weakness and between-limb imbalance in eccentric knee flexor strength are associated with a heightened risk of HSIs in other sports; however, these variables have not been explored in rugby union. Purpose: To determine if lower levels of eccentric knee flexor strength or greater between-limb imbalance in this parameter during the Nordic hamstring exercise are risk factors for HSIs in rugby union. Study Design: Cohort study; Level of evidence, 2. Methods: This prospective study was conducted over the 2014 Super Rugby and Queensland Rugby Union seasons. In total, 178 rugby union players (mean age, 22.6 ± 3.8 years; mean height, 185.0 ± 6.8 cm; mean weight, 96.5 ± 13.1 kg) had their eccentric knee flexor strength assessed using a custom-made device during the preseason. Reports of previous hamstring, quadriceps, groin, calf, and anterior cruciate ligament injuries were also obtained. The main outcome measure was the prospective occurrence of HSIs. Results: Twenty players suffered at least 1 HSI during the study period. Players with a history of HSIs had a 4.1-fold (95% CI, 1.9-8.9; P = .001) greater risk of subsequent HSIs than players without such a history. Between-limb imbalance in eccentric knee flexor strength of ≥15% and ≥20% increased the risk of HSIs by 2.4-fold (95% CI, 1.1-5.5; P = .033) and 3.4-fold (95% CI, 1.5-7.6; P = .003), respectively. Lower eccentric knee flexor strength and other prior injuries were not associated with an increased risk of future HSIs. Multivariate logistic regression revealed that the risk of reinjuries was augmented in players with strength imbalances. Conclusion: Previous HSIs and between-limb imbalance in eccentric knee flexor strength were associated with an increased risk of future HSIs in rugby union. These results support the rationale for reducing imbalance, particularly in players who have suffered a prior HSI, to mitigate the risk of future injuries.

The Effect of Previous Hamstring Strain Injuries on the Change in Eccentric Hamstring Strength During Preseason Training in Elite Australian Footballers

Background: Hamstring strain injuries (HSIs) are the most common injury type in Australian football, and the rate of recurrence has been consistently high for a number of years. Long-lasting neuromuscular inhibition has been noted in previously injured athletes, but it is not known if this influences the athlete’s adaptive response to training. Purpose: To determine if elite Australian footballers with a prior unilateral HSI (previously injured group) display less improvement in eccentric hamstring strength during preseason training compared with athletes without a history of HSIs (control group). Study Design: Cohort study; Level of evidence, 2. Methods: A total of 99 elite Australian footballers (17 with a history of unilateral HSIs in the previous 12-month period) participated in this study. Eccentric hamstring strength was assessed at the start and end of preseason training using an instrumented Nordic hamstring device. The change in eccentric strength across the preseason was determined in absolute terms and normalized to the start of preseason strength. The start of preseason strength was used as a covariate to control for differences in starting strength. Results: The left and right limbs in the control group showed no difference in absolute or relative change (left limb: 60.7 ± 72.9 N and 1.28 ± 0.34 N, respectively; right limb: 48.6 ± 83.8 N and 1.24 ± 0.43 N, respectively). Similarly, the injured and uninjured limbs in the previously injured group showed no difference in either absolute or relative change (injured limb: 13.1 ± 57.7 N and 1.07 ± 0.18 N, respectively; uninjured limb: 14.7 ± 54.0 N and 1.07 ± 0.22 N, respectively). The previously injured group displayed significantly less increase in eccentric hamstring strength across the preseason (absolute change, 13.9 ± 55.0 N; relative change, 1.07 ± 0.20 N) compared with the control group (absolute change, 54.6 ± 78.5 N; relative change, 1.26 ± 0.39 N) for both absolute and relative measures (P < .001), even after controlling for differences in the start of preseason eccentric hamstring strength, which had a significant effect on strength improvement. Conclusion: Elite Australian footballers with a unilateral history of HSIs displayed less improvement in eccentric hamstring strength across preseason training. The smaller improvements were not restricted to the previously injured limb as the contralateral limb also displayed similarly small improvements in eccentric strength. Whether this is the cause of or the result of an injury remains to be seen, but it has the potential to contribute to the risk of hamstring strain reinjuries.