Running is associated with a higher risk of overuse injury (Bertola et al., 2014; Hauret et al., 2015; Salmon et al., 2014) than other forms of aerobic exercise such as walking, swimming and cycling. To unlock the full potential of running as a sport or a vehicle to improve health there is a need to understand the aetiology of injury. In any sport, this process begins by gaining an understanding of the most frequent injuries associated with that sport (Fitzharris et al., 2017).
Preferably, injury epidemiology would be synthesized from high quality studies, using standardised definitions, by way of systematic review and meta-analysis. This poses a challenge to researchers due to the heterogeneity of studies in the literature, which are affected by differences in study populations, designs and injury or exposure definitions. The most recent systematic reviews on running injury (Kluitenberg et al., 2015; Lopes et al., 2012; Nielsen et al., 2012; van der Worp et al., 2015; Videbaek et al., 2015) have highlighted issues such as a lack of standardised injury definitions, the classification of a runner, and the recording of exposure. To minimise the effect of study heterogeneity on the outcome variable of interest, authors of systematic reviews have used strict inclusion-exclusion criteria to answer specific questions about running injury epidemiology or injury epidemiology in specific types of runners. This results in a smaller number of studies being included for review. Reviews that focus on injury incidence require accurate estimates of exposure (van der Worp et al., 2015; Videbaek et al., 2015). Reviews that focus on the prevalence of specific injuries or injuries in a specific population of runners, are limited to those studies including a medical diagnosis or specific type of runner (Kluitenberg et al., 2015; Lopes et al., 2012).
An alternative approach, albeit less sensitive and potentially subject to greater bias, is to use a broad inclusion criteria. This would allow inclusion of a larger population (i.e. recreational, amateur, elite, triathlon, orienteering), and a broader classification of injury (i.e. hip, knee, ankle and foot). Subsequently, sub-group analyses can be performed from studies that clearly describe injury per gender or specific pathology. Gaining a broad understanding of the proportion of running injuries could provide a foundation for the investigation of risk factors associated with running injuries. Furthermore, knowledge of the anatomical locations most commonly affected may assist with the development of standardised study procedures in relation to reporting injury prevalence and incidence. A number of running injury epidemiology studies have recently been published (Altman and Davis, 2016; Hespanhol Junior et al., 2016; Hespanhol Junior et al., 2017b; Kerr et al., 2016; Malisoux et al., 2016b; Smits et al., 2016; van der Worp et al., 2016), therefore the primary aim of this review was to determine the proportion of injuries in male and female runners by anatomical site. A secondary aim was to specify pathologies (self-reported or reported by a health care practitioner), where possible.
Data sources and search strategy
This review was prepared and conducted according to the preferred reporting items for systematic reviews and meta-analysis (PRISMA) guidelines (Moher et al., 2009). The aim of the search strategy was to find published retrospective, cross-sectional, prospective and randomised-controlled studies that provided survey data. The following electronic databases were searched (from inception) without date restriction to July 2017; and included Web of Science (n = 194), Scopus (n = 215), SportDiscus (n = 72), PubMed (n = 691), SCIELO (n = 5) and CINAHL (n = 57). The last electronic search was conducted on 01/07/2018. Search terms included running* (Boolean Phrase); injury* (Boolean Phrase); prevalence* (Boolean Phrase). In addition, manual searches of the reference lists of four recent running injury systematic reviews (Kluitenberg et al., 2015; Lopes et al., 2012; van der Worp et al., 2015; Videbaek et al., 2015) were undertaken by a single author (PF). All citations were imported to EndNote X7 (Thomson Reuters, USA) and duplicates removed by PF. Articles were screened by title, abstract and finally full text, according to predetermined study criteria (Figure 1). Three authors (PF, CW and KS) independently reviewed all titles and abstracts, and selected those for inclusion. Disagreement was resolved via consensus and a third author (MIJ) was to be consulted if no agreement was reached. Full texts were reviewed by one author (PF) to determine which studies met the inclusion criteria. No hand-search of specific sports medicine journals was performed.
