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31 (); 72-77
doi:
10.1016/j.jor.2022.04.003

Hamstrings injuries in football

, , , , ,
a Casa de Saúde São José, Rio de Janeiro, Brazil
b Clínica Espregueira – FIFA Medical Centre of Excellence, Porto, Portugal
c Dom Henrique Research Centre, Porto, Portugal
d Porto Biomechanics Laboratory (LABIOMEP), University of Porto, Porto, Portugal
e Centre of Research, Education Innovation and Intervention in Sport (CIFI2D), Faculty of Sport, University of Porto, Portugal
f Hospital Samaritano Barra, Rio de Janeiro, Brazil
g Real Sporting de Gijon, Hospital Begona, Gijon, Spain
h School of Medicine, University of Minho, Braga, Portugal
i ICVS/3B's–PT Government Associate Laboratory, Braga/Guimarães, Portugal
j 3B's Research Group – Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, Barco, Guimarães, Portugal

∗Corresponding author: Antonio Maestro. doctorantoniomaestro@gmail.com

Received: , Accepted: ,
Disclaimer:
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.

Abstract

Abstract

Hamstrings injuries are a major concern in football (soccer), affecting both recreational players and professional athletes. Although being a recognized issue within the football community, its incidence has been increasing over the last years and still poses a challenge to all practitioners involved.

The goal of this narrative review is to outline hamstrings injuries epidemiology and mechanisms of injury, identify and discuss its risk factors, provide an approach to a proper early diagnosis, evaluate the efficacy of current treatment options and return to sports, and present the best strategies for hamstrings injury prevention. These guidelines will help the sports medicine staff team on how to better manage their players with or at risk of hamstrings injuries.

Despite several breakthroughs in research of hamstrings injuries, there is still heterogeneity across studies and lack of consensus in regards to classification, diagnosis, treatment and prevention. Hamstrings injuries compromise the athlete's performance with time loss due to injury, shortens their highest-level career longevity with higher risk of reinjury rates, and is a defying problem for clubs to balance financial losses due to having their players off the pitch. Further research is warranted to keep moving forward with evidence on treating and preventing hamstrings injuries to mitigate its high incidence and keep the players safe.

Keywords

Hamstrings
Muscle injury
Tendon injury
Football
Soccer
Rehabilitation
Prevention
1

1 Introduction

Hamstrings injuries comprehend muscle or tendon lesions that affect one or more of the muscle-tendon group of the posterior thigh: semimembranosus (SM), semitendinosus (ST) and/or biceps femoris long (BFlh) and short (BFsh) heads. Hamstrings-strain injuries (HSI) are the most prevalent non-contact injuries in profession men's football (soccer).1,2 There are two types of HSI: Type 1 injuries occur while running and sprinting, where the maximum eccentric muscle action activation occurs concomitant with muscle elongation, usually involving the myotendinous junction (MTJ), aponeurosis and adjacent fibers of BFlh; Type 2 injuries occur with excessive lengthening of the hamstrings muscle, with the hip flexed and the knee extended (late swing phase of kicking or stretching the lower limb with extended knee), typically involving the SM and its proximal free tendon.

2

2 Epidemiology

Injuries in football have been well documented, especially for the last two decades among elite professional athletes since the implementation of UEFA's Elite Club Injury Study. Hamstrings injuries are usually regarded as the most prevalent muscle injuries in football, and represent almost 34% of all muscle injuries and 17–26% of all football athletes' lesions.1,2 In elite professional soccer, despite efforts from medical staff and scientific community research, the prevalence of HSI keeps increasing ∼2.3% each year.2

Time-loss due to hamstring injury in football players usually ranges from 0 to 50 days, with an average time of approximately 3 weeks (for a grade II injury).3 However, the type of injury influences tissue healing time (myofascial: approximately 3 weeks; muscle–tendon junction: 4–8 weeks; and intratendinous: 2–4 months).4 Recurrence is not unusual, and may affect more than half of players who have sustained a previous HSI,5,6 with most of these recurrent injuries within the following year of first injury (higher risk in the first two weeks).7 In elite European football, the average time of absence is 6 days for functional hamstrings muscle injuries (16% reinjury rate and further 9 days of absence) and 18 days for structural hamstrings muscle injuries (17.5% reinjury rate and further 21.5 days of absence).6

