Muscle injury classification systems for hamstring injuries have evolved to use anatomy and imaging information to aid management and prognosis. However, classification systems lack reliability and validity data and are not specific to individual hamstring muscles, potentially missing parameters vital for sport-specific and activity-specific decision making. A narrative evidence review was conducted followed by a modified Delphi study to build an international consensus on best-practice decision-making for the classification of hamstring injuries. This comprised a digital information gathering survey to a cohort of 46 international hamstring experts (sports medicine physicians, physiotherapists, surgeons, trainers and sports scientists) who were also invited to a face-to-face consensus group meeting in London . Fifteen of these expert clinicians attended to synthesise and refine statements around the management of hamstring injury. A second digital survey was sent to a wider group of 112 international experts. Acceptance was set at 70% agreement. Rounds 1 and 2 survey response rates were 35/46 (76%) and 99/112 (88.4%) of experts responding. Most commonly, experts used the British Athletics Muscle Injury Classification (BAMIC) (58%), Munich (12%) and Barcelona (6%) classification systems for hamstring injury. Issues identified to advance imaging classifications systems include: detailing individual hamstring muscles, establishing optimal use of imaging in diagnosis and classification, and testing the validity and reliability of classification systems. The most used hamstring injury classification system is the BAMIC. This consensus panel recommends hamstring injury classification systems evolve to integrate imaging and clinical parameters around: individual muscles, injury mechanism, sporting demand, functional criteria and patient-reported outcome measures. More research is needed on surgical referral and effectiveness criteria, and validity and reliability of classification systems to guide management.

Hamstring injuries (HSIs) are the most common athletic injury in running and pivoting sports, but despite large amounts of research, injury rates have not declined in the last 2 decades. HSI often recur and many areas are lacking evidence and guidance for optimal rehabilitation. This study aimed to develop an international expert consensus for the management of HSI. A modified Delphi methodology and consensus process was used with an international expert panel, involving two rounds of online questionnaires and an intermediate round involving a consensus meeting. The initial information gathering round questionnaire was sent to 46 international experts, which comprised open-ended questions covering decision-making domains in HSI. Thematic analysis of responses outlined key domains, which were evaluated by a smaller international subgroup (n=15), comprising clinical academic sports medicine physicians, physiotherapists and orthopaedic surgeons in a consensus meeting. After group discussion around each domain, a series of consensus statements were prepared, debated and refined. A round 2 questionnaire was sent to 112 international hamstring experts to vote on these statements and determine level of agreement. Consensus threshold was set a priori at 70%. Expert response rates were 35/46 (76%) (first round), 15/35 (attendees/invitees to meeting day) and 99/112 (88.2%) for final survey round. Statements on rehabilitation reaching consensus centred around: exercise selection and dosage (78.8%–96.3% agreement), impact of the kinetic chain (95%), criteria to progress exercise (73%–92.7%), running and sprinting (83%–100%) in rehabilitation and criteria for return to sport (RTS) (78.3%–98.3%). Benchmarks for flexibility (40%) and strength (66.1%) and adjuncts to rehabilitation (68.9%) did not reach agreement. This consensus panel recommends individualised rehabilitation based on the athlete, sporting demands, involved muscle(s) and injury type and severity (89.8%). Early-stage rehab should avoid high strain loads and rates. Loading is important but with less consensus on optimum progression and dosage. This panel recommends rehabilitation progress based on capacity and symptoms, with pain thresholds dependent on activity, except pain-free criteria supported for sprinting (85.5%). Experts focus on the demands and capacity required for match play when deciding the rehabilitation end goal and timing of RTS (89.8%). The expert panellists in this study followed evidence on aspects of rehabilitation after HSI, suggesting rehabilitation prescription should be individualised, but clarified areas where evidence was lacking. Additional research is required to determine the optimal load dose, timing and criteria for HSI rehabilitation and the monitoring and testing metrics to determine safe rapid progression in rehabilitation and safe RTS. Further research would benefit optimising: prescription of running and sprinting, the application of adjuncts in rehabilitation and treatment of kinetic chain HSI factors.

