PhD Pinboard: Rethinking Return to Play Criteria After Hamstring Injury
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This PhD Pinboard article by Paolo Perna explores how staff can better structure hamstring injury RTP decisions using a multi-phase, criteria-driven approach rooted in clinical, strength, and performance domains.
I’m Paolo Perna. I currently work as a Physiotherapist in Professional Academy football, which I combine with my PhD at the University of Suffolk.
My research topic is around the Return-to-Play (RTP) stage of rehabilitation. The rehabilitation process is a phased progression to bridge the gap between the loss of function due to the injury and the return to performing at the pre-injury level.
I have always seen my applied role as a mix of these two components: the medical knowledge, which drives what we do in the early phases of rehabilitation, and the performance knowledge, which supports the transition to more sport-specific reconditioning aspects of the rehabilitation.
Why does this research matter?
Epidemiology studies suggest around eight hamstring injuries in a team season, representing 24% of all injuries sustained (1). These injuries have a high re-injury rate. In male professional football, it is around 18% (1), although some studies have reported higher rates of over 50% (2).
If almost one in every five hamstring injuries in professional football ends up with a re-injury, the pressure around the decision becomes higher. All these aspects contribute to the increasing interest from researchers and practitioners in understanding hamstring injury rehabilitation and optimising how we return players to play football.
Therefore, given the prevalence of the topic, challenges I had throughout my career, and my personal interest in the RTP process, I decided to focus my research on hamstring rehabilitation. In particular, I am interested in understanding how we can inform our decision-making by collecting the right and most appropriate information and building a robust battery of criteria.
RTP is based on a stage-by-stage progression starting with a rehabilitation and gym-based preparation phase, followed by an on-field and sport-specific phase, and a performance phase (3). While the initial phases have a prevalent medical component, the late stages need a higher focus on performance. Due to the complexity and broad knowledge required to support the athlete throughout the journey, the topic is interesting from both a medical and performance point of view.
As a medical and performance team, we have to make a decision and suggest an appropriate reintroduction into unrestricted team training and playing match minutes. These decisions are not easy, especially when talking about hamstring injuries. Also, as mentioned before, the RTP process follows several phases and we have to think about the criteria we will use to inform progression between stages.
Key Findings
The first thing we did to start the PhD journey was to complete a literature search to find what criteria are available in professional football (4). The aims were to describe the criteria reported in published research and objectively predict lay-off time, and to assist practitioners with formulating a RTP plan at the time of the injury.
Due to the wide variety of RTP strategies found, we proposed grouping the criteria into three broad categories: clinical, strength, and performance (Table 1).
Clinical RTP Criteria
Clinical criteria were the most widely used. The absence of pain was the most often reported criterion. A variety of measures were described: palpation, flexibility, and strength tests, or functional tasks such as running drills.
Flexibility was a recurring theme, with experts agreeing that a 0–10% difference between legs was acceptable, though the best way to measure this remains unclear. Some modalities, such as the Askling-H test, were discussed by the expert of a Delphi study (5), but there was no agreement despite the wide use of this test in the real world.
The use of imaging in RTP was also present. There are two ways we can look at this: imaging to inform RTP decisions and predict the length of the rehabilitation. Magnetic Resonance Imaging (MRI) was the most commonly described way to assess injury healing, with ultrasound also being described in a case study (6).
Beyond physical factors, psychological readiness was consistently highlighted. Players' subjective confidence, fear of reinjury, and motivation were all seen as vital, although there are currently no validated tools to measure this in elite football (to our knowledge). Clearance by medical staff, and in some cases, the operating surgeon’s opinion, was also essential.
Strength RTP Criteria
Strength criteria were also often described. While most agreed that some form of objective strength testing was necessary, there was no consensus on specific tests and thresholds. The idea of looking for symmetrical strength scores is widely utilised in football for performance and rehabilitation, but the specific percentage of difference relevant for criteria progression is not present in the literature. The Nordic hamstring test, isometric strength measures, and isokinetic testing were all mentioned in our scoping review.
