Factors Associated with Recurrent Hamstring Injuries

Major and Minor League Baseball Hamstring Injuries: Epidemiologic Findings From the Major League Baseball Injury Surveillance System

BACKGROUND

Hamstring strains are a recognized cause of disability for athletes in many sports, but no study exists that reports the incidence and circumstances surrounding these injuries in professional baseball.

HYPOTHESIS

Professional baseball players have a high incidence of hamstring strains, and these injuries are influenced by multiple factors including history of hamstring injury, time period within the season, and activity of base running.

STUDY DESIGN

Descriptive epidemiologic study.

METHODS

For the 2011 season, injury data were prospectively collected for every Major League Baseball (MLB) major and minor league team and recorded in the MLB's Injury Surveillance System. Data collected for this study included date of injury, activity in which the player was engaged at the time of injury, and time loss. Injury rates were reported in injuries per athlete-exposure (A-E). Athlete-exposures were defined as the average number of players on a team who were participating in a game multiplied by the number of games.

RESULTS

In the major leagues, 50 hamstring strains were reported for an injury rate (IR) of 0.7 per 1000 A-Es and averaged 24 days missed. In the minor leagues, 218 hamstring strains were reported for an IR of 0.7 per 1000 A-Es and averaged 27 days missed. Base running, specifically running to first base, was the top activity for sustaining a hamstring strain in both major and minor leagues, associated with almost two-thirds of hamstring strains. Approximately two-thirds of these injuries in both the major and minor leagues resulted in more than 7 days of time loss. Approximately 25% of these injuries kept the player out for 1 month or longer. History of a previous hamstring strain in the prior year, 2010, was found in 20% of the major league players and 8% of the minor league players. In the major leagues, the month of May had a statistically significant higher frequency of hamstring injuries than any other month in the season (P = .0153).

CONCLUSION

Hamstring strains are a considerable cause of disability in professional baseball and are affected by history of hamstring strain, seasonal timing, and running to first base.

A qualitative and quantitative analysis of the attachment sites of the proximal hamstrings

PURPOSE

Proximal hamstring tears represent a challenge. Surgical repair of such tears has been reported utilizing both open and endoscopic techniques. It was hypothesized that the proximal attachments of the hamstring muscle group could be reproducibly and consistently measured from pertinent bony anatomical reference landmarks.

METHODS

Fourteen fresh-frozen, human cadaveric specimens were dissected, and measurements were taken regarding the proximal attachments of the hamstring muscle group in reference to bony landmarks. A highly precise coordinate measuring device was used for three-dimensional measurements of tendon footprints and bony landmarks, and relevant distances between structures were calculated.

RESULTS

The semitendinosus and long head of the biceps femoris shared a proximal origin (conjoined tendon), having an oval footprint with an average area of 567.0 mm(2) [95 % CI 481.0-652.9]. The semimembranosus (SM) footprint was crescent-shaped and located anterolateral to the conjoined tendon, with an average area of 412.4 mm(2) [95 % CI 371.0-453.8]. The SM footprint had an accessory tendinous extension that extended anteromedially forming a distinct footprint. A consistent bony landmark was found at the medial ischial margin, 14.6 mm [95 % CI 12.7-16.5] from the centre of the conjoined tendon footprint, which coincided with the distal insertion of the sacrotuberous ligament.

CONCLUSION

The conjoined tendon was the largest attachment of the proximal hamstring group. Two other distinct attachment footprints were identified as the SM footprint and the accessory tendinous extension. The sacrotuberous ligament insertion served as a bony landmark. The anatomical data established in this study may aid in better restoring the anatomy during repair of proximal hamstring tears.

Immediate Effects of Neurodynamic Sliding versus Muscle Stretching on Hamstring Flexibility in Subjects with Short Hamstring Syndrome

Background. Hamstring injuries continue to affect active individuals and although inadequate muscle extensibility remains a commonly accepted factor, little is known about the most effective method to improve flexibility. Purpose. To determine if an isolated neurodynamic sciatic sliding technique would improve hamstring flexibility to a greater degree than stretching or a placebo intervention in asymptomatic subjects with short hamstring syndrome (SHS). Study Design. Randomized double-blinded controlled trial. Methods. One hundred and twenty subjects with SHS were randomized to 1 of 3 groups: neurodynamic sliding, hamstring stretching, and placebo control. Each subject's dominant leg was measured for straight leg raise (SLR) range of motion (ROM) before and after interventions. Data were analyzed with a 3 × 2 mixed model ANOVA followed by simple main effects analyses. Results. At the end of the study, more ROM was observed in the Neurodynamic and Stretching groups compared to the Control group and more ROM in the Neurodynamic group compared to Stretching group. Conclusion. Findings suggest that a neurodynamic sliding technique will increase hamstring flexibility to a greater degree than static hamstring stretching in healthy subjects with SHS. Clinical Relevance. The use of neurodynamic sliding techniques to improve hamstring flexibility in sports may lead to a decreased incidence in injuries; however, this needs to be formally tested.

Determining return-to-sport status with a multi-component assessment strategy: a case study in rugby

BACKGROUND

The effectiveness of rehabilitation programmes are often distorted by the athlete's desire to return and can result in injury recurrence. Athletic assessments allow for objective and reliable measurements to track rehabilitation progress. This case study used a multi-component assessment strategy to assess a rugby player's lower-extremity strength and symmetry as a primary determinate of their return-to-sport status.

CASE DESCRIPTION

A professional rugby league player was assessed for lower-extremity isokinetic strength and sprint kinetics pre- and 10-weeks post-rehabilitation programme following two consecutive knee injuries involving surgical intervention.

OUTCOMES

Pre-testing analysis showed clinical and functional strength deficits in the injured leg as high as 34% compared to the non-injured leg. Pre- to post-testing showed: increases in peak torque (49%) and decreased asymmetries by 50%; unilateral horizontal force increased (injured: 50%, non-injured: 19%) during sprinting; force production asymmetries decreased up to 18%.

DISCUSSION

The rugby player showed clinical and functional strength deficiencies return to normal ranges following a rehabilitation programme. A return-to-sport decision was made by the athlete's supporting health team based on the sizeable asymmetry decreases and return-to-normative ranges for knee and hip strength and sprint kinetics. The athlete returned to the 2013 National Rugby League season without any major injuries.

