Factors Associated with Recurrent Hamstring Injuries

Rehabilitation of the hip following sports injury

An athlete often presents to the rehabilitation specialist with either a nonspecific referral, such as "hip pain," or with a diagnosis of a more specific hip pathology. The highly skilled clinician is trained to look at the "linkage" between the trunk and all parts of the lower extremity. Why is the hip not transferring the load well? Where is the breakdown? The gluteus medius, pelvic stability, and supportive muscular slings are of great importance when optimizing the function of the hip. The hip is subjected to forces equal to multiples of the body weight and requires osseous, articular and myofascial integrity for stability. This is the mind set when devising an athlete's rehabilitative program, looking at all influential factors that affect joint movement and integrity.

Application of eccentric exercise on an Australian Rules football player with recurrent hamstring injuries

STUDY DESIGN

Case report.

OBJECTIVE

To assess an eccentric based intervention on an Australian Football player with recurrent hamstring injuries.

CASE DESCRIPTION

The athlete attempted several conventional rehabilitation programs in the past (e.g. physical therapy, manual therapy, acupuncture, active release, medial gluteal strengthening) with no sustained progress in regards to pain, soreness, or return to sport.

OUTCOMES

After the first three phases of the intervention (i.e. nine weeks), the optimum angle of peak torque during knee flexion decreased from 37.3 to 23.9 degrees in the injured leg, and from 24.3 to 20.3 degrees in the non-injured leg. After the first nine weeks, the optimum angles then remained constant for another 23 weeks. The optimum angle of peak torque was also shifted in the knee extensors by 3.9 degrees (injured leg) and 3.4 degrees (non-injured leg) after nine weeks and then remained constant for the remaining 23 weeks. Quadriceps to hamstring peak torque ratio's (Q/H ratios) and peak torque during knee flexion and extension remained constant throughout the intervention.

DISCUSSION

An eccentric based intervention was shown to be safe and effective for altering the optimum angle of peak torque (i.e. shifting to longer muscle lengths) for this athlete with recurrent hamstring injuries.

Strength imbalances and prevention of hamstring injury in professional soccer players: a prospective study

BACKGROUND

The relationship between muscle injury and strength disorders remains a matter of controversy.

PURPOSE

Professional soccer players performed a preseason isokinetic testing aimed at determining whether (1) strength variables could be predictors of subsequent hamstring strain and (2) normalization of strength imbalances could reduce the incidence of hamstring injury.

STUDY DESIGN

Cohort study (prognosis); Level of evidence, 1.

METHODS

A standardized concentric and eccentric isokinetic assessment was used to identify soccer players with strength imbalances. Subjects were classified among 4 subsets according to the imbalance management content. Recording subsequent hamstring injuries allowed us to define injury frequencies and relative risks between groups.

RESULTS

Of 687 players isokinetically tested in preseason, a complete follow-up was obtained in 462 players, for whom 35 hamstring injuries were recorded. The rate of muscle injury was significantly increased in subjects with untreated strength imbalances in comparison with players showing no imbalance in preseason (relative risk = 4.66; 95% confidence interval: 2.01-10.8). The risk of injury remained significantly higher in players with strength imbalances who had subsequent compensating training but no final isokinetic control test than in players without imbalances (relative risk = 2.89; 95% confidence interval: 1.00-8.32). Conversely, normalizing the isokinetic parameters reduced the risk factor for injury to that observed in players without imbalances (relative risk = 1.43; 95% confidence interval: 0.44-4.71).

CONCLUSION

The outcomes showed that isokinetic intervention gives rise to the preseason detection of strength imbalances, a factor that increases the risk of hamstring injury. Restoring a normal strength profile decreases the muscle injury incidence.

Cross-sectional investigation of indices of isokinetic leg strength in youth soccer players and untrained individuals

