Abstract
und: Trail running (TR) is an endurance discipline characterized by prolonged exercise, irregular terrain, and marked elevation changes, which increase eccentric mus- cular load and may induce muscular, neuromuscular, and cardiac damage.Objective: This study aimed to systematically review the evidence on muscular, neuromuscular, and cardiac damage associated with TR participation.Methods: This systematic review fol- lowed PRISMA 2020 guidelines and was registered in PROSPERO (CRD420251135043). Five databases (PubMed, Web of Science, Scopus, SportDiscus, and ScienceDirect) were searched up to 31 August 2025. Observational, longitudinal, prospective, and case studies involving healthy adolescent or adult trail runners were included. Outcomes comprised muscle damage biomarkers (e.g., creatine kinase, alanine aminotransferase), neuromus- cular function (e.g., squat jump performance, maximal voluntary isometric contraction), and cardiac biomarkers (e.g., CK-MB, cardiac troponins, NT-proBNP). Methodological quality was assessed using the National Heart, Lung, and Blood Institute Study Quality Assessment Tool. Results were synthesized qualitatively.Results: Fifteen studies met the inclusion criteria, including a total of 247 participants. Post-race analyses consistently showed marked increases in muscle damage biomarkers and significant reductions in neu- romuscular performance. Transient elevations in cardiac biomarkers were also observed, suggesting acute but reversible cardiac stress following TR events.Limitations: Evidence was limited by methodological heterogeneity, small sample sizes, and underrepresentation of female athletes.Conclusions: It
studies met the inclusion criteria, including a total of 247 participants. Post-race analyses consistently showed marked increases in muscle damage biomarkers and significant reductions in neu- romuscular performance. Transient elevations in cardiac biomarkers were also observed, suggesting acute but reversible cardiac stress following TR events.Limitations: Evidence was limited by methodological heterogeneity, small sample sizes, and underrepresentation of female athletes.Conclusions: It was found that trail running induces substantial acute muscular, neuromuscular, and cardiac stress, particularly in events with high eccentric loading. Monitoring biochemical and neuromuscular markers may support training load optimization, recovery strategies, and injury prevention. Keywords:endurance; natural environment; muscle damage; biomarkers; contractile efficiency 1. Introduction Trail running (TR) is a discipline that combines running with the challenge of travers- ing natural mountainous environments with varying levels of technical difficulty. Un- like running on smooth surfaces, this modality exposes athletes to substantial elevation changes, irregular terrain, variable weather conditions, and natural obstacles throughout Muscles2026,5, 9 https://doi.org/10.3390/muscles5010009
Muscles2026,5, 9 2 of 16 the course [1]. This constantly changing and unpredictable environment requires greater physical and mental effort, not only due to the need for continuous adaptation but also because of the increased risk of accidents and/or injuries [2]. In recent years, this discipline has experienced significant growth at both recreational and competitive levels, reflected in the increasing number of official events and participants [3]. Due to its characteristics, TR attracts a wide population range—from young individuals to older adults—and is practiced by both men and women [4]. However, this expansion has also generated uncertainty, as the risk factors associated with TR vary considerably depending on age, sex, previous experience, and training level [5]. Compared with road running, TR requires athletes to cope with uneven terrain, elevation gain and loss, and fluctuating environmental conditions, all of which greatly increase the likelihood of sustaining injuries. Injury incidence is higher during competitions than training, particularly in ultra-distance events [6,7]. The type and distribution of injuries vary according to the nature of the event; multistage competitions show a predominance of knee injuries, whereas continuous long-distance races present higher rates of foot and ankle injuries [8,9]. In general, the most frequent injuries in TR affect the lower limbs and include ankle sprains, Achilles