Our mixed-methods study had three objectives: (1) to systematically review and summarise the clinical and biomechanical evidence for implementing running retraining to treat lower limb injuries; (2) explore the clinical reasoning related to the use of running retraining by international experts; and (3) synthesise these elements to provide guidance for clinicians and researchers who seek to implement and evaluate running retraining interventions in the future.

Many interventions studied in previous running retraining research may not translate to clinical practice well, due to issues with practicality (eg, real-time three-dimensional (3D) motion analysis feedback), and the ‘one size fits all’ approach of associated methodology (eg, all participants transition from a rearfoot to forefoot strike). It also remains unclear how running retraining may interact with other interventions with an established evidence base such as exercise rehabilitation. 27–29 Given this lack of evidence to guide clinicians and researchers in the practical implementation of running retraining, consultation with those already prescribing running retraining in clinical practice may provide valuable insight. Such consultation is part of evidence-based practice, particularly where clinical trials are lacking. 30

Biomechanical studies in asymptomatic populations have examined retraining strategies extensively (including altering step rate, strike pattern, hip and knee motion, trunk position, step width, and impact loading variables), and reported to change running kinematics, kinetics and electromyography. A recent systematic review by Napier et al 26 concluded a number of biomechanical variables can be altered by running retraining interventions. Additionally, they concluded the most effective strategy for reducing impact loading variables including vertical impact peak, and average and instantaneous loading rate was provision of real-time feedback related to kinetics and/or kinematics. However, the importance of these impact loading variables to injury are not supported by strong evidence, and the review by Napier et al 26 did not provide a synthesis of current published clinical outcomes, despite emerging evidence. 22–25

Alteration to running technique may help to treat running injuries by reducing load in certain muscle groups and joints. 19 , 20 This theory was tested by Davis 21 introducing the coaching concept of running retraining to treat lower limb injuries in a case series of five patients who reported pain reduction and maintained a changed running technique. The process involved (1) identifying any theoretical abnormal running mechanics which may be contributing to tissue overload; (2) establishing if running mechanics could be altered; and (3) facilitating the desired running mechanics changes and encouraging motor learning to ensure maintenance of any change. Despite nearly 10 years since the publication of this paper, only four small case series evaluating the effectiveness of running retraining interventions in reducing pain have been published. 22–25

Running as a means of exercise is popular for both recreation, and as a sport in its own right. However, running is not risk free. Injury incidence ranges from 19% to 78% among studies with follow-up periods between 1 week and 18 months. 1–2 Common running injuries include exertional lower leg pain, plantar fasciopathy, Achilles tendinopathy, calf pain, medial tibial stress syndrome, patellofemoral pain (PFP), iliotibial band syndrome (ITBS), patellar tendinopathy, hamstring injury including proximal tendinopathy and gluteal tendinopathy. 1 Proposed intrinsic factors for running-related injury include older age, 3 higher body mass index, 4 history of prior injury, 1 limb length discrepancy, 5 abnormal anatomical alignment 5 and foot posture, 6 , 7 and faulty foot loading patterns. 8 , 9 Proposed extrinsic factors include level of competition, 10 training accumulation, 11 shoe type 5 and training surface. 12 Multiple interventions have been developed in an attempt to mitigate these risks and treat injuries that develop, including exercise programmes to improve strength, neuromuscular control and flexibility, 13 , 14 footwear modification, 13 , 15 foot orthoses, 13 , 16 , 17 and taping techniques. 13 , 18 Despite extensive research in all areas, a lack of effective long-term treatment strategies remains a source of frustration for many runners and clinicians.

Qualitative data were evaluated using a ‘Framework’ approach 33 by a physiotherapist (CJB) with experience in conducting interviews and evaluating data related to qualitative research. Each transcript was read to gain familiarity, and then a thematic framework was formed by mapping the ideas and opinions stated by the interviewees and combining these to generate themes and subthemes, subsequently tabulated with each interviewee being coded to enable anonymous quote attribution. Additional interviews were performed until data saturation, whereby no new themes were identified. An additional physiotherapist (PM) and sports physician (AF-M) also read through each interview transcript to reinforce the analysis. Of particular interest was information related to the current evidence base, appropriateness of running retraining to treat lower limb injuries, specific lower limb conditions and associated retraining strategies which may be effective in clinical practice, and the practical application of specific running retraining strategies and their interaction with other interventions. Triangulation was by means of respondent validation and performed by presenting each interviewee with the final themes, subthemes and accompanying findings, and requesting any free comment. Any new comment was added to the framework analysis.