In this cross-sectional study, the differences in the isokinetic peak torque of the knee joint muscles (dominant and non-dominant) were investigated in three groups of youths (n=45; age, 14.9+/-1.1 years) with different soccer training backgrounds. Significant main effects were observed for training background on the functional hamstrings to quadriceps ratios for knee flexion (H(CON):Q(ECC) ratio; F(2,42)=4.023, P=0.025) and extension (H(ECC):Q(CON) ratio; F(2,42)=8.53, P<0.001) at 4.32 rad/s. Post hoc tests indicated that both ratios were significantly different between conventionally trained players compared with resistance-trained players and controls (mean+/-SD; H(ECC):Q(CON) ratio, dominant limb; 0.91+/-0.10; 1.04+/-0.12; 1.10+/-0.22; non-dominant limb; 0.89+/-0.09; 1.05+/-0.19; 1.06+/-0.15; H(CON):Q(ECC) ratio, dominant limb; 0.36+/-0.06; 0.34+/-0.07; 0.30+/-0.08; non-dominant limb; 0.33+/-0.05; 0.32+/-0.08; 0.28+/-0.07). Results suggest that the muscle-loading patterns experienced in youth soccer may alter the reciprocal balance of strength about the knee under high-velocity conditions. The findings also indicate that these balances may be improved by incorporating resistance training into the habitual exercise routines of youth soccer players.

Hamstring Injuries: Risk Assessment and Injury Prevention

Introduction: Hamstring injuries are one of the most common injuries associated with sports participation. The aim of this review is to outline identified risk factors and examine preventative strategies for reducing the occurrence of this form of injury. Methods: An electronic search of Medline and SCOPUS was carried out for key words related to the area. Results: A number of risk factors, including both intrinsic and modifiable, were identified. Important aspects of an exercise programme were then outlined based on these risk factors. Conclusion: A programme specifically designed to reduce the risk of hamstring injury by taking a strategised approach to exercise prescription may reduce the risk of hamstring injury. However, further research is required to determine the optimal programme for reducing the risk of injury. Key words: Muscle, Rehabilitation, Strain

Muscular strength, functional performances and injury risk in professional and junior elite soccer players

Muscle strength and anaerobic power of the lower extremities are neuromuscular variables that influence performance in many sports activities, including soccer. Despite frequent contradictions in the literature, it may be assumed that muscle strength and balance play a key role in targeted acute muscle injuries. The purpose of the present study was to provide and compare pre-season muscular strength and power profiles in professional and junior elite soccer players throughout the developmental years of 15-21. One original aspect of our study was that isokinetic data were considered alongside the past history of injury in these players. Fifty-seven elite and junior elite male soccer players were assigned to three groups: PRO, n=19; U-21, n=20 and U-17, n=18. Players benefited from knee flexor and extensor isokinetic testing consisting of concentric and eccentric exercises. A context of lingering muscle disorder was defined using statistically selected cut-offs. Functional performance was evaluated throughout a squat jump and 10 m sprint. The PRO group ran faster and jumped higher than the U-17 group (P<0.05). No significant difference in isokinetic muscle strength performance was observed between the three groups when considering normalized body mass parameters. Individual isokinetic profiles enabled the identification of 32/57 (56%) subjects presenting lower limb muscular imbalance. Thirty-six out of 57 players were identified as having sustained a previous major lower limb injury. Of these 36 players, 23 still showed significant muscular imbalance (64%). New trends in rational training could focus more on the risk of imbalance and implement antagonist strengthening aimed at injury prevention. Such an intervention would benefit not only athletes recovering from injury, but also uninjured players. An interdisciplinary approach involving trainers, a physical coach, and medical staff would be of interest to consider in implementing a prevention programme.

The relationship between previous hamstring injury and the concentric isokinetic knee muscle strength of Irish Gaelic footballers

Background

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.

Methods

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.

Results

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.

Conclusion

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.

Reliability of isokinetic strength imbalance ratios measured using the Cybex NORM dynamometer

The main aim of this study was to examine the absolute and relative reliability of some commonly used strength imbalance indices such as concentric hamstring-to-concentric quadriceps ratio, eccentric hamstring-to-concentric quadriceps ratio and bilateral concentric and eccentric strength ratios. An additional aim was to examine the reliability of the peak torque and work of the knee extensor and flexor muscles measured using the Cybex NORM dynamometer. Eighteen physically active healthy subjects (mean +/- standard deviation, age 23 +/- 3 years, height 176 +/- 5 cm, body mass 74 +/- 8 kg) were tested three times with 96 h between sessions. Peak torque, average work, unilateral and bilateral ratios were determined at 60, 120, 180 and -60 degrees s(-1). Low (0.34) to moderate (0.87) relative reliability (intraclass correlation coefficient, ICC) was found for strength imbalance ratios with eccentric hamstring-to-concentric quadriceps ratio showing the greater ICC (>0.80). High ICC values (0.90-0.98) were found for peak torque and average work. Absolute reliability (standard error of measurement) ranged from 3.2% to 8.7% for strength imbalance ratios and from 4.3% to 7.7% for peak torque and average work measurements. This study established the reliability of the most common strength imbalance ratios and of absolute isokinetic muscle strength assessed using the Cybex NORM.

