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Hamstring strain injuries are among the most common injuries seen in sports. Management is made difficult by the high recurrence rates. Typical time to return to sport varies but can be prolonged with recurrence. Eccentric strength deficits remain post‐injury, contributing to reinjury. Eccentric training has shown to be an effective method at prevention of hamstring injury in multiple systematic reviews and prospective RCTs but limited prospective rehabilitation literature. Functional dry needling is a technique that has been reported to be beneficial in the management of pain and dysfunction after muscle strains, but there is limited published literature on its effects on rehabilitation or recurrence of injury.
The purpose of this case report is to present the management and outcomes of a patient with hamstring strain, treated with functional dry needling and eccentric exercise.
Case Description:
The subject was an 18‐year‐old collegiate pole‐vaulter who presented to physical therapy with an acute hamstring strain and history of multiple strains on uninvolved extremity. He was treated in Physical Therapy three times per week for 3 weeks with progressive eccentric training and 3 sessions of functional dry needling.
By day 12, his eccentric strength on the involved extremity was greater than the uninvolved extremity and he reported clinically meaningful improvement in outcome scores. By Day 20, he was able to return to full sports participation without pain or lingering strength deficits.
The patient in this case report was able to return to sport within 20 days and without recurrence. He demonstrated significant decreases in pain and dysfunction with dry needling. He had greater strength on the injured extremity compared to contra‐lateral previously injured extremity.
This case illustrates the use of functional dry needling and eccentric exercise leading to a favorable outcome in a patient with hamstring strain.
Level of Evidence:
Level 4
PMCID: PMC3679638  PMID: 23772348
Functional Dry Needling; Hamstring; Eccentric Exercise
2.  Outcome of Grade I and II Hamstring Injuries in Intercollegiate Athletes 
Sports Health  2011;3(6):528-533.
Hamstring muscle strains represent a common and disabling athletic injury with variable recurrence rates and prolonged recovery times.
To present the outcomes of a novel rehabilitation protocol for the treatment of proximal hamstring strains in an intercollegiate sporting population and to determine any significant differences in the rate of reinjury and time to return to sport based on patient and injury characteristics.
Study Design:
Retrospective case series.
A retrospective review was performed of 48 consecutive hamstring strains in intercollegiate athletes. The rehabilitation protocol consisted of early mobilization, with flexible progression through supervised drills. Athletes were allowed to return to sport after return of symmetrical strength and range of motion with no pain during sprinting. Primary outcomes included time to return to sport and reinjury rates.
All patients returned to their sports, and 3 sustained repeat hamstring strains (6.2% reinjury rate) after a minimum follow-up of 6 months. The average number of days missed from sport was 11.9 (range, 5-23 days). There was no statistically significant difference for time to return to sport between first-time and recurrent injuries and between first- and second-degree injuries (P > 0.05).
Grade I and II hamstring strains may be aggressively treated with a protocol of brief immobilization followed by early initiation of running and isokinetic exercises—with an average expected return to sport of approximately 2 weeks and with a relatively low reinjury rate regardless of injury grade (I or II), injury characteristics (including first-time and recurrent injuries), or athlete characteristics.
PMCID: PMC3445226  PMID: 23016054
hamstring muscle; injury; athletes; rehabilitation; return to sports
3.  Hamstring Strain Injuries: Recommendations for Diagnosis, Rehabilitation and Injury Prevention 
Hamstring strain injuries remain a challenge for both athletes and clinicians given the high incidence rate, slow healing, and persistent symptoms. Moreover, nearly one-third of these injuries recur within the first year following a return to sport, with subsequent injuries often being more severe than the original. This high reinjury rate suggests that commonly utilized rehabilitation programs may be inadequate at resolving possible muscular weakness, reduced tissue extensibility, and/or altered movement patterns associated with the injury. Further, the traditional criteria used to determine the readiness of the athlete to return to sport may be insensitive to these persistent deficits, resulting in a premature return. There is mounting evidence that the risk of reinjury can be minimized by utilizing rehabilitation strategies that incorporate neuromuscular control exercises and eccentric strength training, combined with objective measures to assess musculotendon recovery and readiness to return to sport. In this paper, we first describe the diagnostic examination of an acute hamstring strain injury, including discussion of the value of determining injury location in estimating the duration of the convalescent period. Based on the current available evidence, we then propose a clinical guide for the rehabilitation of acute hamstring injuries including specific criteria for treatment progression and return to sport. Finally, we describe directions for future research including injury-specific rehabilitation programs, objective measures to assess reinjury risk, and strategies to prevent injury occurrence. Level of evidence: Diagnosis/therapy, level 5.
PMCID: PMC2867336  PMID: 20118524
functional rehabilitation; muscle strain injury; radiology/medical imaging; running; strength training
4.  Hamstring Musculotendon Dynamics during Stance and Swing Phases of High Speed Running 
Hamstring strain injuries are common in sports that involve high speed running. It remains uncertain whether the hamstrings are susceptible to injury during late swing phase, when the hamstrings are active and lengthening, or during stance, when contact loads are present. In this study we used forward dynamic simulations to compare hamstring musculotendon stretch, loading and work done during stance and swing phases of high speed running gait cycles.