3

3 Mechanism of injury

Most HSIs occur during matches comparatively to training situations,1,2 typically presenting as a sudden pain in the posterior thigh, sometimes associated with an audible snap with immediate player impairment and inability to keep playing. An HSI in football usually occurs by an indirect mechanism (∼80%)2 during sprint-running, kicking or high-speed movement with hip flexion and knee extension,8 more likely to occur during late swing and the late stance phase of running kinematics, whilst anterior pelvic tilt and extensive lengthening of the hamstrings muscle group as the lower limb decelerates in preparation for initial foot contact.9 Stretching injuries are more common at the proximal SM muscle or tendon.10,11 A recent video-analysis study12 showed that in professional men's football the mechanism of injury is equally divided into sprint-related (48%) and stretch-related injuries (52%), which most injuries affecting the BM (79%).

4

4 Risk factors

Understanding risk factors for HSI is cornerstone for rehabilitation and prevention strategies. Risk factors for developing a HSI can be defined as intrinsic or extrinsic and as modifiable or non-modifiable.13,14 The unique anatomy of the hamstrings group may be considered for itself as a risk factor for injury. Its biarticular nature crossing the two largest joints of lower limb, participating in both hip extension and knee flexion, its divided proximal insertion (SM and ST and BFlh) with a long intramuscular tendon (SM), as also anatomical variations of muscle fascicles and lengths are some characteristics which have been proposed as reasons injury risk. The dual innervation of BF is also another feature for complexity of neuromuscular function.13

Non-modifiable risk factors include intrinsic factors that are related to athletes’ individual features, including age, gender, ethnicity and previous HSI injury. Previous anterior cruciate ligament or calf strain injury have also been identified as significant risk factors for HSI.15 Older age and previous history of a HSI are the most consensual and strongest risk factors for HSI.15

A previous HSI has been widely reported as the main risk factor for a new hamstrings injury.15 Athletes who have sustained a HSI have an almost 3-fold risk of sustaining a new hamstrings injury and around a 5-fold increased risk if the last HSI had occurred in the same season.15 Other studies have reported a 11.6-fold increased risk hamstrings recurrence in football.16 Recurrent HSI may occur in up to 60% of athletes, commonly in the same or following season after first injury.17

Advancing age is also associated with a significantly increased risk of HSI in several studies,15 although reasons are still unclear. A main reason may be that older athletes generally have longer time of practice and playing participation, therefore being more exposed for sustaining a previous HSI, further increasing their risk of injury.15

The HSI literature is limited when relating to gender, ethnicity and player position epidemiology as risk factors for injury.18–20 Most HSIs occur in men's football athletes, with men being almost two times more affected than women, and presenting twice the recurrence rates.21 Specific ethnicities are more likely to have HSI,22 but the literature is still elusive in this regard. Player position appears to relate to sprint high-speed running requests during activity, with forwards and midfielders being more at increased risk of HSI than defenders and goalkeepers.23

Muscle strength imbalances have been traditionally hypothesized as modifiable risk factors for HSI - particularly when bilateral deficit overcomes 10% comparing to contralateral side and hamstrings:quadriceps (H:Q) ratio discrepancies of 0.6 or more24,25 - however, muscle imbalance has shown weak association with HIS.15,26,27

5

5 Diagnosis

Early and accurate diagnosis of HSI is key to establish the best therapeutic plan, although estimating an exact prognosis and the right time to RTS are still challenging, considering the wide variable of injury grades and stages. Notably, scientific knowledge is limited, and in football daily practice real world scenarios, is not unusual that some low-grade acute cases might not always be identified at first occasions and go underdiagnosed and undertreated for a while, leading to subacute or chronic presentations and sequelae cases, which are often more challenging for treatment approaches to rehabilitation.11

Clinical evaluation of acute HSI is objective and history taking is generally quite compatible: the injured athlete often complains of a sudden pain at posterior thigh, commonly described as a sharp twinge, during activity as noted mechanisms of injury. Physical examination observes the sign of the injured athlete reaching for the affected region with the ipsilateral hand. An array of clinical tests is available to diagnose HSI.28 Mobility testing evaluates active and passive range of motion (ROM), with presenting pain while stretching in flexed hips and extended knees; and subsequently pain or incapacity with resistance at different angles of hip extension and knee flexion, either prone or supine position. Through palpation clinicians may detect presence or absence of pain and/or muscle defect/gap, and help to determine suspicion of anatomical location of HSI.29 Pain close to ischial tuberosity suggests proximal hamstrings tendon injury/tendinopathy or avulsion fracture, both usually requiring more complex treatments, and only in those suspicion cases the imagining exams include plain radiographs.29 For all other typical myotendinous HSI compatible presentations, MRI and ultrasonography are enough to assess hamstrings injury.

