Introduction
The popularity of running continues to rise. Meanwhile, trail running has emerged as a distinct branch of road or track running. Trail running involves outdoor running across diverse natural settings such as forests, deserts, mountains, coastal zones, and jungles (Malliaropoulos, Mertyri and Tsaklis, 2015). This form of off-road running is not defined by specific distances or changes in elevation, and it encompasses a variety of terrains, including forest paths, single tracks, dirt roads, and beach sands. Notably, less than 20% of the competition distance occurs on paved or asphalt surfaces (Scheer et al., 2020; Viljoen et al., 2021d). The sport has witnessed a surge in popularity, as evidenced by the global increase in organized trail races. Approximately 20 million participants engage in trail running, marking a 15% rise in the past ten years (Viljoen et al., 2022). The International Trail Running Association (ITRA) reported that 195 countries organized 25,700 trail competitions from 2013 to 2019.
There is evidence to suggest that participating in sporting activities in outdoor settings have a more positive result on mental health than in indoor activities (Thompson Coon et al., 2011). Trail running has been associated with improvements in mental health and resilience, as reported by its participants (Lincoln, 2021). Despite its various health benefits, trail running poses a higher injury risk due to the challenging terrain and varied conditions it involves (Jooste et al., 2023; Malliaropoulos, Mertyri and Tsaklis, 2015; Krabak, Waite and Schiff, 2011). Previous studies have primarily concentrated on the epidemiology of injuries related to road running (Dempster, Dutheil and Ugbolue, 2021; Jiang et al., 2021; Van Gent et al., 2007). However, applying these findings to trail running can be challenging owing to the unique characteristics of the sport. Trail running requires a distinct type of endurance effort that is affected by factors like significant elevation changes, varying environmental conditions, the distance covered, and uneven terrain (Viljoen et al., 2021b). The need to continually adjust to varying running conditions requires increased effort, which exposes the body to heightened physiological and biomechanical stress. These distinct aspects make it challenging to generalize the results from road running studies to trail running.
Several studies have examined acute metabolic responses to trail running races (Waśkiewicz et al., 2012; Jouffroy et al., 2019; Atkins et al., 2022), but there has been limited research on injuries associated with trail running, particularly those affecting the lower limbs. Ultra-endurance running, involving long hours, can significantly strain the musculoskeletal system, potentially leading to injuries (Almekinders and Engle, 2019). Both racing and training can cause overuse injuries if the physical demands exceed the body’s ability to adapt. These injuries primarily affect the lower limbs and include conditions like patellofemoral pain syndrome, medial tibial stress syndrome, and Achilles tendon injuries, as well as joint sprains and fractures (Krabak, Waite and Schiff, 2011; Scheer and Krabak, 2021). Additionally, trail runners often train or compete in remote areas, which complicates the task for medical providers who may need to reach or evacuate injured participants (Hoffman et al., 2014). This underscores the significance of discovering runners who are at risk of injury prior to training or racing, aiming not only to prevent severe injuries but also to maintain the health benefits of running (Viljoen et al., 2021b; Viljoen et al., 2022).
The growing awareness of demand and potential risks associated with outdoor sports has underscored the importance of understanding how injuries occur among trail runners. Researchers have investigated several risk factors linked to running injuries among trail runners, which can be categorized into three main groups: personal factors (such as age, sex, and BMI) (Owen et al., 2024; Easthope et al., 2010; Krabak, Waite and Schiff, 2011), training or racing-related factors (including distance, intensity, and footwear) (Vercruyssen et al., 2016; Knobloch, Yoon and Vogt, 2008; Matos et al., 2020), and health-related factors (including medication use, previous injuries, and chronic diseases) (Viljoen et al., 2021c; Scheer and Murray, 2011; Viljoen et al., 2021a). Appropriate medication for injuries in trail running is crucial for preventing long-term problems (Krabak, Waite and Lipman, 2014). Thus, it is essential to study and collect data on musculoskeletal injuries in various aspects of trail running, including during competitions and training sessions. Lower extremity injuries are the most common in sports, with a particular focus on their prevalence in running, as extensively discussed in numerous research articles (Emery and Pasanen, 2019). Despite various studies on running injuries among trail runners (Easthope et al., 2010; Gajardo-Burgos et al., 2021; Graham et al., 2012; Hamill et al., 2022), the specific risk factors and types of running-related injuries remain unclear in the existing literature. The aim of our review is to analyze various studies on this topic to discover the characteristics (incidence, injury region and type of injury) of lower extremity injuries among trail runners. Insights gained from this review will establish baseline data, guide future studies and inform the development of effective prevention and treatment approaches for this particular style of running.