The key indications for surgical repair of hamstring injuries (HSIs) remain unclear in the literature due to a lack of high-level evidence and expert knowledge. The 2020 London International Hamstring Consensus meeting aimed to highlight clear surgical indications and to create a foundation for future research. A literature review was conducted followed by a modified Delphi process, with an international expert panel. Purposive sampling was used with two rounds of online questionnaires and an intermediate round involving a consensus meeting. The initial information gathering (round 1) questionnaire was sent to 46 international experts, which comprised open-ended questions covering decision-making domains in HSI. Thematic analysis of responses outlined key domains, which were evaluated by a smaller international subgroup (n=15) comprising clinical academic sports medicine physicians, physiotherapists and orthopaedic surgeons in a consensus meeting. After group discussion of each domain, a series of consensus statements were prepared, debated and refined. A round 2 questionnaire was sent to 112 international hamstring experts to vote on these statements and determine level of agreement. The consensus threshold was set a priori at 70% agreement. Rounds 1 and 2 survey respondents were 35/46 (76%) and 99/112 (88.4%), respectively. The consensus group agreed that the indications for operative intervention included: gapping at the zone of tendinous injury (87.2% agreement) and loss of tension (70.7%); symptomatic displaced bony avulsions (72.8%); and proximal free tendon injuries with functional compromise refractory to non-operative treatment (72.2%). Other important considerations for operative intervention included: the demands of the athlete/patient and the expected functional outcome (87.1%) based on the anatomy of the injury; the risk of functional loss/performance deficit with non-operative management (72.2%); and the capacity to restore anatomy and function (87.1%). Further research is needed to determine whether surgery can reduce the risk of reinjury as consensus was not reached within the whole group (48.2%) but was agreed by surgeons (70%) in the cohort. The consensus group did not support the use of corticosteroids or endoscopic surgery without further evidence. These guidelines will help standardise treatment of HSIs, specifically the indications and decision-making for surgical intervention.

Background: The multidisciplinary consensus panel included 14 International specialists on the management of hamstring injuries.

Introduction Hamstring injuries are a common problem in elite sport and particularly in men’s professional soccer, where the annual injury rate is rising by 2.3% a year (1,2). Garrett et al. (3) have previously argued that the musculotendinous junction (MTJ) is the most common site of muscle injury, and this has been reiterated in magnetic resonance imaging (MRI) review studies for hamstring injuries (4,5). However, recent improvements in MRI resolution and diagnostic reporting have led to advancements in muscle classification to better reflect the detail of a given injury (6). A key result of this is recognizing damage to the intramuscular (IM) tendon and understanding its potentially protracted effects on healing times (7). Each hamstring muscle has a central tendon running throughout its length as well as a proximal and distal free tendon (8,9). In footballers, the most commonly injured of these is the biceps femoris (10) during high-speed running where the structural failure at the muscle commonly causes disruption off this anchoring IM tendon. Having previously been likened to the central rachis of a feather (7) or the central support of a suspension bridge, injury to this central anchor itself and accurate diagnosis has been highlighted for importance by medical professionals within sport (11). Given the tendon tissue’s prolonged healing time in comparison to muscle tissue, perhaps due to its inferior blood supply (12), premature progression within rehabilitation could shed light on the high recurrence rates reported for hamstring injuries (13). Intramuscular tendons that have been significantly damaged have been observed radiologically to appear wavy, irregular, and in some cases, retracted (7,14). Perhaps this potential loss of tension within the tendon has performance implications for an athlete. Optimal tension within a tendon is pivotal for force production, so what on the surface may present like a normal hamstring strain could have limiting effects on an athlete’s ability to generate force and speed. Though adaptation through healing is possible, in recent years, surgical intervention has become more common in elite athletes with these high-grade injuries to restore the morphology and thus the tension of the tendon with a view to mitigating performance loss. Currently, the optimal management for significant IM tendon injury is unclear with comparisons to conservative management needing further investigation. Research has highlighted that acute spikes in training load above the chronic average can elevate the