The association of aerobic fitness with injuries in the fire service

The aim of the present study was to understand the risk of injury in relation to fitness in a retrospective occupational cohort of firefighters in Tucson, Arizona, from 2005 to 2009. Annual medical evaluations and injury surveillance data were linked to compare levels of aerobic fitness in injured employees with those in noninjured employees. The individual outcomes evaluated included all injuries, exercise-related injuries, and sprains and strains. Time-to-event analyses were conducted to determine the association between levels of fitness and injury likelihood. Fitness, defined by relative aerobic capacity (Vo2max), was associated with injury risk. Persons in the lowest fitness level category (Vo2max <43 mL/kg/minute) were 2.2 times more likely (95% confidence interval: 1.72, 2.88) to sustain injury than were those in the highest fitness level category (Vo2max >48 mL/kg/minute). Those with a Vo2max between 43 and 48 mL/kg/minute were 1.38 times (95% confidence interval: 1.06, 1.78) more likely to incur injury. Hazard ratios were found to be greater for sprains and strains. Our results suggest that improving relative aerobic capacity by 1 metabolic equivalent of task (approximately 3.5 mL/kg/minute) reduces the risk of any injury by 14%. These findings illustrate the importance of fitness in reducing the risk of injury in physically demanding occupations, such as the fire service, and support the need to provide dedicated resources for structured fitness programming and the promotion of injury prevention strategies to people in those fields.

Evaluation and management of hamstring injuries

Muscle injuries are the most common injuries in sports, with hamstring injuries accounting for 29% of all injuries in athletes. These injuries lead to prolonged impairment and have a reinjury risk of 12% to 31%. They range from mild muscle damage without loss of structural integrity to complete muscle tearing with fiber disruption. Novel MRI scores are increasingly being used and allow a more precise prediction of return to sport. In this article, the authors review the history, mechanisms of injury, and classification systems for hamstring injuries as well as present the latest evidence related to the management of hamstring injuries, including intramuscular and both proximal and distal insertional injuries. Indications for surgical treatment of certain proximal and distal avulsions, biological augmentation to the nonoperative treatment of midsubstance injuries, and advances in risk reduction and injury prevention are discussed.

Muscle injury: review of experimental models

Skeletal muscle is the most abundant tissue in the human body. Its main characteristic is the capacity to regenerate after injury independent of the cause of injury through a process called inflammatory response. Mechanical injuries are the most common type of the skeletal muscle injuries and are classified into one of three areas strain, contusion, and laceration. First, this review aims to describe and compare the main experimental methods that replicate the mechanical muscle injuries. There are several ways to replicate each kind of mechanical injury; there are, however, specific characteristics that must be taken into account when choosing the most appropriate model for the experiment. Finally, this review discusses the context of mechanical injury considering types, variability of methods, and the ability to reproduce injury models.

Reliability of Concentric, Eccentric and Isometric Knee Extension and Flexion when using the REV9000 Isokinetic Dynamometer

The aim of this study was to assess the reliability of isokinetic and ISO knee extensor and flexor muscle strength when using the REV9000 (Technogym) isokinetic dynamometer. Moreover, the reliability of several strength imbalance indices and bilateral ratios were also examined. Twenty-four physically active healthy subjects (age 23±3 years) underwent three testing sessions, two on the same day and a third, 7 days later. All sessions proceeded in the same order: five concentric contractions at 60ºs-1 followed by an isometric contraction (5 seconds) and five eccentric contractions (60ºs-1). The results of this study showed a high reproducibility in eccentric (0.95-0.97), concentric (0.95-0.96) and isometric (0.93-0.96), isokinetic strength for knee extensor and flexor muscles, thus indicating that the REV9000 isokinetic dynamometer can be used in future sports performance studies. A low-to-moderate reliability was found in the isokinetic strength bilateral ratios while the Hamstring:Quadricep concentric ratio showed moderate reliability. The highest reliability (>0.90) was observed in the dynamic control ratio (Hamstring eccentric:Quadricep concentric) which consequently confirms that it is a more valid indicator for imbalanced reciprocal parameters and can be used in rehabilitation and sports medicine.

Comparison of hamstring strain injury rates between male and female intercollegiate soccer athletes

BACKGROUND

Hamstring strains are common among soccer athletes, and they have a high incidence of recurrence. Among American collegiate soccer players, men have an overall higher incidence rate of hamstring strains than women.

PURPOSE

This research compares the hamstring strain injury rates in event and athlete characteristics between male and female college soccer athletes.

STUDY DESIGN

Descriptive epidemiology study.

METHODS

Data describing partial and complete hamstring strains were obtained from the National Collegiate Athletic Association (NCAA) Injury Surveillance System (ISS) for men's and women's soccer from 2004 to 2009. Incidence rate ratios (IRRs) comparing the incidence of hamstring strains between the sexes as well as during games versus practices and the preseason versus the in-season were calculated. χ(2) tests were used to compare the occurrence of hamstring strains across different event and athlete characteristics.

RESULTS

Men were 64% more likely than women to sustain a hamstring strain (IRR, 1.64; 95% CI, 1.37-1.96). Men had significantly higher rates of hamstring strains than women during both games (IRR, 2.42; 95% CI, 1.82-3.23) and practices (IRR, 1.34; 95% CI, 1.06-1.68). There were no differences between men and women in injury rates during the preseason, but men were significantly more likely to sustain a hamstring strain during the in-season (IRR, 1.98; 95% CI, 1.56-2.52). Men had a significantly higher proportion of recurrent hamstring strains compared with women (men, 22%; women, 12%; P = .003). There were no significant differences in the distribution of strains in event or athlete characteristics between men and women for first-time or recurrent hamstring strains.

CONCLUSION

In collegiate soccer, men have significantly higher rates of hamstring strains than women, and regardless of the recurrence status, the event and athlete characteristics were similar for both sexes. Identifying common characteristics may assist in the targeted development of preventive and rehabilitative programs as well as continued research on hamstring strains among collegiate soccer players.

