An ultramarathon is defined as any footrace longer than the traditional marathon distance of 26.2 miles (or 42.195 km). An ultramarathon is also commonly referred to as ultra distance or ultra running. There are two types of ultramarathon events: those that cover a specified distance (for example, 100 miles) and events that take place during time (with the winner covering the most distance in that time). The most common ultramarathon distances are 50 kilometers (50k), 100 kilometers (100k), 50 miles, and 100 miles.


Running could be classified as the oldest sport practiced by humans because it likely started from the time Homo sapiens walked the earth upright. Of course, it was more a matter of survival at certain times rather than a sport. Many myths and legends are told about running becoming a sport, from Native American multi-day footraces to the early days of the Olympic games. The sport of running has grown in popularity and is considered one of the most accessible sports; all that is necessary is a pair of feet and some open space.

America has seen a few distinct booms in the level of interest in the sport. Starting in the 1970s, likely spurred by Frank Shorter's incredible performance at the 1972 Olympics, this boom was followed by another in the 1990s, with many celebrities publicly taking part in half-marathons and marathon challenges. At the same time, another running movement was slowly brewing in the background. Christopher MacDougall's Born to Run brought to light the amazing Tarahumara natives of Mexico, who took part in incredibly long running journeys over hundreds of miles with nothing but huaraches on their feet. The book also highlighted some legendary, yet little-known, American ultradistance footraces with small numbers of participants. These competitions that became known as ultramarathons were defined by the mainstream as “any distance greater than 26.2 miles.” Several hundred ultramarathons are held annually in North America.

One of the best known is the Western States Endurance Run, the world's oldest 100-mile trail run. The race began unofficially in 1974, when local horseman Gordy Ainsleigh's horse for the 100-mile Tevis Cup horse race came up lame. Ainsleigh decided to travel the course on foot, finishing in 23 hours and 47 minutes. Over the past few decades, the development and participation in ultra-endurance events (running, cycling, triathlon) with performance exceeding six hours has grown. The IAU (International Association of Ultrarunners) reports that more than 100,000 runners compete in over 1,000 events worldwide.


Although humans seem to be “Born to Run,” participating in such ultra-endurance events, particularly when they take place in extreme environments, has health ramifications that can affect participants even after the competition has finished. In particular, negative impacts on immune function puts runners at a higher risk for infections, such as upper respiratory tract infections (URTIs). The literature shows that ultra-endurance athlete bodies are under tremendous physiological stress leading to up to 25% higher risk of infection, decreased fat and skeletal mass, dehydration, along with other possible risks to their longterm health. It has been reported in the scientific literature that 33%–68% of ultra-marathoners contract some type of respiratory infection within two weeks of competition.

Nicolas Martin of France finishes second in the Transvulcania ultramarathon in La Palma, Canary Islands, May 2016. An ultramarathon is any foot race longer than a traditional marathon (or longer than 26.2 miles).

Nicolas Martin of France finishes second in the Transvulcania ultramarathon in La Palma, Canary Islands, May 2016. An ultramarathon is any foot race longer than a traditional marathon (or longer than 26.2 miles).

Many factors that stress the immune systems of ultramarathon runners. Researchers have demonstrated that psychological stress, sleep deprivation, and inadequate nutrition can depress the immunity of ultramarathon athletes because their lungs are more exposed to airborne bacteria and viruses as a result of their increased rate and depth of breathing. Other factors, such as allergies or inflammation of the airways from breathing cold, dry, or polluted air can sometimes cause issues that are mistaken for respiratory infection. Exposure to altitude might also increase the risk of infection in ultramarathon athletes, which suggests that there are multiple causes for the increased incidence in respiratory and immune function in this population. The longer duration of training bouts and competition means a lengthier sustained exertion, in part due to the negative energy balance that occurs as ultramarathon athletes are not able to adequately replenish expended calories. In fact, many case studies and field reports have shown that most ultra-endurance athletes struggle to self-monitor their nutritional intake and exercise intensities enough to avoid this negative energy balance. In turn, this negative energy balance plays a role in the loss of body mass experienced by ultra-endurance athletes, along with malnutrition and low intake of antioxidant vitamins.

Strategies to Remain Healthy during Training

Table 1. Strategies to Remain Healthy during Training.


Numerous strategies can assist ultramarathon athletes in staying healthy during training and competition. Recognizing that athletes are individuals, no one-size-fits-all plan can be recommended. Instead, coaches should view each athlete as an individual and consider all factors that might lead to stress outside of training and competition, including lifestyle, nutrition, sleep habits, and mental health.


Sample Training Program for an Ultramarathon

Figure 1. Sample Training Program for an Ultramarathon.