One interviewer (JC) completed and recorded all interviews via Skype or in person where possible. Each was then transcribed for further analysis. The interviewer was a physiotherapist with 9 years clinical experience, and used running retraining interventions as part of their clinical practice. To facilitate discussion, a topic guide (see online supplementary file 3 ) was presented to each participant during the interview process. Content of the topic guide was based on a preliminary review of the literature and discussion between the research team.

Prospective interview participants were initially identified from author lists of running retraining-related literature. Experts were required to be actively participating in running retraining research, have at least 5 years clinical experience, and be prescribing running retraining regularly to treat patients with running injuries. It was felt that experts with a good blend of clinical experience and research knowledge would be able to provide the best information on the perceptions of current evidence (published and unpublished), and its external applicability for clinical practice. Sixteen international experts from the UK, the USA, Canada and Australia were included and interviewed. Among them were 11 physiotherapists, 2 physical therapists, 1 sports physician, 1 medical doctor and 1 running coach. Further details related to participant characteristics are detailed in online supplementary file 2 . Ethical approval was granted by La Trobe University's Faculty of Human Ethics Committee (FHEC13/151). Each participant provided informed consent.

Two independent reviewers (CJB and DRB) evaluated the methodological quality of each included study using the Downs and Black quality index which consists of 27 items (maximum score of 28). 31 A third reviewer (BSN) was available to resolve any disagreements. Based on quality assessment scores, studies were categorised as high quality (≥20), moderate quality (17–19) or low quality (≤16). Owing to the lack of randomised controlled trials and high-quality studies identified, meta-analysis was not performed. However, where possible, similar findings were combined in results tables for various retraining interventions, and the quality of these associated studies subsequently used to determine the level of evidence for each finding based on a modified version of the van Tulder et al 32 criteria:

Titles and abstracts found during the initial electronic search were uploaded into Endnote X6 (Thomson Reuters, New York, USA), duplicates removed, and each screened for inclusion by two independent reviewers (DRB and BSN). To resolve disagreement about exclusion, a third reviewer (CJB) was available. Where necessary, the full text was retrieved.

Studies with less than 10 participants in total or in the running retraining intervention group were excluded. This criteria were applied to minimise the risk of potentially false-positive or false-negative findings influencing the evidence synthesis.

Running retraining was defined as ‘the implementation of any cue or strategy to alter an individual's running technique’. 21 Studies evaluating other interventions in conjunction with running retraining were considered if the effects of retraining could be clearly delineated (eg, altering footwear combined with instruction of strike pattern, compared with altering footwear alone). Two streams of studies were sought:

Four studies 22–25 investigating clinical outcomes were identified ( table 1 ). Limited evidence indicates 6-weeks of visual (video) and verbal feedback to transition from rearfoot strike (RFS) to midfoot strike (MFS) or forefoot strike (FFS) and increased step rate can reduce pain 24 , 25 and compartmental pressures 24 in patients with running-related anterior exertional lower leg pain. 24 Limited evidence indicates 2-weeks (eight sessions) of visual and verbal feedback to reduce peak hip adduction in female patients with PFP possessing more than 20° peak hip adduction can reduce pain at 1-month 22 , 23 and 3-month follow-up. 22

Results of the quality assessment can be found in online supplementary file 4 . Of the 46 included studies, 13 were high quality, 25 were moderate quality and 8 were low quality. Of particular note, no study attempted to blind the participants or assessors; only 6 studies 22 , 55–59 reported whether adverse events were experienced by participants, and 21 of the 46 studies did not report actual probability values. Additionally, 27 of the 46 studies lacked adequate justification of the statistical tests used to assess the main outcome data, commonly using parametric tests without describing whether the distribution of data was screened for normality prior to analysis. Accordingly, the use of parametric tests was considered inappropriate for such studies.

