What Does It Take To Run An Ultra-Marathon?

Posted byAnnabel CritchlowPosted inPhysiologyTags:, , ,

Over the last few decades there has been a huge surge in the popularity of ultra-running, with the number of participants increasing exponentially since the 1970’s.1 An ultra-marathon can be defined as a running event that is longer than 42.195km.2 Common race distances include 50km, 100km, 50 miles or 100 miles, however they can also be significantly longer or completed over multiple stages. The longest official ultra-marathon is the ‘Self-Transcendence 3100 Mile Race’. To provide you with an idea of how long this takes to complete, the 2017 winner finished the race in a time of 46 days, 17 hours and 38 minutes.

It is clear that ultra-running is an extremely tough sport, both mentally and physically, but what exactly does it take to be able to complete an ultra-marathon? This article is going to investigate the key characteristics of a successful ultra-runner, the energy requirements and the potential physiological challenges that may come as a result of completing an ultra-marathon.

Key characteristics of an ultra-runner

For those of you who are unfamiliar with the sport, it may be surprising to learn that out of a cohort of 1345 current and former ultra-runners, the average age of first participation in an ultra-marathon was 37 years old.3 Compared to marathon runners, an ultra-runner’s best performance usually occurs later in life at about 35 years old, and the age of peak performance appears to increase with increasing race distance.2 For example, peak performance for a 6 hour run occurs at about 34 years old, compared to 47 years old for a 48 hour run.2

Another key factor for ultra-marathon performance is running experience. In the same sample of 1345 ultra-runners, an average of 3000km of running was completed in the year prior to an event.3 The consensus amongst the research is that most successful ultra-runners tend to have several years of experience of ultra-marathons.4 It has been suggested that approximately 4 years of ultra-running are needed to reach peak running speeds in competition.5 Possibly related is the fact that more even pacing strategies are typically found in the most successful runners, which could be a result of greater competition experience.2

Anthropometry is also very important to consider. In a study of 392 runners at the 100-mile Western States Endurance run, the mean BMI was 23.2kg/m2 and 20.6kg/m2 for men and women respectively.6 Understandably, a direct linear relationship was found between body fat percentage and race time; runners with a lower body fat percentage completed the race in a faster time. The paper concluded that percentage body fat and BMI were the most important variables when considering the relationship between anthropometric measures and ultra-marathon performance.

Of course an ultra-marathon is not just a physical challenge, but also a mental one. So what psychological characteristics drive an ultra-runner to push themselves to the limit? Research has found that ultra-runners are highly intrinsically motivated, i.e. that the reasons for doing it originate from within, not from external factors such as competition.2 It was found that of 1349 surveyed ultra-runners, 74% of them would not stop if they learnt that it was bad for their health.7 In the questionnaire, these runners had lower health orientation scores, and greater scores of personal goal achievement, psychological coping and life meaning. It makes sense that strong, unwavering motivation is a requirement when pushing the boundaries of human endurance.

Energy requirements of an ultra-marathon

When running across such vast distances, it is necessary to fuel the body sufficiently. To quantify just how much energy is required, a study measured the energy expenditure of 6 male runners during an 800km race. The average race time was just over 6 days, during which the mean energy expenditure was 80,000 calories. This is equivalent to about 12,600 calories per day.8 For the most part, ultra-runners are unable to meet the energy demands and therefore fall into an energy deficit. This can lead to a reduction in both fat mass and fat free mass, possibly due to suppression of appetite or gastrointestinal (GI) problems.8,9 Of the energy that is consumed, carbohydrate is the most valuable source. For example, during a 100km ultra-marathon, 7 male runners had an average energy intake of 1011 calories, 88.6% of which came from carbohydrate, 6.7% from fat and 4.7% from protein.10

Physiological challenges of ultra-running

It’s unsurprising that along with running for such extreme periods of time, many physiological challenges become apparent. Particularly prevalent are GI problems. A questionnaire at the 100 mile Western States Endurance run found that of 272 runners, 96% experienced GI symptoms, with nausea and flatulence being the most common.11 Out of the runners who did not finish the race, 36% claimed that their GI discomfort was the reason for dropping out and 90% of these non-finishers complained of nausea. It has been suggested that a possible cause of GI symptoms during prolonged exercise is endotoxemia.12 Due to the redistribution of blood flow during exercise, gut permeability increases and endotoxins are absorbed into the blood, therefore promoting an inflammatory response.13 Currently there seems to be a lack of treatment, and runners are advised to eat according to individual preference.2

Another prevalent challenge amongst ultra-runners is the risk of hyponatremia. In order to avoid dehydration, runners often consume large amounts of fluid, but this can lead to dangerously low levels of sodium in the blood.14 When the plasma sodium concentration drops below 135mmol/l it fulfils the clinical definition of hyponatremia.15 Some common symptoms include altered behaviour, seizures, oedema, and feet swelling, but if left untreated, serious cases can result in permanent neurological damage.2,16 Particularly hot climates may increase the risk of hyponatremia due to fluid overconsumption. During a 225km, 5 stage ultra-marathon in ambient temperatures of 40 degrees celcius, as many as 42% of the runners were found to have asymptomatic hyponatremia.15 Although sodium supplementation is very commonly used amongst ultra-runners, studies have concluded that this is unnecessary to maintain sufficient hydration in high ambient temperatures.17

We also cannot overlook the probability of musculoskeletal injury when running for such extended periods of time. As one would expect, injuries are most common in the lower limb, particularly the knee when road running and the ankle when running on trails.18,19 For instance, during a 1005km ultra-marathon, 32 runners had a total of 64 injuries, 31% of which were of the knee and 28% of the ankle.18 This is not to say that all runners experience such injuries; more experienced runners seem to be less prone to overuse injuries compared to beginners.2