Categorising sports injuries in epidemiological studies: the subsequent injury categorisation (SIC) model to address multiple, recurrent and exacerbation of injuries

Objective

Sports injuries are often recurrent and there is wide recognition that a subsequent injury (of either the same or a different type) can be strongly influenced by a previous injury. Correctly categorising subsequent injuries (multiple, recurrent, exacerbation or new) requires substantial clinical expertise, but there is also considerable value in combining this expertise with more objective statistical criteria. This paper presents a new model, the subsequent injury categorisation (SIC) model, for categorising subsequent sports injuries that takes into account the need to include both acute and overuse injuries and ten different dependency structures between injury types.

Methods

The suitability of the SIC model was demonstrated with date ordered sports injury data from a large injury database from community Australian football players over one playing season. A subsequent injury was defined to have occurred in the subset of players with two or more reported injuries.

Results

282 players sustained 469 subsequent injuries of which 15.6% were coded to categories representing injuries that were directly related to previous index injuries. This demonstrates that players can sustain a number of injuries over one playing season. Many of these will be unrelated to previous injuries but subsequent injuries that are related to previous injury occurrences are not uncommon.

Conclusion

The handling of subsequent sports injuries is a substantial challenge for the sports medicine field—both in terms of injury treatment and in epidemiological research to quantify them. Application of the SIC model allows for multiple different injury types and relationships within players, as well as different index injuries.

Risk factors for lower extremity muscle injury in professional soccer: the UEFA Injury Study

BACKGROUND

Muscle injury is the most common injury type in professional soccer players. Despite this, risk factors for common lower extremity injuries remain elusive.

PURPOSE

To evaluate the effects of various player- and match-related risk factors on the occurrence of lower extremity muscle injury in male professional soccer.

STUDY DESIGN

Cohort study; level of evidence, 2.

METHODS

Between 2001 and 2010, 26 soccer clubs (1401 players) from 10 European countries participated in the study. Individual player exposure and time loss muscle injuries in the lower extremity were registered prospectively by the club medical staffs during 9 consecutive seasons. Hazard ratios (HRs) were calculated for player-related factors from simple and multiple Cox regression, and odds ratios (ORs) were calculated for match-related variables from simple and multiple logistic regression, presented with 95% confidence intervals (CIs).

RESULTS

There were 2123 muscle injuries documented in the major lower extremity muscle groups: adductors (n = 523), hamstrings (n = 900), quadriceps (n = 394), and calf (n = 306). Injuries to the adductors (56%; P = .015) and quadriceps (63%; P< .001) were more frequent in the kicking leg. Multiple analysis indicated that having a previous identical injury in the preceding season increased injury rates significantly for adductor (HR, 1.40; 95% CI, 1.00-1.96), hamstring (HR, 1.40; 95% CI, 1.12-1.75), quadriceps (HR, 3.10; 95% CI, 2.21-4.36), and calf injuries (HR, 2.33; 95% CI, 1.52-3.57). Older players (above mean age) had an almost 2-fold increased rate of calf injury (HR, 1.93; 95% CI, 1.38-2.71), but no association was found in other muscle groups. Goalkeepers had reduced injury rates in all 4 muscle groups. Match play on away ground was associated with reduced rates of adductor (OR, 0.56; 95% CI, 0.43-0.73) and hamstring injuries (OR, 0.76; 95% CI, 0.63-0.92). Quadriceps injuries were more frequent during preseason, whereas adductor, hamstring, and calf injury rates increased during the competitive season.

CONCLUSION

Intrinsic factors found to increase muscle injury rates in professional soccer were previous injury, older age, and kicking leg. Injury rates varied during different parts of the season and also depending on match location.

Recurrent hamstring muscle injury: applying the limited evidence in the professional football setting with a seven-point programme

Recurrent hamstring injuries are a major problem in sports such as football. The aim of this paper was to use a clinical example to describe a treatment strategy for the management of recurrent hamstring injuries and examine the evidence for each intervention. A professional footballer sustained five hamstring injuries in a relatively short period of time. The injury was managed successfully with a seven-point programme—biomechanical assessment and correction, neurodynamics, core stability, eccentric strengthening, an overload running programme, injection therapies and stretching/relaxation. The evidence for each of these treatment options is reviewed. It is impossible to be definite about which aspects of the programme contributed to a successful outcome. Only limited evidence is available in most cases; therefore, decisions regarding the use of different treatment modalities must be made by using a combination of clinical experience and research evidence.

Rate of torque and electromyographic development during anticipated eccentric contraction is lower in previously strained hamstrings

BACKGROUND

The effect of prior strain injury on myoelectrical activity of the hamstrings during tasks requiring high rates of torque development has received little attention.

PURPOSE

To determine if recreational athletes with a history of unilateral hamstring strain injury will exhibit lower levels of myoelectrical activity during eccentric contraction, rate of torque development (RTD), and impulse (IMP) at 30, 50, and 100 milliseconds after the onset of myoelectrical activity or torque development in the previously injured limb compared with the uninjured limb.

STUDY DESIGN

Case control study; Level of evidence, 3.

METHODS

Twenty-six recreational athletes were recruited. Of these, 13 athletes had a history of unilateral hamstring strain injury (all confined to biceps femoris long head), and 13 had no history of hamstring strain injury. Following familiarization, all athletes undertook isokinetic dynamometry testing and surface electromyography (integrated EMG; iEMG) assessment of the biceps femoris long head and medial hamstrings during eccentric contractions at -60 and -180 deg·s(-1).

RESULTS

In the injured limb of the injured group, compared with the contralateral uninjured limb, RTD and IMP was lower during -60 deg·s(-1) eccentric contractions at 50 milliseconds (RTD: injured limb, 312.27 ± 191.78 N·m·s(-1) vs uninjured limb, 518.54 ± 172.81 N·m·s(-1), P = .008; IMP: injured limb, 0.73 ± 0.30 N·m·s vs uninjured limb, 0.97 ± 0.23 N·m·s, P = .005) and 100 milliseconds (RTD: injured limb, 280.03 ± 131.42 N·m·s(-1) vs uninjured limb, 460.54 ± 152.94 N·m·s(-1), P = .001; IMP: injured limb, 2.15 ± 0.89 N·m·s vs uninjured limb, 3.07 ± 0.63 N·m·s, P < .001) after the onset of contraction. Biceps femoris long head muscle activation was lower at 100 milliseconds at both contraction speeds (-60 deg·s(-1), normalized iEMG activity [×1000]: injured limb, 26.25 ± 10.11 vs uninjured limb, 33.57 ± 8.29, P = .009; -180 deg·s(-1), normalized iEMG activity [×1000]: injured limb, 31.16 ± 10.01 vs uninjured limb, 39.64 ± 8.36, P = .009). Medial hamstring activation did not differ between limbs in the injured group. Comparisons in the uninjured group showed no significant between limbs difference for any variables.