Methods
Data Sources and Search Strategy
The design of the present review was systematic, adhering to the guidelines specified in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. Figure 1 is a flowchart that shows the search procedure. We performed an online literature search utilizing three databases: PubMed, Web of Science, and Scopus, along with Google Scholar. The search employed a combination of keywords including “trail running,” “trail race,” “trail runner,” “injury,” “lower limb,” “lower extremity,” “injury factor,” and “prevalence,” using Boolean operators “AND” and “OR.” To ensure the review’s relevance and timeliness, only peer-reviewed papers published in English since 2000 were included.
Figure 1
Flowchart of articles selection procedure.
Inclusion and exclusion criteria
We retrieved full papers when abstracts did not provide enough information to determine eligibility. The term “trail running” generally denotes running on unsealed, natural surfaces without specific requirements concerning distance, the proportion of off-road surface, terrain, or elevation. However, the definition provided by the International Trail Running Association (ITRA) is the most comprehensive, offering clear details on the surface, terrain, support, and route markings, without imposing limits on elevation or distance (Scheer et al., 2020; Viljoen et al., 2021b). Consequently, for this systematic review, we have adopted the ITRA’s definition of trail running to determine the inclusion of studies.
The inclusion criteria included: 1) studies addressing lower body injuries, the injury data in this review includes self-reported data and medical data; 2) studies involving trail runners as participants, they were classified as trail runners if they had taken part in a race or training session that met the ITRA’s definition; 3) research discussing the prevalence or incidence of injuries; 4) studies published in peer-reviewed journals as prospective cohorts, retrospective cohorts, cross-sectional, observational, or randomized controlled studies; 5) articles written in English.
Exclusion criteria included: 1) review articles; 2) research involving participants in sports other than running; 3) studies concerning acute physiological changes due to running, such as kidney injury; 4) studies focusing solely on biochemical markers like lactate, creatine kinase, and cortisol; 5) studies that only analyzed injured runners or failed to clarify whether all trail runners were free from injury at baseline; 6) studies focusing on the psychological impacts of sports on mental health; 7) multiple publications from the same cohort study.
Data extraction and quality assessment
Initially, one author conducted data extraction from the included studies. A second reader then verified and completed the data extraction when necessary. The extracted information included: 1) author and year of articles; 2) participant demographics, including gender (male/female) and age; 3) study setting, such as country, race distance, and elevation changes; 4) risk factors; 5) injury epidemiology, detailing injury rates, the anatomical regions affected, and the types of injuries.
A modified version of the Downs and Black assessment tool (Downs and Black, 1998) was employed to evaluate the quality of each included study, with two authors conducting the assessment. This modified tool, previously applied in systematic reviews of running-related injuries (Ceyssens et al., 2019; Neal et al., 2016), consists of 15 items across 4 categories: reporting (items 1, 2, 3, 5, 6, 7, 9 and 10), external validity (items 11 and 12), bias (items 16, 18 and 20), and selection bias (items 25 and 26). The maximum attainable score was 15, and studies scoring positively on more than 50% of the items were deemed high quality. The scores for each item given by the two authors were compared. Any discrepancies between the two authors were addressed through a consensus meeting. The third author was brought in to make the final decision once they could not reach an agreement.
Results
We initially searched a total of 851 articles, as shown in Figure 1. After removing 575 duplicates, we left 276 records for screening. After reviewing titles and abstracts, 195 articles were excluded, narrowing the pool to 81 articles. Subsequent application of the exclusion and inclusion criteria further reduced the selection to the 24 articles that were included in this study. These selected articles are all considered to be of high quality.
