Abstract
Injuries in male professional football present a multi-faceted and complex challenge for practitioners with significant consequences across performance, psychosocial and financial domains. Medical and performance staff encounter considerable pressure to maximise player availability and advance rehabilitation timeframes, whilst minimising the risk of subsequent injury. Decisions involving increased risk promise, potentially, higher rewards and may significantly influence a player's career and team performance. Therefore, it is crucial that rehabilitation and return to play (RTP) procedures are evidence-informed and strategically designed to mitigate subsequent injury risk. Due to the complex nature of injuries, and the multidisciplinary approach required during the rehabilitation process, a wide range of knowledge and skills are essential to inform a shared decision-making process and successful RTP. To support the understanding of the competencies required, this narrative review gives an overview of existing aetiological models, decision-making frameworks and RTP approaches within the current literature. The current role of criteria-based progressions in rehabilitation frameworks are evaluated and potential future research, that could improve rehabilitation procedures and inform better RTP decision-making and post-RTP care in the professional football environment, is highlighted.
Introduction
The implications of injury within professional football are multi-faceted, complex and can have significant performance, psychosocial, and financial implications.1,2 Significant pressure is placed upon medical and performance departments to maximise player availability and accelerate rehabilitation. Usually, riskier options promise higher returns and the decision to progress or delay a player's return to play (RTP) may have a significant impact on a player's career and a team's future performances. 3 Therefore, it is vital that the support given to a player during rehabilitation, and the RTP process, is well informed, timely and minimises the risk of subsequent injury. This dilemma challenges the practitioner to balance multiple processes, influential contextual factors and specific individual needs, by blending ‘art’ and ‘science’ through effectively applying current research into practice. 4
Several studies have been conducted globally on injury epidemiology in male professional football.5–13 Reportedly, teams competing at the highest level in Europe typically suffer 50 injuries per season. 5 Injury incidence studies across male professional football reports ranges between 6.5–9.1/1000hours5–12,14 with injury incidence rates similar between professional leagues and countries. 10 The variation in reported overall incidence may be due to studies reporting single season estimates 9 compared to others using inter-seasonal differences.5,7,8,11 Inter-seasonal changes give important information on injury trends and are critical in the development of injury prevention strategies. 11 Furthermore, dense fixture schedules, alongside the increasing physical and psychological demands of the game,15–17 add complexity to the rehabilitation process, to ensure a player is fully prepared for RTP.
Match injuries have a higher incidence (20.9–58/1000 h), compared to training (2.8–6.8/1000 h).5,8–12 Lower extremity injury incidence was most frequent (6.8/1000 h), with muscle and tendon injuries the most frequent type (4.6/1000 h). 10 It is important to consider the severity of injury and associated time-loss. Severe injuries (>28 days lost) accounted for between 15–23% of injuries sustained with moderate injuries (8–28 days lost) between 33–47%.5,8–11 On average, each player misses 37 days per season meaning approximately 12% of the season is lost due to severe injury, 5 with the most severe injuries resulting in longer rehabilitation periods and potential threats to player's careers. 18
Injury severity can strongly impact the physical and psychosocial characteristics of the player demonstrating the need for a holistic approach to rehabilitation.19,20 High severity of injury can negatively affect individual player performance, across mental, physical and technical domains18,21,22 with injury burden known to negatively affect team performance and results.1,2 Reportedly, lower injury incidence was correlated with higher league position, more games won, more goals scored and greater total points. 2 Consequently, this has the potential to influence job security of the head coach, with the average tenure reported to be less than 16 months, 23 or the surrounding multidisciplinary team (MDT). 24 The financial implications are significant. For English Premier League teams, an average cost of approximately £45 million per season per team 25 has been reported, in Australian football costs range between AUD$ 187,990 to 332,680 annually, 26 for a Brazilian club hamstring injuries alone reportedly caused a potential loss of $43.2 million USD in a single season 27 and the cost of muscle injuries, for Spanish First Division teams, equates to a total monthly cost of €7.3 million. 26 This provides professional football clubs with a strong economic incentive to invest and improve injury prevention and rehabilitation processes.
An index injury is defined as the first injury to occur or any subsequent injury that is clinically unrelated to the previous injury. 28 Reinjury is defined as “an injury of the same type and at the same site as an index injury and which occurs after a player's return to full participation”. 25 Incidence of reinjury is relatively low (1.3/1000 h), however, they reportedly account for 6.1–18.8% of injuries.5,10,29 High recurrence rates have been reported for hamstring (12–43%), groin injuries (31–50%), knee sprains (30–40%) and lateral ankle sprains (17%).6,7,14,30 These findings demonstrate that some reinjuries are higher risk, however, could be attributable to inadequate rehabilitation or premature RTP. 14 Most identified studies recognise the longer timeframe of rehabilitating a reinjury causing a higher burden than initial injuries.5,8–11,31 Further considerations are the increased time loss suffered and the psychological impact, including player mental health, faith in the rehabilitation process and the trust between player and practitioner. 32 Reinjury anxiety had been identified as a mediating factor in psychological readiness to return.33–35 Therefore, the process from initial injury assessment to final return to performance (RTPerf) is crucial to promote a reduction in subsequent injury and to maintain player performance.