Whole body kinematics, EMG activities and ground reactions were collected as 12 subjects ran on an instrumented treadmill at speeds ranging from 80% to maximum (average of 7.8 m/s). Subject-specific simulations were then created using a whole body musculoskeletal model that included fifty-two Hill-type musculotendon units acting about the hip and knee. A computed muscle control algorithm was used to determine muscle excitation patterns that drove the limb to track measured hip and knee sagittal plane kinematics, with measured ground reactions applied to the limb.
The hamstrings lengthened under load from 50% to 90% of the gait cycle (swing), and then shortened under load from late swing through stance. While peak hamstring stretch was invariant with speed, lateral hamstring (biceps femoris) loading increased significantly with speed, and was greatest during swing at the fastest speed. The biarticular hamstrings performed negative work on the system only during swing phase, with the amount of negative work increasing significantly with speed.
We concluded that the large inertial loads during high speed running appear to make the hamstrings most susceptible to injury during swing phase when compared to stance phase. This information is relevant for scientifically establishing effective muscle injury prevention and rehabilitation programs.
PMCID: PMC3057086  PMID: 20689454
Acute strain injury; motion analysis; forward dynamic simulation; musculoskeletal model; muscle mechanics
5.  Hamstring Strength and Morphology Progression after Return to Sport from Injury 
Hamstring strain re-injury rates can reach 30% within the initial two weeks following return to sport (RTS). Incomplete recovery of strength may be a contributing factor. However, relative strength of the injured and unaffected limbs at RTS is currently unknown. PURPOSE: Characterize hamstring strength and morphology at the time of RTS and six months later. METHODS: Twenty-five athletes that experienced an acute hamstring strain injury participated, following completion of a controlled rehabilitation program. Bilateral isokinetic strength testing and magnetic resonance imaging (MRI) were performed at RTS and 6-months later. Strength (knee flexion peak torque, work, angle of peak torque) and MRI (muscle and tendon volumes) measures were compared between limbs and over time using repeated measures ANOVA. RESULTS: The injured limb showed a peak torque deficit of 9.6% compared to the uninjured limb at RTS (60°/s, p<0.001), but not 6-months following. The knee flexion angle of peak torque decreased over time for both limbs (60°/s, p<0.001). MRI revealed that 20.4% of the muscle cross-sectional area showed signs of edema at RTS with full resolution by the 6-month follow-up. Tendon volume of the injured limb tended to increase over time (p=0.108), while muscle volume decreased 4–5% in both limbs (p<0.001). CONCLUSION: Residual edema and deficits in isokinetic knee flexion strength were present at RTS, but resolved during the subsequent six months. This occurred despite MRI evidence of scar tissue formation (increased tendon volume) and muscle atrophy, suggesting that neuromuscular factors may contribute to the return of strength.
PMCID: PMC3580023  PMID: 23059864
magnetic resonance imaging; knee flexion torque; rehabilitation; muscle volume
6.  Clinical and Morphological Changes Following 2 Rehabilitation Programs for Acute Hamstring Strain Injuries: A Randomized Clinical Trial 
Randomized, double-blind, parallel-group clinical trial.
To assess differences between a progressive agility and trunk stabilization rehabilitation program and a progressive running and eccentric strengthening rehabilitation program in recovery characteristics following an acute hamstring injury, as measured via physical examination and magnetic resonance imaging (MRI).
Determining the type of rehabilitation program that most effectively promotes muscle and functional recovery is essential to minimize reinjury risk and to optimize athlete performance.
Individuals who sustained a recent hamstring strain injury were randomly assigned to 1 of 2 rehabilitation programs: (1) progressive agility and trunk stabilization or (2) progressive running and eccentric strengthening. MRI and physical examinations were conducted before and after completion of rehabilitation.
Thirty-one subjects were enrolled, 29 began rehabilitation, and 25 completed rehabilitation. There were few differences in clinical or morphological outcome measures between rehabilitation groups across time, and reinjury rates were low for both rehabilitation groups after return to sport (4 of 29 subjects had reinjuries). Greater craniocaudal length of injury, as measured on MRI before the start of rehabilitation, was positively correlated with longer return-to-sport time. At the time of return to sport, although all subjects showed a near-complete resolution of pain and return of muscle strength, no subject showed complete resolution of injury as assessed on MRI.
The 2 rehabilitation programs employed in this study yielded similar results with respect to hamstring muscle recovery and function at the time of return to sport. Evidence of continuing muscular healing is present after completion of rehabilitation, despite the appearance of normal physical strength and function on clinical examination.
Therapy, level 1b–. J Orthop Sports Phys Ther 2013;43(5):284-299. Epub 13 March 2013. doi:10.2519/jospt.2013.4452
PMCID: PMC3751188  PMID: 23485730
MRI; muscle; return-to-sport criteria
7.  Influence of Hip-Flexion Angle on Hamstrings Isokinetic Activity in Sprinters 
Journal of Athletic Training  2012;47(4):390-395.