The review incorporated 24 studies published between 2020 and 2024, with a summary provided in Table 1. These studies sampled populations from Chile, France, Germany, Greece, Italy, the Netherlands, Portugal, Scotland, South Africa, Spain, Sweden, and the USA. Collectively, they involved 17,664 trail runners, with 44.5% being female (Figure 2). All studies focused on lower limb injuries and presented a variety of injuries among trail runners. Risk factors related to trail running were examined in 22 of the studies, 19 reported injury rates, and 16 described the race settings.
Table 1
Description of studies included.
| STUDY | PARTICIPANTS | AGE | COUNTRY OF ORIGIN | RACE SETTING | RISK FACTORS | INJURY RATE | INJURY REGION | TYPE OF INJURY |
|---|---|---|---|---|---|---|---|---|
| Knobloch et al. (2008) | N = 291 (248 males, 41 females and) | 42 ± 9 years | Germany | / | Running surface and running experience | The injury rate was 0.08/1000 km (2.93 per runner) | Achilles tendon, knee, tibia, and plantar | Achilles tendon overuse injury (56.6%), anterior knee pain (46.4%), shin splints (35.7%), and plantar fasciitis (12.7%) |
| Scheer et al. (2011) | N = 69 (48 males and 21 females) | Male: 46 years, female: 40 years | Spain | A 219-km, 5-day competition | Musculoskeletal, dermatological and other illness | 39 runners (or 56.5 %) were deemed to have a medical condition | Hip, knee, Achilles, ankle and muscle | Foot blisters (33.3%), chafing (9.1%). Lower body musculoskeletal injuries (22.2%) |
| Krabak et al. (2011) | N = 407 (323 males and 84 females) | / | USA | 7 days, staged, 240-km ultramarathon running race | Age and sex | The injury or illness rates were 3.86 per runner and 65 per 1000 h | Foot (73.7%), lower limb (8.6%), ankle (4.9%), and knee (3.5%) | Skin-related disorders (74.3%), musculoskeletal injuries (18.2%), and medical illnesses (7.5%) |
| Graham et al. (2012) | N = 11 (11 males) | 33 ± 11 years | Scotland | 150 miles in 7 days, Gobi Desert, Mongolia | Mood alterations and sleep duration | The injury rate was 100% | Lower limb | Skin and soft tissue injuries |
| Scheer et al. (2014) | N = 50 (30 males and 20 females) | 40.4 ± 7.9 years | Spain | Al Andalus Ultimate Trail (219 km) | Race experience | A blistering incident was reported in 76% of the participants | Toes (65%), ball of the foot (16%), heel (14%), and sole (5%) | Blisters |
| Hoffman et al. (2015) | N = 376 (320 males and 56 females) | / | USA | A 161-km ultramarathon | Muscle fatigue | The prevalence of cramping was 14.3%, and near cramping was 26.8% | Calf (54%), quadriceps (44%), and hamstring (33%) muscles | Muscle cramping (14.3%) and near cramping (26.8%) |
| Malliaropoulos et al. (2015) | N = 40 (36 males and 4 females) | 38.4 ± 8.73 years | Greece | / | Training and surfaces | At least one injury was reported by 90% of the runner | Lower back, Achilles tendon and hip joint | Overuse bone stress injuries (22%) and iliotibial band syndrome (16%) |
| Giandolini et al. (2016) | N = 23 (23 males) | 39 ± 11 years | France | A downhill route of 6.5 km, consisting primarily of forest trails, that descends 1264 m. | Musculoskeletal damage and fatigue | / | Knee and plantar | Deficit in voluntary activation |
| Vercruyssen et al. (2016) | N = 13 (13 males) | 38.2 ± 4.8 years | France | An 18.4-km trail running exercise | Footwear | / | Calf | Calf pain |