A plethora of research supports the importance of eccentric strength training during hamstring injury rehabilitation and injury prevention. Despite the role of eccentric strength, there is limited and conflicting evidence regarding the use of eccentric strength measures as a RTP criterion:
Moreno-Pérez et al. (2020) suggested using the Nordic hamstring test in the late stages of rehabilitation (7).
Tol et al. (2014) used an isokinetic eccentric muscle test as RTP criterion, but the majority of the players tested (67%) had a significant strength deficit at the moment of RTP (8).
In contrast, van der Horst et al. (2017) found the use of eccentric strength did not reach a consensus as a RTP criterion amongst the experts (9).
Performance RTP Criteria
Performance criteria looked at a player’s ability to tolerate football-specific movement and load. A combination of performance measures were described. From field-based testing, such as the Repeated Sprint Ability test, to the use of Global Positioning System (GPS) metrics to guide load progression and the completion of sport-specific skills.
Taberner et al. (2022) used the “control-chaos” framework to progress training load (6). This framework gradually increases the unpredictability and intensity of the rehab drills and the volume and intensity of training.
Other studies relied on achieving GPS metrics like maximal sprinting, deceleration, and achieving position-specific loads. Although there is a clear need to quantify performance indicators, precise thresholds are rarely reported, and there is no consensus on how to progress training exposure.
Quality of Research
One of the most striking findings delving into the world of RTP criteria following a hamstring injury is the overall lack of high-quality research specific to professional football. Many studies relied on surveys, expert panels, or case studies. This lack of rigorous research means current RTP criteria are often based on expert opinion rather than validated evidence. This is very common when the topic is relatively new and there is limited research published. The researchers, to find out more and understand what is done in practice, ask the practitioners about their opinion and what they are currently doing. This gives useful information on where we are and what we are doing to face the problem, but it should also push the research towards finding those answers.
This work has opened the road to more questions and ideas for continuing research throughout the PhD. Future work will address how to differentiate criteria between the different phases of the RTP, the impact of the type of hamstring injury on the criteria selection, and the validation of new methods to assess readiness for RTP.
How can we apply these findings in practice?
While it would be ideal to provide simple protocols, the perfect criterion and the perfect combination of tests do not exist. Based on our knowledge and clinical reasoning, we can approach this problem and try to find solutions.
There is a plethora of tests and things that we can check to assess the readiness to RTP. We have to think about the three categories of tests and decide which tests we will use for each. Use clinical criteria to guide our medical decisions, assess the healing process, subjectively test readiness, and confidence. Use strength criteria to assess capacity and muscle function. Finally, do not forget the understanding of the performance aspect of RTP and the tests to assess those qualities.
Multidisciplinary collaboration is crucial. Medical staff, strength coaches, and technical staff must share information and make collective decisions. Everyone involved has a different set of competencies and should contribute by informing the group on their area of expertise. All the information should be analysed together to finalise a decision and reach a consensus.
Context is an essential determinant of decision-making. Despite the individual and player-specific case, having a robust battery of RTP criteria helps support the decisions and present objective reasons why the advice on RTP has been given.
Final Reflections
Returning to play after a hamstring injury in professional football is a high-stakes, high-pressure process with no universally accepted roadmap. My work highlights the diversity in RTP approaches and the urgent need for more robust, football-specific research. In the meantime, blending clinical judgment with objective measures and team-based decision-making seems to be the most effective strategy. There is still a lot of work that can be done.
The RTP process has many phases, and we should use exit criteria to decide when to progress to the next phase. Also, we should be more specific in the way we decide which criteria we want to use. There are several factors we could consider and that could make us think more deeply about the characteristics of each injury and how we could tailor the criteria to the injury we are dealing with (Figure 1).
Research has focused mainly on the last decision before RTP, but we know other important milestones need to be achieved before returning to match minutes. The questions around how we make decisions and what criteria should be used throughout the journey are yet to be answered.