6

6 Classification

The relevance of classification in HSI is to provide a prognosis for the injured players and determine the appropriate management and treatment. Many classification systems have been described, combining injury severity, mechanisms of injury, athletes’ symptoms, clinical signs and imaging findings. The Munich consensus muscle injury system classification (Table 1) includes a combination of clinical and imaging findings to define the nature of muscle injury (direct and indirect, functional or structural),30 but studies revealed a wide variation predicting RTP durations.31 The BAMIC32 (Table 2) classifies the hamstrings injury severity from grades 0 to 4 based on a combination of clinical and MRI features. This classification system is user-friendly and has substantial intra- and inter-rater agreement33 Conversely to the Munich classification, the BAMIC differentiates according to anatomic location (e.g., intramuscular tendon injuries which have a different prognosis).34,35 The BAMIC has a reliable prognostic value for the time to RTS and risk of reinjury34–36 and has clinically relevant guidelines for rehabilitation according to the grading of injury.4,36 The MLG-R system (Table 3) - referring to the mechanism of injury (M), location of injury (L), grading of severity (G), and number of muscle re-injuries (R) - includes a re-injury feature,37 and may therefore be relevant for rehabilitation and RTS, although has not been validated on the potential of prognoses.

Table 1 Munich consensus statement classification of acute muscle disorders and injuries.31
INDIRECT MUSCLE DISORDER/INJURY DIRECT MUSCLE INJURY
Functional muscle disorder
Type 1 Overexertion-related muscle disorder Contusion
Type 1A: Fatigue-induced muscle disorder
Type 1B: Delayed-onset muscle soreness (DOMS)
Type 2 Neuromuscular muscle disorder
Type 2A: Spine-related neuromuscular muscle disorder
Type 2B: Muscle-related neuromuscular muscle disorder
Structural muscle injury
Type 3 Partial muscle tear Laceration
Type 3A: Minor partial muscle tear
Type 3B: Moderate partial muscle tear
Type 4 (Sub)total tear Subtotal or complete muscle tear
Tendinous avulsion
Table 2 British athletics muscle injury classification.32
Grade Anatomical location Combined Classification
Grade 0Negative MRI 0a normal MRI0b MRI normal or patchy high signal changes throughout one or more muscles
Grade 1Small injuries (tears) (to the muscle) a Myofascialb Musculo-tendinousc Intra-tendon 1a High signal changes evident at the fascial border1b High signal changes <10% MTJ; longitudinal length <5 cm (may note fiber disruption <1 cm)
Grade 2Moderate injuries (tear) (to the muscle) 2a High signal changes evident at fascial border with extension into the muscle. High signal changes CSA between 10% and 50% at maximal site. High signal changes of length >5 cm2b HSC evident at the MTJ. High signal changes CSA of between 10% and 50% at maximal site. High signal changes of length >5 cm2c High signal changes extends into the tendon with longitudinal length of tendon involvement
Grade 3Extensive tears (to the muscle) 3a High signal changes evident at fascial border with extension into the muscle. High signal changes CSA of >50% at maximal site. High signal changes of length of >15 cm. Architectural fiber disruption usually noted >5 cm3b High signal changes CSA >50% at maximal site. High signal changes of length >15 cm. Architectural fiber disruption usually noted >5 cm3c High signal changes extends into the tendon. Longitudinal length of tendon involvement >5 cm. CSA of tendon involvement >50% of maximal tendon CSA (may be loss of tendon tension, although no discontinuity is evident)
Grade 4Complete tears (to either the muscle or tendon) 4b Complete discontinuity of the muscle with retraction4c Complete discontinuity of the tendon with retraction
Table 3 MLG-R muscle injury classification.37
Mechanism of injury (M) Locations of injury (L) Grading of severity (G) Number of muscle re-injuries (R)
Hamstrings direct injuries
T (direct) P Injury located in the proximal third of the muscle belly 0–3 0: 1st episode
M Injury located in the middle third of the muscle belly 1: 1st re-injury
D Injury located in the distal third of the muscle belly 2: 2nd re-injury, and so on.
Hamstrings indirect injuries
I (indirect) plus subindex s for stretching-type, or subindex p for sprinting-type. P Injury located in the proximal third of the muscle belly. The second letter is a subindex p or d to describe the injury relation with the proximal or distal MTJ respectively 0–3 0: 1st episode
M Injury located in the middle third of the muscle belly, plus the corresponding subindex. 1: 1st re-injury
D Injury located in the distal third of the muscle belly, plus the corresponding subindex. 2: 2nd re-injury, and so on.
Negative MRI injuries (location is pain related)
N plus subindex s for indirect injuries stretching-type, or subindex p for sprinting-type N p proximal third injury 0–3 0: 1st episode
N m middle third injury 1: 1st re-injury
N d distal third injury 2: 2nd re-injury, and so on.
Grading of injury severity
0: When codifying indirect injuries with clinical suspicion but negative MRI, a Grade 0 injury is codified. In these cases, the second letter describes the pain locations in the muscle belly.
1: Hyperintense muscle fibers edema without intramuscular hemorrhage or architectural distortion (fiber architecture and pennation angle preserved). Edema pattern: interstitial hyperintensity with feathery distribution on FSPD or T2 FSE + STIR images
2: Hyperintense muscle fibers and or peritendon edema with minor muscle fibers architectural distortion (fiber blurring and/or pennation angle distortion) ± minor intermuscular hemorrhage, but no quantifiable gap between fibers. Edema pattern, same as for grade 1.
3: Any quantifiable gap between fibers in craniocaudal or axial planes. Hyperintense focal defect with partial Any quantifiable gap between fibers in craniocaudal or axial planes. Hyperintense focal defect with partial retraction of muscle fibers ± intermuscular hemorrhage. The gap between fibers at the injury's maximal area in an axial plane of the affected muscle belly should be documented. The exact percentage of CSA should be documented as a subindex to the grade.
r: When codifying an intra-tendon injury or an injury affecting the MTJ or intramuscular tendon showing disruption/retraction or loss of tension exist (gap), a superscript (r) should be added to the grade.