| Vernillo et al. (2016) | N = 77 (64 males and 13 females) | 43.6 ± 10.9 years | Italy | A 65-km race (altitude between 725 and 2100 m) | General fatigue and muscle cramps | The overall injuries/illnesses were 1.9 per runner and 13.1/1000 h | Plantar (28.6%), ankle (28.6%), knee (14.3%), thigh (14.3%), Achilles (7.1%) and neck/cervical spine strain (7.1%) | Medical illnesses (50.3%), musculoskeletal injuries (32.8 %), and skin related disorders (16.9 %) |
| von Rosen et al. (2016) | N = 64 (31 males and 33 females) | 17 ± 1 years | Sweden | / | Training volume, competition time and surfaces | The injury incidence rate was 18/1000h of training | Foot/lower leg (48.6%), knee (22.9%), hip (11.9%) and lower back (6.4%) | Overuse injuries (78.0%,) and acute injuries (22.0%) |
| Hespanhol et al. (2017) | N = 228 (171 males and 57 females) | 43.4 years | Netherlands | The median of the distance was 28.0 km, ranging from 3 to 230 km | / | The injury rate was 10.7 injuries per 1000 h and the mean prevalence of RRIs (22.4%) | Knee, Achilles tendon, calf and ankle | Achilles tendon injury (12.8%), calf muscle injury (10.7%), knee pain undiagnosed (8.7%) and ankle sprain (7.0%). |
| Kerhervé et al. (2017) | N = 14 (14 males) | 21.7 ± 3.0 years | France | Two 24-km trail runs | Calf compression sleeves | / | Achilles tendon and calf | Achilles tendon pain and delayed onset calf muscles soreness |
| Matos et al. (2020) | N = 719 (529 males and 190 females) | 38.01 ± 7.78 years | Portugal | / | Exposure time | 87.8% of the sample reported an injury, the injury rate was 10.0 per 1000 h | Toenail (24.8%), knee (17.5%), and ankle (14.5%) | Blisters (20%), irritation (chafing) (14%), superficial wounds (12%), sprains (11%), and iliotibial band syndrome (7%) |
| Gajardo-Burgos et al. (2021) | N = 654 (413 males and 241 females) | 36.2 years | Chile | Several trail runs from 11 to 63 km | Training following injury | Injury frequency rates (31.3%) and illness frequency rates (22.3%) | Knee | gradual onset injuries |
| Temesi et al. (2021) | N = 32 (32 males) | Long group: 38 ± 10 years, short group: 35 ± 8 years | France | Long race (>100 km) or short race (<60 km) | Race distance | / | Knee and plantar | Muscle contractile property impairment |
| Viljoen et al. (2021a) | N = 152 (120 males, 32 females) | 37.1 ± 9.1 years | South Africa | / | A history of previous injury and chronic disease | A mean prevalence of 12.3% and an overall injury rate of 19.6 injuries per 1000 hours | Knee (29.8%), shin/lower leg (18.0%) and foot/toes (13.7%) | Tendinopathies (27.8%), muscle injuries (20.5%) and joint sprains (8.8%) |
| Viljoen et al. (2021c) | N = 2824 (1597 males and 1227 females) | / | South Africa | A 10-km and a 22-km race | Distance, chronic disease and history of allergies | The annual incidence of injuries (13%) | Knee (35%), shin/lower leg/calf (16%) and thigh (11%) | Iliotibial band syndrome (22%), Achilles tendon injury (10%) and hamstring injury (9%) |
| Viljoen et al. (2021d) | N = 305 (213 males and 92 females) | 38.3 years | South Africa | 2019 Sky Run races | Training and demographic variables | The incidence was 49.5 injuries per 1000h | Knee (26.5%), ankle (21.6%), and foot (16.7%) | Tendinopathy (27.5%), joint sprain (19.6%), and muscle injury (15.7%) |
| Hamill et al. (2022) | N = 1016 (518 males and 498 females) | 39.0 ±13.2 years | USA | N/A | Trails, terrains and footwear | Injury was reported by 39.8% of the runner during running on a trail | Ankle, foot, Shin, hip, plantar, knee, Achilles | Ankle sprain, hip stress fractures |