risk of injury in athletes (15). With regard to high-speed running, this can have particular implications for hamstring injury risk (16) given their key role in horizontal force production (17). Though optimal high-speed running dosage can be a useful hamstring prevention tool for sports medicine clinicians, under/overloading of the involved tissues can leave athletes ill-prepared for the demands of the sport (18). In this case study, we aim to discuss the rehabilitation of a surgically repaired biceps femoris IM hamstring injury in an English Premier League (EPL) soccer player. We highlight how an uncontrolled training drill 1 d before the injury potentially acted as an inciting event, leaving a player unusually fatigued and overexposed for that point in the training week. By deconstructing the mechanism of injury (MOI), we suggest using objective feedback and technology to safely accelerate progressions through to return to play (RTP) ahead of recommended surgical timeframes. Clinical Presentation, Diagnosis, and Surgery A 23-year-old left winger with no relevant history of previous lower-limb injury sustained a hamstring injury in a training session during a high-speed run after a recent spike in high-speed running volume (Fig. 1). On assessment, the injury presented as a high-grade II strain with a distinct loss of range (Fig. 2) and contractile power. This was later confirmed on MRI as a grade 3c injury (6) (Fig. 3) showing 90% disruption to the biceps femoris proximal IM tendon. After consultation with an orthopedic surgeon, the decision was made to manage the injury surgically rather than conservatively. This offered an enhanced chance of protecting the athlete’s key performance attributes, such as a high peak speed (9.8 m·s−1) and powerful acceleration. The IM tendon was surgically repaired, and because there was a thread of continuity remaining, the tendon was mobilized and reinforced with sutures along the IM tendons length until the tension was restored. Surgically improving the initial stability of the repair in this way may have positively influenced the rate at which rehabilitation could be progressed.Figure 1: Comparison of the athlete’s very high-speed and sprint volumes from previous training weeks including the week of injury. This highlights an acute spike in training load at week 23 in particular for sprint distance.Figure 2: Initial assessment of range of movement in a passive SLR and a hip and knee 90° passive knee extension test. SLR, straight leg raise.Figure 3: T2-weighted coronal image highlighting the wavy, retracted nature of the injured central tendon that has lost tension.Early Management (0 to 4 Wk) An injury timeline was created (Fig. 4) that would objectify progression, reflect the MOI, and target key performance attributes as well as challenge conventional surgical time frames. The early stages of rehabilitation were based on postoperative wound management and respecting tendon healing time frames. The player was transitioned through the weight-bearing status to normal gait. General low-level activation exercises were initiated 2 wk postsurgery with the initial focus on abdominal and adductor co-contractions. At 3 to 4 wk, early single leg isometric hamstring work commenced at varying ranges to apply load through the healing tendon as is essential for its structural integrity (19).Figure 4: The injury timeline used to not only guide the rehabilitation process incorporating surgical postoperative constraints but also allowing scope for symptom-based progression.Progressing the Demand on the Hamstring Through Key Treadmill Landmarks (4 to 6 Wk) When it was deemed a safe timeframe for tendon healing as the proliferation and remodeling phases began to overlap (20), the treadmill was used to objectively progress the eccentric demand on the hamstring. A pain free isometric contraction (5/5) and full range of movement was demonstrated on assessment. Then treadmill speeds were correlated to Global Positioning System (GPS) thresholds (m·s−1) used to quantify high-speed (4 to 5.5 m·s−1) and very high-speed runs (5.5 to 7 m·s−1). Following the rationale that the hamstring is a self-limiting muscle-tendon unit, we proposed that the increase in speed would only be tolerated if the integrity of the healing tissue is in a condition to not elicit a nociceptive response. Through this repeatable measure, a symptom led approach could be used to challenge the healing IM tendon to build the rate of force development (RFD) gradually. Consequently, normal movement patterns would be recruited to lessen likely neuromuscular inhibition (21) and a training volume would be maintained. The player was asked to complete repeated pain free/minor discomfort (VAS, 0 to 4) 2 km runs from walking pace until a speed of 14.4 kph (4.0 m·s−1) could be sustained throughout. The player then repeated 1 km runs until a speed of 16.5 kph (4.5 m·s−1) was sustained safely and finally, 30 s on 30 s off runs at 18 kph (5 m·s−1) and 19.4 (5.5 m·s−1). These speed zones account for safe transition to outdoor rehabilitation, where force generation comes at a greater