The popularity of ultramarathon races continues to grow with an estimated 70,000 runners participating in running races throughout the world (16,20). They represent any foot race >42 km and can occur over a single day or multiple days. Most races are point-to-point continuous races occurring over a specific period (i.e., 1 to 2 d). Multi-day races are point-to-point staged races that occur over 3 to 7 d. Unlike marathons, ultramarathons typically occur in more extreme environments with variations in terrain (mountains, snow, sand dunes, river crossings, or slot canyons) temperature, and humidity. Additionally ultramarathon runners will require different equipment depending upon the length of the race. In multi-day races, runners must be prepared to carry all their gear (i.e., food, water, and protective clothing) throughout the course of the race.
There are limited studies relating to the common injuries and illness in ultramarathon runners. Early studies from the 1990s focused on musculoskeletal injuries, noting that most running-related injuries were due to Achilles tendinopathy (2% to 18%) and patellofemoral pain (7% to 15%) (16). More recently, a 2011 prospective study of multi-day ultramarathon runners suggested that 95% of injuries are minor in nature and due to skin-related disorders (74.3%), musculoskeletal injuries (18.2%), and medical illnesses (7.5%) (20). Other studies have focused on exercise-associated hyponatremia (EAH), reporting an incidence of 8% to 50% (11–13). Little is known about cardiovascular events during ultramarathon races (17).
As one can appreciate, the growth in ultramarathons with the inherent challenges of the unique environments, training demands, nutritional preparation, and equipment provides education and research opportunities for both physician and athlete. Those that are ill prepared for these challenges will be at risk from injury and illness. By better understanding the ultramarathon athlete, the sports medicine physician can provide optimal care and hopefully prevent significant morbidity and mortality. The goal of this article is to review the existence of and need for future research in preventive strategies for managing commonly encountered musculoskeletal injuries and medical illnesses in ultramarathon runners.
Injuries to the musculoskeletal system are common in running sports (31,40). Reported musculoskeletal injury incidence varies depending on the methodology of the study with a greater number of studies focused on the marathon runner. Musculoskeletal injury rates range from 19% to 75% (14,27,29,39) in marathons, 2% to 18% in continuous ultramarathons (21), and 19% to 22% in staged, multi-day ultramarathons (20,33). In multi-day ultramarathons, musculoskeletal injuries accounted for 18% of the minor encounters (able to continue racing), accounted for 22% of the major injury encounters (unable to continue racing), and most likely are to occur during stages 3 or 4 of a 7-stage race, highlighting the potential cumulative effect of running long distances on the musculoskeletal system. While general muscle soreness affects most ultramarathoners, true musculoskeletal injuries, whether minor or major, may decrease performance and result in decreased training or medical withdrawal from a race.
Lower extremity injuries predominate, with the knee and ankle being most affected (8,20,21). A review of incidence and prevalence of running-related musculoskeletal injuries found the most common to be medial tibial stress syndrome (incidence, ranging from 13.6% to 20.0%; prevalence, 9.5%), Achilles tendinopathy (incidence, 9.1% to 10.9%; prevalence, 6.2% to 9.5%), and plantar fasciitis (incidence, 4.5% to 10.0%; prevalence, 5.2% to 17.5%) (16,21). The main ultramarathon musculoskeletal injuries were Achilles tendinopathy (prevalence, 2.0% to 18.5%) and patellofemoral syndrome (prevalence, 7.4% to 15.6%) (16,21).
The majority of studies evaluating risk factors for preventing musculoskeletal injuries has been conducted in marathon runners and military recruits. Studies have estimated that 60% to 72% of running injuries are due to training errors, including excessive mileage or sudden change in routine (9,38). Factors associated with lower extremity injuries include a prior history of running injuries, training >64 km·wk−1 in men (odds ratio, 2.9), and participation in more than 6 races in the previous 12 months (9,37,38). Interestingly the study by Fields et al. (9) that showed higher mileage training had a protective effect for knee injuries but not thigh or hamstring injuries. There is limited and conflicting evidence regarding the impact of age and body mass index on running injuries (37). However a study of multi-day ultramarathon runners reported that a 10-year increase in age was associated with 0.5 fewer injuries per runner (20).