Hamstrings strains are common and debilitating injuries in many sports. Most hamstrings exercises are performed at an inadequately low hip-flexion angle because this angle surpasses 70° at the end of the sprinting leg's swing phase, when most injuries occur.
To evaluate the influence of various hip-flexion angles on peak torques of knee flexors in isometric, concentric, and eccentric contractions and on the hamstrings-to-quadriceps ratio.
Descriptive laboratory study.
Research laboratory.
Patients and Other Participants
Ten national-level sprinters (5 men, 5 women; age = 21.2 ± 3.6 years, height = 175 ± 6 cm, mass = 63.8 ± 9.9 kg).
For each hip position (0°, 30°, 60°, and 90° of flexion), participants used the right leg to perform (1) 5 seconds of maximal isometric hamstrings contraction at 45° of knee flexion, (2) 5 maximal concentric knee flexion-extensions at 60° per second, (3) 5 maximal eccentric knee flexion-extensions at 60° per second, and (4) 5 maximal eccentric knee flexion-extensions at 150° per second.
Main Outcome Measure(s)
Hamstrings and quadriceps peak torque, hamstrings-to-quadriceps ratio, lateral and medial hamstrings root mean square.
We found no difference in quadriceps peak torque for any condition across all hip-flexion angles, whereas hamstrings peak torque was lower at 0° of hip flexion than at any other angle (P < .001) and greater at 90° of hip flexion than at 30° and 60° (P < .05), especially in eccentric conditions. As hip flexion increased, the hamstrings-to-quadriceps ratio increased. No difference in lateral or medial hamstrings root mean square was found for any condition across all hip-flexion angles (P > .05).
Hip-flexion angle influenced hamstrings peak torque in all muscular contraction types; as hip flexion increased, hamstrings peak torque increased. Researchers should investigate further whether an eccentric resistance training program at sprint-specific hip-flexion angles (70° to 80°) could help prevent hamstrings injuries in sprinters. Moreover, hamstrings-to-quadriceps ratio assessment should be standardized at 80° of hip flexion.
PMCID: PMC3396298  PMID: 22889654
injury prevention; eccentric exercises; length-tension relationship; hamstrings-to-quadriceps ratio; muscle strains
8.  Evaluation and Imaging of an Untreated Grade III Hamstring Tear: A Case Report 
Muscle strains are one of the most common complaints treated by physicians. High-force lengthening contractions can produce very high forces resulting in pain and tissue damage; such strains are the most common cause of muscle injuries. The hamstring muscles are particularly susceptible as they cross two joints and regularly perform lengthening contractions during running. We describe a patient with return to full function after a large hamstring tear.
Case Description
We report the case of a 26-year-old man who presented 1 year after a noncontact, left-sided proximal hamstring tear incurred while sprinting. He received no medical treatment or formal rehabilitation. He was able to return to all sports and activities 1 to 2 months after injury, but noted a persistent deformity of the proximal thigh, which led him to seek evaluation. Physical examination, MRI functional tests, and specific muscle tests 1 year after his injury documented a major hamstring tear at the musculotendinous junction with muscle retraction, but no avulsion of the proximal tendon attachment.
Literature Review
Surgery often is recommended for major proximal hamstring tendon tears, especially when more than one tendon of origin is ruptured from the ischial tuberosity. Myotendinous tears are treated nonoperatively, but may be associated with decreased strength, prolonged recovery, and recurrence.
Purpose and Clinical Relevance
We describe the case of a young man who sustained a hamstring tear, with retraction, at the proximal myotendinous junction, where the biceps femoris and semitendinosus arise from the conjoint tendon. He achieved full functional recovery without medical attention, but had a persistent cosmetic deformity and slight hamstring tightness. This case suggests a benign natural history for this injury and the appropriateness of noninvasive treatment.
PMCID: PMC3183192  PMID: 21850562
Journal of biomechanics  2012;45(4):647-652.
Hamstring strain injury is one of the most common injuries in athletes, particularly for sports that involve high speed running. The aims of this study were to determine whether muscle activation and internal morphology influence in vivo muscle behavior and strain injury susceptibility. We measured tissue displacement and strains in the hamstring muscle injured most often, the biceps femoris long head muscle (BFLH), using cine DENSE dynamic magnetic resonance imaging. Strain measurements were used to test whether strain magnitudes are (i) larger during active lengthening than during passive lengthening and (ii) larger for subjects with a relatively narrow proximal aponeurosis than a wide proximal aponeurosis. Displacement color maps showed higher tissue displacement with increasing lateral distance from the proximal aponeurosis for both active lengthening and passive lengthening, and higher tissue displacement for active lengthening than passive lengthening. First principal strain magnitudes were averaged in a 1 cm region near the myotendinous junction, where injury is most frequently observed. It was found that strains are significantly larger during active lengthening (0.19 SD 0.09) than passive lengthening (0.13 SD 0.06) (p < 0.05), which suggests that elevated localized strains may be a mechanism for increased injury risk during active as opposed to passive lengthening. First principal strains were higher for subjects with a relatively narrow aponeurosis width (0.26 SD 0.15) than wide (0.14 SD 0.04) (p < 0.05). This result suggests that athletes who have BFLH muscles with narrow proximal aponeuroses may have an increased risk for BFLH strain injuries.