After screening title and abstract, full texts were obtained for 70 studies. The primary reason for exclusion on obtainment of full text was inadequate participant numbers (ie, less than 10 participants per group), and included six studies on step rate manipulation, 34–38 five studies on strike pattern comparison 36 , 39–42 including one in a PFP population, 41 one study on step width manipulation, 43 one study on cues to reduce hip adduction, 44 two studies on reducing impact loading variables 45 , 46 and three combination studies. 40 , 47–49 Additional reasons for exclusion included one combination study for absence of clinical or biomechanical analysis, 50 one combination study for including transition to minimalist footwear during gait retraining, 51 two step rate manipulation studies 52 , 53 for absence of statistical comparison of biomechanical differences and one step rate manipulation study 54 which combined hill running. A total of 46 studies met the inclusion criteria. A flow chart of the search results can be found in online supplementary file 4 .

Discussion

There is limited evidence to support running retraining in the treatment of exertional lower leg pain24 ,25 and PFP.22 ,23 Additionally, the expert panel were advocates of running retraining for cases of chronic or recurrent injury, and where potential biomechanical deficiencies linked to injury can be established (see online supplementary file 9.2). Experts interviewed suggested lower limb injuries which may benefit from running retraining include (but are not limited to) exertional lower leg pain, plantar fasciopathy, Achilles tendinopathy, calf pain, medial tibial stress syndrome, PFP, ITBS, patellar tendinopathy, hamstring injury including proximal tendinopathy and gluteal tendinopathy (tables 2 and 3; and online supplementary file 9.3). Despite a paucity of current evidence in injured populations, there is substantial evidence for the immediate biomechanical effects of running retraining interventions in an uninjured population (see online supplementary files 5–8). Given the current state of evidence, this information is important to assist guidance of current clinical practice and future research, and is incorporated throughout the discussion.

Practical application of running retraining Addressing overstride and increasing step rate Addressing the presence of overstriding was considered one of the most beneficial running retraining strategies (table 4), with experts frequently discussing the importance of the foot landing closer to a runner's COM. Despite strong recommendation from experts, evidence to support the importance of overstriding or horizontal distance between foot strike and COM to running injury is lacking. Defining what constitutes overstriding (eg, the distance which may lead to injury), how this relates to injury and how to address it should be priorities for future research. Increasing step rate will move foot strike closer to the COM,66 and was suggested to be beneficial for many injuries. One key recommendation is that increases to step rate should be gradual (between 5% and 10% at a time) to ensure manageable changes and avoid excessive fatigue.66 Experts proposed a range of cues to increase step rate, including metronomes, music and verbal cues (eg, ‘take shorter faster steps’), and all could be considered clinically. Strike pattern alteration Experts proposed a range of potential benefits of strike pattern alteration, including both transition from rearfoot towards forefoot or midfoot (eg, knee injuries), and from forefoot towards rearfoot or midfoot strike (eg, Achilles tendinopathy and calf pain). However, caution was recommended when considering changing a runner's strike pattern, with a substantial adaptation period suggested if choosing to make alterations, especially towards a forefoot strike pattern (table 5). Additionally, potentially greater importance of other retraining interventions was stressed, including reducing overstride, which transitioning from a rearfoot to forefoot strike may be detrimental to.81 Additionally, other interventions including proximal retraining strategies, increasing step rate,61 ,71 ,72 and use of minimalist footwear or barefoot running102 were proposed to potentially have desired effects on foot strike. Proximal retraining (cues to modify hip, pelvic and trunk mechanics) A number of strategies additional to visual (3D motion feedback or mirrors) and verbal (‘tighten your buttocks’ and ‘point your knees straight ahead’) cues published in the literature were proposed to reduce hip adduction and internal rotation (table 6). Considerations to both internal (eg, squeeze gluteals) and external (eg, point knees forward) cues were apparent, but consensus was lacking regarding the most appropriate approach, and it is possible the most effective cue may be specific to the individual. A number of retraining interventions may indirectly reduce peak hip adduction, including increasing step rate66 or step width.84 ,85 Possible cues to increase step width used in the literature include both visual (taped lines on the floor)84 ,87 and verbal instruction (eg, ‘widen your stance’).85 ,86 Although verbal instruction may be easier to implement in clinical practice, experts stressed the need to ensure individuals do not ‘overcorrect’ (table 6). Further research is needed to determine the most effective cues for reducing hip adduction and increasing step width and its effect of running-related pain. Reducing impact loading variables Some experts considered kinetic variables, including joint forces, tibial accelerations and loading rates, may be more important in relation to injury than kinematic variables (table 4), although evidence to support this premise is lacking. Additionally, most clinicians lack the required equipment to directly measure kinetics during running. It was suggested that impact noise during running may be closely related to actual impact loading variables such as vertical loading rates, and therefore may be used as a proxy measure. Additionally, moderate relationships between sagittal plane kinematics and subsequent loading (kinetic) variables during stance of running were recently reported, including increased step rate, decreased vertical COM excursion, decreased foot inclination angle at foot strike, and reduced horizontal distance between foot strike and COM (ie, decreased overstride).103 Considering these variables along with strategies to reduce impact noise may be a focus of retraining interventions where clinicians seek to reduce impact loading variables.

