Epidemiology and etiology of lower limb injuries in Iranian recreational runners

Background Knowledge about of injuries (RRIs) is important to tailor an effective RRI prevention program. We aimed to investigate the prevalence and etiology of RRIs in Iranian recreational runners. Methods An internet-based self-developed questionnaire was sent to recreational runners recruited through social media. The questionnaire asked about personal and training characteristics, psychological factors (passion, BERQ-2, RAND-36), SQUASH, sleep, foot type and RRIs over the last six months. Data were analyzed descriptively and using logistic regression. Results Self-reported data from 804 questionnaires were analyzed. Twenty-five potential risk factors for RRIs were investigated. The male-to-female proportion was 57.5:42.5. 54% of runners reported at least one RRI. Patellofemoral pain syndrome was the most-reported injury (19.8%), followed by medial tibial stress syndrome (16.9%). Knee was the most-affected location (44.6%), followed by lower leg (19.2%). The variables associated with RRIs were: overweight (odds ratio (OR):1.77), pes planus (OR:1.81), running over 20 km/week (OR:1.62), hard-surface running (OR:1.38), running company (OR:1.74), following a training program (OR:1.50), obsessive passionate attitude (OR:1.05), RAND-36 (OR:0.96), and sleep quality (OR:1.46). Associated factors for all different RRI types were analyzed too. Conclusions Overweight, running over 20 km/week, hard-surface running, having pes planus or cavus, higher obsessive passion, lower RAND-36, and poor sleep quality were the most predictive risk factors for RRIs types. This study highlighted the importance of psychological factors besides abnormal foot arch and some training-related risk factors for RRIs in Iranian runners. These results may be useful

for runners and coaches to tailor effective training programs and to design RRI prevention programs that may help clinicians when managing RRIs.

Introduction
Running has become the most popular physical activity [1]. Thanks to its affordability and convenience, needing less equipment than many other sports, the number of runners has increased in recent decades [2]. Regular, leisure-time running is considered recreational. Running has many benefits, like improvement of mental and physical health: a study reported a 45% lower risk of cardiovascular mortality in runners compared to non-runners [3].
In Iran too, recreational running has become more popular because people have found it an easy and accessible way to stay healthy. This is important for Iranians ever since a recently published review about cardiovascular disease in Iran reported insufficient physical activity as one of the leading causes of the high prevalence of cardiovascular disease [4].
A major drawback of running is that it is accompanied by running-related injuries (RRIs), with incidence rates varying from 19.4% to 79%, depending on the definition used and the population studied [5].
To develop preventive measures for RRI, more knowledge about etiologic factors is needed. According to the Translating Research into Injury Prevention Practice framework (TRIPP) [6], upon injury surveillance the second stage is establishing the etiology of injury. Accordingly, identifying and understanding causal factors for RRIs as well as the most commonly affected anatomical locations are important steps toward developing an effective prevention program [7]. There is evidence that the etiology of RRI is multifactorial and includes both extrinsic and intrinsic risk factors, some modifiable [8]. Several studies have reported risk factors predisposing runners to injuries [8][9][10][11], including abnormal biomechanics, previous injuries, trainingrelated risk factors and insufficient running experience. However, there is still no consensus on the exact etiology of RRIs and there might even be differences between populations from different countries, regions or cultures.
Besides running/training and personal factors, RRIs may also be impacted by health, psychological, and lifestyle factors. These factors have not been explored extensively in runners yet, and not enough information on their effects on RRIs (and vice versa) is available. Recent reviews emphasize the importance of psychological factors for sports injuries [12,13], indicating that alterations in stress can predict sports injury incidence. A study has also been designed to investigate the effect of mental aspects on RRIs [14].
Recreational runners comprise the largest group of runners worldwide [15]; according to a recent systematic review, a minority of studies investigating RRIs involve recreational runners [16]. Studies mostly target runners participating in running events or organized running groups which cannot be a real-life representation of recreational runners. In Iran, recreational runners run mostly individually or in small groups. Many of them, especially women, prefer running on treadmills in indoor gyms due to religious and general beliefs.
RRIs may also have negative psychological and physical effects, and may cause individuals to quit sports or/and physical activities temporarily or even permanently [17]. RRIs can additionally result in high treatment costs and costs related to work absenteeism, which can lead to discontinuing running or reducing individual motivation [18]. Hence the need for investigating epidemiology and etiology of RRIs specifically in Iranian recreational runners is warranted.
Although several studies addressed risk factors in a small sample size of recreational runners in Iran [19][20][21], information about epidemiology and etiology of RRIs in Iranian recreational runners is still lacking. As the knowledge of prevalence and etiology of RRIs is the first step to effectively tailor RRI preventive programs, the aim of the current study is to describe the epidemiology, etiology and impact of RRIs among Iranian recreational runners.