CONCLUSION

Previously injured hamstrings displayed lower RTD and IMP during slow maximal eccentric contraction compared with the contralateral uninjured limb. Lower myoelectrical activity was confined to the biceps femoris long head. Regardless of whether these deficits are the cause of or the result of injury, these findings could have important implications for hamstring strain injury and reinjury. Particularly, given the importance of high levels of muscle activity to bring about specific muscular adaptations, lower levels of myoelectrical activity may limit the adaptive response to rehabilitation interventions and suggest that greater attention be given to neural function of the knee flexors after hamstring strain injury.

Acute effects of static and dynamic stretching on hamstring eccentric isokinetic strength and unilateral hamstring to quadriceps strength ratios

The main purposes of this study were to investigate the acute effects of static and dynamic lower limb stretching routines: (a) on peak torque, total external work and joint angle at peak torque of the hamstrings during maximal eccentric isokinetic leg flexion; (b) on unilateral hamstring to quadriceps (H/Q) strength ratios; as well as (c) to determine whether static and dynamic routines elicit similar responses. A total of 49 active adults completed the following intervention protocols in a randomised order on separate days: (a) non-stretching (control condition), (b) static stretching, and (c) dynamic stretching. After the stretching or control intervention, eccentric isokinetic peak torque, the angle of peak torque and total external work were assessed with participants prone at 1.04 and 3.14 rad · s(-1). Unilateral strength ratios of the knee were also recorded. Measures were compared via a fully-within-groups factorial analysis of variance (ANOVA). There were no main effects for eccentric isokinetic peak torque, angle of peak torque, total external work and unilateral H/Q strength ratios. The results suggest that dynamic and static stretching has no influence on eccentric strength profile and unilateral H/Q strength ratios and hence both forms of stretching do not reduce these two primary risk factors for muscle injury.

Knee joint strength ratios and effects of hip position in rugby players

Measures of knee joint function, although useful in predicting injury, can be misleading because hip position in traditional seated isokinetic tests is dissimilar to when injuries occur. This study aimed to determine the differences between seated and supine peak torques and strength ratios and examine the interaction of position with joint velocity. This was a cross-sectional, repeated measures study. Isokinetic knee extensor and flexor concentric and eccentric peak torque was measured seated and supine (10° hip flexion) at 1.04 and 3.14 rad·s(-1) in 11 Rugby players. Repeated measures analysis of variance and paired t-tests were used to analyze peak torques and strength ratios. Bonferroni post hoc, limits of agreement, and Pearson's correlation were applied. Seated peak torque was typically greater than that for supine for muscle actions and velocities. The values ranged from 109 ± 18 N·m (mean ± σ) for supine hamstring concentric peak torque at 1.04 rad·s(-1) to 330 ± 71 for seated quadriceps eccentric peak torque at 1.04 rad·s(-1). There was a significant position × muscle action interaction; eccentric peak torque was reduced more than concentric in the supine position. Knee joint strength ratios ranged from 0.47 ± 0.06 to 0.86 ± 0.23, with a significant difference in means between supine and seated positions for functional ratio at 3.14 rad·s(-1) observed; for seated it was 0.86 ± 0.23; and for supine, it was 0.68 ± 0.15 (p < 0.05). Limits of agreement for traditional and functional ratios ranged from 1.09 ×/÷ 1.37 to 1.13 ×/÷ 1.51. We conclude that hip angle affects isokinetic peak torques and knee joint strength ratios. Therefore, the hip angle should be nearer 10° when measuring knee joint function because this is more ecologically valid. Using similar protocols, sports practitioners can screen for injury and affect training to minimize injury.

An evidence-based approach to hamstring strain injury: a systematic review of the literature

Background:

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.

Objective:

To present the current best evidence for hamstring strain injury risk factors and the management of hamstring strain injury.

Methods:

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.

Results:

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.

Conclusion:

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.

Absolute reliability of isokinetic knee flexion and extension measurements adopting a prone position

The main purpose of this study was to determine the absolute and relative reliability of isokinetic peak torque (PT), angle of peak torque (APT), average power (PW) and total work (TW) for knee flexion and extension during concentric and eccentric actions measured in a prone position at 60, 180 and 240° s(-1). A total of 50 recreational athletes completed the study. PT, APT, PW and TW for concentric and eccentric knee extension and flexion were recorded at three different angular velocities (60, 180 and 240° s(-1)) on three different occasions with a 72- to 96-h rest interval between consecutive testing sessions. Absolute reliability was examined through typical percentage error (CV(TE)), percentage change in the mean (ChM) and relative reliability with intraclass correlations (ICC(3,1)). For both the knee extensor and flexor muscle groups, all strength data (except APT during knee flexion movements) demonstrated moderate absolute reliability (ChM < 3%; ICCs > 0·70; and CV(TE) < 20%) independent of the knee movement (flexion and extension), type of muscle action (concentric and eccentric) and angular velocity (60, 180 and 240° s(-1)). Therefore, the current study suggests that the CV(TE) values reported for PT (8-20%), APT (8-18%) (only during knee extension movements), PW (14-20%) and TW (12-28%) may be acceptable to detect the large changes usually observed after rehabilitation programmes, but not acceptable to examine the effect of preventative training programmes in healthy individuals.

Statistical modelling for recurrent events: an application to sports injuries

BACKGROUND

Injuries are often recurrent, with subsequent injuries influenced by previous occurrences and hence correlation between events needs to be taken into account when analysing such data.

OBJECTIVE

This paper compares five different survival models (Cox proportional hazards (CoxPH) model and the following generalisations to recurrent event data: Andersen-Gill (A-G), frailty, Wei-Lin-Weissfeld total time (WLW-TT) marginal, Prentice-Williams-Peterson gap time (PWP-GT) conditional models) for the analysis of recurrent injury data.