PMCID: PMC3695609  PMID: 22236527
acute strain injury; muscle; dynamic magnetic resonance imaging; in vivo measurement; active lengthening
10.  An Evidence-Based Approach to Hamstring Strain Injury 
Sports Health  2009;1(2):154-164.
Hamstring strain injury is a common problem within sport. Despite research interest, knowledge of risks for and management of hamstring strain is limited, as evidenced by high injury rates.
To present the current best evidence for hamstring strain injury risk factors and the management of hamstring strain injury.
MEDLINE, AMED, SportDiscus, and AUSPORT databases were searched (key terms “hamstring” and “strain,” “injury,” “pull,” or “tear”) to identify relevant literature published between 1982 and 2007 in the English language. Studies of adult athlete populations (older than 18 years) pertaining to hamstring strain incidence, prevalence, and/or intervening management of hamstring strain injury were included. Articles were limited to full-text randomized, controlled studies or cohort studies. Twenty-four articles were included. Articles were critically appraised using the McMaster Quantitative Review Guidelines instrument. Data pertaining to injury rates and return to sport outcomes were extracted. Each author undertook independent appraisal of a random selection of articles after establishing inter-rater agreement of appraisal.
Previous strain, older age, and ethnicity were consistently reported as significant risks for injury, as was competing in higher levels of competition. Associations with strength and flexibility were conflicting. Functional rehabilitation interventions had preventive effects and resulted in significantly earlier return to sport. Additionally, weak evidence existed for other interventions.
Current evidence is inconclusive regarding most interventions for hamstring strain injury, while the effect of potentially modifiable risks is unclear. Further high-quality prospective studies into potential risks and management are required to provide a better framework within which to target interventions.
PMCID: PMC3445075  PMID: 23015867
hamstring; muscle strain; prevention; management; systematic review
11.  Type of acute hamstring strain affects flexibility, strength, and time to return to pre‐injury level 
To investigate possible links between aetiology of acute, first time hamstring strains in sprinters and dancers and recovery of flexibility, strength, and function as well as time to return to pre‐injury level.
Eighteen elite sprinters and 15 professional dancers with a clinically diagnosed hamstring strain were included. They were clinically examined and tested two, 10, 21, and 42 days after the acute injury. Range of motion in hip flexion and isometric strength in knee flexion were measured. Self estimated and actual time to return to pre‐injury level were recorded. Hamstring reinjuries were recorded during a two year follow up period.
All the sprinters sustained their injuries during high speed sprinting, whereas all the dancers were injured while performing slow stretching type exercises. The initial loss of flexibility and strength was greater in sprinters than in dancers (p<0.05). At 42 days after injury, both groups could perform more than 90% of the test values of the uninjured leg. However, the actual times to return to pre‐injury level of performance were significantly longer (median 16 weeks (range 6–50) for the sprinters and 50 weeks (range 30–76) for the dancers). Three reinjuries were noted, all in sprinters.
There appears to be a link between the aetiologies of the two types of acute hamstring strain in sprinters and dancers and the time to return to pre‐injury level. Initially, sprinters have more severe functional deficits but recover more quickly.
PMCID: PMC2491922  PMID: 16371489
hamstrings; injury; sprinters; dancers; recovery
12.  The Influence of Prior Hamstring Injury on Lengthening Muscle Tissue Mechanics 
Journal of biomechanics  2010;43(12):2254-2260.
Hamstring strain injuries often occur near the proximal musculotendon junction (MTJ) of the biceps femoris. Post-injury remodeling can involve scar tissue formation, which may alter contraction mechanics and influence re-injury risk. The purpose of this study was to assess the affect of prior hamstring strain injury on muscle tissue displacements and strains during active lengthening contractions. Eleven healthy and eight subjects with prior biceps femoris injuries were tested. All previously injured subjects had since returned to sport and exhibited evidence of residual scarring along the proximal aponeurosis. Subjects performed cyclic knee flexion-extension on an MRI-compatible device using elastic and inertial loads, which induced active shortening and lengthening contractions, respectively. CINE phase-contrast imaging was used to measure tissue velocities within the biceps femoris during these tasks. Numerical integration of the velocity information was used to estimate two-dimensional tissue displacement and strain fields during muscle lengthening. The largest tissue motion was observed along the distal MTJ, with the active lengthening muscle exhibiting significantly greater and more homogeneous tissue displacements. First principal strains magnitudes were largest along the proximal MTJ for both loading conditions. The previously injured subjects exhibited less tissue motion and significantly greater strains near the proximal MTJ. We conclude that localized regions of high tissue strains during active lengthening contractions may predispose the proximal biceps femoris to injury. Furthermore, post-injury remodeling may alter the in-series stiffness seen by muscle tissue and contribute to the relatively larger localized tissue strains near the proximal MTJ, as was observed in this study.