2.1
Study design This is a cross-sectional survey investigating the prevalence, risk factors and psychological impact of running-related injuries in Iranian runners using an electronic/web-based questionnaire. Ethical approval for this study was obtained from the Tehran university institutional review board (IR.SSRI. 1398.154).

Participants
Recreational runners were invited to participate through social media and by contacting them at sports and health departments in universities, running clubs, gyms, and sports shops in Tehran, Mashhad, and Shiraz. Because of their geographical differences, these cities can be considered most representative of the Iranian runners' population. A recreational runner was defined as someone who has been running for at least 9 months prior to completing the questionnaire with a minimum of 5 km/week and not classified as an elite runner by track and field federation. Eligibility as a recreational runner was first confirmed by a running club manager (either a university or public running club) or one of the researchers.

Data collection
A specific questionnaire in Farsi, tailored with the help of the "Start to Run" study questionnaire [22], with questions on personal characteristics, medical information, running characteristics, running-related injuries, and questionnaires of passion scale, RAND 36-items, BERQ-2 and SQUASH was developed using Google Form. This questionnaire was pilot-tested in 12 runners with varying running experience, after which some changes were made to arrive at the final questionnaire.
An electronic link to the online questionnaire was sent to each eligible runner.
Runners were advised to consult their physicians or physiotherapists about their foot type and possible previous RRIs. According to the consensus definition of RRI [23], an RRI was defined as "Runningrelated (training or competition) musculoskeletal pain in the lower limbs that causes a restriction on or stoppage of running (distance, speed, duration, or training) for at least 7 days or 3 consecutive scheduled training sessions, or that requires the runner to consult a physician or other health professional."

Data analysis
Participants' characteristics are presented in Table 1 using descriptive statistics.
Mann-Whitney and Chi-square tests were used to compare data between runners with and without any history of RRIs. Since no quantitative variables were distributed normally, data were reported as median and interquartile range; categorical variables were reported as frequency and percentages. A univariate logistic regression analysis was used to assess a likely association between the risk factors and having RRI. Those variables with a p<0.20 were included in the multivariate logistic regression model [15] with backward elimination, whereby variables remained in the model if their associated multivariate p-value <0.05. Only modifiable factors were entered into multivariate logistic regression, therefore sex and age were not entered into multivariate logistic models. To establish the assumption of no multicollinearity among the independent variables and enhance model fitting, the high correlated variables (obsessive passion and BERQ-2 scores (r=0.81, p<0.001) were not entered together into the multivariate logistic analysis.
In such cases, either variable having a lower univariate p-value was entered into the multivariate logistic analysis. We reported the results as odds ratios (OR) and 95%CI (confidence interval). The OR in continuous variables represents the change in odds of injury for a one-unit increase. The OR in categorical variables represents the change in odds of injury relative to referenced category determined in Table 3.
Sleep quality was rated as very good (1), good (2), medium (3), poor (4), and very poor (5). The OR in sleep quality represents the change in odds of injury for a one-rank increase in sleep rating. Factors were considered risk factors if OR>1 and protective factors if OR<1.

Results
3.1 P a r t i c i p a n t s The questionnaire was filled out by 826 runners, 22 of them excluded due to missing or incorrect data. Total data from 804 questionnaires were analyzed -644 from Tehran city, 102 from Mashhad, and 58 from Shiraz city.     Table 2B shows the anatomical sites of RRIs. The knee (44%) was the most frequently reported injury location, followed by the lower leg (19.9). Tables S1 and S2 (additional file) describe running injury type and location by gender .