Other articles have focused on the role of strength, biomechanics, stretching, and shoe type in preventing running injuries (14,21,30). Hip abductor, hip flexor, and vastus medialis weakness are potential risk factors for lower extremity injury, including iliotibial band syndrome and patellofemoral pain. However there are no prospective studies regarding the utilization of specific strengthening exercises for preventing injuries in ultramarathon runners. Athletes with cavus feet have an increased risk of stress fractures and patellofemoral pain (9); however no prospective studies have shown interventions, such as orthotics or arch support, that decrease the rate of injury. Other malalignment issues, including genu valgum, are not risk factors for injury. A Cochrane review of orthotics suggests that shock-absorbing insoles probably reduce the incidence of stress fractures in military recruits, but their impact in runners is less clear (30). Several studies examining the role of stretching have concluded that preexercise stretching does not reduce running injuries (9). Finally despite the numerous studies highlighting the difference in impact forces on the lower extremity between running and minimalist shoes, their effects on injury rates are still awaiting prospective studies (9,30).
Though the given findings are helpful, no evidence exists that identifies the ideal strategy for preventing musculoskeletal injuries in ultramarathon runners. Therefore the following represented recommendations are based on the experience of the authors and research in marathon runners. It might seem unreasonable to recommend an ultramarathon runner limit their total running mileage to <64 km·wk−1 to prevent injury on the basis of previous research in marathon runners (37,38). However future studies should help identify mileage limits, perhaps based on the specific distance and/or days of an ultramarathon race that help prevent injury without sacrificing performance. Correcting other training errors represents a more appropriate opportunity for musculoskeletal injury prevention. Strategies could include limiting the number of competitions in a race season, adhering to a gradual increase in mileage during training and proper pacing over the course of a race, especially in multi-day races where musculoskeletal injuries typically occur later in a race (20). It seems reasonable to adhere to the general guidelines of limiting any increase in time or mileage to no more than 10% to 20% wk−1 in hopes of injury avoidance (9). Runners preparing for a race should incorporate training runs primarily on the same surface on which the race will be held (road, trail, sand, etc.). Incorporating additional environmental factors into training that are similar to race parameters (such as presence of hills, ambient temperature, and elevation) is recommended also. Finally a strengthening program focusing on the hip abductors or flexors and knee muscles should be part of any training or prevention program.
Unique to ultramarathons is the type and amount of gear utilized during a race, especially multi-day competitions. Gear recommendations can vary by the type of ultramarathon (continuous vs multistaged) and the terrain. Appropriate clothing, shoes, backpack, and access to back-up gear, food, and hydration may affect the risk of musculoskeletal injury. Ultramarathon runners should be cognizant of gear weight, though it is unclear how much this impacts the risk of injury. A runner is less likely to be distracted, affected, or hindered by environmental factors if they have proper gear specific to their race environment. This may allow the runner to focus on avoiding hazards that may cause a fall or twisting injury. Additionally comfortable appropriate gear may allow runners to maintain ideal gait mechanics, thus avoiding abnormal load responses that could lead to acute, insidious onset or overuse injuries. All gear should be utilized and tested prior to the start of any race.
Exercise-associated collapse (EAC) is the most common reason for a medical encounter during a long-distance race (3,5). It is common in marathons, representing 59% to 69% of all medical encounters at the finish line, resulting in 10.1 to 13.7 medical illnesses per 1000 runners (29). It is less common during an ultramarathon race, representing 6.6% of all medical encounters during a multi-day ultramarathon compared with skin-related (74.3%) and musculoskeletal (18.2%) injuries (20). However EAC accounted for 65% of medical illnesses that lead to removal from the race, resulting in 118 medical illnesses per 1000 runners (20). EAC may be secondary to a variety of causes, including heat-related illness, electrolyte abnormalities, cardiovascular compromise, respiratory compromise, and seizures (3). This section will focus on the two most common preventable medical causes, heat-related illness and EAH. The unique environment of the ultramarathon will dictate the likelihood of other medical illnesses encountered, such hypothermia, altitude illness, or infectious diarrhea. A complete discussion of the prevention of these medical problems is outside the scope of this article, but articles specific to the environmental challenge should be reviewed.
The majority of heat-related illness is mild in nature and responds to minimal interventions. However heat-related illness that is more severe involving heat exhaustion and heat stroke can lead to significant morbidity and mortality. Identification of potential risk factors and early intervention are key to managing heat-related illnesses (2).