METHODS

Empirical evaluation and comparison of different models were performed using model selection criteria and goodness-of-fit statistics. Simulation studies assessed the size and power of each model fit.

RESULTS

The modelling approach is demonstrated through direct application to Australian National Rugby League recurrent injury data collected over the 2008 playing season. Of the 35 players analysed, 14 (40%) players had more than 1 injury and 47 contact injuries were sustained over 29 matches. The CoxPH model provided the poorest fit to the recurrent sports injury data. The fit was improved with the A-G and frailty models, compared to WLW-TT and PWP-GT models.

CONCLUSIONS

Despite little difference in model fit between the A-G and frailty models, in the interest of fewer statistical assumptions it is recommended that, where relevant, future studies involving modelling of recurrent sports injury data use the frailty model in preference to the CoxPH model or its other generalisations. The paper provides a rationale for future statistical modelling approaches for recurrent sports injury.

Platelet-rich plasma (PRP): an adjuvant to hasten hamstring muscle recovery. A randomized controlled trial protocol (ISCRTN66528592)

BACKGROUND

Muscle injuries are one of the commonest injuries affecting athletes. It often leads to significant pain and disability causing loss of training and competition time. With current treatment, the duration to return-to-play ranges form six weeks to never, depending on injury severity. Recent researches have suggested that autologous platelet-rich plasma (PRP) injection into the injured site may hasten soft tissues healing. To-date, there has been no randomised clinical trials to evaluate the effects of PRP on muscle healing. The aim of this study is to examine the effects of autologous PRP on duration to return-to-play after muscle injury.

METHODS AND DESIGN

A randomised, single blind controlled trial will be conducted. Twenty-eight patients aged 18 years and above with a recent grade-2 hamstring injury will be invited to take part. Participants will be randomised to receive either autologous PRP injection with rehabilitation programme, or rehabilitation programme only. Participants will be followed up at day three of study and then weekly for 16 weeks. At each follow up visit, participants will be assessed on readiness to return-to-play using a set of criteria. The primary end-point is when participants have fulfilled the return-to-play criteria or end of 16 weeks.The main outcome measure of this study is the duration to return-to-play after injury.

CONCLUSION

This study protocol proposes a rigorous and potential significant evaluation of PRP use for grade-2 hamstring injury. If proven effective such findings could be of great benefit for patients with similar injuries.

TRIAL REGISTRATION

Current Controlled Trials ISCRTN66528592.

Imaging of muscle injury in the elite athlete

Injuries to muscle in the elite athlete are common and may be responsible for prolonged periods of loss of competitive activity. The implications for the athlete and his/her coach and team may be catastrophic if the injury occurs at a critical time in the athlete's diary. Imaging now plays a crucial role in diagnosis, prognostication and management of athletes with muscle injuries. This article discusses the methods available to clinicians and radiologists that are used to assess skeletal muscle injury. The spectrum of muscle injuries sustained in the elite athlete population is both discussed and illustrated.

Preventive effect of eccentric training on acute hamstring injuries in men's soccer: a cluster-randomized controlled trial

BACKGROUND

The incidence of acute hamstring injuries is high in several sports, including the different forms of football.

PURPOSE

The authors investigated the preventive effect of eccentric strengthening of the hamstring muscles using the Nordic hamstring exercise compared with no additional hamstring exercise on the rate of acute hamstring injuries in male soccer players.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

Fifty Danish male professional and amateur soccer teams (942 players) were allocated to an intervention group (461 players) or a control group (481 players). Players in the intervention group conducted a 10-week progressive eccentric training program followed by a weekly seasonal program, whereas players in the control group followed their usual training program. The main outcome measures were numbers of overall, new, and recurrent acute hamstring injuries during 1 full soccer season.

RESULTS

Fifty-two acute hamstring injuries in the control group compared with 15 injuries in the intervention group were registered. Comparing intervention versus the control group, overall acute hamstring injury rates per 100 player seasons were 3.8 versus 13.1 (adjusted rate ratio [RR], 0.293; 95% confidence interval [CI], 0.150-0.572; P < .001). New injury rates per 100 player seasons were 3.1 versus 8.1 (RR, 0.410; 95% CI, 0.180-0.933; P = .034), whereas recurrent injury rates per 100 player seasons were 7.1 versus 45.8 (RR, 0.137; 95% CI, 0.037-0.509; P = .003). Number needed to treat [NNT] to prevent 1 acute hamstring injury (new or recurrent) is 13 (95% CI, 9-23) players. The NNT to prevent 1 new injury is 25 (95% CI, 15-72) players, and NNT to prevent 1 recurrent injury is 3 (95% CI, 2-6) players.

CONCLUSION

IN male professional and amateur soccer players, additional eccentric hamstring exercise decreased the rate of overall, new, and recurrent acute hamstring injuries.

Acute effects of static stretching on peak torque and the hamstrings-to-quadriceps conventional and functional ratios

Recent evidence has shown acute static stretching may decrease hamstring-to-quadriceps (H:Q) ratios. However, the effects of static stretching on the functional H:Q ratio, which uses eccentric hamstrings muscle actions, have not been investigated. This study examined the acute effects of hamstrings and quadriceps static stretching on leg extensor and flexor concentric peak torque (PT), leg flexor eccentric PT, and the conventional and functional H:Q ratios. Twenty-two women (mean ± SD age=20.6 ± 1.9 years; body mass=64.6 ± 9.1 kg; height=164.5 ± 6.4 cm) performed three maximal voluntary unilateral isokinetic leg extension, flexion, and eccentric hamstring muscle actions at the angular velocities of 60 and 180°/s before and after a bout of hamstrings, quadriceps, and combined hamstrings and quadriceps static stretching, and a control condition. Two-way repeated measures ANOVAs (time × condition) were used to analyze the leg extension, flexion, and eccentric PT as well as the conventional and functional H:Q ratios. Results indicated that when collapsed across velocity, hamstrings-only stretching decreased the conventional ratios (P<0.05). Quadriceps-only and hamstrings and quadriceps stretching decreased the functional ratios (P<0.05). These findings suggested that stretching may adversely affect the conventional and functional H:Q ratios.