3.5
Association between running injury types and risk factors Figure 1 shows the distribution of each RRI between male and female runners.   Table 3. PFPS patellofemoral pain syndrome, MTSS medial tibial stress syndrome, ITBS iliotibial band syndrome, AT Achilles tendo

Discussion
This study aimed to describe the epidemiology and etiology of RRIs specifically in Iranian recreational runners. We analyzed 804 questionnaires, 432 (54%) reporting at least one RRIs. Male-to-female proportion was 57-43%. Most-reported injury was PFPS (19.8%), followed by MTSS (16.9%). Most-affected injury location was the knee (44.6%), followed by the lower leg (19.2%). Of all variables analyzed together in multivariate logistic regression, overweight, running over 20 km/w, participating in other sports, having pes planus and/or cavus, poor sleep quality, greater obsessive passion, and lower RAND-36 score were associated with RRIs. Our study highlights the potential role of sleep quality, psychological factors, and the effects of abnormal foot arch in RRIs. Our findings will help researchers, trainers, clinicians, and policymakers develop preventive strategies and programs, eventually helping runners remain healthy and injury-free.
The prevalence of RRIs over the previous six months was 54%, fitting with previous studies on RRIs in recreational runners reporting a 36.5%-79.3% prevalence [5,15,24,25]. The period over which injuries are reported and injury definition may affect injury incidence. Most-reported injury was PFPS, in line with previous studies [2,26,27]. MTSS was the second-most commonly reported RRI. Prevalence of PFPS (19.8) and MTSS (16.9) exceed other RRIs (<8.7). Men reported more AT and PT than women; women reported more ankle sprains than men. We found only one study that classified RRIs by gender, reporting more AT in men than women [28]. Knee was the most-affected injury site, with 47% of injuries attributed to a higher proportion of PFPS, fitting with previous studies identifying the knee as the mostcommon injured location in runners [2,24,26,29]. The high knee injury rate may be attributed to the greater accumulated impact forces imposed on it when running.
Running over 20 km/w (OR 1.62-8.91) was associated with RRIs, which implies that runners may reduce their weekly running distance to a lower level of 20 km/w to prevent RRI. However, it seems that a safe running distance may vary between populations and is related to other training factors. Contradictory results have been reported so far on running distance. A systematic review investigating RRIs did not reach agreement on the most appropriate and safe running distance [30].
Running on hard surfaces had between 1.35 and 1.72 higher odds of RRIs. Two studies highlighted hard-surface running as a risk for RRIs [27,31]. By contrast, a prospective study reported that hard surface is not associated with RRIs in recreational runners [15]. Our results showed that hard-surface running was one of the contributing factors for the four most common RRIs. These results may account for hard-surface running causing greater musculoskeletal stress to the lower limbs than any other surface [32]. About 82% of participants reported at least one session/week running on asphalt and/or cement, surfaces that are most easily accessible. Results showed that treadmill running seems to result in less MTSS (OR 0.71), maybe because it reduces the total stress on lower leg musculoskeletal system compared to hard surfaces. Sub-group analyses indicated that female runners reported more treadmill sessions per week than men. About 62% of women reported at least one treadmill session/week, compared to 35% of men. Iranian female recreational runners usually prefer indoor running due to religious beliefs or hijab rules, making treadmills the best accessible indoor running option. Treadmill running was not a significant factor for other RRI types.
Besides physical demands, mental aspects also play an important role in sports performance such as running. These psychological factors affect both injury incidence [33] and injury rehabilitation [34]. Psychological factors influence training variables such as the training loads that a runner can tolerate before incurring an injury [35]. Our results showed that runners reporting a history of injury had more obsessive passion for running than those without such history. More importantly, obsessive passion or BERQ-2 (high correlation with obsessive passion in our study) was one of the factors associated with most RRIs. The effect of obsessive passion gained significance when an analysis of our participants revealed that runners reporting multiple injuries scored significantly higher obsessive passion than those with one injury. In fact, obsessive passion drives runners to keep on running while injured. This can lead to multiple and chronic injuries. Our results are in line with a previous study showing that long-distance runners with more obsessive passion were more prone to injury [36]. Because of their obsessive passion for running these runners do not sufficiently weigh the situation and circumstances leading to running excesses, thereby predisposing themselves to RRIs.
Injuries might have an impact on general well-being [37]. We also found an association between perceived health and RRIs. Runners with a history of injury reported lower RAND 36-item scores than those without any such history. A reduced RAND-36 score was shown for all types of RRIs (except for PT). Our analysis showed that injured female runners reported significantly lower perceived health than injured male runners. Injuries are speculated to have more health effects in women than men, or women with lower perceived health are more prone to injury than men.
Due to our study design, it remains unclear whether the lower perceived health is cause or consequence of the RRI.
Our results also showed that poor sleep quality is associated with increasing RRIs odds by 3.78. Previous studies highlighted lack of sleep as a risk factor for sports injuries [38][39][40][41] while considering quantification of sleep. It seems that exploring sleep quality, as measured in our study, can be more relevant to studying sports injuries than exploring sleep quantity. Good sleep quality is necessary for skeletal musculature to adapt, repair, and increase [38] concentration to better perform a sports activity like running, while poor sleep quality can reduce these factors and leads to injuries [39].
Pes planus and cavus are significantly associated with most of the RRIs. Runners with pes planus compared to those with normal feet had an odds ratio of 1.7 for MTSS to 43 for PF; those with pes cavus compared to normal feet had an odds ratio of 4.63 for ankle sprain to 4.87 for PFPS. A subgroup analysis revealed that about 50% of runners reporting multiple injuries had either pes planus or pes cavus.
Previous studies also highlighted the importance of foot arch for RRIs [42][43][44]. A recent study showed that pes planus and cavus are associated with 20 to 77 times higher odds of RRIs than normal feet, respectively [43]. A systematic review reported that pes planus and cavus are associated with lower-limb injuries [45].
Another systematic review reported strong and limited evidence that pes planus is a risk factor for MTSS and PFPS, respectively [46].
Running in a group was associated by 2.3 times higher odds of reporting injuries.
Nevertheless, it is difficult to conclude the causative effect of the association between running in a group or alone and RRIs. Our results showed that about 61% of runners who ran in a group followed a training program. Also, those following a training program showed higher odds of RRIs and MTSS. Group runners most likely follow the same training program. It could therefore be concluded that following the same group running program may increase the odds of RRIs. This indeed underlines the individuality principle in sports training. We therefore recommend individualization of training programs for runners.