Inclusion and exclusion criteria
The inclusion criteria were: (1) published peer-reviewed prospective cohort; retrospective cohort; cross-sectional; or randomised controlled studies, (2) reported running injury data in adult (mean age: [greater than or equal to] 18 years) runners, (novice, recreational, amateur, elite runners, triathletes and orienteers) competing in distances [greater than or equal to] 800m-[less than or equal to] marathon), (3) provided the anatomical location of lower limb running injury separate to other injuries/illness (e.g. upper body), (4) written in English, (5) interventions that did not alter the volume of running undertaken, use strategies designed to directly alter pain, and did not report a difference in running related injury (RRI) between intervention and control groups (e.g. the influence of footwear on running injury), (6) included shod injuries separate to barefoot injuries in studies investigating these conditions, (7) not duplicate publications or multiple studies on the same cohort, (8) did not include service personnel (e.g. police, fire service, military) (9) separated lower limb running injuries from other lower limb injuries (e.g. triathlon injuries divided into swim, bike and running), (10) did not recruit participants with a specific type of injury, (11) did not describe track and field competition injuries, (12) presented data as running injury or any lower limb pain regardless of its interference with running.
Data from included studies were extracted by a single author (PF), and checked by MIJ. A standardised data extraction sheet was developed by PF (available on request) where the following data related to study characteristics and injury were extracted: (1) author, year, (2) runner type, (3) gender, age, (4) injury definition, yes/no, (5) study design, (6) time period for retrospective/prospective analysis (7) gender split of injuries, yes/no, (8) sampling method, (9) 6-month or 12-month follow up for prospective or retrospective studies respectively, yes/no, (10) the sample included versus analysed, (11) injury as self-reported, reported by a health professional or diagnosed by a medical doctor (12) injury proportion expressed as a total of all injury, yes/no, (13) consistent mode of data collection, yes/no, (14) all injuries reported, yes/no, (15) running injuries separate, yes/no, (16) anatomical location or specific injury identifiable, yes/no, (17) number of runners, number of injured runners, total injuries, (18) anatomical location of injury, (19) specific type of injury. The primary outcome variable was the proportion of lower limb running injury. Due to the heterogeneity of studies, studies were grouped according to anatomical location, and subsequent subgroup analyses were conducted on data pertaining to specific pathologies. Injuries were categorized by the anatomical regions 'hip' (hip joint/pelvis/groin), 'thigh' (upper leg), 'knee', 'shank' (lower leg), 'ankle-foot' (including toes) and 'other' (not clear diagnosis/location/upper extremity/illness)(Kluitenberg et al., 2015; van Gent et al., 2007). Overall injury prevalence was defined as the number of injured runners divided by the total number of runners in the study. This was calculated from 26-studies where injured runners could be separated from the total number of runners and the total number of running injuries. Descriptive statistics for prevalence were calculated using SPSS. Injury proportions were defined as the total injury number per anatomical region or specific pathology divided by the total number of injuries reported from all sites or pathologies. Specific pathology refers to a pathology with a self-reported or confirmed medical diagnosis.
Recent systematic reviews on running injury prevalence, incidence and risk factors have used different tools to assess the quality of studies (Lopes et al., 2012; Nielsen et al., 2012; van der Worp et al., 2015; Videbaek et al., 2015). Most tools that have been used can be traced back to epidemiological or occupational studies on general musculoskeletal pain (van der Worp et al., 2015). The tool is often modified to be more 'running' specific and subsequent running reviews often modify it further (Nielsen et al., 2012; Videbaek et al., 2015) or propose their own criteria based on the aims of their review (Lopes et al., 2012). A score out of the total number of criteria or a percentage of positive responses (from yes-no answers) are used to express quality (Kluitenberg et al., 2015; Nielsen et al., 2012; van der Worp et al., 2015).
The main purpose of this study was to determine the proportion of injuries at different anatomical locations in runners and where possible specify the pathology responsible. The level of runner, cause, prevalence or incidence of injury were not of interest thus minimising the importance of methods for randomization for the quality of outcome. Therefore, we used the 10 yes/no criteria proposed by Lopes et al. (2012) as their review was mainly concerned with prevalence and also because the 10 criteria also encapsulated 7 of the 8 criteria recently used by Videbaek et al...