| Sanchez-Garcia et al. (2022) | N = 51 (35 males and 16 females) | 15 to 22 years | Spain | N/A | The characteristics of the mountain terrain | 2.2±1.8 injuries per 1000 h | Ankle (49.5%), knee (17.9%), and lower leg (9.5%), | Joint sprain (43.2%), tendinopathy (18.9%) and non-specific injuries (11.6%) |
| Jooste et al. (2023) | N = 251 (181 males and 70 females) | 40 years | South Africa | 2021 Mac Ultra race | / | The incidence was 19.92/100 runner | Lower limb (26%), thigh (22%), ankle and foot (13%) | Muscle injury (36%), tendinopathy (24%), and joint sprain (9%) |
| Owen et al. (2024) | N = 9835 (4725 males and 5110 females) | / | USA | N/A | Sex, age and racial disparities | / | Females: elbow, wrist, knee, lower leg, and ankle; males: shoulder, upper trunk, and hand | Females: strains/sprains and fractures; males: lacerations |
| Viljoen et al. (2024) | N = 162 (103 males and 59 females) | / | South Africa | 2022 Mac Ultra races (46 km, 80 km, 161 km, and 322 km) | Race distance categories | The injury rate was 1.66 injuries per 1000 h | Knee (28%), (19%), and lower leg (17%) | Muscle and tendon tissue injuries (56%), muscle injuries (31%) and tendinopathies (25%) |
Figure 2
Characteristic information: (a) Gender distribution of runners, (b) The number of studies according to the nationality.
Discussion
The objective of this review is to explore the literature from 2020 to 2024 concerning the characteristics (incidence or prevalence, injury region, and type of injury) of lower limb injuries in trail runners. This review included 24 articles that met the inclusion criteria. The diverse study designs and varying definitions of injury among these studies posed challenges in forming definitive conclusions about injury epidemiology in trail runners. Nevertheless, we managed to compile a unified discussion on shared injury characteristics, including injury rates, the anatomical regions involved, injury types, and risk factors.
Running injuries frequently arise from overuse, in which the musculoskeletal system is subjected to excessive strain. Runner typically attributes such injuries to repeated microtrauma instead of a single, identifiable event. The reported overall prevalence of injuries to the lower limb revealed a great range (12.3% to 100%), with injury incidence ranging from 2.2 to 65 injuries per 1000 hours of running. Running injuries frequently arise from overuse, in which the musculoskeletal system undergoes excessive strain (Wen, 2007). Repeated microtrauma, rather than a single identifiable event, typically causes such injuries (Saragiotto et al., 2014). This review revealed that the most frequently injured sites of the lower limb are the knee, ankle, Achilles tendon, foot, plantar area, calf, and hip. The knee joint is particularly vulnerable, often cited in literature as a frequent site for overuse injuries related to running (Van Gent et al., 2007). This review aligns with those findings, with 17 studies identifying the knee as a common site of injury. For instance, Viljoen et al. (2021b) noted that 29.8% of running-related injuries in the lower body during trail running were at the knee. Similarly, Scheer and Murray (2011) found that knee complaints led to the majority of musculoskeletal consultations. Gajardo-Burgos et al. (2021) also observed a high prevalence of knee injuries among both male and female trail runners. The increased knee joint loading over long-term trail running, especially on more technically demanding and uneven surfaces compared to road running, may explain the higher incidence of knee injuries.