Altering the Length-Tension Relationship with Eccentric Exercise

The effects of eccentric exercise on muscle injury prevention and athletic performance are emerging areas of interest to researchers. Of particular interest are the adaptations that occur after a single bout, or multiple bouts of eccentric exercise. It has been established that after certain types of eccentric exercise, the optimum length of tension development in muscle can be shifted to longer muscle lengths. Altering the length-tension relationship can have a profound influence on human movements. It is thought that the length-tension relationship is influenced by the structural makeup of muscle. However, the mechanism responsible for the shift in optimum length is not readily agreed upon. Despite the conflict, several studies have reported a shift in optimum length after eccentric exercise. Unfortunately, very few of these studies have been randomised, controlled training studies, and the duration of the shift has not yet been established. Nonetheless, this adaptation may result in greater structural stability at longer muscle lengths and consequently may have interesting implications for injury prevention and athletic performance. Both contentions remain relatively unexplored and provide the focus of this review.

Incidence, risk, and prevention of hamstring muscle injuries in professional rugby union

BACKGROUND

The incidence of hamstring muscle injuries in professional rugby union is high, but evidence-based information on risk factors and injury-prevention strategies in this sport is limited.

PURPOSE

To define the incidence, severity, and risk factors associated with hamstring muscle injuries in professional rugby union and to determine whether the use of hamstring strengthening and stretching exercises reduces the incidence and severity of these injuries.

STUDY DESIGN

Cohort study (prevention); Level of evidence, 3.

METHODS

Team clinicians reported all hamstring muscle injuries on a weekly basis and provided details of the location, diagnosis, severity, and mechanism of each injury; loss of time from training and match play was used as the definition of an injury. Players' match and training exposures were recorded on a weekly basis.

RESULTS

The incidence of hamstring muscle injuries was 0.27 per 1000 player training hours and 5.6 per 1000 player match hours. Injuries, on average, resulted in 17 days of lost time, with recurrent injuries (23%) significantly more severe (25 days lost) than new injuries (14 days lost). Second-row forwards sustained the fewest (2.4 injuries/1000 player hours) and the least severe (7 days lost) match injuries. Running activities accounted for 68% of hamstring muscle injuries, but injuries resulting from kicking were the most severe (36 days lost). Players undertaking Nordic hamstring exercises in addition to conventional stretching and strengthening exercises had lower incidences and severities of injury during training and competition.

CONCLUSION

The Nordic hamstring strengthening exercise may reduce the incidence and severity of hamstring muscle injuries sustained during training and competition.

Assessment of physical examination and magnetic resonance imaging findings of hamstring injury as predictors for recurrent injury

STUDY DESIGN

Prospective cohort study.

OBJECTIVE

To examine clinical and magnetic resonance imaging (MRI) features of hamstring muscle injury to determine if any are predictive for recurrent injury.

BACKGROUND

Hamstring muscle strain injury and subsequent recurrent injury are common. Little information exists on factors that may increase the risk for recurrent injury.

METHODS AND MEASURES

The subjects were athletes from 3 professional Australian Rules football teams (n = 162). Anthropometric measurements, clinical signs, convalescent interval, and MRI assessment and measurement were undertaken and recorded in athletes with hamstring muscle strain injury. Athletes were followed for the presence, or absence, of recurrent injury to the same-side posterior thigh over the same and subsequent playing seasons.

RESULTS

Thirty athletes met criteria for hamstring injury. Twelve (40%) of 30 athletes had recurrent injury within the same season, with an additional 7 athletes having recurrent injury in the subsequent season. None of the features examined were associated with increased recurrent injury risk within the same playing season. Statistical analysis demonstrated that when combining the same with the subsequent playing season a larger size of initial hamstring injury, as measured by MRI, was associated with an increased risk for recurrent injury (P<.01). A measured transverse size of injury greater than 55% of the muscle, or calculated volume of injury greater than 21.8 cm3, resulted in an increased risk for hamstring recurrence of 2.2 (95% CI, 0.88-5.32) and 2.3 (95% CI, 0.94-5.81) times, respectively, when compared to athletes with hamstring injuries below these measurements.

CONCLUSIONS

A larger size of hamstring injury was indicative of higher risk for recurrent injury but only after the subsequent playing season was considered along with the same playing season. None of the other parameters tested, including a shorter convalescent interval and clinical features, were associated with an increased risk for recurrent injury. However, due to low sample size the certainty of these conclusions may be limited.