Epidemiological data emphasises the importance of effective injury rehabilitation programming, informed through a multidisciplinary approach,19,36,37 and the need for evidence informed return to training (RTT) and RTP protocols.5–11 Several rehabilitation and RTP frameworks have been developed in male professional football including the “control-chaos continuum”,38–40 a five stage on-field program 41 and a criteria-based return to performance pathway. 42 To continually improve and inform rehabilitation procedures, and RTP decision-making, further development and understanding of objective criteria is vital to minimise the risk of further injury. The factors described provide a clear rationale for the continued advancement of injury prevention and rehabilitation strategies 39 to ensure player reintegration post-injury is optimised and reinjury risk minimised.
The aim of this narrative review is to give an overview of aetiological models, decision-making frameworks and return to sport (RTS) approaches reported within the current literature. The role of criteria-based progressions in rehabilitation frameworks, and their application within male professional football, are evaluated through the identification of potential future research, that could improve rehabilitation procedures and inform better RTP decision-making and post-RTP care. Common phrases used to describe the ‘return’ of a player during different phases of rehabilitation in football are defined in Table 1 and used within the subsequent sections of this review.
Descriptions of different phases of ‘return’ of a player during different phases of the rehabilitation process.
Aetiological models
An understanding of injury prevention and aetiological models can assist practitioners in discussing possible causes of injury whilst appreciating the complex nature of the event. A mechanism of injury refers to the method by which damage or trauma occurs, and can be defined as the process of considering the forces involved in an injury-causing event. 45 Injuries in sport are related to some form of overload, either involving direct trauma, mechanical failure through ‘stress’ or ‘strain’ or a combination of both. 46 When the ‘stress’ (i.e., the internal forces experienced by a structure defined as force per unit of area) and/or ‘strain’ (i.e., the amount of deformation or length change in the direction of the applied force) 46 exceeds the maximal strength or failure strain capacity of a particular tissue type, this results in injury.46–48 Traditional injury prevention models have been reductionist in an attempt to simplify multifaceted components, to identify relationships or a sequence of events, but fail to acknowledge injuries involve complex interactions between numerous factors. 49 Aetiological models have cited the interaction between both intrinsic and extrinsic factors such as age, injury history, neural inhibition, fascicle length alteration, strength deficiencies, neuromuscular fatigue, movement efficiency, training load and competition schedule amongst others.50,51 Therefore a multidisciplinary, holistic approach is vital to accommodate the complex and individual nature of injury and rehabilitation. 49 An overview of the development of aetiological models is presented in Table 2.
An overview of the development of aetiological models.
Legend: BMSAIH, Biopsychosocial Model of Stress and Athletic Injury and Health; CLD, Causal Loop Modelling; TIP, Team-sport Injury Prevention Cycle; TRIPP, Translating Research into Injury Prevention Practice framework.
Reviewing, understanding and applying aetiological models, can help practitioners to build injury mitigation strategies,50,71 analyse load/response75,76 and inform RTP with the aim of reducing injury risk. It is important to acknowledge the dynamic, recursive and complex nature of interacting internal (e.g., age, sex, physical fitness, psychological factors) and external (e.g., sports rules, environment) risk factors alongside the situational patterns and mechanisms that can lead to injury. 65 Furthermore, contextual factors, such as team dynamics, coaching philosophy, game model, positional switching, season phase and fixture congestion may impact injury occurrence and rehabilitation processes. 77 For example, studies have shown, during congested fixture schedules, overall injury incidence to increase from 15.6 to 33.7 per 1000 h and match injury incidence from 44.8 to 50.3 per 1000 h. 78 The application of aetiological models into injury prevention frameworks 71 is, therefore, an important consideration for practitioners to understand. It is also important to acknowledge the concept of quaternary prevention 79 and integrate this into prevention programming and contemporary prevention models. Quaternary prevention aims to protect athletes from interventions that may cause more harm than good, e.g., overdiagnosis (identifying problems that were never going to cause harm), overtreatment (providing unnecessary medical interventions), and overmedication (prescribing too much or unnecessary medication). 79 Furthermore, it is proposed that rehabilitation programming should implement the principles of quaternary prevention to protect athletes from excessive interventions and use reliable, validated tools and testing protocols to accurately evaluate and help make informed RTP decisions. 79 Future research into injury associations and causal pathways, acknowledging the complex nature of injury, can further inform the progression of these models, and their role within injury prevention frameworks.