and patellar tendinopathies, various types of muscular overload, and even stress fractures [10,11]. One of the most relevant aspects of injury analysis in TR is muscle damage induced during performance—particularly during the eccentric phase of muscle contraction that occurs on downhill sections, where mechanical stress on muscle fibers is substantial [12,13]. During eccentric contractions, the muscle lengthens while producing tension, which can lead to sarcomere disruption, cell membrane damage, and the release of muscle damage biomarkers, such as creatine kinase (CK), lactate dehydrogenase (LDH), alanine amino- transferase (ALT), and myoglobin (MB). These responses reflect structural microdamage and inflammation [14]. This downhill-related eccentric stress compromises not only muscle tissue integrity but also neuromuscular function, altering motor coordination, reducing maximal voluntary force, and increasing both peripheral and central fatigue [15]. Neuromuscular fatigue—defined as a transient decline in the neuromuscular system’s ability
kinase (CK), lactate dehydrogenase (LDH), alanine amino- transferase (ALT), and myoglobin (MB). These responses reflect structural microdamage and inflammation [14]. This downhill-related eccentric stress compromises not only muscle tissue integrity but also neuromuscular function, altering motor coordination, reducing maximal voluntary force, and increasing both peripheral and central fatigue [15]. Neuromuscular fatigue—defined as a transient decline in the neuromuscular system’s ability to generate force—is closely related to muscle damage, with both phenomena influ- encing one another [16]. Damaged muscle exhibits reduced contractile efficiency, potentially increasing mechanical load on other structures and contributing to compensatory patterns that elevate injury risk [17]. Reduced motor control may also lead to technical errors, further increasing the likelihood of musculoskeletal injuries [16]. In TR, neuromuscular function can be profoundly affected due to irregular terrain, frequent pace changes, and prolonged uphill and downhill segments [18]. Similarly to the muscle damage biomarkers described above (CK and LDH), sev- eral studies have associated muscular fatigue with substantial reductions in lower-limb strength [19,20]. These alterations—particularly in ultra-trail events—can even progress to severe conditions such as rhabdomyolysis or myopathies [21]. In fact, the literature reports extremely pronounced muscular alterations in TR, in some cases exceeding those documented in high-intensity sports such as CrossFit [22], where cardiac muscle has also shown acute stress responses [23,24]. Cardiac stress has been investigated in TR, especially in ultra-distance races [25], through specific biomarkers and diagnostic imaging techniques, including echocardio- graphy, magnetic resonance imaging and computed tomography [26]. These methods provide parameters such as the left ventricular ejection fraction (LVEF), a key marker of cardiac contractile function, which is typically altered in pathologies such as heart failure or myocardial infarction [27,28]. LVEF represents the percentage of blood ejected from the left ventricle with each heartbeat relative to its end-diastolic volume [29] with normal https://doi.org/10.3390/muscles5010009
Muscles2026,5, 9 3 of 16 values ranging from 55–70% [30]. While moderate aerobic exercise positively affects LVEF compared with sedentary individuals [31], elite athletes may present similar or slightly reduced values due to chronic physiological adaptations [32,33]. Another widely studied parameter is heart rate variability (HRV), which reflects parasympathetic regulation and has been linked to cardiac stress and autonomic imbalance during high-intensity efforts, though its prognostic value in ultra-endurance running remains debated [34]. Over the past years, advances in clinical cardiology have led to the development of new biomarkers to help diagnose cardiac stress in athletes, including cardiac troponin (cTn), high-sensitivity troponin (hs-cTn), creatine kinase MB isoenzyme (CK-MB), and N-terminal pro–B-type natriuretic peptide (NT-proBNP) [35]. The increase in these biomarkers during TR suggests that athletes are exposed to specific systemic risks that produce transient cardiac stress without necessarily implying permanent myocardial injury [36–38]. However, these