Barriers and facilitators Pain and irritability may prevent the implementation of running retraining in the early stages of rehabilitation (see online supplementary file 10.1 which summarises expert discussion of barriers and facilitators to running retraining implementation). Inconsistent beliefs related to whether a runner should be allowed to run in pain or not were evident. Importantly, experts suggesting running-related pain could be allowed, believed so only if pain was minimal (eg, 3/10). This fits with previous research in Achilles tendinopathy, which indicates that continued sports participation with minimal pain did not impair rehabilitation outcomes if guided by a similar pain monitoring model.29 An additional consideration is that pain reduction may provide vital feedback to aid compliance to running retraining interventions.104 Other key potential barriers discussed included muscle function capacity, joint flexibility and skeletal structure. Further research is needed to determine how these variables impact on biomechanical and clinical outcomes with running retraining. Fatigue resulting from running retraining was suggested to limit how much could be changed at once (eg, magnitude of step rate increase), and the duration runners may be able to maintain these changes. However, it was suggested that fatigue associated with running retraining was likely to diminish with habituation. Of the studies providing limited evidence for running retraining to reduce pain,22–25 two evaluated a programme including eight sessions of up to 30 min over a 2-week period,22 ,23 another used 18 sessions over 6-weeks24 and one used just 3 sessions over 6-weeks.25 Three22–24 of these four approaches are unlikely to reflect clinical practice due to associated costs they would entail, and are more intensive then those proposed by experts interviewed. The optimum number of sessions and time frame suggested to facilitate required changes varied among experts, and it was suggested this may be different for each runner. Some runners may be able to make clinically significant changes immediately, while others may take many months due to barriers such as pathology and associated pain, weakness, flexibility deficits, and intrinsic motivation. Importantly, experts highlighted these barriers may need to be addressed concurrently or prior to attempts to retraining running technique. Variable beliefs exist regarding the potential for changes as a result of running retraining to become habitual. Although few studies have explored this, limited evidence indicates a reduction in both peak hip adduction and running-related pain at 1–3 months follow-up can be achieved in females with PFP.22 ,23 Further longer term studies are needed to determine if habituation from running retraining interventions in injured runners can be facilitated. Limiting cues to one or two at a time was recommended. Additionally, an individual response to cues is considered likely, meaning clinicians need to be able to adapt and tailor cues to ensure desired biomechanical changes. Video analysis and feedback may assist compliance, allowing visualisation of running technique before and after the running retraining. Use of mirrors was suggested by some experts to assist reductions in hip adduction and knee valgus, and changes to trunk position and strike pattern. However, this was not recommended by all experts interviewed. With just one study published supporting the use of mirrors in running retraining,22 further research is needed to establish their usefulness, along with other forms of clinically feasible biofeedback. Undertaking running retraining on a treadmill was suggested to be practically easier than overground, although potential limitations in carry over to overground running gait were acknowledged. Vertical ground reaction forces have been reported to be similar between conditions.105 However, treadmill running has been reported to decrease peak and range of knee flexion,106–111 decrease ankle dorsiflexion range of motion, velocity and peak,111 ,112 and increase peak rearfoot/ankle eversion110 ,111 ,113 when compared with overground running. Further research is needed to establish to what extent clinical and biomechanical effects of running retraining on a treadmill translate to overground running.