Selective strength loss and decreased muscle activity in hamstring injury

STUDY DESIGN

Cross-sectional, controlled laboratory study.

OBJECTIVES

To determine whether thigh muscle isokinetic torque patterns and activity, measured by electromyography (EMG), of individuals with hamstring injury differ from control individuals.

BACKGROUND

Neuromuscular control during thigh muscle strength assessment following hamstring injuries has not been reported.

METHODS

Fifteen athletes with prior hamstring injury (hamstring-injured group [HG]) were compared to 15 uninjured athletes (control group [CG]). The injuries were incurred 6 weeks to 12 months prior to participation, and all injured athletes had returned to at least partial training. Participants performed 5 isokinetic concentric extensor, concentric flexor, and eccentric flexor torque tests at 60°/s in the seated position. Peak torque was determined for each contraction type, as well as average torque for each of 4 time-based movement quartiles. EMG root-mean-squares were calculated in these movement quartiles for the biceps femoris and medial hamstrings.

RESULTS

No significant differences were found for peak torque for all contractions, when comparing HG injured and uninjured sides to CG bilateral averages. The HG injured limb eccentric flexor torque was significantly lower in the fourth quartile (approximately 25° to 5° knee flexion, hamstring lengthened range) compared to the CG bilateral average (P = .025). Eccentric flexor biceps femoris and hamstrings EMG root-mean-squares of the HG injured and the uninjured sides were significantly lower in the second to fourth quartiles (towards the lengthened range), compared to the CG bilateral averages (P<.05).

CONCLUSION

Decreased strength and EMG activation in a lengthened hamstrings range for the athletes with prior hamstring injury suggested a change in neuromuscular control. Lengthened range assessment of isokinetic eccentric flexor torque may be useful for the assessment of athletes with a prior injury; however, results should be confirmed with prospective studies.

Interventions for preventing hamstring injuries: a systematic review

OBJECTIVES

To assess, by systematic review, the effects of interventions used for preventing hamstring injuries in physically active individuals.

SELECTION CRITERIA

Randomised or quasi-randomised trials of interventions for preventing hamstring injuries were included, as were trials testing interventions for the prevention of lower limb injuries, provided that hamstring injuries were reported. Risk ratios (RRs) and 95% confidence intervals (95% CIs) were calculated for dichotomous variables and are reported for individual and pooled data.

MAIN RESULTS

Seven randomised controlled trials involving 1919 participants were included. Some trials were compromised by poor methodology, including lack of blinding and incomplete outcome data. Four trials, including 287 participants, examined interventions directly targeted at preventing hamstring injuries. Three of these trials, which tested hamstring strengthening protocols, had contradictory findings, with one small trial showing benefit, although the control rate of mainly minor hamstring injury was unusually high. The other two trials found no benefit, with a greater incidence of hamstring injury in the intervention group. One unpublished and underpowered trial provided some evidence that manual therapy may prevent lower limb muscle strain (RR 0.13, 95% CI 0.02 to 0.97), although the finding for hamstring injury did not reach statistical significance (RR 0.21, 95% CI 0.03 to 1.66).

CONCLUSIONS

There is insufficient evidence from randomised controlled trials to draw conclusions on the effectiveness of interventions used to prevent hamstring injuries in people participating in football or other high-risk activities. The findings for manual therapy need confirmation.

Functional differences in the activity of the hamstring muscles with increasing running speed

In this study, we examined hamstring muscle activation at different running speeds to help better understand the functional characteristics of each hamstring muscle. Eight healthy male track and field athletes (20.1 +/- 1.1 years) performed treadmill running at 50%, 75%, 85%, and 95% of their maximum velocity. Lower extremity kinematics of the hip and knee joint were calculated. The surface electromyographic activities of the biceps femoris and semitendinosus muscles were also recorded. Increasing the running speed from 85% to 95% significantly increased the activation of the hamstring muscles during the late swing phase, while lower extremity kinematics did not change significantly. During the middle swing phase, the activity of the semitendinosus muscle was significantly greater than that of the biceps femoris muscle at 75%, 85%, and 95% of running speed. Statistically significant differences in peak activation time were observed between the biceps femoris and semitendinosus during 95%max running (P < 0.05 for stance phase, P < 0.01 for late swing phase). Significant differences in the activation patterns between the biceps femoris and semitendinosus muscles were observed as running speed was increased, indicating that complex neuromuscular coordination patterns occurred during the running cycle at near maximum sprinting speeds.

High hamstring tendinopathy: MRI and ultrasound imaging and therapeutic efficacy of percutaneous corticosteroid injection

OBJECTIVE

The goals of this study were to review the MRI and sonographic findings in patients diagnosed clinically with high hamstring tendinopathy and to evaluate the efficacy of ultrasound-guided corticosteroid injections in providing symptomatic relief.

CONCLUSION

MRI is more sensitive than ultrasound in detecting peritendinous edema and tendinopathy at the proximal hamstring origin. Fifty percent of patients had symptomatic improvement lasting longer than 1 month after percutaneous corticosteroid injection, and 24% of patients had symptom relief for more than 6 months.

A return-to-sport algorithm for acute hamstring injuries

Acute hamstring injuries are the most prevalent muscle injuries reported in sport. Despite a thorough and concentrated effort to prevent and rehabilitate hamstring injuries, injury occurrence and re-injury rates have not improved over the past 28 years. This failure is most likely due to the following: 1) an over-reliance on treating the symptoms of injury, such as subjective measures of "pain", with drugs and interventions; 2) the risk factors investigated for hamstring injuries have not been related to the actual movements that cause hamstring injuries i.e. not functional; and, 3) a multi-factorial approach to assessment and treatment has not been utilized. The purpose of this clinical commentary is to introduce a model for progression through a return-to-sport rehabilitation following an acute hamstring injury. This model is developed from objective and quantifiable tests (i.e. clinical and functional tests) that are structured into a step-by-step algorithm. In addition, each step in the algorithm includes a treatment protocol. These protocols are meant to help the athlete to improve through each phase safely so that they can achieve the desired goals and progress through the algorithm and back to their chosen sport. We hope that this algorithm can serve as a foundation for future evidence based research and aid in the development of new objective and quantifiable testing methods.