PMCID: PMC2922492  PMID: 20472238
phase contrast velocity; magnetic resonance imaging; hamstring muscle; muscle strain
13.  Concentric Versus Enhanced Eccentric Hamstring Strength Training: Clinical Implications 
Journal of Athletic Training  1998;33(3):216-221.
Hamstring injuries can be quite debilitating and often result in chronic problems. Eccentric muscle actions are often the last line of defense against muscle injury and ligament disruption. Traditionally, the focus of hamstring strength rehabilitation has been on concentric muscle actions. The purpose of our study was to compare hamstring muscle strength gains in concentric and eccentric hamstring strength training.
Design and Setting:
A randomized-group design was used to examine differences in 1-repetition maximum (1 RM) and isokinetic strength values among 3 groups of subjects. Subjects were tested in a biomechanics laboratory using an isokinetic dynamometer, while training was carried out in a physical therapy outpatient clinic.
Twenty-seven healthy male subjects (age = 22.9 ± 3.1 years, wt = 81.8 ± 12.9 kg, ht = 178.6 ± 7.2 cm) participated in this study. Subjects were randomly assigned to 1 of 3 treatment groups: eccentric training, concentric training, or control.
Subjects performed hamstring curls using an isotonic weight training device. Pretest 1 RM weight values were determined for all subjects using a standardized 1 RM protocol. In addition, maximum concentric and eccentric isokinetic strength values for knee-flexion strength were determined. Control group subjects refrained from weight training for 6 weeks. Subjects in the training groups trained 2 days per week for 6 weeks (12 sessions). After 6 weeks of training, all subjects returned for 1RM and isokinetic posttesting.
The concentric group improved 19%, while the eccentric group improved 29%. The control group subjects did not show any significant change over the 6 weeks. In addition, there were improvements in eccentric isokinetic peak torque/ body weight ratios at both 60 °s and 180° from pretesting to posttesting in the eccentric training group only.
Our results demonstrate the effectiveness of isotonic strength training on the development of hamstring muscle strength. More important is the dramatic effect of eccentric strength training on overall hamstring muscle strength, both isotonic and isokinetic. Clinicians should consider using eccentric hamstring strengthening as part of their rehabilitation protocols for hamstring and knee injuries.
PMCID: PMC1320426  PMID: 16558513
1RM; peak torque/body weight ratios; enhanced eccentrics; isotonic; isokinetic
14.  Examination and Treatment of Hamstring Related Injuries 
Sports Health  2012;4(2):107-114.
There is a wide spectrum of hamstring-related injuries that can occur in the athlete. Accurate diagnosis is imperative to prevent delayed return to sport, injury recurrence, and accurate clinical decision making regarding the most efficacious treatment.
Evidence Acquisition:
This review highlights current evidence related to the diagnosis and treatment of hamstring-related injuries in athletes. Data sources were limited to peer-reviewed publications indexed in MEDLINE from 1988 through May 2011.
An accurate diagnostic process for athletes with posterior thigh–related complaints should include a detailed and discriminative history, followed by a thorough clinical examination. Diagnostic imaging should be utilized when considering hamstring avulsion or ischial apophyseal avulsion. Diagnostic imaging may also be needed to further define the cause of referred posterior thigh pain.
Differentiating acute hamstring strains, hamstring tendon avulsions, ischial apophyseal avulsions, proximal hamstring tendinopathies, and referred posterior thigh pain is critical in determining the most appropriate treatment and expediting safe return to play.
PMCID: PMC3435908  PMID: 23016076
athletes; tendinopathy; avulsion; referred posterior thigh pain; ischial apophyseal avulsions
15.  The relationship between previous hamstring injury and the concentric isokinetic knee muscle strength of irish gaelic footballers 
Hamstring injury is one of the most common injuries affecting gaelic footballers, similar to other field sports. Research in other sports on whether residual hamstring weakness is present after hamstring injury is inconsistent, and no study has examined this factor in irish gaelic footballers. The aim of this study was to examine whether significant knee muscle weakness is present in male Irish gaelic footballers who have returned to full activity after hamstring injury.
The concentric isokinetic knee flexion and extension strength of 44 members of a university gaelic football team was assessed at 60, 180 and 300 degrees per second using a Contrex dynamometer.
Fifteen players (34%) reported a history of hamstring strain, with 68% of injuries affecting the dominant (kicking) limb. The hamstrings were significantly stronger (p < 0.05) on the dominant limb in all uninjured subjects. The previously injured limbs had a significantly lower (p < 0.05) hamstrings to quadriceps (HQ) strength ratio than all other non-injured limbs, but neither their hamstrings nor quadriceps were significantly weaker (p > 0.05) using this comparison. The previously unilaterally injured hamstrings were significantly weaker (p < 0.05) than uninjured limbs however, when matched for dominance. The hamstring to opposite hamstring (H:oppH) strength ratio of the previously injured players was also found to be significantly lower (p < 0.05) than that of the uninjured players.