Decision-Making and multidisciplinary approaches to return to play procedures
Given the dynamic, recursive nature of injuries, the multiple stakeholders involved, and the financial implications within the rehabilitation process, debate around who is responsible in making the final RTP decision and how that decision is made within a complex environment remains a contemporary topic. Traditionally, medical practitioners have been accountable for injury records within clubs, however, evidence suggests an association with head coach leadership styles and the quality of internal communication.32,80–83 Other important factors include the growing influence and size of medical and performance departments, 24 the dynamics of the performance structure, sharing individual expertise, psychologically safe environments, clearly defining problems and applying solutions, the need for fast, intuitive decision-making and the quality of internal communication within the MDT and across departments.83–85 Therefore, it is important that practitioners develop an understanding of decision-making frameworks, the importance of multidisciplinary approaches and have clear communication procedures to create an informed, shared decision-making process and develop purposeful application of critical thinking skills. 83 Table 3 presents an overview of decision-making frameworks that are applicable in a sporting environment to guide the RTP decision-making process.
An overview of decision-making frameworks that can be used to guide return to play decision-making processes.
Legend: AI, Artificial intelligence; RTP, return to play; StARRT, Strategic Assessment of Risk and Risk Tolerance.
Ardern et al. 86 state that, ideally, decisions are guided by accepted clinical criteria, however, many have little empirical evidence and there is a lack of agreement on the best criteria. It was proposed, a logical step would be a consensus statement on RTS and to ascertain agreement in key areas.43,86 The consensus statement on RTS presented by Ardern at al. 43 is divided into 4 main sections: 1) definitions related to RTS, 2) models to guide RTS, 3) evidence to inform decision-making and 4) future research. A key concept highlighted is advocating an athlete-centred approach, placing them in the position of active decision-maker, alongside other relevant stakeholders, as part of a shared decision-making process.43,87 The authors cited three models to guide the RTS process: 1) the StARRT framework, 88 2) the biopsychosocial model 20 and 3) optimal loading. 89 The authors state that load progression is key and maintaining ‘optimal’ loading, by gradually increasing workload and avoiding ‘spikes’, 90 are important clinical considerations. 43 The importance of biological, psychological and social factors influencing decision-making are presented and the role of ‘load’ in rehabilitation and post-RTS were defined. 43 The lack of consensus and scientific evidence for RTS criteria for the majority of sport injuries is highlighted and a future priority was identified to address the identification of positive and negative predictive (or prognostic) factors for RTS outcomes. 43
Shared decision-making
Dijkstra et al. 92 acknowledged multiple individuals are involved in the decision-making process, and including the athlete in the process fulfils psychosocial needs and supports an athlete-centred approach. 95 The fluid nature of decision-making is acknowledged, however, only three stakeholders (healthcare professional, athlete and coach) are highlighted. Within the context of professional football, medical and performance departments, the player, technical coaches and directors are also involved. 96 Furthermore, with significant quantities of subjective and objective data available, and influential contextual factors (e.g., player status, match importance), informing RTT and RTP decision-making a flexible structure may be required. Developing a flexible structure, specific to each unique club environment, allows practitioners to incorporate different individual experiences and skillsets, be guided by subjective and objective data and consider the context of the decision to allow an informed, shared approach.
Within professional football RTP practices have been investigated and the translation of research into practice has been highlighted to enhance the process. 97 It was reported that a shared decision-making process was used by 80% of teams although there was a lack of agreement in the level of involvement across phases by different practitioners. 97 This could be accounted for by potential bias, however, the inconsistency found in the composition raises some potential concerns about the specific dynamics of the communication among staff. 97 Shared decision-making was demonstrated across the phases of rehabilitation with different weighting of importance given as rehabilitation progressed, however, challenges were acknowledged relating to team hierarchy, particularly as players returned to matches. 97 This demonstrates a positive use of shared decision-making in football, however, further research into MDT dynamics has demonstrated uncertainty around who makes decisions and how they are made can be an issue. 84 Additionally, department growth, resulting in more lines of communication, and modernising methods of communication (i.e., mobile phones, email, social media rather than face to face conversations) 24 further complicate the shared decision-making process. With leadership styles and communication potentially impacting injury,80–82 clearer processes, communication pathways and RTP decision strategies are evidently important and required. 83
Criterion-Based decision-making
Whilst respecting biological healing timeframes, a paradigm shift towards criterion-based approach to RTS is evident and studies have shown a reduction in reinjury rates when individuals have passed objective criteria before RTS. 98 It is evident that practitioners are utilising evidence-based research and testing procedures throughout the rehabilitation process, informing decisions and adapting decision-making frameworks, although further research is required into RTP criteria in practice.43,99 There is consensus for criteria-based RTP factors that a range of clinical, physical, functional and psychological measures should be used.43,100 These influence and inform decision-making, and several studies have investigated their use and role within injury, rehabilitation and decision-making frameworks.43,97–104 In a survey by Dunlop et al., 97 the use of criteria-based evaluations and clinical criteria were reported during early phases, with sport-specific functional criteria (e.g., acceleration/deceleration, maximal sprints) assessed across all phases and a greater focus placed on psychological readiness in the latter stages. Despite the translation into practice no information was given to advance knowledge on specific metrics or thresholds to be used within the professional football environment.