Substance that acts to reduce inflammation (e.g., fever, swelling).
Substance that prevents another molecule from oxidizing.
Creatine kinase (CK)—
An enzyme found in the brain, heart, and skeletal muscle. Elevated concentrations of CK are indicative of muscle damage.
Category of small proteins involved in cell signaling.
Colorless cells that are part of the immune system.
The annual 52-weektraining program.
The shortest block of training, typically one to two weeks.
Globular protein involved in muscle contraction.
White blood cell—
Class of colorless cells involved in immune function that circulate in bloodstream and lymph.

To ensure athletes remain healthy, it is important to examine their training and competition schedule to ensure that they schedule appropriate time for training and recovery. It also essential to provide time for acclimatization to new environments, especially when extreme temperatures and altitude will be involved. The addition of cross-training to the training plan is beneficial not only for adding muscle mass, but also for adding some mental variety. Specific strategies to remain healthy during training are highlighted in Table 1.

During competition, athletes should keep their well-being at the forefront and ensure that they are fueling and hydrating appropriately, in addition to pacing themselves for the course and environment. Again, all athletes are different, but some evidence supports that carbohydrate supplementation before and during competition increases blood neutrophil and monocyte counts, stress hormones, and antiinflammatory cytokines.

Post-competition, athletes must dedicate themselves to self-care during the two-week window of lessened immunity. Proper sleep and nutrition during this time are of key importance, along with avoiding exposure to sick individuals. Although many athletes have difficulty taking breaks, they should learn to recognize the dangers and symptoms of overtraining and fatigue, and respect these feelings. For the first 36 hours post-race, they should focus on rest, sleep, nutrition, and hydration. Activities should be limited to light exercise, such as walking, in these first few days. From that point on, athletes must pay attention to their energy levels as well as ensure that their body weight and composition return to normal levels before adding some light hiking, running, or cycling for more active recovery before resuming full training at the end of this two-week period. A few weeks of self-care and fewer training demands can lead to less illness and greater performance going forward.

  • How can I best prepare for an ultramarathon?
  • Do I have a medical condition that would exclude me from participating in an ultramarathon?
  • What are the acute and chronic risks involved with participating in an ultramarathon?
  • What equipment is required for an ultramarathon?
  • Would it be beneficial to see a registered dietician to help with the nutritional requirements of the ultramarathon?
  • What are some of the environmental challenges of the ultramarathon?

Scheduling races into the overall training program is key, and it has been suggested that for proper training and recovery, no more than two ultra-endurance events per year are recommended. Studies done on athlete recovery have shown that although muscle pain and fatigue can resolve within five days following a 100-mile race, functional recovery requires more time. This evidence also supports the idea that a proper training plan is critical to maintaining the health of an ultramarathoner and enhancing recovery post-race. Runners also need to take into account the environment and terrain of the key races to best prepare for the extra stress of altitude or harsh (hot or cold) climates. If possible, it is beneficial to perform a few weeks of training in the location of the race, or attempt to simulate the terrain and conditions that will be encountered. A sample training program for an ultramarathon is shown in Figure 1.

See also Nutrient timing ; Overtraining ; Running .



McDougall, Christopher. Born to Run: A Hidden Tribe, Superathletes, and the Greatest Race the World Has Never Seen.. New York: Alfred A. Knopf, 2009.


Edler, Jessica R., et al. “Ultra Endurance Athletes At-Risk.” International Journal of Athletic Therapy and Training 19, no. 4 (July 2014): 10–3.

Hoffman, Martin D., et al. “Determinants of Recovery from a 161-km Ultramarathon.” Journal of Sports Sciences 35, no. 7 (April 2017): 669–77.

Hoffman, Martin D., and Kevin Fogard. “Demographic Characteristics of 161-km Ultramarathon Runners.” Research in Sports Medicine 20, no. 1 (January 2012): 59–69.

Stuempfle, Kristin J., et al. “Nausea Is Associated with Endotoxemia during a 161-km Ultramarathon.” Journal of Sports Sciences 34, no. 17 (September 2016): 1662–8.


“Scientific Publications.” Western States Endurance Run Foundation. http://www.wser.org/research/scientificpublications (accessed February 7, 2017).

“What Is the IAU?” International Association of Ultrarunners. http://www.iau-ultramarathon.org (accessed February 7, 2017).


International Association of Ultrarunning, 6-8, Quai Antoine 1er, BP 359, MC, Monaco, 98007 Monaco Cedex, info@iau-ultramarathon.org, http://www.iau-ultramarathon.org .

Lance C. Dalleck, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.