Effect of stretch positions on hamstring muscle length, lumbar flexion range of motion, and lumbar curvature in healthy adults

Hamstring stretching is a common practice in physical therapy to change not only hamstring muscle length (HML), but also lumbar flexion range of motion (LROM) or lumbar curvature (LC). Yet limited published research compares the effectiveness of two commonly used hamstring stretch positions, sitting and standing. The purposes of this study were to determine the effect of (1) stretch position on HML; and 2) HML on LROM and LC. Thirty-six participants (M=44.8 years, SD=17.1) with short HML (i.e., with shortness for men ≥45° and for women ≥ 24° of active knee flexion with 90° hip flexion) were measured for HML, LROM, and LC; randomly allocated to one of three groups: (1) hamstring stretching in sitting (SI); (2) standing (ST); or (3) no stretching (control); and remeasured after 4 weeks. Participants in the stretching groups performed two 30-second static stretches 4 days per week for 4 weeks. Multivariate analysis of covariance (MANCOVA) showed significance between the stretching groups and nonstretching group for HML only. Nonsignificance was shown for HML between the stretch positions (i.e., SI-active knee extension (AKE) and ST-AKE), indicating that both were equally effective for increasing HML. However, there was no change in LROM or in LC even though HML increased.

A descriptive study of a manual therapy intervention within a randomised controlled trial for hamstring and lower limb injury prevention

Background

There is little literature describing the use of manual therapy performed on athletes. It was our purpose to document the usage of a sports chiropractic manual therapy intervention within a RCT by identifying the type, amount, frequency, location and reason for treatment provided. This information is useful for the uptake of the intervention into clinical settings and to allow clinicians to better understand a role that sports chiropractors offer.

Methods

All treatment rendered to 29 semi-elite Australian Rules footballers in the sports chiropractic intervention group of an 8 month RCT investigating hamstring and lower-limb injury prevention was recorded. Treatment was pragmatically and individually determined and could consist of high-velocity, low-amplitude (HVLA) manipulation, mobilization and/or supporting soft tissue therapies. Descriptive statistics recorded the treatment rendered for symptomatic or asymptomatic benefit, delivered to joint or soft tissue structures and categorized into body regions. For the joint therapy, it was recorded whether treatment consisted of HVLA manipulation, HVLA manipulation and mobilization, or mobilization only. Breakdown of the HVLA technique was performed.

Results

A total of 487 treatments were provided (mean 16.8 consultations/player) with 64% of treatment for asymptomatic benefit (73% joint therapies, 57% soft tissue therapies). Treatment was delivered to approximately 4 soft tissue and 4 joint regions each consultation. The most common asymptomatic regions treated with joint therapies were thoracic (22%), knee (20%), hip (19%), sacroiliac joint (13%) and lumbar (11%). For soft tissue therapies it was gluteal (22%), hip flexor (14%), knee (12%) and lumbar (11%). The most common symptomatic regions treated with joint therapies were lumbar (25%), thoracic (15%) and hip (14%). For soft tissue therapies it was gluteal (22%), lumbar (15%) and posterior thigh (8%). Of the joint therapy, 56% was HVLA manipulation only, 36% high-HVLA and mobilization and 9% mobilization only. Of the HVLA manipulation, 63% was manually performed and 37% mechanically assisted.

Conclusions

The intervention applied was multimodal and multi-regional. Most treatment was for asymptomatic benefit, particularly for joint based therapies, which consisted largely of HVLA manipulation techniques. Most treatment was applied to non-local hamstring structures, in particular the knee, hip, pelvis and spine.

Effects of prior hamstring strain injury on strength, flexibility, and running mechanics

BACKGROUND

Previous studies have shown evidence of residual scar tissue at the musculotendon junction following a 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.

METHODS

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 the hamstrings:quadriceps strength ratio, as well as muscle activations and peak hamstring stretch during sprinting. MR images were used to measure the volumes of the proximal tendon/aponeurosis of the biceps femoris, with asymmetries considered indicative of scar tissue.

FINDINGS

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.

INTERPRETATION

Injury-induced changes in morphology do not seem discernable from strength measures, running kinematics, or muscle activation patterns. Further research is warranted to ascertain whether residual scarring alters localized musculotendon mechanics in a way that may contribute to the high rates of muscle re-injury that are observed clinically.

Characteristics of locomotion, muscle strength, and muscle tissue in regenerating rat skeletal muscles

Although numerous studies have aimed to elucidate the mechanisms used to repair the structure and function of injured skeletal muscles, it remains unclear how and when movement recovers following damage. We performed a temporal analysis to characterize the changes in movement, muscle function, and muscle structure after muscle injury induced by the drop-mass technique. At each time-point, movement recovery was determined by ankle kinematic analysis of locomotion, and functional recovery was represented by isometric force. As a histological analysis, the cross-sectional area of myotubes was measured to examine structural regeneration. The dorsiflexion angle of the ankle, as assessed by kinematic analysis of locomotion, increased after injury and then returned to control levels by day 14 post-injury. The isometric force returned to normal levels by day 21 post-injury. However, the size of the myotubes did not reach normal levels, even at day 21 post-injury. These results indicate that recovery of locomotion occurs prior to recovery of isometric force and that functional recovery occurs earlier than structural regeneration. Thus, it is suggested that recovery of the movement and function of injured skeletal muscles might be insufficient as markers for estimating the degree of neuromuscular system reconstitution.

