Caffeine is one of the most evidence-supported supplements for endurance performance, but ultrarunners need to use it strategically rather than simply taking more.

The key message is that caffeine is not fuel. Carbohydrates provide energy for the muscles; caffeine mainly helps with alertness, focus, motivation, and perceived effort. This makes it especially useful in long ultras, where mental fatigue, sleepiness, low mood, and poor decision-making can become as limiting as physical fatigue.

For shorter races, caffeine before the start can be useful. But in longer ultras, especially races lasting over 8–15 hours or through the night, it is often better to delay caffeine until the second half, the night section, or the final third, when its benefits are more valuable.

A practical starting point is 25–50 mg per hour once caffeine use begins, adjusted based on tolerance. Some runners may tolerate more, but higher doses increase the risk of stomach issues, anxiety, jitters, and sleep disruption.

The episode emphasises that caffeine should never replace proper fuelling. When energy drops, the first question should be: have I taken enough carbohydrates?

Main takeaway: Fuel with carbohydrates. Focus with caffeine. Caffeine is not the engine; it is the light you switch on when the road gets dark.

Key references:

• Guest, N. S. et al. (2021). International Society of Sports Nutrition Position Stand: Caffeine and Exercise Performance. Journal of the International Society of Sports Nutrition. Australian Institute of Sport. Caffeine: Performance Supplement Guide.
• Wang, Z. et al. (2022). Effects of Caffeine Intake on Endurance Running Performance and Time to Exhaustion: A Systematic Review and Meta-analysis. Nutrients.
• Shen, J. G. et al. (2019). Establishing a relationship between the effect of caffeine and duration of endurance athletic time trial events. Journal of Science and Medicine in Sport.
• Goldstein, E. R. et al. (2010). International Society of Sports Nutrition Position Stand: Caffeine and Performance. Journal of the International Society of Sports Nutrition.
• Benchetrit, S. et al. (2024). The effects of sleep deprivation and extreme exertion on cognitive performance in ultra-marathon runners.
• Martinez Gonzalez, B. (2022). Sleep Deprivation and Ultra-endurance Performance. University of Kent thesis.
• Office of Dietary Supplements, NIH. Dietary Supplements for Exercise and Athletic Performance: Health Professional Fact Sheet.