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.

In this episode, we explore why many trail and ultra runners feel that their breathing is still under control, but their legs simply stop working.

The main idea is that ultra running is not limited only by cardiovascular fitness. It is also limited by local muscular endurance: the ability of the quads, calves, glutes and stabilising muscles to keep producing force for hours.

Climbing, descending and technical terrain all place specific demands on the legs. Uphills require repeated force production, downhills create muscle damage through braking and impact, and trails constantly challenge stability and control. This is why a runner can still have a strong aerobic engine but lose performance when the legs are no longer able to absorb, stabilise and push.

The episode explains that the solution is not simply more mileage. Runners need race-specific preparation: uphill muscular endurance, downhill conditioning, purposeful hiking, and consistent strength training.

Key message: Train the engine, but build the chassis. In ultras, strong legs protect good fitness.

Key references:

• Millet et al. 2011 — neuromuscular fatigue in mountain ultras.
• Bontemps et al. 2020 — downhill running and eccentric damage.
• Pradas et al. 2021 — ultratrail racing, muscle damage and neuromuscular function.
• Balsalobre-Fernández et al. 2016 — strength training and running economy.
• Llanos-Lagos et al. 2024 — updated systematic review on strength training and running economy.

This episode explains why running performance drops in hot conditions and why it is not simply a loss of fitness or lack of toughness. In the heat, the body has two jobs: keep running and protect itself from overheating. More blood is directed towards the skin for cooling, sweat rate increases, heart rate rises, and the same pace costs more energy.

The key message is that on hot days, effort matters more than pace. A pace that feels easy in cool weather may become moderate or hard in the heat. Trying to force normal pace often leads to overheating, dehydration, gut problems, and a major slowdown later.

If a hot race is expected, heat acclimation over 10–14 days can improve tolerance. But when a heatwave arrives suddenly, the goal is damage control: slow down early, reduce intensity, walk climbs sooner, use shade, cool aggressively, hydrate sensibly, and protect the gut.

Main takeaway: In the heat, do not fight for your normal pace. Manage your effort, stay cool, and slow down before your body forces you to slow down.

Key references:

• González-Alonso, J. 2007. The cardiovascular challenge of exercising in the heat. Journal of Physiology.
• Wingo, J. E., Ganio, M. S., & Cureton, K. J. 2012. Cardiovascular drift during heat stress: implications for exercise prescription. Exercise and Sport Sciences Reviews.
• Périard, J. D., Eijsvogels, T. M. H., & Daanen, H. A. M. 2021. Exercise under heat stress: thermoregulation, hydration, performance implications, and mitigation strategies. Physiological Reviews.
• Racinais, S. et al. 2015. Consensus recommendations on training and competing in the heat. Scandinavian Journal of Medicine & Science in Sports.
• Racinais, S. et al. 2023. IOC consensus statement on recommendations and regulations for sport events in the heat. British Journal of Sports Medicine.
• Heathcote, S. L. et al. 2018. Reviewing practical heat acclimation strategies for endurance athletes. Frontiers in Physiology.
• Zurawlew, M. J. et al. 2018. Post-exercise hot water immersion elicits heat acclimation adaptations in endurance trained and recreationally active individuals. Frontiers in Physiology.
• Wierick, S. C. et al. 2025. Hydration Strategies in Ultra-Endurance Running. Sports Medicine - Open / PMC.
• Knechtle, B. et al. 2019. Exercise-associated hyponatremia in endurance and ultra-endurance performance. Medicina.
• Hoffman, M. D. et al. 2015. Sodium Intake During an Ultramarathon Does Not Prevent Muscle Cramping, Dehydration, Hyponatremia, or Nausea. Sports Medicine - Open.