The development of injury specific criteria is important.43,100,104,105 With particular reference to hamstring injuries in professional football five core domains were identified as part of criteria-based rehabilitation progression presented by Zambaldi et al.: 104 1) functional performance, 2) strength, 3) flexibility, 4) pain and 5) player's confidence. Following this a RTS continuum was proposed for professional athletes in which measures of progression should be tested to progress through six categories: 1) movement and core, 2) strength and endurance, 3) power, 4) general and sport conditioning, 5) load performance testing and 6) self-reported outcome. 98 Criteria-based progressions assist practitioners in being transparent in the decision-making process, however, sporting environments are complex adaptive systems extending into injury and rehabilitation protocols whereby contextual factors play an important role in the development of effective RTS frameworks.
The complex and multifactorial nature of RTS decisions provides a significant challenge to practitioners with potential impacts on the athlete's well-being and performance, and the overarching performance of the team. With multiple stakeholders involved it is important to have a clear shared decision-making process with players and coaches active in the process. This may allow for important balance between intuitive and analytical processes, therefore, practitioners are encouraged to adopt models that suit the context and environment to enhance the quality of decision-making. 106 The development of artificial intelligence (AI), data driven algorithms and machine learning techniques, to inform clinical decision-making, is a prominent, and evolving, area of interest in sports medicine. Machine learning models, such as decision trees, Markov processes and neural networks, analyse multidimensional data to identify subtle patterns and potential signs of injury risk and tracking algorithms provide information on body movements in real-time allowing the identification of biomechanical inefficiencies 107 which may prove crucial as part of the rehabilitation process. Due to methodological limitations and high risk of bias, current models cannot be recommended to be used in practice,108–110 however, once these limitations have been addressed, machine learning could provide enhanced systematic analysis that could provide future solutions to the training load/injury paradox.110–112 Further advancement of the evidence base supporting injury prediction models, RTS and rehabilitation protocols, may improve the ability of practitioners to make high quality, evidence informed decisions to manage training load and reduce injury-risk.
Return to sport models and on-field rehabilitation
It is widely accepted the use of competency-based criteria is vital in progressing through different phases of rehabilitation and several factors, such as muscle strength, psychological readiness, sport specific load and cardiovascular fitness, contribute to an athlete's readiness for RTS.19,30,38,42,43,98–100,102,104,105,113–115 The traditional notion that RTS is a single decision at a point in time has developed into the concept of an evolving continuum supporting the athlete from the onset of injury to full RTP, whilst mitigating the risk of further injury.42,98,113 The identified multidisciplinary input throughout the process can result in differing timeframes and objective criteria being recommended depending on the practitioner's specialist area87,99 increasing the relevance of having a reliable shared decision-making process in place.
Return to sport clearance Continuum (Draovitch et al., 2022)
To foster efficient progression, Draovitch et al., 98 proposed a ‘Return to Sport Clearance Continuum’ (RTSCC). This continuum consists of 5 sequential phases comprising: 1) repair phase (to minimise swelling, increase range of motion and develop muscle activation), 2) rehabilitation and recovery phase (restoring normal arthrokinematics), 3) reconditioning phase (focusing on skill and force development and load-volume tolerance), 4) performance phase (transition to full training), and 5) preseason/training camp phase (to be properly managed for an upcoming season). 98 The RTSCC states training load should be monitored throughout, to avoid overloading tissues, and testing criteria is suggested to ensure objective progress through the phases. 98 The scope of practice for staff involved at each phase is not considered as part of the continuum, despite the different skills required. Specialised personnel and team work between the medical and performance departments is important, 19 yet the specific involvement is often unclear. 97 The RTSCC provided a general framework for RTS processes and decision-making to be developed, although more detail of practitioner responsibilities may be useful to develop an understanding of the specialist skills and knowledge required throughout different phases of rehabilitation.