Imaging of hamstring injuries: therapeutic implications

Though recent research into the diagnosis and management of hamstring disorders has resulted in early and accurate recognition of injury, hamstring strain remains the most common form of muscle injury in the active population. With prompt recognition of hamstring strain, an appropriate rest and rehabilitation routine may be devised by the sports clinician in the hope of avoiding future and possibly more debilitating injury. As such, imaging has played a pivotal role in assisting athletes, both elite and recreational, in returning to activity expeditiously.

Type of acute hamstring strain affects flexibility, strength, and time to return to pre-injury level

OBJECTIVES

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. [figure: see text].

METHODS

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.

RESULTS

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.

CONCLUSION

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.

The effect of relaxin treatment on skeletal muscle injuries

BACKGROUND

Injured skeletal muscle can repair itself via spontaneous regeneration; however, the overproduction of extracellular matrix and excessive collagen deposition lead to fibrosis. Neutralization of the effect of transforming growth factor-beta 1, a key fibrotic cytokine, on myogenic cell differentiation after muscle injury can prevent fibrosis, enhance muscle regeneration, and thereby improve the functional recovery of injured muscle.

HYPOTHESIS

The hormone relaxin, a member of the family of insulin-like growth factors, can act as an antifibrosis agent and improve the healing of injured muscle.

STUDY DESIGN

Controlled laboratory study.

METHODS

In vitro: Myoblasts (C2C12 cells) and myofibroblasts (transforming growth factor-beta 1-transfected myoblasts) were incubated with relaxin, and cell growth and differentiation were examined. Myogenic and fibrotic protein expression was determined by Western blot analysis. In vivo: Relaxin was injected intramuscularly at different time points after laceration injury. Skeletal muscle healing was evaluated via histologic, immunohistochemical, and physiologic tests.

RESULTS

Relaxin treatment resulted in a dose-dependent decrease in myofibroblast proliferation, down-regulated expression of the fibrotic protein alpha-smooth muscle actin, and promoted the proliferation and differentiation of myoblasts in vitro. Relaxin therapy enhanced muscle regeneration, reduced fibrosis, and improved injured muscle strength in vivo.

CONCLUSION

Administration of relaxin can significantly improve skeletal muscle healing.

CLINICAL RELEVANCE

These findings may facilitate the development of techniques to eliminate fibrosis, enhance muscle regeneration, and improve functional recovery after muscle injuries.

Identifying the time of occurrence of a hamstring strain injury during treadmill running: a case study

BACKGROUND

While hamstring strain injuries are common during sprinting, the mechanisms of injury are not well understood. In this study, we analyzed the running kinematics of an athlete obtained at the time of an acute hamstring strain injury. The purpose was to identify the period of the gait cycle during which the hamstring was likely injured, as well as to characterize the biomechanical conditions associated with the injury.

METHODS

A male professional skier injured his right biceps femoris long head while running at 5.36 m/s on a treadmill with a 15% incline. Whole body kinematics were recorded at the time of injury. A linear periodic prediction model was used to determine when individual marker trajectories deviated from a cyclic periodic pattern, indicating the mechanical response to injury. A three-dimensional musculoskeletal model was used to compute joint angles and hamstring musculotendon lengths during the injurious running trial. These data were used with estimates of neuromuscular latencies and electromechanical delays to identify the most likely time period of injury.

FINDINGS

Based upon the earliest indications in marker trajectories, a 130 ms period during the late swing phase of the gait cycle was identified as the period of injury. During this period, the biceps femoris reached a peak musculotendon length that was estimated to be 12% beyond the length seen in an upright posture and exceeded the normalized peak length of the medial hamstrings.

INTERPRETATION

This case provides quantitative data suggesting that the biceps femoris muscle is susceptible to an lengthening contraction injury during the late swing phase of the running gait cycle.

Return to play following muscle strains

OBJECTIVE

To assess return to play strategies following muscle strains with the desired outcomes of decreased competition play lost and minimized risk for recurrent injury.

METHODS

Literature review of previous studies that examine return to play criteria for the commonly seen muscle strain injuries in sport.

RESULTS

There have been no studies directly comparing different return to play approaches. Studies have instead concentrated on recurrence risk factors and prognosis assessment, particularly for hamstring injuries. There is some literature support for risk factors for recurrence such as persisting strength deficits, larger injuries seen on diagnostic imaging, players in high-risk positions or sports, inability to complete functional tasks without pain, and strains of specific high-risk muscles (biceps femoris, central tendon of rectus femoris, medial head of gastrocnemius, adductor longus or magnus).