risks may be exacerbated under conditions such as dehydration and/or fatigue [39]. The litera- ture also highlights multiple injury risk factors in TR, including experience level, terrain type, footwear selection and individual characteristics of runners [5]. Although several preventive measures have been proposed—such as strength training, improved downhill technique, and proprioceptive work—the evidence supporting their effectiveness remains limited, especially for women and non-professional athletes [40]. Taken together, trail and ultra-endurance running are characterized by marked but largely transient alterations in blood biomarkers that reflect the combined muscular, neu- romuscular, cardiac, inflammatory, and metabolic stress imposed by these events. Across studies, elevations in muscle damage markers have been consistently associated with substantial, short-term reductions in lower-limb strength and neuromuscular performance, with recovery timelines ranging from several days to more than one week after prolonged or multi-stage competitions [37,41]. In parallel, ultra-trail races elicit acute increases in cardiac biomarkers, sometimes exceeding clinical reference values, which generally reflect transient myocardial stress without evidence of persistent structural damage in healthy runners [42–44]. Overall, the magnitude and temporal profile of these biomarker responses appear closely linked to acute performance impairment and recovery demands, with potential implications for subsequent training tolerance and adaptation. Given this background, this review aimed to synthesize
cardiac biomarkers, sometimes exceeding clinical reference values, which generally reflect transient myocardial stress without evidence of persistent structural damage in healthy runners [42–44]. Overall, the magnitude and temporal profile of these biomarker responses appear closely linked to acute performance impairment and recovery demands, with potential implications for subsequent training tolerance and adaptation. Given this background, this review aimed to synthesize evidence on muscular, neuro- muscular, and cardiac damage responses in healthy trail runners following competition or simulated trail running events. 2. Materials and Methods 2.1. Criteria for Study Search and Selection This study consisted of a systematic review of the available scientific evidence related to muscle damage in TR. The review followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines [45] and was registered according to the recommendations of the National Institute for Health and Care Research (NIHR) in the International Prospective Register of Systematic Reviews (PROSPERO), under registration code CRD420251135043, accessible at CRD420251135043, accessed on 27 August 2025. No amendments to the review protocol were made after registration. Articles related to the research topic and published during the last 15 years were selected, with the search cutoff date set for 31 August 2025. A structured and selective search was carried out in the health and sport sciences fields using five databases: PubMed, Web of Science, Scopus, Sport Discus, and ScienceDirect. The search strategy combined medical subject headings (MeSH) and free-text terms associated with trail running (“trail running” OR “mountain running”) AND (injury). The final search equation included the following https://doi.org/10.3390/muscles5010009
Muscles2026,5, 9 4 of 16 keywords: (“Trail Running” OR “trail running” OR “ultra-trail” OR “mountain running”) AND (“Muscle Damage” OR “muscle injury” OR “exercise-induced muscle damage”) AND (“Neuromuscular Fatigue” OR “neuromuscular function” OR “neuromuscular fatigue”) OR (“Cardiac Biomarkers” OR “troponin” OR “CK-MB” OR “NT-proBNP” OR “high- sensitivity cardiac troponin I”) AND (“Prevention” OR “performance” OR “recovery”). The full electronic search strategy for PubMed is provided in Supplementary Material Table S1. No trial registers, preprint servers, or gray literature sources were searched. 2.2. Inclusion Criteria Studies were eligible if they involved healthy adolescent or adult trail runners and assessed muscular, neuromuscular, or cardiac damage using biochemical or functional outcomes. Studies were grouped according to the primary damage domain assessed. To ensure methodological quality, the following inclusion criteria were established: 1. 