Understanding the body’s thermoregulation system is crucial to preventing heat-related illness. Body temperature regulation occurs through the hypothalamus, which balances heat generation versus heat loss. Significant heat generation occurs with exercise, where skeletal muscles can increase their metabolic consumption by up to 20 times, with approximately 75% to 80% of that energy converted into heat (23). Heat lost to the environment occurs by four major methods: conduction, convection, radiation, and evaporation. Evaporation is the most important method of heat loss during exercise, and significant exercise can produce 1 to 2 L·h−1 of sweat loss (15). High environmental humidity rates will hamper the ability of sweat to evaporate, leading to subsequent heat loss. When the body senses a rise in core temperature, the thermal center of the hypothalamus increases cardiac output, triggers dilation of surface vessels, and increases sweating. Hyperthermia occurs when the body’s natural ability to maintain its core temperature is compromised, leading to a rise in body temperature.
There is a variety of factors that contributes to the development of heat-related illness (2,34). Intrinsic factors relate to the athlete, including a history of heat-related illness, poor fitness level, fatigue, sleep deprivation, hypo- or hyperhydration, and lack of acclimatization to the race environment. Comorbidities such as cardiovascular disease, diabetes, gastrointestinal illness, and respiratory illness can impact the body’s ability to regulate heat. Medications including stimulants (increase heat production), anticholinergics (decrease sweating), and drugs (alcohol) will contribute to heat-related illness (2). Extrinsic factors relate to the environment, including temperature >35°C, humidity, intensity or duration of exercise, and poor access to water or shade. As single-day and multi-day ultramarathons typically occur in remote locations, athletes likely will have a greater opportunity to experience more extremes of temperature in a setting with fewer resources than a typical marathon. Though beyond the scope of this article, wet globe temperature readings can be helpful for assessing the risk of heat-related illness (3,29). Runners competing in a multi-day ultramarathon race most likely are to experience a medical-related illness during the first stage of the race, thought to be secondary to the lack of acclimatization (20).
Early recognition of symptoms and signs of heat-related illness are crucial to preventing serious injury. Mild forms of illness include heat rash (miliaria rubra), heat cramps, heat edema (painless swelling of limbs), or heat syncope that is uncomfortable but often self-limiting. However even milder forms of heat-related illness should be evaluated thoroughly. Forms of heat-related illness that are more severe include heat exhaustion and heat stroke. Heat exhaustion is associated with mild temperature elevation (37% to 40°C), malaise, nausea, vomiting, headache, weakness, and an increased heart rate. Sweating may be present or absent, and skin may or may not feel warm to the touch. Mental status is preserved. Heat stroke is the third leading cause of death in athletes (23). It is defined as a core temperature of at least 40°C with altered sensorium — such as confusion, unconsciousness, disorientation, or bizarre behavior. Seizures, vomiting, diarrhea, shortness of breath, increased heart rate, and multiorgan failure may occur, with mortality approaching 10%, when present with hypotension increasing to 33% (4,23).
Preventive strategies for hyperthermia and heat illness involve modifying intrinsic and extrinsic factors that should help the body balance heat generation and heat loss. All athletes planning to compete in an ultramarathon race or who have experienced a heat-related illness should undergo a proper medical evaluation by a physician to identify and correct any potential illnesses that may contribute to hyperthermia prior to competing in a future race. Ultramarathon runners should train appropriately for the specific race distance, whether a single-day or multi-day event. Training in an environment similar to the race or arriving several weeks early will allow time for acclimatization, for the body to sweat more efficiently (greater volume of sweat and a decreased relative concentration of electrolytes), to lose heat more efficiently with greater peripheral vasodilation, to lower heart rate, and to increase water and salt conservation by the kidneys (2,3). Runners competing in a multi-day ultramarathon should proceed cautiously during the first few stages of a race to minimize the risk of experiencing a medical illness (20). Proper hydration strategies should be implemented during training and continued through competition. Recommendations vary but might include drinking 8 to 16 oz of an electrolyte drink 1 h before exertion and continued fluid intake over the course of the race based on thirst (28). Cautions should be taken to avoid overhydrating, which can lead to hyponatremia (see the latter part of this article). Urine color and output should be monitored closely, as dark urine and/or decreased output are concerns for dehydration and potential hyperthermia. The medications noted previously should be avoided if possible. Finally athletes should wear appropriate, breathable clothing suited for the environment and temperature.