The synergistic effect of treadmill running on stem-cell transplantation to heal injured skeletal muscle

Muscle-derived stem-cell (MDSC) transplantation presents a promising method for the treatment of muscle injuries. This study investigated the ability of exercise to enhance MDSC transplantation into the injured muscle. Mice were divided into four groups: contusion + phosphate-buffered saline (C + PBS; n = 14 muscles), C + MDSC transplantation (n = 12 muscles), C + PBS + treadmill running (C + PBS + TM; n = 17 muscles), and C + MDSC + TM (n = 13 muscles). One day after injury, the TM groups began running for 1 or 5 weeks. Two days after injury, muscles of C + MDSC and C + MDSC + TM groups were injected with MDSCs. One or 5 weeks later, the number and differentiation of transplanted MDSCs, myofiber regeneration, collagen I formation, and vascularity were assessed histologically. In vitro, MDSCs were subjected to mechanical stimulation, and growth kinetics were quantified. In vitro, mechanical stimulation decreased the MDSC population doubling time (18.6 +/- 1.6 h) and cell division time (10.9 +/- 0.7 h), compared with the controls (population doubling time: 23.0 +/- 3.4 h; cell division time: 13.3 +/- 1.1 h) (p = 0.01 and 0.03, respectively). In vivo, 5 weeks of TM increased the myogenic contribution of transplanted MDSCs, compared with the controls (p = 0.02). C + MDSC, C + PBS + TM, and C + MDSC + TM demonstrated decreased fibrosis at 5 weeks, compared with the C + PBS controls (p = 0.00, p = 0.03, and p = 0.02, respectively). Results suggest that the mechanical stimulation favors MDSC proliferation, both in vitro and in vivo, and that exercise enhances MDSC transplantation after injury.

Explosive strength imbalances in professional basketball players

CONTEXT

Despite the high rate of lower limb injuries in basketball players, studies of the dominant-limb effect in elite athletes often neglect injury history.

OBJECTIVE

To determine lower limb explosive-strength asymmetries in professional basketball players compared with junior basketball players and control participants.

DESIGN

Cohort study.

SETTING

Academic medical institution.

PATIENTS OR OTHER PARTICIPANTS

15 professional basketball players, 10 junior basketball players, and 20 healthy men.

MAIN OUTCOME MEASURE(S)

We performed an isokinetic examination to evaluate the knee extensor (Ext) and flexor (Fl) concentric peak torque at 60 degrees .s(-1) and 240 degrees .s(-1) and (Fl only) eccentric peak torque at 30 degrees .s(-1) and 120 degrees .s(-1). Functional evaluation included countermovement jump, countermovement jump with arms, 10-m sprint, single-leg drop jump, and single-leg, 10-second continuous jumping. Variables were compared among groups using analysis of variance or a generalized linear mixed model for bilateral variables.

RESULTS

The 2 groups of basketball players demonstrated better isokinetic and functional performances than the control group did. No differences in functional or relative isokinetic variables were noted between professional and junior basketball players. Professional players with a history of knee injury failed to reach normal knee extensor strength at 60 degrees .s(-1). Knee Ext (60 degrees .s(-1)) and Fl (eccentric 120 degrees .s(-1)) torque values as well as 10-second continuous jumping scores were higher in those professional players without a history of knee injury than those with such a history. Compared with the group without a history of knee injury, the group with a history of knee injury maintained leg asymmetry ratios greater than 10% for almost all isokinetic variables and more than 15% for unilateral functional variables.

CONCLUSIONS

The relative isokinetic and functional performances of professional basketball players were similar to those of junior players, with no dominant-side effect. A history of knee injury in the professional athlete, however, was reflected in bilateral isokinetic and functional asymmetries and should be considered in future studies of explosive strength.

Hamstring strain injuries: recommendations for diagnosis, rehabilitation, and injury prevention

Hamstring strain injuries remain a challenge for both athletes and clinicians, given their 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/prevention, level 5.

Evidence-based treatment of hamstring tears

Hamstring tears are exceedingly common in a variety of athletic populations and contribute to a significant amount of morbidity and time lost from sport. Many modifiable and nonmodifiable risk factors have been identified with hamstring injury. There is strong evidence that Nordic hamstring exercises can decrease the risk of hamstring injury, limited evidence that sports specific anaerobic interval training and isokinetic strengthening can reduce injury rates, and limited evidence that daily static stretching after injury can increase recovery rate. The majority of medical, surgical, and rehabilitative intervention studies have limitations based on the total number of hamstring injuries included in a given study, reliance on retrospective cohort studies, and conclusions based on case series that limit the utility of the information. Most do not provide a level of evidence greater than expert opinion.

Interventions for preventing hamstring injuries

BACKGROUND

Some sports, such as football, have a high incidence of hamstring injuries. Various interventions targeting the prevention of such injuries are in common use.

OBJECTIVES

To assess the effects (primarily, on the incidence of hamstring injuries) of interventions used for preventing hamstring injuries in physically active individuals.

SEARCH STRATEGY

We searched the Cochrane Bone, Joint and Muscle Trauma Group Specialised Register (to December 2008), the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2008, Issue 4), MEDLINE and other databases (to December 2008), reference lists and clinical trials registers.

SELECTION CRITERIA

Randomised or quasi-randomised trials of interventions for preventing hamstring injuries were included; as were trials testing interventions for the prevention of lower-limb injuries, provided that hamstring injuries were reported. Secondary outcomes included compliance, severity and the occurrence of other leg injuries.

DATA COLLECTION AND ANALYSIS

Two authors independently screened search results, assessed methodological quality and extracted data. Risk ratios (RR) and 95% confidence intervals (95% CI) were calculated for dichotomous variables and are reported for individual and pooled data.

MAIN RESULTS

Seven randomised controlled trials involving 1919 participants were included. All trials involved people, predominantly young adults, participating in regular sporting activities. Some trials were compromised by poor methodology, including lack of blinding and incomplete outcome data.Four trials, including 287 participants, examined interventions directly targeted at preventing hamstring injuries. Three of these trials, which tested hamstring strengthening protocols, had contradictory findings, with one small trial showing benefit (although the control rate of mainly minor hamstring injury was unusually high). The other two trials found no benefit, with a greater incidence of hamstring injury in the intervention group. One unpublished and underpowered trial provided some evidence that manual therapy may prevent lower-limb muscle strain (RR 0.13, 95% CI 0.02 to 0.97), although the finding for hamstring injury did not reach statistical significance (RR 0.21, 95% CI 0.03 to 1.66).Three trials testing interventions for preventing lower limb injuries for which data for hamstring injury were available found no statistically significant effect for hamstring injury for either proprioceptive protocols (two cluster randomised trials) or a warm up/cool down and stretching protocol (one trial).

AUTHORS' CONCLUSIONS

There is insufficient evidence from randomised controlled trials to draw conclusions on the effectiveness of interventions used to prevent hamstring injuries in people participating in football or other high risk activities for these injuries. The findings for manual therapy need confirmation.