Hamstring muscle weakness was observed in male Irish gaelic footballers with a history of hamstring injury. This weakness is most evident when comparisons are made to multiple control populations, both within and between subjects. The increased strength of the dominant limb should be considered as a potential confounding variable in future trials. The study design does not allow interpretation of whether these changes in strength were present before or after injury.
PMCID: PMC2289821  PMID: 18325107
16.  Regeneration of hamstring tendons after anterior cruciate ligament reconstruction 
Primary aim of the study was analysis of hamstring tendon regeneration after anterior cruciate ligament reconstruction (ACLR). Secondary aim was analysis of isokinetic muscle strength in relation to hamstring regeneration. The hypothesis was that regeneration of hamstring tendons after ACLR occurs and that regenerated hamstring tendons contribute to isokinetic hamstring strength with regeneration distal to the knee joint line.
Twenty-two patients scheduled for ACLR underwent prospective MRI analysis of both legs. MRI parameters were tendon regeneration and morphology, muscle retraction and muscle cross-sectional area. A double-blind, prospective analysis of isokinetic quadriceps and hamstrings strength was performed.
Regeneration of the gracilis tendon after ACLR occurred in all patients. Regeneration of the semitendinosus tendon occurred in 14 patients. At 1 year, the surface area of the semitendinosus and gracilis muscle decreased compared to both preoperatively (P < 0.01) and the contralateral leg (P < 0.01). The cross-sectional area of the semitendinosus muscle decreased in the absence of tendon regeneration (P = 0.05). The cross-sectional area of the gracilis muscle was greater in case of regeneration distal to the joint line (P = 0.01). Muscle retraction of the semitendinosus muscle was increased in case of nonregeneration (P = 0.02). There was no significant relationship between isokinetic flexion strength and tendon regeneration.
Hamstring tendons regenerated after harvest of both semitendinosus and gracilis tendons for ACLR. There was no relation between isokinetic flexion strength and tendon regeneration.
Level of evidence
Prognostic study, Level II.
PMCID: PMC3604585  PMID: 22763570
Anterior cruciate ligament reconstruction; Hamstring; Semitendinosus; Gracilis; Regeneration; MRI
17.  Isokinetic strength testing does not predict hamstring injury in Australian Rules footballers 
OBJECTIVE: To determine the relation of hamstring and quadriceps muscle strength and imbalance to hamstring injury using a prospective observational cohort study METHOD: A total of 102 senior male Australian Rules footballers aged 22.2 (3.6) years were tested at the start of a football season. Maximum voluntary concentric and eccentric torque of the hamstring and quadriceps muscles of both legs was assessed using a Kin-Com isokinetic dynamometer at angular velocities of 60 and 180 degrees/second. Twelve (11.8%) players sustained clinically diagnosed hamstring strains which caused them to miss one or more matches over the ensuing season. RESULTS: There were no significant differences for any of the isokinetic variables comparing the injured and non-injured legs in players with unilateral hamstring strains (n=9). Neither the injured nor the non-injured leg of injured players differed from the mean of left and right legs in non-injured players for any isokinetic variable. The hamstring to opposite hamstring ratios also did not differ between injured and non-injured players. A hamstring to opposite hamstring ratio of less than 0.90 and a hamstring to quadriceps ratio of less than 0.60 were not associated with an increased risk of hamstring injury. A significantly greater percentage of players who sustained a hamstring strain reported a history of hamstring strain compared with non-injured players (p=0.02). However, this was not related to muscle weakness or imbalance. CONCLUSIONS: Isokinetic muscle strength testing was not able to directly discriminate Australian Rules football players at risk for a hamstring injury. 

PMCID: PMC1756115  PMID: 9865403
18.  Non contact Hamstring injuries in sports 
Hamstring muscle injuries are frequent in different sports and are a clinical challenge for Sports Medicine Teams. Injury Mechanics are import to know while assessing the injured athlete. There are at least two distinctly different types of acute hamstring injuries, which are best distinguished by the different injury situations. Classifying the severity of the injury is equally important. Active Range of motion measurements, proper imaging selection and the anatomical location of the injury must be considered. Once the diagnosis is established rehabilitation issues must be considered. Recurrence rate of the injury and prevention are issues that must always be included in our Hamstring Injuries approach as Clinicians.
PMCID: PMC3666535  PMID: 23738316
non contact; Hamstring injuries; sports
19.  Effects of Prior Hamstring Strain Injury on Strength, Flexibility, and Running Mechanics 
Previous studies have shown evidence of residual scar tissue at the musculotendon junction following an acute hamstring strain injury, which could influence re-injury risk. The purpose of this study was to investigate whether bilateral differences in strength, neuromuscular patterns, and musculotendon kinematics during sprinting are present in individuals with a history of unilateral hamstring injury, and whether such differences are linked to the presence of scar tissue.
