The Science of Ultramarathons


Ultramarathons have quickly become “the next” race for runners of all shapes, sizes and experience, as the number of ultramarathon races has increased by a thousand per cent over the last decade. The term “ultramarathon” is most commonly defined as any race longer than a marathon (42.2 km) and run in a single stage. In 2018, there were more than 1800 ultramarathon events held in over 75 countries. 

Up until 10 years ago, these types of athletes—and the science behind competing in such an event—were barely on the scientific radar, so I thought it would be interesting to discuss some of the latest cutting-edge research.

Recent research evaluated fatigue for male and female ultramarathoners before and after they completed a 110 km race with almost 6000 metres in elevation change. What they found was that the magnitude of fatigue within the central nervous system and brain (general fatigue) was similar for both male and female runners. However, they measured greater amounts of local fatigue in the  quadriceps and calf muscles for males, which may partly explain the reports of great performance by females in extremely long duration running races compared to their male counterparts. 

Another interesting study looked at changes in foot strike pattern as a function of muscle fatigue over the course of a 161 km ultramarathon race. At the 16 km mark, 80% of all runners had a rearfoot strike pattern and 20% were either mid-foot or forefoot strikers. However, by the 90 km mark, 89% of the runners were exhibiting a rearfoot strike pattern. These authors also found that the increase in rearfoot striking by the race midpoint was due to local muscle fatigue. In other words, the greater muscular demands of being a midfoot or forefoot striker resulted in higher levels of blood creatine phosphokinase (a measure of muscle injury or stress) after the race. I’ve discussed similar results in previous articles from marathon research showing that a rearfoot strike pattern is more energy efficient—a critical factor for completing an ultramarathon.

The biggest question is: how can these runners tolerate this type of punishment? An interesting study looked at physiological responses during an ultramarathon held in extreme heat, and the results are truly amazing. By taking various measures throughout a 217 km run across Death Valley, California,  scientists found that runners exhibited an average core body temperature of only 37.49°C (resting normal is 37.0°C), an average heart rate of 107 beats/min (typical resting is 70 beats/min), and average blood pressure of 128/86 mmHg (normal resting is 120/80 mmHg). Even though the daytime high temperature was 47°C, and the average temperature was 28°C, these runners had very “typical” physiological measures that were, in fact, close to resting values. In fact, the fastest finisher demonstrated a lower overall core body temperature (36.91°C) when compared with the group mean of 37.49°C. The authors concluded that “success in longer duration events requires an ability to maintain a lower core body temperature [as opposed to] tolerating a higher core body temperature.” In other words, some runners can tolerate them heat while others are simply genetically equipped to handle it.

Age is another factor that has been analyzed in ultramarathon research and has been found to be a strong predictor of success. The best performances in the half marathon and marathon are generally achieved by younger runners, whereas top performances in ultras are seen in the age group between 35 and 45. For example, in the 100-mile ultramarathons, the fastest men are approximately 37 years of age and the fastest women are around age 39. In the 24-hour ultramarathon, with a distance of 200 km or more, the fastest men are generally around age 44 and the fastest women are around 43. 

Whether an ultramarathon is on your radar or not, you have to appreciate the physicality, and mental fortitude of attempting and completing such an extreme race.  It takes careful planning, lots of training, and obviously some well-earned experience to perform your best.



Dr. Reed Ferber is the director of the Running Injury Clinic, a world leader in running-related research and 3D gait analysis technology. For more information, visit

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