EAH represents a serum sodium concentration of <135 mmol·L−1 during or up to 24 h after prolonged exercise (11). Though the majority of runners who experience EAH are asymptomatic, a smaller subset will experience symptoms leading to significant morbidity or even death. The prevalence and incidence of EAH will vary depending upon the length of the specific running race. Studies of marathon runners suggest 3% to 28% of runners experience some form of hyponatremia (1,28). Studies of ultramarathon runners vary from an incidence of 5% to 50% for single-day (12,13,19) events to 1% to 12% for multi-day events (20). Thus preventing hyponatremia is an important part of counseling the ultramarathon athlete.
The etiology of hyponatremia is multifactorial in nature, relating to the balance of fluid overload and sodium depletion. The primary etiology of hyponatremia in the marathon runner is thought to be secondary to overhydration from excessive hydration (28). Increased consumption of hypotonic solutions along the course of the race leads to intravascular overload resulting in lower sodium levels. Several studies of marathon runners have found a strong association between higher incidences of EAH and drinking volumes >3 to 3.5 L during a marathon (1,28). Race logistics, including the spacing of fluid stations every 1 or 2 miles along the course of the race, provides an opportunity for an inexperienced runner to overhydrate. Other risk factors for marathon runners include slower race pace (>4 h), female sex, and low body weight (2,11).
Interestingly studies of ultramarathons have reported EAH in overhydrated and dehydrated runners, suggesting other potential etiologies. A study of single-day ultramarathoners with EAH noted that only 23.8% were classified as overhydrated, while 35.6% were dehydrated (weight change less than −3%) (12). In this study, there was a weaker association between postrace sodium levels and change in body weight, with hyponatremia more common in runners with increased weight loss. The finding would suggest that other causes of hyponatremia might contribute to fluid overload or sodium depletion. Individual factors may include inappropriate arginine vasopressin secretion, the body’s response to nonosmotic stimuli (prolonged exercise, stress, and hypovolemia), excessive sweating, or inadequate sodium supplementation (3,11,12). Race logistics for ultramarathons differ from marathons, including greater spacing of fluid stations along the course (every 10 km), more extreme environments (temperature, altitude, or humidity), and greater distances leading to greater running times. Multi-day ultramarathoners offer a unique opportunity for runners to self-regulate their food and fluid intake, since the majority of races require the athlete to be self-sufficient in their supplies.
Recognizing the common symptoms of EAH is important in hopes of avoiding illness that is more significant. Early symptoms include a sensation of bloating, puffiness, nausea, vomiting, and headaches. These symptoms should not be attributed to athlete fatigue but should prompt a thorough medical evaluation. As symptoms progress, athletes experience altered mental status (confusion, disorientation, agitation, and delirium). Severe symptoms can lead to seizures, respiratory compromise, and death. Cases of suspected hyponatremia or undergoing intravenous rehydration should have on-site point-of-care testing (i.e., iStat) to measure the sodium level, if available. In locations where point-of-care testing is not available or not feasible (i.e., remote locations with extreme temperatures outside the capabilities of the point-of-care equipment), physicians should proceed cautiously with rehydration balancing their clinical assessment, the cardiovascular or emergent needs of the athlete, and potential risk of exacerbating hyponatremia. In cases of known hyponatremia, initial treatment should include avoidance of isotonic and hypotonic fluids. Milder forms due to overhydration can be treated successfully with fluid restriction, close observation, and natural dieresis. For moderate or severe cases, athletes can be given 100 mL of 3% NaCl over 10 min × 2, oxygen supplementation, and transfer to a medical facility. Caution should be taken in the ultramarathon runner as Hyponatremia can be seen in the setting of dehydration. Thus fluid restriction may help the hyponatremia but could worsen the dehydration.