There are however many other classification systems and there is a need for consensus on which system is better to implement and allow for comparison across studies. Overall, classification systems display a high intra- and interrater reliability when scored by experienced radiologists, but are limited to the variability for subcategories38,39 and thus with poor comparability. Moreover, there is still no classification system that is able to predict with confidence the prognosis and time to RTS after an HIS.39

7

7 HSI treatment

The main treatment goal of a HSI is to allow football players to RTS as fast as possible to the highest performance level and with minimal risk of reinjury. Although there is no consensus on an optimal approach to guide rehabilitation,40 there are some features that can aid the treatment planning. Identifying the underlying risk factors that may have predisposed the player for HSI will enable the clinician to better orientate to the most adequate approach to minimize the effect of modifiable risk factors. An accurate structural diagnosis is also cornerstone and should consider the type of injury (intramuscular, MTJ or intratendinous) and location (of specific affected muscle), which are fundamental to prognosis time of rehabilitation4 and establish a progressive and specific selection of exercise-based therapeutic plan. For example, injuries to the intramuscular tendon (particularly important in BF injuries) have prolonged rehabilitation and RTS times and should be treated differently to HSI.41 In these cases, as for total tendon ruptures or proximal avulsion, surgical treatment may be indicated.

Conservative treatment of HSI is mainly focused on exercised-based rehabilitation. The Askling L-protocol (Fig. 1) - ‘The Extender’, ‘The Diver’ and ‘The Glider’ – is a common approach and focus on lengthening of hamstrings myotendinous group while performing eccentric muscle actions. The Nordic and Russian hamstrings eccentric knee flexion exercises have shown better outcomes in RTS, but without influencing the recurrence rates.42 A multifactorial criteria-based algorithm that individualized to the player's needs is superior to general rehabilitation complemented with running-based program and L-protocol in decreasing the rate of new hamstrings injuries (4.2% vs. 25.0%).43 Progressive agility and trunk stability training has still limited evidence on the effect on reducing the re-injury rates.7,44 Currently, few comparative studies exist on conservative recovery from HSI, and so the existing body of evidence should be taken with a grain of salt.