Eighteen subjects with a previous hamstring injury (>5 months prior) participated in a magnetic resonance (MR) imaging exam, isokinetic strength testing, and a biomechanical assessment of treadmill sprinting. Bilateral comparisons were made for peak knee flexion torque, angle of peak torque, and hamstrings:quadriceps strength ratio during strength testing, and muscle activations and peak hamstring stretch during sprinting. MR images were used to measure the volumes of the proximal tendon/aponeurois of the biceps femoris, with asymmetries considered indicative of residual scar tissue.
A significantly enlarged proximal biceps femoris tendon volume was measured on the side of prior injury. However, no significant differences between the previously injured and uninjured limbs were found in strength measures, peak hamstring stretch, or muscle activation patterns. Further, the degree of asymmetry in tendon volume was not correlated to any of the functional measures.
The results of this study indicate that injury-induced changes in morphology do not seem discernable from strength measures, running kinematics, or muscle activity patterns. Further research is warranted to ascertain whether residual scarring alters localized musculotendon tissue mechanics in a way that may contribute to the high rates of muscle re-injury that are observed clinically.
PMCID: PMC2923440  PMID: 20621753
muscle injury; running; electromyography; magnetic resonance imaging; isokinetic strength
20.  Distal tears of the hamstring muscles: review of the literature and our results of surgical treatment 
Hamstring strains are among the most frequent injuries in sports, especially in events requiring sprinting and running. Distal tears of the hamstring muscles requiring surgical treatment are scarcely reported in the literature.
To evaluate the results of surgical treatment for distal hamstring tears.
A case series of 18 operatively treated distal hamstring muscle tears combined with a review of previously published cases in the English literature. Retrospective study; level of evidence 4.
Mehiläinen Sports Trauma Research Center, Mehiläinen Hospital and Sports Clinic, Turku, Finland.
Between 1992 and 2005, a total of 18 athletes with a distal hamstring tear were operated at our centre.
Main outcome measurements
At follow‐up, the patients were asked about possible symptoms (pain, weakness, stiffness) and their return to the pre‐injury level of sport.
The final results were rated excellent in 13 cases, good in 1 case, fair in 3 cases and poor in 1 case. 14 of the 18 patients were able to return to their former level of sport after an average of 4 months (range 2–6 months).
Surgical treatment seems to be beneficial in distal hamstring tears in selected cases.
PMCID: PMC2658938  PMID: 17138628
21.  Diagnosis and prognosis of acute hamstring injuries in athletes 
Identification of the most relevant diagnostic and prognostic factors of physical examination and imaging of hamstring injuries in (elite) athletes.
A literature search was conducted in MEDLINE and EMBASE for articles between 1950 and April 2011. A survey was distributed among the members of the European Society of Sports Traumatology, Knee Surgery and Arthroscopy, which focused on physical examination, prognosis, imaging and laboratory tests of hamstring injuries in (elite) athletes.
Medical history, inspection and palpation of the muscle bellies and imaging are most valuable at the initial assessment according to the literature. Experts considered medical history, posture and gait inspection, inspection and palpation of muscle bellies, range of motion tests, manual muscle testing, referred pain tests and imaging to be most important in the initial assessment of hamstring injuries. Magnetic resonance imaging (MRI) is preferred over ultrasonography and should take place within 3 days post-trauma. Important prognostic factors are injury grade, length of the muscle tear on MR images, MRI-negative injuries and trauma mechanism.
Posture and gait inspection, inspection and palpation of muscle bellies, range of motion tests, manual muscle testing and referred pain tests within 2 days post-trauma were identified as the most relevant diagnostic factors.
Level of evidence
Literature review and expert opinion, Level V.
PMCID: PMC3549245  PMID: 22622781
Hamstring strain injury; Sports injury; Physical examination; Imaging
22.  A Comparison of the Immediate Effects of Eccentric Training vs Static Stretch on Hamstring Flexibility in High School and College Athletes 
A pre-event static stretching program is often used to prepare an athlete for competition. Recent studies have suggested that static stretching may not be an effective method for stretching the muscle prior to competition.
The intent of this study was to compare the immediate effect of static stretching, eccentric training, and no stretching/training on hamstring flexibility in high school and college athletes.
Seventy-five athletes, with a mean age of 17.22 (+/- 1.30) were randomly assigned to one of three groups - thirty- second static stretch one time, an eccentric training protocol through a full range of motion, and a control group. All athletes had limited hamstring flexibility, defined as a 20° loss of knee extension measured with the femur held at 90° of hip flexion.
A significant difference was indicated by follow up analysis between the control group (gain = -1.08°) and both the static stretch (gain = 5.05°) and the eccentric training group (gain = 9.48°). In addition, the gains in the eccentric training group were significantly greater than the static stretch group.
Discussion and Conclusion
The findings of this study reveal that one session of eccentrically training through a full range of motion improved hamstring flexibility better than the gains made by a static stretch group or a control group.