mechanical demand (22). The progressions and corresponding heart rate responses can be found in Figure 5.Figure 5: A graph highlighting the progressive treadmill sessions completed and their associated heart rate responses. The gradual drop in heart rate response at each speed zone represents the athletes’ improved ability to cope with the metabolic demand.Early Eccentric Integration Through Band Assisted Nordic Falls (4 to 7 Wk) Increased eccentric strength has been highlighted as a protective mechanism for hamstring injury (23) and an effective mode of eliciting architectural adaptation in the biceps femoris (24). While the Nordic fall is an efficient way of providing an eccentric stimulus (25), it is a largely maximal exercise that is difficult to perform through range early in rehab with a compromised tendon. We hypothesized that integration of eccentric exercises early in the healing process would complement the eccentric demand of the running protocol. To modify this, we used a Nordbord to objectify eccentric strength and used elastic training bands to alleviate bodyweight (Fig. 6) and allow full range of this exercise at an earlier stage than would previously be possible. Through gradually reducing the quantity and strength of the bands in the absence of symptoms, we could objectively track for force increments safely through to the free bodyweight exercise providing eccentric stimuli to the hamstring in an accelerated fashion (Fig. 7).Figure 6: The use of the Nordbord to objectify force in Newton’s bilaterally throughout a Nordic fall. The elastic strength band rigged to a frame reduces total body weight/force exposure to the tendon, allowing for it to be progressed gradually.Figure 7: A graph illustrating improvements in force development/force exposure to the hamstrings through band-assisted Nordic fall progressions.Objectifying High-speed Running Drills With GPS for Outdoor Rehabilitation (7 to 9 Wk) The aim of the outdoor rehabilitation was to continue the gradual speed and RFD increases through to >90% of the preinjury peak speed recorded (9.8 m·s−1). This was deemed an acceptable figure for RTP. To safely progress speeds already cleared on the treadmill, GPS was used to quantify outdoor rehabilitation sessions, providing feedback of running volumes and peak speeds to ensure a graduated return to the MOI. Using a high-speed drill called a “runway” comprised of an acceleration phase (20 m), speed maintenance phase (20 m) and deceleration phase (20 m), the player gradually increased subjective effort levels with an objective output (m·s−1). This was sustained until a symptom-free buildup to maximal velocity sprinting was achieved over a number of sessions (Fig. 8). The demand to generate peak speed was then challenged further by reducing the distance of the acceleration and deceleration phases, forcing the athlete to ramp up the RFD in the muscle (Fig. 9). This drill was then used as an optional top up within the training week to ensure high-speed exposure in the continually remodeling tendon was maintained after RTP.Figure 8: The GPS feedback on peak speed achieved in each outdoor rehabilitation session. Incorporated within each session is a graduated return to >90% preinjury speed used as a safe return to play figure.Figure 9: The high-speed running drill progressions throughout the rehabilitation. After progressing through to maximal velocity in run A), the progressions below are used to challenge the athlete to generate similar speeds over a shorter distance.Conclusions This case study followed the rehabilitation of a surgically repaired biceps femoris IM tendon. It outlines how safe passage to successful RTP can be accelerated through objectified, symptom led approaches to speed development and eccentric strength progression.

Headline Hamstring injuries remain a major burden in sport (1) despite enormous research efforts and the development of apparently effective prevention (2,3) and rehabilitation practices.(4) Interventions that work in amateur and lower levels of professional sport may not be fully implemented in the more crowded training and playing schedules of elite sport (5) and perhaps they work only in less fit athletes or their benefits are ‘drowned out’ by other training methods? We suggest that belief systems and philosophies shared widely by expert coaches also reduce adoption of some evidence-based practices. van Hooren and Bosch recently argued that isometric conditioning may be more effective at reducing hamstring injuries and more readily programmed into busy competition schedules than eccentric exercise.(6, 7) Here, we critique these arguments and offer some insights into an eccentric strength and sprint-oriented injury prevention program that has been employed to good effect in the English Premier League. We do not claim that anecdotal evidence is in any way definitive. Nor do we claim that isometric training doesn’t work or that eccentric hamstring conditioning is the only effective means of prevention. Instead we argue that recommendations to employ an isometric approach instead of an eccentric one are premature.