The return to performance pathway (Mitchell and Gimpel, 2024)
A football specific framework has been initially proposed by Mitchell et al. 113 and developed by Mitchell and Gimpel. 42 The ‘Return to Performance Pathway’ includes eleven phases from a diagnosis and planning phase, into an acute phase and then progression through multiple gym and grass phases. A key component of the pathway is the objective exit criteria for each phase in an attempt to ensure safe progression. 42 Mitchell and Gimpel's 42 framework demonstrates the importance of a progressive multistage rehabilitation process and has adapted previous frameworks for the end-stage rehabilitation phases known as on-field rehabilitation (OFR).38,41,42,116 The RTPerf Pathway framework 42 provides a comprehensive overview of the rehabilitation process by introducing acute and gym phases prior to starting OFR, whereas previous frameworks had focused primarily on OFR.38,41,116–119 These final phases are highlighted as being important to prepare the athlete for re-entry into sport and where the overlap between rehabilitation and RTS processes occurs. This overlap requires specialised personnel, and teamwork between the medical, performance and coaching departments, to transition the athlete and bridge the gap between rehabilitation and sports specific training.19,36 OFR represents these final phases as the athlete needs to be physically prepared for the demands of their sport, from both an injury specific and a general conditioning perspective. A stronger focus is required in these phases to prepare the athlete as there is a lack of validated competency criteria for final RTP protocols, particularly for moderate-severe (>14 days) injuries.31,36,49,116,120 Risk of subsequent injury and inter-injury relationships need to be evaluated and specific player monitoring post-RTP is not considered. In the period following RTP a ‘one month risk decay’ of subsequent non-contact injuries has been reported. 121 Following return, initial risk of non-contact subsequent injury was about two times higher than baseline. This risk diminished by half after approximately 25 days and levels off afterwards. 121 The severity of injury should be considered with severe injuries showing an increasing injury risk within the first ten days and remaining relatively high thereafter. 121 The continuous hazard curve of non-contact injuries shows a decline towards four weeks post RTP 121 indicating additional phases may be required to assess exposure to pre- and post-RTT loads and to further inform tertiary injury mitigation strategies. 122
On-Field rehabilitation
Table 4 presents conceptual models specific to OFR that have been developed38,41,116–119 and re-evaluated to ensure rehabilitation processes are representative of most recent evidence and practice design.39,40 The frameworks and studies presented demonstrate the strength of progressive OFR protocols and the impact on reinjury risk and subsequent physical performance. Cited limitations include the prescriptive nature of programmes and the individual nature of injury and responses to load interventions. 49 These conceptual frameworks can offer increased flexibility to support decision-making and allow for individual criteria-based progression throughout different stages of rehabilitation. This empowers practitioners to continually evolve their practice and understanding of the process. 49 These frameworks provide a solid conceptual guide for practitioners to utilise during rehabilitation, however, they are based upon expert opinion, inductive reasoning and case study applications.123–125 There is a need for validation through experimental evidence and testing alongside practical insights into how OFR is currently executed.49,126
An overview of conceptual models for on-field rehabilitation in football.
Legend: ACL, anterior cruciate ligament; GPS, global positioning system; OFR, on-field rehabilitation; On Fi.Re, On-Field Rehabilitation; RTP, return to play; RTS, return to sport; RTT, return to training.
Developing on-field rehabilitation
The concept of ‘load’ has been highlighted through the aetiological, decision-making, RTS and OFR frameworks previously described.38,41,43,46,57,64,70,105,115,117–119 A survey of practitioners has shown ‘training load’ was one of the most frequently used criteria when progressing through the final stages of rehabilitation 97 and specific metrics are available, although, more evidence is needed for the practical application of certain thresholds.36,97,126,127 This has been further highlighted in a survey by Armitage et al. 36 regarding OFR practices within professional football. During OFR, wearable technology, such as global positioning systems (GPS) and heart rate monitors, 128 was ranked as the most popular monitoring technique and is used daily in 97% of cases. Furthermore, wearable technology was ranked the second most important factor for decision-making between sessions and, as rehabilitation progresses, monitoring techniques shifted from subjective to objective measures with GPS deemed most important. 36 This demonstrates the influence of GPS within rehabilitation, particularly during the late OFR phases before RTP, however, there is a lack of consensus with regards to specific metrics and thresholds used. Some practitioners using targets that “are arbitrary (set at a squad level), relative (set at an individual level) or a combination of both”. 36 In some cases, there was a change from using absolute to relative units and different thresholds were reported for acceleration and deceleration metrics. 36 Despite this, it is widely accepted that systematic load progression/management and the development of tissue tolerance of an injury site is vital alongside restoring sport specific qualities.38,41,42,49,116
Previous methods of measuring load progressions within rehabilitation have been demonstrated to be ineffective.129–131 As part of a progressive rehabilitation, acute loads are ‘high’ due to injured players having no chronic load, therefore, models such as acute:chronic ratio 132 or percentage change are insufficient due to this divergence.129,131,133 Based on preinjury data, current running loads and previous injury ‘benchmarks’, chronic load can be developed, taking player tolerance into consideration, with appropriate planning and incremental load progressions. 77 Lolli et al. 129 states acute load alone could be a useful predictor of injury in absolute terms and may not require normalisation for chronic load through different statistical approaches, i.e., analysing the actual amount of measurable acute load (e.g., total distance, sprint distance or total accelerations/decelerations) without normalising or comparing it relative to any other factors (e.g., chronic load) may be suitable to assess injury risk. Improving our understanding of ‘load’ within each phase of rehabilitation, and potential progression targets, would aid in the development of RTS frameworks. 49 In an applied setting, practitioners, through progressive overload, should aim to increase chronic load depending on the severity of the injury and with consideration towards the tissue type and healing process.