2. Adolescent or adult populations of both sexes (>15 years old) without medical condi- tions or pathology. 3. 4. 5. Publications analyzing muscle damage using blood biomarkers such as creatine kinase (CK), lactate dehydrogenase (LDH), or AST/ALT (Aspartato Aminotrans- ferasa/Alanine Aminotransferase); peripheral neuromuscular fatigue evaluated using dynamic tests of lower-limb elastic–explosive strength (SJ, CMJ, ABA) or maximal vol- untary isometric contractions (MVIC); and cardiac damage assessed through biomark- ers including Pro-BNP, CK-MB, cTnI, high-sensitivity cardiac troponin I (hs-cTnI), and N-terminal pro–brain natriuretic peptide (NT-proBNP). For the purposes of this review, trail running was operationally defined to include outdoor trail and mountain races, ultra-trail and multi-stage off-road events, as well as controlled treadmill protocols designed to replicate the eccentric and mechanical demands characteristic of trail running. 2.3. Exclusion Criteria The following exclusion criteria were applied: 1. 2. Publications that did not address muscle damage or muscle fatigue, defined as con- tractile force loss or cardiac damage; 3. 2.4. Data Extraction Two authors (I.G.-V. and F.P.) independently screened the articles identified through the selected databases. Titles and abstracts were screened first, followed by full-text assessment. No automation tools were used in the selection process. During the review process, the following information was extracted from each study: publication year; authors; participant characteristics (sample size, age, performance level, sex); type of event (distance, number of
(I.G.-V. and F.P.) independently screened the articles identified through the selected databases. Titles and abstracts were screened first, followed by full-text assessment. No automation tools were used in the selection process. During the review process, the following information was extracted from each study: publication year; authors; participant characteristics (sample size, age, performance level, sex); type of event (distance, number of stages, positive elevation gain); muscle damage biomarkers (CK and ALT); cardiac biomarkers (CK-MB, Pro-BNP, cTnI, hs-cTnI and NT-proBNP); and neuromuscular outcomes such as reductions in squat jump (SJ) performance and maximal voluntary isometric contraction (MVIC). For each outcome, all reported time points (pre-, post-race, and recovery) were extracted when available. After applying the inclusion and exclusion criteria, two authors (I.G.-V. and F.P.) independently extracted all data using Microsoft https://doi.org/10.3390/muscles5010009
Muscles2026,5, 9 5 of 16 Excel ® 2024 (Microsoft Corporation, Redmond, WA, USA). No assumptions were made for missing or unclear data, and no data were imputed. Disagreements were resolved through discussion, and when necessary, a third reviewer (M.Á.O.-Z.) participated to reach consensus. No standardized effect measures or quantitative effect sizes were calculated. 2.5. Overall Quality of Included Studies The articles included were screened by two independent reviewers (I.G.-V. and M.L.) based on the predefined inclusion and exclusion criteria. Duplicate articles were removed using Mendeley Desktop ® v.2112.0 (Elsevier, Amsterdam, The Netherlands), and titles and abstracts were analyzed. When required, full texts were consulted for additional evaluation. All decisions were approved by both reviewers; disagreements were resolved by consulting a third reviewer (M.Á.O.-Z.). The full analysis process lasted four weeks. A detailed summary of the selection process is shown in Figure. Figure 1.Flow diagram describing the study selection process. 2.6. Synthesis Methods Given the heterogeneity in study designs, outcome measures, and reporting formats, a quantitative synthesis (meta-analysis) was not performed. Instead, a narrative qualita- tive synthesis was conducted. Studies were grouped according to the primary domain assessed (muscular damage, neuromuscular function, or cardiac damage), and results were summarized descriptively across studies. https://doi.org/10.3390/muscles5010009