Prevention strategies for hyponatremia focus on greater education of the ultramarathon runner. The primary focus should be on adequate fluid consumption with avoidance of overhydration. The American College of Sports Medicine position statement on fluid replacement recommends adequate fluid intake to prevent >2% of body weight loss from dehydration and excessive changes in electrolyte balance based on an individualized program (32). More recently, the 2007 International EAH Consensus Development Conferences recommended advocating drinking “to thirst” rather than higher volumes (11). Athletes should train appropriately for distance, temperature, and humidity. If possible, the athlete can minimize the change in sweat rate for the new environment by training in a similar environment or acclimating to the new race environment over several weeks. Athletes may consider measuring their hourly sweat rate and fluid consumption during training (ideally similar to race environment) in preparation for a race. Proper planning of food and hydration should occur during the training schedule and should not significantly change during the course of the race. As noted previously, runners are more likely to experience a medical illness during the first stage of a multi-day ultramarathon race, so fluid management should be adjusted minimally on the first day. Studies would suggest that most ultramarathon athletes should avoid weight gain and can afford a loss of 2% to 3% of their body weight without significantly impacting running performance (12,28). A few studies have reported hyponatremia in a significant number of athletes who are dehydrated, highlighting the multifactorial etiology of hyponatremia (12). Some ultramarathon races will monitor athlete’s weight in hopes of identifying any athlete who is gaining weight. Caution should be taken in utilizing weights in light of the given findings. Though a significant number of athletes will utilize sodium supplementation, the exact role and impact of supplementation in preventing hyponatremia are not clear. Finally all athletes should be educated regarding the typical symptoms of hyponatremia and need to seek medical evaluation, as appropriate.
Friction blisters are arguably the most common medical problem encountered in any endurance race. For some, a foot blister may be considered merely a training nuisance; for others, it may be an unavoidable injury that can ruin a run, necessitate dropping out of an event, or even progress to cellulitis or sepsis. Blister rates vary by distance ranging from 0.2% to 39% for marathons (22), 32% to 45% for multi-day adventure events (24,36), and up to 70% of all medical visits in multi-day ultramarathons (20). For multi-day ultramarathons, skin-related foot injuries most likely are to occur during stages 3 and 4 of the race, highlighting the impact of cumulative running and opportunity for prevention. In this study, gender did not have an impact on injury rates, but older athletes were less likely to experience skin-related injuries for unclear reasons (20). In the authors’ experience of providing medical support over the past years for ultramarathon around the world, blisters and foot care remain the most often encountered and troubling injury in the endurance athlete.
Understanding the mechanism of a friction blister injury can help in addressing prevention. The main etiology is the repeated action of skin rubbing against another surface. As the external contact of either sock or footwear moves across the skin, the frictional force (Ff) opposes this movement. When horizontal shear forces overcome this resistance, repeated sliding at a friction point causes exfoliation of the stratum corneum and erythema in and around this zone (26). This is experienced as an initial sensation of heat — the “hot spot.” Continued friction on a hot spot causes epidermal cells in the stratum spinosum to delaminate and split, leading to fluid accumulation and formation of a blister (Fig. 1) (35). The intact superficial cells of the stratum corneum and stratum granulosum form the blister’s “roof.” Blister prevention and treatment are aimed at minimizing friction to prevent hot spot occurrence or progression of injury and, when a blister forms, protecting further friction to keeping the roof intact.
Various sock layer combinations can create a nonspecific weak shear layer, exploiting the coefficients of friction and minimizing the friction forces against the skin of the foot itself. The goal is to have friction occur between the two layers of socks, not between the skin and socks. A smooth, thin, snug-fitting synthetic sock worn as an inner layer against the foot will move with the foot, while a thick, woven sock tends to move with the footwear and cushions against shocks (7). The thinner synthetic liner sock also will assist in humidity control by retaining less moisture and wicking moisture and perspiration away from the skin surface (10). Furthermore synthetic fiber socks were associated with fewer blister events and size when compared to cotton fiber socks (10).
The key to preventing blisters involves decreasing shear forces on the skin. There are few studies examining efficacy of various products such as powders, antiperspirants, lubricants, or tapes. The concept of a prevention layer at a high friction spot is to have a layer over the skin such that the following resulting shear will occur between the barrier and the footwear, not the footwear and the skin. The shelves of drugstores and running stores are stocked with potential products (i.e., Blist-O-Ban®, Elastikon®, Leukotape®). Ideally taping products should be thin, easy to apply, adhere well, and provide limited seams that may themselves be friction points. Paper tape is anecdotally useful, and while not ideal in overly wet conditions, due to its low cost, ease of use, and silky feel, it is the authors’ first-line product to apply on a hot spot to prevent blister formation.