Research has shown a focus placed on psychological readiness during the latter stages of rehabilitation, 97 yet, with the reported shift of monitoring from subjective to objective measures through the rehabilitation phases, 36 practitioners must be cautious not to neglect subjective feedback as the player transitions through RTT, RTP and post-rehabilitation phases. Studies have acknowledged the importance of blending subjective and objective measures to monitor training and rehabilitation loads,36,134 however, physical and psychological readiness may not coincide 35 and, therefore, may be overlooked, misinterpreted or misunderstood. Despite the acknowledged importance of psychological readiness there is limited research into the efficacy and effectiveness of psychological strategies specifically facilitating readiness to return. 35 Furthermore, with the potential for injury severity to significantly impact mental health, 135 with anxiety and reinjury concerns being reported as key factors when players are close to RTP,32–35 subjective measures may prove invaluable. Competence (i.e., sense of proficiency in their sporting capabilities), autonomy (i.e., a sense of control over their desired RTS trajectory) and relatedness (i.e., feelings of social connection and affiliation) have been shown to be key components influencing the final stages of rehabilitation, 35 therefore, monitoring and strategies to develop these skills are recommended. As sport-specific training is progressed visual-cognitive demands (e.g., high speed decision-making, dual-task processing) increase 39 leading to a subsequent increase in mental fatigue. Mental fatigue has been shown to impact physical and technical performance,136,137 therefore, progressive exposure, resilience and recovery from mental fatigue may be important to consider.
Several studies cite the importance of progressive sport-specific training in the late stages of rehabilitation and as a key component of OFR frameworks.4,38,39,41,42,44,49,97,98,113,116,123,138 Furthermore, the understanding of the physical and cognitive demands of the sport is key in individualising injury risk management strategies throughout different stages of the season. 50 Within professional football the demands of match-play are well documented, and studies show a variation in demands depending on a number of factors, such as positional differences, formational changes and player status.139–146 With studies showing high numbers of matches and increasing intensity the physical and mental load on players is significant.15,16,147 Furthermore, high-intensity actions (i.e., accelerations, decelerations, sprinting) have been shown to be important in match defining events (i.e., scoring goals) and winning games.148–151 With constantly evolving demands, requiring players to perform more frequent high intensity actions,15–17 consistent re-evaluation is required to ensure the best support to players during the rehabilitation process. Less fit players have been shown to perform fewer high-intensity actions and a quicker fatigue progression impacting technical performance143,144,152 and potential injury-risk. 153 This has motivational connotations for a rehabilitating player and should be a consideration for practitioners when returning players, ensuring an adequate fitness level.
There is a significantly increased injury risk in the first match after RTT and ensuring sufficient loads have been achieved and tolerated is an important factor.42,89,154,155 Research in Australian rules football has shown subsequent injuries to a different site or tissue were more common than reinjury155,156 and it has been reported that, in professional football, subsequent and recurrent injuries could account for 14% of injuries. 157 The reporting of subsequent injuries in sport is inconsistent and there is a paucity of data regarding severity, type and associated risk factors.158,159 This is an issue for injury prevention strategies, which rely on accurate injury surveillance data, as it does not provide an adequate understanding of injury risk.157,159 It is proposed the mechanism could be a general state of under-loading that predisposes the athlete to subsequent injury.155,156 This raises the question are athletes receiving enough ‘general load’ prior to RTT or are practitioners placing too much focus solely on ‘injury-specific’ rehabilitation?
Stares et al. 155 demonstrated higher running loads, achieved during rehabilitation, delayed RTP timeframes, however, moderate to high sprint loads could be protective against subsequent injury. The authors proposed that the accumulation of sprint loads increased chronic training load facilitating adaptation and minimising workload spikes, although chronic load was not identified as a significant factor in subsequent injury. 155 This demonstrates the complexity of RTP decision-making as accelerating rehabilitation protocols may not allow sufficient time for progressive overload, however, extending RTP timeframes will result in additional missed games potentially affecting team success.1,2,155 With medical and performance departments under pressure to ensure efficient RTP, whilst trying to minimise further injury risk, further investigation into accelerated protocols, workload progressions and thresholds is required. The high physical demands of professional football, and the ever-increasing intensity and density of these demands, are important factors in rehabilitation programming. There is a pressing need for further investigation of the final phases of rehabilitation to ensure sufficient conditioning, and to develop specific objective thresholds, to inform progression and the final RTP decision.