Muscles2026,5, 9 6 of 16 2.7. Risk of Bias Assessment and Methodological Quality Most studies included in this review were observational with descriptive designs. Due to their non-experimental nature, tools such as the PEDro scale [46] or the Cochrane Collaboration tool [47], commonly used in clinical trials, could not be applied. Instead, methodological quality was assessed using tools adapted to observational descriptive studies, focusing on qualitative criteria [48]. Methodological quality was evaluated using the National Heart, Lung, and Blood Institute (NHLBI) Study Quality Assessment Tool (Figure), available at nhlbi.nih.gov/health-topics/study-quality-assessment-tools, accessed on 9 November 2025. This tool was selected due to the predominance of observational and descriptive study designs. It includes 14 items rated as “yes” (green), “no” (red), “not reported” (yellow), or “cannot determine” (gray). Studies were categorized as good (>11 “yes” items), fair (7–10 “yes” items), or poor (<6 “yes” items). The 14 items were assessed independently by two authors (M.L. and A.G.-G.), and disagreements were resolved through consensus or, when necessary, arbitration by a third reviewer (M.Á.O.-Z.). Figure 2.Methodological quality assessment of included studies using the NHLBI Study Quality Assessment Tool for Observational Cohort and Cross-Sectional Studies Green indicates “yes”, red “no”, yellow “not reported”, and gray “cannot determine”. Level of evidence categories were defined as A = good methodological quality and B = fair methodological quality, following previously published criteria, 1 Quality assessment tool for Observational Cohort and Cross-Sectional Studies, 2 LoF; Level of Evidence, 1–14, check list criteria; Q, quality; G, good; F, fair [14,37,41,43–45,49–57]. 2.8. Reporting Bias Assessment Formal assessment of reporting bias was not conducted due to the absence of a quantitative synthesis and the limited number of studies available for each outcome. 2.9. Certainty of Evidence The certainty of evidence was not formally assessed using tools such as GRADE due to heterogeneity in study designs, outcomes, and reporting formats. 3. Results A total of 408 potentially relevant studies were initially identified (Figure). After removing duplicates, 137 articles remained. The inclusion and exclusion criteria were then https://doi.org/10.3390/muscles5010009
assessed using tools such as GRADE due to heterogeneity in study designs, outcomes, and reporting formats. 3. Results A total of 408 potentially relevant studies were initially identified (Figure). After removing duplicates, 137 articles remained. The inclusion and exclusion criteria were then https://doi.org/10.3390/muscles5010009
Muscles2026,5, 9 7 of 16 applied through title and abstract screening, resulting in 80 studies selected for full-text evaluation. Of these, 57 were classified according to their main thematic focus. Finally, fifteen studies were included in this review, selected for specifically addressing the effects of TR on muscle damage, neuromuscular function, and/or cardiac stress. Reasons for exclusion of full-text articles are reported in the PRISMA flow diagram (Figure). 3.1. Studied Population and Type of Event Table populations and the events analyzed. A total of 15 studies involving 247 participants, 30 of them females, were included. Regarding age, studies reported mean or median ages, generally ranging between 30 and 50 years, although one study included adolescent participants aged 15–20 years. Only one of the fifteen studies differentiated participants based on performance level, categorizing them as amateur versus high-level runners. Table 1.Characteristics of the runners and the events. Author Participants Age±SD (Years) Level Race Distance (km) Stages Elevation Gain/Loss Giovanelli et al. (2020) [41] 10 38.2 ±12.4 NR TR 22.48 and 40 3 NR Lecina et al. (2022) [37] 4 38 ±4.11 NR U 768 11 46,865 m+ Saugy et al. (2013) [49] 9 8 CG 41.6±13.1 29.3±8.1 NR U 330 1 24,000 m+ Coratella et al. [14] 10 22 ±3 NR T 30 (s: 10 km/h) 1 −20% Birat et al. (2020) [58] 12 14.40 NR U 48.2 and 66 2 NR Pradas et al. (2021) [50] 20 43.3 ±4.52 10 A 10 HT U 108 1 5800 m+ Martinez-Navarro et al. (2019) [43] 46 M 42 ±7.49 A U 118 1 5439 m+ 4227 m− Belli et al. (2018) [51] 6 M 47 ±5 HT U 217 1 12,200 m+ 12,200 m− Rubio-Arias et al. (2019) [52] 6 M 30.5 ±8 A U 111 1 4474 m+ 4420 m− Kim et al. (2012) [53] 20 EIH 10 CG 46.8±1.23 47.5±1.33 A U 100 1 NR Le Goff et al. (2022) [44] 17 M 11 F M: 45.3±7.8 F: 43.3±9.8 A U 105 1 5600 m ± Burger et al. (2024) [57] 14 M 42.9 ±8.0 P U 130 1 1170
Description
Trail running induces substantial acute muscular, neuromuscular, and cardiac stress.