CONCLUSIONS

There are no consensus guidelines or agreed-upon criteria for safe return to sport following muscle strains that completely eliminate the risk for recurrence and maximize performance. At this time, it may be a sensible strategy to allow earlier return to play in team sports and accept a low to moderate injury recurrence rate. Improved prognostic assessment of muscle strains with injury identification (MRI) and injury assessment (isokinetic testing) may be assist practitioners to lower, but not eliminate, recurrent injuries.

Hamstring injury management--Part 2: Treatment

The management of hamstring injuries can be described as vexed at best. One reason for this may be because of a lack of high-quality research into the methods of treatment, rehabilitation and prevention. As a result, an evidence-based approach to injury management does not exist. Management is based on clinical experience, anecdotal evidence and the knowledge of the biological basis of tissue repair. Previous hamstring injury is the most recognized risk factor for injury, which indicates that treatment approaches may be suboptimal under certain conditions. The identification of these risk factors and the methods best designed to manage them should be addressed with future research efforts. Much anecdotal and indirect evidence exists to suggest that several non-local factors contribute to injury. Despite the knowledge that these factors may exist, the literature appears almost devoid of research investigating their possible identification and treatment. Treatment has traditionally been in the form of altering the muscle repair process through the application of electrophysical therapy and various soft-tissue-based and exercise-based techniques. Little research has investigated the role of other forms of manual therapy particularly when directed at non-local structures. This paper will explore and speculate on this potential connection and offer some new contributive factors for hamstring injury management.

Evidence based prevention of hamstring injuries in sport

A common soft tissue injury in sports involving sprinting and jumping is the hamstring strain. A major problem with hamstring strains is the high incidence of reinjury. Muscle injuries can be classified as direct or indirect and are typically grouped into three categories according to severity. A number of potential risk factors have been proposed for hamstring strains. Only a few are evidence based and some are mainly based on theoretical assumptions. There is a lack of clinical research on the effectiveness of rehabilitation programmes for hamstring strains. Although the initial treatment of rest, ice, compression, and elevation is accepted for muscle strains, no consensus exists for their rehabilitation. Not much evidence based research has been carried out on prevention of hamstring strain. To our knowledge only two prospective studies have so far been published. As the injuries are common in football and other sports involving sprinting and jumping, there is a need for further research preferably in the form of randomised controlled trials.

The management of hamstring injury—Part 1: Issues in diagnosis

Hamstring injuries are the most prevalent muscle injury in sports involving rapid acceleration and maximum speed running. Injury typically occurs in an acute manner through an eccentric mechanism at the terminal stages of the swing phase of gait. Biceps femoris is most commonly injured. Re-injury rates are high and management is a challenge given the complex multi-factorial aetiology. The high rates of hamstring injury and re-injury may result from a lack of high-quality research into the aetiological factors underlying injury. Re-injury may also result from inaccuracy in diagnosis that results from the potential multi-factorial causes of these conditions. Inaccuracy in diagnosis could lead to multiple potential diagnoses that may result in the implementation of variable management protocols. Whilst potentially useful, such variability may also lead to the implementation of sub-optimal management strategies. Previous hamstring injury is the most recognized risk factor for injury, which indicates that future research should be directed at preventative measures. Much anecdotal and indirect evidence exists to suggest that several non-local factors contribute to injury, which may be addressed through the application of manual therapy. However, this connection has been neglected in previous research and literature. This paper will explore and speculate on this potential connection and offer some new contributive factors for hamstring injury management. This first paper of a two part series on hamstring injury will explore diagnostic issues relevant to hamstring injury and the second will investigate various established and speculative management approaches.

Successful management of hamstring injuries in Australian Rules footballers: two case reports

Hamstring injuries are the most prevalent injury in Australian Rules football. There is a lack of evidence based literature on the treatment, prevention and management of hamstring injuries, although it is agreed that the etiology is complicated and multi-factorial. We present two cases of hamstring injury that had full resolution after spinal manipulation and correction of lumbar-pelvic biomechanics. There was no recurrence through preventative treatment over a twelve and sixteen week period. The use of spinal manipulation for treatment or prevention of hamstring injury has not been documented in sports medicine literature and should be further investigated in prospective randomized controlled trials.