Are Ultramarathoners Just Built Different? - Science Friday Recap

Podcast: Science Friday

Published: 2026-01-02

Duration: 18 minutes

Guests: Dr. Brandee Waite, Dr. Andrew Best

Summary

Ultramarathoners push the limits of human endurance, balancing extreme physical demands with psychological resilience. Their success hinges not only on physical training but also on the ability to mentally reframe suffering.

What Happened

Flora Lichtman opens the episode by expressing her fascination with ultramarathoners, athletes who run 50 to 100 miles in a day, and questions the physical limits of such feats. She is joined by Dr. Brandi Waite and Dr. Andrew Best to explore what makes these athletes capable of such endurance. Dr. Waite describes her recent experience on the medical team for a staged ultramarathon in Greece, emphasizing the physical and logistical challenges these races present.

Dr. Best explains the physiological demands of ultramarathons, including the need for increased oxygen and nutrients to muscles, while maintaining overall body homeostasis. He highlights the importance of balancing energy allocation among bodily systems, describing it as caring for an unruly child without neglecting others. The discussion turns to the limits of energy intake during races, noting that athletes can only replace about 40 to 50 percent of the calories they burn.

The episode discusses the theoretical possibility of infinite endurance if fueling could match depletion rates, but acknowledges practical limits like sleep and physical injuries. Dr. Waite recounts the remarkable achievements of ultrarunner Dean Karnazes, who ran for 80 hours without sleep, covering 350 miles. The conversation touches on the psychological aspects of endurance, with Dr. Best noting that ultramarathoners often find a productive way to reframe their suffering.

Flora asks about the physiological differences between ultramarathoners and average individuals. Dr. Waite asserts that while there may be minor differences, the significant factor is the training effect. She notes that many ultramarathoners are not competing to win but are challenging themselves to finish.

Dr. Best discusses a recent study on calorie consumption during ultramarathons, highlighting the immense caloric demands of events like the Western States 100, where athlete Kilian Jornet burned 16,000 calories. He explains that over long durations, the variability in metabolic rates narrows, suggesting different mechanisms for long-term endurance.

The episode concludes with reflections on the mental and physical resilience required for ultramarathoning. Dr. Waite and Dr. Best agree that while physiological factors are important, psychological resilience plays a critical role in an athlete's success in ultramarathons.

Key Insights

• Ultramarathoners can only replace about 40 to 50 percent of the calories they burn during races, highlighting the extreme energy deficit they operate under.
• Dean Karnazes achieved a remarkable feat by running 350 miles over 80 hours without sleep, demonstrating the physical and mental endurance required in ultramarathoning.
• During the Western States 100 ultramarathon, athlete Kilian Jornet burned 16,000 calories, illustrating the immense caloric demands of such endurance events.
• While there are minor physiological differences between ultramarathoners and average individuals, the significant factor in their endurance capabilities is the training effect rather than inherent physical traits.