PMCID: PMC2953312  PMID: 21522215
23.  Eccentric and concentric isokinetic moment characteristics in the quadriceps and hamstrings of the chronic isolated posterior cruciate ligament injured knee 
OBJECTIVE: Functional strength deficits associated with chronic isolated posterior cruciate ligament (PCL) insufficiency have received limited attention in the literature. The purpose of this study was to determine the eccentric and concentric isokinetic moment characteristics of the quadriceps and hamstrings in a sample of patients with isolated PCL injury. METHODS: Eccentric and concentric mean average and average peak moments were measured for 17 patients with a history of conservatively treated isolated PCL injury using an isokinetic dynamometer. Quadriceps and hamstring isokinetic moments were recorded from 10 degree to 90 degree of knee flexion. Strength ratios were calculated and compared with those reported in the literature for healthy subjects. RESULTS: The hamstrings of the involved side (eccentric/concentric (E/C) ratio = 1.06) were significantly weaker (p<0.05) eccentrically than those of the contralateral side (E/C ratio = 1.29). All hamstrings/quadriceps (H/Q) ratios were less than the universally accepted value of 0.60 and the eccentric H/Q ratio for the injured extremity was significantly lower than the non-injured (p<0.05). In a bilateral comparison, the injured/non-injured (I/N) ratio was less than 1.00 for concentric quadriceps, eccentric quadriceps, and hamstring isokinetic moments. Calculation of the E/C ratio showed that, for the quadriceps, it was 1.08 on the injured side and 1.07 on the non-injured extremity. CONCLUSIONS: Eccentric strengthening should be an integral part of functionally rehabilitating the quadriceps and hamstrings of athletes who suffer from the complications associated with chronic isolated PCL insufficiency. 

PMCID: PMC1756212  PMID: 10597850
24.  The effect of sports specific training on reducing the incidence of hamstring injuries in professional Australian Rules football players 
Objectives: To assess in a single team of Australian Rules football players the effect of a specific intervention program on the incidence and consequence of hamstring muscle strain injuries.
Method: A prospective study was performed with a single team being followed for four playing seasons for hamstring injury. Magnetic resonance imaging was used to confirm the diagnosis of hamstring muscle injury. After two playing seasons an intervention program was implemented with the number of athletes with hamstring injury, competition days missed, and incidence of hamstring match injuries per 1000 h of playing time being compared pre- and post-intervention. The intervention program involved stretching whilst fatigued, sport specific training drills, and an emphasis on increasing the amount of high intensity anaerobic interval training.
Results: In the seasons prior to the intervention, nine and 11 athletes sustained hamstring injury compared to two and four following intervention. Competition days missed reduced from 31 and 38 to 5 and 16 following intervention and match incidence decreased from 4.7 to 1.3 per 1000 h of playing time. A beneficial effect was demonstrated with a smaller number of players having hamstring injuries (p = 0.05), a lower number of competition games missed being recorded (p<0.001), and a decrease in hamstring strain incidence per 1000 h of playing time (p = 0.01) following the intervention program.
Conclusions: Increasing the amount of anaerobic interval training, stretching whilst the muscle is fatigued, and implementing sport specific training drills resulted in a significant reduction in the number and consequences of hamstring muscle strain injuries.
PMCID: PMC1725238  PMID: 15911608
25.  Thigh Strength and Activation as Predictors of Knee Biomechanics During a Drop Jump Task 
To examine whether normalized quadriceps and hamstring strength would predict quadriceps and hamstring muscle activation amplitudes, and whether these neuromuscular factors would predict knee kinematics and kinetics during a drop jump task.
39 females and 39 males were measured for isometric quadriceps and hamstring strength, and were instrumented to obtain sEMG, kinematic and kinetic measures during the initial landing of a drop jump. Multiple linear regressions first examined the relationship between thigh strength and activation, then examined whether these neuromuscular variables were predictive of hip and knee flexion excursions, knee extensor moments and anterior knee shear forces during the deceleration phase of the drop jump.
Females versus males produced lower normalized thigh strength, and demonstrated greater quadriceps and hamstring activation amplitudes during the drop jump. Lower thigh muscle strength was a weak (males) to moderate (females) predictor of greater quadriceps activation amplitudes. However, thigh strength and activation were poor predictors of hip and knee joint excursions and knee extensor moments. Regardless of sex and thigh strength, anterior shear forces were greater in individuals who demonstrated less hip flexion and greater knee flexion excursions, and greater peak quadriceps activation and internal knee extensor moments during the landing.
While thigh muscle strength explained some of the variance in quadriceps and hamstring activation levels as measured with sEMG, we failed to support the hypothesis that these neuromuscular factors are strong predictors of sagittal plane hip and knee flexion excursions or knee extensor moments. Although greater quadriceps activation amplitude was a significant predictor of greater anterior tibial shear forces, its contribution was relatively small compared to kinematic and kinetic variables.
PMCID: PMC2744399  PMID: 19300140
Quadriceps dominance; ACL risk factors; landing biomechanics; peak torque to body weight

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