Frequently Asked Questions (FAQs)
What is the prevalence of hamstring injuries in men's professional football?
Hamstring injuries are the most frequently reported injury in professional male football. They account for 24% of all injuries and each team could expect around 8 injuries during a season. Hamstring injuries are often discussed because of their high re-injury rate, which is around 18% in male professional football (1).
What makes the Return to Play process so complex?
Return to Play (RTP) incorporates many different phases and demands, from accurately diagnosing the injury to managing training load on the pitch. A wide variety of skills and expertise is needed to safely return a player to a pre-injury level (or higher). This complexity needs a multidisciplinary approach, where practitioners with different expertise contribute and offer support to the final decision. There is also little high-quality research on RTP in professional football players.
I am planning the RTP for a footballer following a hamstring injury. Where do I start?
The first thing is to have an accurate diagnosis and understanding of the injury characteristics. The second step is to map out the phases of rehabilitation, considering the end goal. I suggest starting from the end and working backwards to define the milestones to complete before RTP.
Once the stages and the milestones are clear, it is time to focus on the criteria to determine if the player is ready to move to the next stage and is finally ready to return to match minutes. When selecting the RTP criteria, follow our suggestion of clinical, strength and performance to avoid missing any critical information.
References
1. Ekstrand J, Bengtsson H, Waldén M, Davison M, Khan KM, Hägglund M. Hamstring injury rates have increased during recent seasons and now constitute 24% of all injuries in men’s professional football: the UEFA Elite Club Injury Study from 2001/02 to 2021/22. Br J Sports Med. 2023;57(5):292-298. doi:10.1136/bjsports-2021-105407
2. Entwisle T, Ling Y, Splatt A, Brukner P, Connell D. Distal Musculotendinous T Junction Injuries of the Biceps Femoris: An MRI Case Review. Orthop J Sports Med. 2017;5(7):232596711771499. doi:10.1177/2325967117714998
3. Buckthorpe M, Della Villa F, Della Villa S, Roi GS. On-field Rehabilitation Part 1: 4 Pillars of High-Quality On-field Rehabilitation Are Restoring Movement Quality, Physical Conditioning, Restoring Sport-Specific Skills, and Progressively Developing Chronic Training Load. J Orthop Sports Phys Ther. 2019;49(8):565-569. doi:10.2519/jospt.2019.8954
4. Perna P, Kerin F, Greig N, Beato M. Return-to-play criteria following a hamstring injury in professional football: a scoping review. Research in Sports Med. 2024;33(2):175-194. https://doi.org/10.1080/15438627.2024.2439274
5. Zambaldi M, Beasley I, Rushton A. Return to play criteria after hamstring muscle injury in professional football: a Delphi consensus study. Br J Sports Med. 2017;51(16):1221-1226. doi:10.1136/bjsports-2016-097131
6. Taberner M, O’keefe J, Dunn A, Cohen DD. Return to sport and beyond following intramuscular tendon hamstring injury: A case report of an English Premier League football player. Phys Ther Sport. 2022;56:38-47. doi:10.1016/j.ptsp.2022.05.013
7. Moreno-Pérez V, Méndez-Villanueva A, Soler A, Del Coso J, Courel-Ibáñez J. No relationship between the nordic hamstring and two different isometric strength tests to assess hamstring muscle strength in professional soccer players. Phys Ther Sport. 2020;46:97-103. doi:10.1016/j.ptsp.2020.08.009
8. Tol JL, Hamilton B, Eirale C, Muxart P, Jacobsen P, Whiteley R. At return to play following hamstring injury the majority of professional football players have residual isokinetic deficits. Br J Sports Med. 2014;48(18):1364-1369. doi:10.1136/bjsports-2013-093016
9. van der Horst N, Backx F, Goedhart EA, Huisstede BM. Return to play after hamstring injuries in football (soccer): a worldwide Delphi procedure regarding definition, medical criteria and decision-making. Br J Sports Med. 2017;51(22):1583-1591. doi:10.1136/bjsports-2016-097206
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