Limitations and recommendations for future studies
Our survey results should be interpreted with caution. This is a retrospective study, so it is difficult to determine the causative association between risk factors and RRIs. Recall bias could also be a limitation of our study because all data were collected using a self-reported questionnaire. Although 89% of injuries and 60% of foot types were diagnosed by a physician or physiotherapist, which we believe increases the accuracy of data, injuries and foot type were self-reported. We also provided runners with a clear definition for each RRI to minimize this bias. Future prospective studies are warranted among Iranian recreational runners to substantiate RRI risk factors obtained from our study.

Practical implications
Our study describes potential risk factors for RRIs in Iranian recreational runners, which may be useful toward preventing and managing RRIs. Our findings are also important for runners who want to be aware of factors predisposing them to developing an RRI. These factors may be considered when preventing and/or managing RRIs: 1) correcting pes planus and cavus, 2) avoiding or reducing running on hard surfaces, 3) counseling for obsessive passion for running to avoid overdoing it, 4) controlling running distance, 5) personalizing the training program, 6) improving overall physical and mental health, and 7) enhancing sleep quality.

Conclusion
In

Consent for publication
Not applicable.

Availability of data and materials
The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests. Continuous data are expressed as medians and interquartile ranges (tested by the Mann-Whitney test). All categorical data are expressed by number of runners and percentages (using Chi-square test). Type of surface: hard (cement, asphalt), treadmill, soft (gravel, grass, off-road track), and other (synthetic, sand). Bold Pvalue shows the statistically significant difference between those with and without injury history (P<0.05).