Askling L-protocol: (a) ‘The Extender’, (b) ‘The Diver’ and (c) ‘The Glider’.
Fig. 1 Askling L-protocol: (a) ‘The Extender’, (b) ‘The Diver’ and (c) ‘The Glider’.

Both corticosteroids injections and oral non-steroidal anti-inflammatory drugs (NSAIDs) are not recommended as they may alter muscle healing process and have no relevant efficacy administrating pain.45,46 The use of platelet-rich plasma (PRP) injections has been used as a complementary treatment intervention aiming to accelerate muscle injury healing and accelerate recovery time and benefits for younger professional players with severe HSI,47 but there is lack of high-level evidence in literature regarding PRP treatments efficacy.40 Furthermore, there is still no consensus into the exact contents and dosages of PRP injections.

8

8 Return to sports

The decision to RTS after HSI must be a consensus multidisciplinary decision among all medical staff involved in the rehabilitation process, as well as coaching staff and players will to confidently reassume practice and play. This decision must rely on objective criteria.48–50-similar hamstrings flexibility and muscle strength, compared with preinjury level (when registered data available) or contralateral (uninjured) side (∼10–15%),-absence of pain on palpation and activities;-psychological readiness;-functional performance test, including position-specific, global positioning system (GPS) targeted, match-specific rehabilitation;-repeated sprint ability test;-single leg bridge;-deceleration drills;-equivalent strength endurance tests.

9

9 Prevention strategies

Several studies have attempted to evaluate hamstrings muscle strengthening, myotendinous stretching and playing warm-up protocols to mitigate risk of HSI. Despite the substantial research on the topic, the evidence of exercise-based prevention strategies for HSI is still limited.51 Eccentric strengthening and sprinting exercises are considered as pivotal for prevention programs.52,53 Both Askling and Nordic protocols of eccentric strengthening exercises significantly decreased HSI incidence, with strong scientific relevance through clinical trials and systematic reviews with meta-analysis.54–56 In addition, the FIFA 11 and 11+ warm-up programs are also evidenced to reduce HSI by almost a third during a team football season.53,57,58 However, the quality of the evidence has been questioned and also the optimal dose-response relationships are currently unknown.

Among athletes who have had HSI, ongoing athlete monitoring after returning to sports is cornerstone for secondary prevention of HSI recurrence.59 Although the increasing evidence on hamstrings injury prevention to reduce the risk of new acute hamstrings injuries in football (up to 59%),56 the implementation of the Nordic hamstrings exercise at the high-level European football is still low.60 The Nordic hamstrings exercise (Fig. 2) does not directly translate into the main mechanism of injury (high sprint running)61 and should thus be complemented with other potential preventive measures, such as high-speed running bouts,61,62 core stability training to decrease hamstrings stiffness63 and pelvic stability to reduce hip flexor tightness which leads to reciprocal inhibition of gluteus maximus and synergistic dominance of the hamstrings.64Furthermore, the evidence supporting such high levels of efficacy of the Nordic hamstrings exercise have been put to question by more rigorous data analysis.65

Nordic hamstrings exercise: (a) starting position, (b) eccentrically controlling descent with proper lumbopelvic control, and (c) final position with upper body close to the ground.
Fig. 2 Nordic hamstrings exercise: (a) starting position, (b) eccentrically controlling descent with proper lumbopelvic control, and (c) final position with upper body close to the ground.
10

10 Conclusion

Hamstrings injuries are a complex entity. Individualized evaluation of football athletes is fundamental to identify players at high-risk of injury and implementing up-to-date and evidence-based eccentric exercises and prevention programs. Global education of the football community is key to tackle the high incidence and recurrence of HSIs. Early accurate diagnosis and initiation of goal-based progressive and functional rehabilitation are of utmost importance, but there is no definitive consensus on the diagnosis methods and classification systems. Functional load management and match scheduling are part of continuous monitoring to keep the player safe and away from high risk of HSI reinjury. Implementing primary and secondary prevention strategies is crucial to tackle the high incidence of index and recurrent HSI.

Funding/sponsorship

None to disclose.

Authors contributions

All authors participated in the design and conception of this review. AGG wrote the initial draft, and RA and JA co-wrote the manuscript. All authors contributed to reviewing, editing and revising the manuscript, and approved the final submitted version.

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