Future research suggestions
Research acknowledges the importance and development of progressive rehabilitation pathways. Current frameworks,38,39,41,42,116 utilised in professional football, are presented in this review and provide a stepwise progression for practitioners with evidence suggesting their influence in contemporary practice, 36 however, a multicomponent model adopting a non-linear, concurrent approach has been proposed for a general population with potential applications for sport models. 160 There has been a paradigm shift towards a criteria-based approach supporting progression and it has been stated an absence of valid objective criteria risks inadequate rehabilitation.42,43,98,100,104 Specific practitioner competencies and knowledge, to provide optimal support, throughout the phases is still unclear and requires further evaluation.19,97 There is a lack of empirical evidence and knowledge of causality between ‘load’ application and successful outcomes in RTP and, 49 given the protective effects of moderating physical capacities (i.e., developing force-velocity profiles, energy system capacity, movement quality), further investigation is required throughout the rehabilitation process. There are significant challenges for research due to the heterogeneity of injuries, multiple, interacting moderators of risk and limited accessible sample sizes reducing statistical power, 161 particularly with athlete populations. Despite this, conceptual frameworks are essential to aid practice 126 and development, understanding and evaluation of objective criteria informing progression is an important next step. Further informing and validating frameworks49,126 may improve the decision-making process for athletes, practitioners and coaches.
External load metrics for return to play
Within current OFR frameworks external load metrics are acknowledged as an important objective criterion,38,41,42,100,125 with metrics of interest emerging, such as very high speed running, peak speed, acceleration and deceleration distance,162,163 for specific injury pathologies. However, caution is advised as the metrics suggested lack empirical evidence, are based on anecdotal experiences or there is an absence of post-OFR information or pre-injury data.36,49,138,163 When examining the relationship between ‘training load’ and injury risk it is important to acknowledge this is likely to be associative and not causal,49,126,164 a clear aetiology has not been established 165 and many studies have used inadequate analysis. 126 Insights into applied practice and expertise are crucial in evolving evidence-based practices.36,127,166 A survey of practitioners suggests that research exploring “reduced risk of reinjury based on achieving specific markers/thresholds” would be beneficial when considered within the complex nature of injury 36 and an association with workload and injury risk has been demonstrated in non-injured players.75,167 Although ‘training load’ is associative, these metrics may assist in setting targets for successful RTP and support practitioners and athletes by providing objective information to make informed decisions. 168
GPS monitoring is widely used to quantify external load36,138 and theoretical justification for load progression and management within rehabilitation is strong, although the optimal strategy is unknown. 138 Despite issues within football stadia potentially affecting signal quality, 169 GPS monitoring has been shown to be a reliable and validated measurement tool for evaluating movement demands within sports.170–172 That said, due to the rapid nature of high-intensity actions (i.e., accelerations and decelerations), the validity of these has been questioned, with sampling rate, minimal effort duration173,174 and signal-filtering techniques important factors to consider.172,175–177 Given the high musculoskeletal forces that can accompany accelerations and decelerations178,179 and the critical importance of these actions for player performance and injury resilience,142,180 further research is necessary to investigate effective rehabilitation assessment, monitoring and programming (i.e., progression of exercises) to ensure players are optimally prepared to meet the demands of these specific actions during RTT and RTP. Furthermore, the role injury site and severity may have on acceleration and deceleration mechanics and the effect this may have on altering tissue forces and properties during, and following, the rehabilitation process requires investigation.
There is consensus in using match-specific GPS targets to inform RTP decisions. 99 Given the high demands a player is returning to, and the variation in physical demands due to playing position, there may be value in targeting individual within-session and acute (7 days) loads prior to RTT. Alongside this, individualised response to ‘load’ (i.e., subjective and objective measures of internal / external load and ‘fatigue monitoring’) and movement quality are important factors alongside training quantity.36,116 Training load has only recently been incorporated into models of injury aetiology70,103 despite being a risk factor for injury within a web of determinants.43,69 Future research should investigate this factor, acknowledging the role of ‘load’ within the complex nature of injuries, and further informing decision-making for RTT in an applied setting.
Within professional football, alongside GPS, the external load from specific technical actions can be quantified. 181 This allows for the analysis of technical actions within rehabilitation in combination with physical output. Further research is required to assess physical and technical outputs, through drill level analysis and positional specific training demands, to help inform the training reintegration process. Achieving load through sport-specific exposure may be beneficial from a physical perspective, 155 improve physical-cognitive capabilities, 39 and impact the psychology/perception of the player's readiness to return, potentially allowing an earlier RTT and RTP.