Adjunctive interventions Experts highlighted that running retraining is only part of the solution for the treatment of running injuries (see online supplementary file 10.2 which summarises expert discussion of adjunctive interventions during running retraining implementation). The importance of concurrently addressing muscle function and flexibility deficits was frequently discussed. References were made to both strength and motor control, with the latter being considered by some to be more important to an individual's ability to make changes to running technique. Manual therapy to address soft tissue flexibility and joint mobility restrictions was also considered as a potential adjunctive intervention by some experts. Further research to establish the impact of addressing muscle function and flexibility deficits through exercise and manual therapy on running retraining outcomes is needed. The influence of footwear on injury and running retraining appears to be a divisive topic. While some experts believed footwear had minimal impact on outcomes, others considered footwear as vitally important. Those emphasising the importance of footwear generally promoted a more minimalistic approach, to assist in reducing impact loading variables and overstride, and transitioning towards a midfoot or forefoot strike. Importantly, caution and slow transition towards minimalist footwear was encouraged if choosing to implement this as an intervention, which is supported by recent evidence indicating an increased risk of pain and injury,114 and foot bone marrow oedema115 during 10–12-week transition periods. Barefoot running was suggested by some experts to potentially facilitate increased step rate, a more forefoot or midfoot strike, and reduced impact loading variables. Biomechanical rationale supports this premise,102 but importantly, some experts suggested barefoot running may be injurious if the transition is too fast or running retraining is not concurrently implemented. The interaction of barefoot running and footwear modification with running retraining interventions requires investigation. Substantial supporting evidence for the effectiveness of foot orthoses to treat lower limb injuries exists.16 ,17 However, the perceived value of foot orthoses in running injury treatment varied among experts, with some considering them only as a ‘last resort’. Additionally, those advocating their use generally saw them as only a temporary solution or a tool to facilitate desired running retraining strategies. Taping was viewed in similar light, with its value perceived to be in reducing symptoms in the short term and facilitating desired running retraining changes.

Prevention, performance and ideal running pattern Some experts suggested running retraining may play a role in injury prevention, although a lack of available evidence to guide implementation exists (see online supplementary file 10.3 which summarises expert discussion of prevention, performance and and ideal running pattern in relation to running retraining). One commonly discussed approach was reducing impact loading variables such as vertical loading rates, indicating research to investigate the merits of this may be warranted in the future. When discussing running performance and economy, experts suggested acute changes may reduce running economy. However, some, but not all experts, suggested that economy may then improve over the first couple of months, with possible improvements to performance in the longer term with interventions such as increasing step rate. Beliefs related to the presence of an ideal running pattern in relation to both injury and performance were inconsistent, with some experts suggesting this to be individual to each patient. Others stated certain running characteristics could be considered better than others for all runners, including higher step rates and a forefoot/midfoot strike. The topic of strike pattern is controversial, with the recent growing interest of barefoot running leading to a strong promotion of rearfoot runners to transition to a forefoot strike to both treat injury and improve performance.116 Considering the lack of evidence to support this notion in relation to injury102 and performance,42 ,79 further research is needed on this topic.

Limitations and future research directions This study provides what might be reported as a biased sample of ‘experts’ because we selected those who use and study running retraining. A sports biomechanics researcher or clinician who has moved away from this area of research because he/she feels it is not effective would not be included among our ‘experts’. The topic guide (see online supplementary file 3) used to facilitate discussion between the researcher and interviewee was based primarily on literature included in the systematic review, which may have biased discussions towards topics with current biomechanical evidence. To address this, the topic guide included scope for and encouraged discussion of clinical reasoning regarding interventions lacking evidence. Initial evaluation and framework analysis was completed by an experienced physiotherapist with more than 5 years’ experience of providing running retraining as a specialist focus in clinical practice (CJB), which is another potential source of bias. To remove one level of bias, data accuracy and interpretation were checked by an additional researcher with qualitative research experience (PM), and two other researchers were also involved (AF-M and JC). Validity of qualitative findings was then further strengthened through triangulation of findings via respondent validation. Only 5 of 46 studies included investigated an injured population, limiting the clinical applicability of findings from the evidence synthesis. We believe randomised controlled trials of running retraining efficacy in symptomatic populations are justified on the basis of current evidence. Such trials should also consider evaluating potential clinical predictors and biomechanical mechanisms, which may help tailor running retraining interventions to individuals and specific conditions. Other priorities highlighted by experts include development of technologies to provide more efficient feedback, developing options to allow mobile monitoring of compliance, and investigating the interaction of running retraining with other evidence-based interventions (see online supplementary file 9.1).