The ankle was highlighted as a frequently injured anatomical region in trail running, with 10 studies noting its vulnerability. Sanchez-Garcia et al. (2022) found that 49.5% of trail running injuries occurred at the ankle, with 40.4% happening during competitions and 42.6% during training sessions. Most of these injuries were reported as joint sprains by several sources, emphasizing the importance of ankle stability in trail running (Sanchez-Garcia et al., 2022; Hespanhol, Van Mechelen and Verhagen, 2017; Viljoen et al., 2021a). In terms of overuse injuries, the Achilles tendon also proved significant, with 7 studies citing it as a common region of injury. Specifically, Knobloch et al. (2008) identified Achilles tendinopathy as the primary overuse injury among master running athletes, a finding echoed by Malliaropoulos et al. (2015). Moreover, the relationship between running pace and Achilles tendinopathy is particularly notable in trail running, where maintaining a constant speed is challenging due to the varied inclines and declines of the terrain, further stressing the Achilles tendon. The foot was reported as an injured anatomical site in 6 studies, highlighting its vulnerability among trail runners, particularly due to frequent occurrences of blisters (Scheer and Murray, 2011; Matos et al., 2020; Scheer et al., 2014). Injuries to the plantar area and calf were each noted in 5 studies, indicating these areas are also commonly affected. Specifically, plantar fasciitis frequently affects the plantar area (Knobloch, Yoon and Vogt, 2008), while calf pain and muscle injuries are typical in the calf region (Vercruyssen et al., 2016; Hespanhol, Van and Verhagen, 2017). Additionally, the hip was noted as an injured site in 4 studies, emphasizing its importance in the spectrum of lower extremity injuries faced by trail runners, with conditions such as iliotibial band syndrome often occurring (Viljoen et al., 2021c; Malliaropoulos, Mertyri and Tsaklis, 2015; Matos et al., 2020).
Several risk factors linked to running-related injuries in trail running can be categorized into three primary categories: personal factors, training or racing-related factors, and health-related factors. Personal factors include age, sex, and racial disparities, which can influence susceptibility to injuries (Owen et al., 2024; Krabak, Waite and Schiff, 2011; Viljoen et al., 2021d). Training or racing-related factors encompass a wide range, such as training volume, race experience, competition time, race distance, exposure time, terrains, surface conditions, use of calf compression sleeves, and footwear, all of which can impact injury risk (Knobloch, Yoon and Vogt, 2008; Kerhervé et al., 2017; Temesi et al., 2021; Vercruyssen et al., 2016; von Rosen, Heijne and Frohm, 2016; Malliaropoulos, Mertyri and Tsaklis, 2015; Hamill et al., 2022). Health-related factors involve previous injuries or illnesses, a history of allergies, chronic diseases, mood alterations, and sleep duration. These can significantly affect a runner’s risk profile (Scheer and Murray, 2011; Viljoen et al., 2021a; Gajardo-Burgos et al., 2021; Viljoen et al., 2021c; Graham et al., 2012). Studies often do not explore the interaction effects between these potential injury-causing factors. Given the multifactorial nature of running-related injuries and the interdependence of etiological factors, a comprehensive exploration of all potential confounding factors is necessary. The process of lesion production is complex and varied, making it challenging to precisely identify factors that contribute to injuries.
Our study has several limitations. First, trail running encompasses a variety of forms, and different types of trails running (e.g., terrain, distance, climate) may result in different types of injuries. Second, all included studies were assessed using the same quality checklist; however, different types of studies might benefit from more tailored quality assessments. Third, this review did not include a sensitivity analysis. The primary reason for this omission is that most systematic reviews on running injuries do not incorporate sensitivity analysis, leading to a lack of standardized methods for conducting such analyses and making it challenging for researchers to perform systematic sensitivity analysis. Additionally, the diversity in methodologies and outcome measurements among the included studies may hinder cross-study comparisons and the synthesis of results, particularly concerning the definition of injuries.
Conclusions
Running-related injuries are prevalent among trail runners, predominantly affecting the lower limbs and often resulting from overuse. The reported prevalence of lower limb injuries among trail runners displays a wide range, spanning from 12.3% to 100%. Additionally, the incidence of these injuries ranges from 2.2 to 65 injuries per 1000 hours of running. Notably, the knee emerges as the most frequently injured region, followed closely by the ankle and Achilles tendon. Running injuries have multifactorial origins, indicating that personal or training-related factors cannot be their sole cause. This enhanced knowledge is essential for the development of training plans and protective strategies aimed at reducing injury risk. Ultimately, these efforts will enhance safety for trail runners, ensuring more protected and informed participation in the sport.
Competing Interests
The authors have no competing interests to declare.