Injury surveillance and subsequent injury
An issue within applied rehabilitation is the lack of consensus and discrepancies in injury tracking/surveillance.157,159 These inconsistencies in reporting make it difficult to research and understand subsequent relationships between injuries. Subsequent injury is a poorly defined and reported area within rehabilitation. 158 Further research is required to understand the inter-injury relationship and inform tertiary prevention programming.157,159,182 Furthermore, workload monitoring to assess a potential association between post-RTT load, player status (i.e., key, squad or development player) and subsequent injury risk would be beneficial. This may help inform practitioners as to possible optimal loading strategies post-RTT. Understanding subsequent injury risk may provide a timeframe for a ‘post-rehabilitation phase’ based on the severity of the index injury and improve the development of injury specific monitoring strategies for both reinjury, and possible subsequent injuries, to alternative sites. 122 Furthermore, mechanism of subsequent injury is a further factor to investigate. Establishing a potential pattern of mechanisms may be beneficial to guide injury prevention programming. Previous injury and subsequent injury associations are rarely considered, despite previous injury modifying the complex interactions between determinants of injury. 158 Further studies are required into current practices within subsequent injury surveillance and specific athlete support post-RTT.
Player perceptions of rehabilitation processes
The role of multiple stakeholders within rehabilitation has been widely acknowledged,81,183 however, despite being part of the decision-making process,92,95 player perception and role within rehabilitation is not thoroughly discussed. A lack of consensus between players and coaches regarding the RTP decision has been previously noted. 184 Players are a key stakeholder in rehabilitation and anxiety, the need for a plan, evaluating the risk of early return, demonstrating progress and social support are important factors in the process.32,35 Furthermore, establishing athlete satisfaction post-injury requires further research. 43 Feedback of GPS training data within professional football has been shown to support the coaching process and understanding player feedback preference is key to elicit engagement. 185 However, little exists around RTP procedures and player perceptions regarding the use of specific GPS targets within the rehabilitation setting and feedback of this data.
Injury specific metrics
Different load metrics may have varying relationships to injury risk126,186–188 and the specific stress/strain capacity, resilience and adaptation of different tissues.46,165,189 In a survey of practitioners, “GPS metrics for certain injuries” was referred to as a useful future development in RTP protocols. 36 Quantifying the success of a rehabilitation process is an important consideration 36 and a continuum of importance for injury specific targets for different injury sites could be developed. These insights could give practitioners greater understanding of key injury specific metrics for load management during rehabilitation and post-RTT, although this should be acknowledged within the complex nature of injury.
Limitations and perspectives
An acknowledged limitation of the article is the use of a narrative review and, therefore, a clear, systematic search methodology was not utilised resulting in potential bias. 186 The limitations of narrative reviews are documented, 190 however, using this method allowed for a wider search strategy exploring interdisciplinary topics and to reflect the complex nature of applied rehabilitation and decision-making for practitioners.
The review focuses on literature within the domain of male professional football, however, the frameworks presented may be further applicable to female professional football and developmental players. Research understanding the gender specific differences in injury and rehabilitation is growing,191,192 however, more is warranted specific to female football players and to academy players investigating the potential impact on long-term athlete development programming if an injury occurs. This may help to reduce disparity and improve understanding and application of the frameworks presented. Ultimately, a long-term objective of developing bespoke models for different sports, injury pathologies, age groups and genders, with multidisciplinary inputs, is crucial in future research and applied practices.
Conclusion
The purpose of this review was to give an overview of existing aetiological models, decision-making frameworks and RTS approaches within the current literature and evaluate the role of criteria-based progressions in rehabilitation frameworks and their application within male professional football. General sporting, and football specific models and frameworks are presented to demonstrate approaches and different interpretations of RTP and RTS terminology. Further consensus in terminology used to define phases, and subphases (i.e., RTT subphases), within the rehabilitation procedure is required to help guide intention and impact phase specific monitoring, and performance markers to inform safe return. By understanding injury type, mechanism, severity and location, the demands of the sport and multiple interacting risk factors, evidence-based RTP criteria can be used to guide decisions alongside practitioner intuitions and experiences. However, research of subsequent injury risk, and inter-injury relationships, is lacking in male professional football with current RTP frameworks using a stepwise progression through different rehabilitation phases and objective exit criteria to inform decision making. Development of flexible, bespoke frameworks, using validated objective criteria, is required and further research is needed to ensure effective rehabilitation procedures, with successful RTP outcomes, to guide programming, and decision-making, that minimises subsequent injury risk. Through improved practitioner knowledge and understanding of aetiological models, decision-making and rehabilitation frameworks, and the future development of these topic areas, the support of injured athletes can be enhanced during, and following, the rehabilitation process.
Footnotes
Acknowledgements
Not applicable.
Ethics considerations
Not applicable.
Consent to participate
Not applicable.
Consent for publication
Not applicable.
Author contributions
BD was responsible for the conception and writing of the review. DH and JA contributed and provided supervision and feedback throughout. All authors critically reviewed the manuscript and approved the final version.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of conflicting interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Data availability
Not applicable.