Antiperspirants and powders have been proposed as preventive measures to decrease the amount of moisture at the foot-sock interface. The largest antiperspirant trial found it effective in blister prevention, but its high incidence in skin irritation (57% vs 6% of controls) likely limits its usefulness to those experiencing hyperhidrosis (18). Despite wide spread marketing of powder compounds, there is no published scientific evidence to suggest that these products prevent foot blisters. Lubricants ostensibly prevent blister formation by decreasing friction at the foot-contact material interface. Several studies have shown that after applying lubricating substances to skin, there is an initial decrease of the coefficient of friction, but that within an hour, it returns to baseline with a subsequent increase in friction 35% over baseline over the next 4 to 6 h (6,25). The studies suggest that with prolonged exercise, the use of lubricants might contribute to blister formation, so if used, the lubricants need to be reapplied frequently.
Treating a blister as soon as possible improves outcome, reduces pain, and minimizes complications from either subsequent tissue damage or infection. In the early stages of blister formation, the initial sensation of warmth from the hot spot is a warning sign. Prompt attention and rapid treatment can stop the abrasive process to prevent progressive blister formation. Proper blister care is not complicated, yet it may be time intensive depending on the extent of damage to the feet. Individuals should become familiar with techniques before heading outside and facing a blister predicament. The authors’ medical experiences with ultraendurance races have shown that implementation of mandatory personal foot care kits for competitors and the expectation of self-care takes a huge burden off the medical team.
General Taping Rules
Any tape used for blister treatment or prevention should be applied as smoothly as possible. The tape ideally acts as a second layer of skin, so rubbing acts upon the tape, not on the underlying skin. Any folds or wrinkles in the tape should be avoided because they may lead to high pressure and friction areas. Cutting the tape corners to round them and avoiding “dog ears” will help in avoiding blisters. All tape should be cut long enough to extend well beyond the border of the blister and any blister pads underneath the tape. Constriction through overlapping of tape and circumferential wrapping of the feet should be avoided as it may lead to venous congestion and swelling.
Prior to taping, one should ensure the skin is clean of dirt and grit and as dry as possible, which will enhance natural adhesion of tape. One should consider using an adhesive substance, such as benzoin, to ensure security of the applied dressing. As a general rule, one should not remove blister tape unless it is peeling off or there is increasing discomfort at the tape site. Ideally soaking the bandages prior to removal will loosen adhesion and minimize chances of ripping open intact blisters. The best protection for a blister is its own “roof,” so efforts should be taken to maintain this natural skin protection. Small friction blisters that are not causing significant discomfort can be left intact. Larger, noninfected blisters can be drained utilizing a sterile needle or safety pin. The blister should be punctured at the base, and fluid should be expressed cautiously while maintaining the integrity of the covering skin (roof). Extra protection can be provided by taping over the blister, if needed.
There is no one correct way to care for feet. For every technique and product mentioned, there are several different options. The authors recommend avoiding draining of blood-filled blisters as these represent injury to the dermal plexus and are a potential route for bacteria to enter the wound and bloodstream, which can lead to cellulitis or sepsis. Blood blisters should be left intact unless they are large, fluctuant, extremely painful, and at risk of spontaneous rupture. These may be drained as noted previously. Likewise, blisters deep to a callus should not be drained. These blisters are painful to access, yield little blister fluid, and quickly refill after drainage. A blister with murky hazy fluid or pus may be infected. The blister should be opened (deroofed), be irrigated with povidone-iodine, and then have antiseptic or antibiotic ointment applied to the cavity prior to being covered with the “open blister” technique. If the individual begins to show signs of worsening local infection or systemic symptoms, such as chills, fevers, nausea, or generalized weakness, definitive care including oral or intravenous antibiotics should be utilized to avoid morbidities that are more severe, including sepsis. The goals of blister treatment are to optimize comfort for continued activity, maximize prevention of infection, assist with epidermal recovery, and prevent further blister enlargement when resting and staying off your feet is not an option.
Athletes participating in ultramarathons need to prepare for a variety of unique factors that may contribute to injury and illness. Strategies for preventing injury should include appropriate training for the race based on distance, stages, and environment as well as optimization of fitness, nutrition, and gear. When possible, athletes should acclimate to the race environment, if possible. In multi-day races, athletes should race within their fitness level during the early stages to avoid medical illnesses and monitor or quickly treat musculoskeletal or skin issues as they develop. With proper preparation, ultramarathon runners should be able to compete with minimal risk of injury or illness.
The authors declare no conflicts of interest and do not have any financial disclosures.
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