It is interesting to investigate the extent to which skeletal muscle damage occurs during an ultra-marathon. There is no doubt that all runners are familiar with the days after an event when dreaded muscle soreness takes over and walking down the stairs becomes a huge challenge. Muscle soreness originates not from fatigue but from damage of the skeletal muscle fibres, which can be monitored by blood markers such as myoglobin or creatine kinase.2 Levels of creatine kinase are greatest approximately 1 hour after completion of an ultra-marathon and can remain elevated for up to 72 hours. Eccentric loading, i.e. running downhill, can show significantly increased levels of creatine kinase, indicating that much greater levels of muscle damage occur.2 It is possible to reduce the amount of skeletal muscle damage by completing high volumes of training, which may be related to the fact that the most successful runners have lower levels of creatine kinase (and therefore muscle damage) than slower runners.2

To conclude, this article has highlighted some of common characteristics that are associated with successful ultra-running, and investigated the many physiological challenges that accompany this gruelling sport. While it is easy to discuss the quantitative measures of an ultra-marathon, we absolutely cannot overlook the psychological strength that it takes to push the limits of human endurance. Ultra-runners need to be able to push on when their whole body is screaming at them to stop, and while this is difficult to measure, it is arguably the most important trait.

References

  1. Hoffman MD. Performance trends in 161-km ultramarathons. Int J Sports Med. 2010;31(1):31-37. doi:10.1055/s-0029-1239561
  2. Knechtle B, Nikolaidis PT. Physiology and Pathophysiology in Ultra-Marathon Running. Front Physiol. 2018;9:634. Published 2018 Jun 1. doi:10.3389/fphys.2018.00634
  3. Hoffman MD, Krishnan E. Exercise behavior of ultramarathon runners: baseline findings from the ULTRA study. J Strength Cond Res. 2013;27(11):2939-2945. doi:10.1519/JSC.0b013e3182a1f261
  4. Knechtle B. Ultramarathon runners: nature or nurture?. Int J Sports Physiol Perform. 2012;7(4):310-312. doi:10.1123/ijspp.7.4.310
  5. Rae DE, Bosch AN, Collins M, Lambert MI. The interaction of aging and 10 years of racing on ultraendurance running performance. J Aging Phys Act. 2005;13(2):210-222. doi:10.1123/japa.13.2.210
  6. Hoffman MD. Anthropometric characteristics of ultramarathoners. Int J Sports Med. 2008;29(10):808-811. doi:10.1055/s-2008-1038434
  7. Hoffman MD, Krouse R. Ultra-obligatory running among ultramarathon runners. Res Sports Med. 2018;26(2):211-221. doi:10.1080/15438627.2018.1431533
  8. Enqvist JK, Mattsson CM, Johansson PH, Brink-Elfegoun T, Bakkman L, Ekblom BT. Energy turnover during 24 hours and 6 days of adventure racing. J Sports Sci. 2010;28(9):947-955. doi:10.1080/02640411003734069
  9. Knechtle B, Wirth A, Knechtle P, Rosemann T, Senn O. Do ultra-runners in a 24-h run really dehydrate?. Ir J Med Sci. 2011;180(1):129-134. doi:10.1007/s11845-010-0500-8
  10. Fallon KE, Broad E, Thompson MW, Reull PA. Nutritional and fluid intake in a 100-km ultramarathon. Int J Sport Nutr. 1998;8(1):24-35. doi:10.1123/ijsn.8.1.24
  11. Stuempfle KJ, Hoffman MD. Gastrointestinal distress is common during a 161-km ultramarathon. J Sports Sci. 2015;33(17):1814-1821. doi:10.1080/02640414.2015.1012104
  12. Stuempfle KJ, Valentino T, Hew-Butler T, Hecht FM, Hoffman MD. Nausea is associated with endotoxemia during a 161-km ultramarathon. J Sports Sci. 2016;34(17):1662-1668. doi:10.1080/02640414.2015.1130238
  13. Lamprecht M, Frauwallner A. Exercise, intestinal barrier dysfunction and probiotic supplementation. Med Sport Sci. 2012;59:47-56. doi:10.1159/000342169
  14. Knechtle B, Knechtle P, Rüst CA, et al. Regulation of electrolyte and fluid metabolism in multi-stage ultra-marathoners. Horm Metab Res. 2012;44(12):919-926. doi:10.1055/s-0032-1312647
  15. Costa RJ, Teixeira A, Rama L, et al. Water and sodium intake habits and status of ultra-endurance runners during a multi-stage ultra-marathon conducted in a hot ambient environment: an observational field based study. Nutr J. 2013;12:13. Published 2013 Jan 15. doi:10.1186/1475-2891-12-13
  16. Seay NW, Lehrich RW, Greenberg A. Diagnosis and Management of Disorders of Body Tonicity-Hyponatremia and Hypernatremia: Core Curriculum 2020. Am J Kidney Dis. 2020;75(2):272-286. doi:10.1053/j.ajkd.2019.07.014
  17. Hoffman MD, Stuempfle KJ. Is Sodium Supplementation Necessary to Avoid Dehydration During Prolonged Exercise in the Heat?. J Strength Cond Res. 2016;30(3):615-620. doi:10.1519/JSC.0000000000001138
  18. Fallon KE. Musculoskeletal injuries in the ultramarathon: the 1990 Westfield Sydney to Melbourne run. Br J Sports Med. 1996;30(4):319-323. doi:10.1136/bjsm.30.4.319
  19. Bishop GW, Fallon KE. Musculoskeletal injuries in a six-day track race: ultramarathoner’s ankle. Clin J Sport Med. 1999;9(4):216-220. doi:10.1097/00042752-199910000-00006

Photo by David Marcu on Unsplash

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