Nutrition for Endurance Sports: The Complete Guide to Boost Your Performance

Javier Colomer 7 min. of reading Running Leave a comment

The popularity of endurance sports has grown exponentially. More and more athletes are taking on distances such as the half marathon, full marathon, ultramarathons, or long-distance triathlons (Ironman), competing in events that require sustained efforts ranging from 2 to more than 15 hours.

At this level of demand, physical training alone is not enough. Optimizing performance through proper sports nutrition makes the difference between crossing the finish line strong or facing the dreaded extreme fatigue commonly known as “hitting the wall”.

Index

1 What causes fatigue in running and triathlon?
2 Carbohydrate strategy: The primary fuel source
3 Hydration and electrolytes: Before and during the event
4 Caffeine as an ergogenic aid for endurance performance
5 Key takeaways for endurance athletes

What causes fatigue in running and triathlon?

In continuous activities lasting more than 45-60 minutes, fatigue is not solely caused by muscle damage. There are systemic and metabolic limiting factors:

Depletion of glycogen stores: The primary fuel source for working muscles.
Dehydration and electrolyte loss: Which impair muscle contraction and thermoregulation.
Gastrointestinal problems: Very common due to inadequate fluid intake or the consumption of hyperosmotic nutrients during the race.
Central Nervous System (CNS) fatigue: A reduced ability of the brain to send efficient signals to the muscles.

Carbohydrate strategy: The primary fuel source

Muscle glycogen and blood glucose are the most important energy substrates. Current guidelines from the American College of Sports Medicine (ACSM) state that maintaining high carbohydrate availability is essential for sustaining exercise intensity.

1. Pre-competition carbohydrate loading

Performing glycogen supercompensation during the days leading up to competition can improve performance in events lasting longer than 90 minutes.

Requirements range from 5 to 12 g of carbohydrates per kg of body weight per day, depending on the athlete’s level. It is important to prioritize low-glycemic-index carbohydrate sources and reduce fiber intake during the final 24 hours before competition to minimize digestive discomfort.

2. Carbohydrate intake during exercise

During the event, the goal is to maintain blood glucose levels and spare liver glycogen. Current scientific evidence (based on research by experts such as Asker Jeukendrup) establishes the following recommendations according to exercise duration:

Exercise duration	Recommended carbohydrate intake	Recommended carbohydrate type
Less than 45 min	Not strictly necessary	Water
45–75 minutes	Carbohydrate mouth rinses or small intakes	Rapidly absorbed carbohydrates
1 to 2.5 hours	30–60 g per hour	Single-source carbohydrates (Glucose / Maltodextrin)
More than 2.5 hours	60–90 g (up to 120 g in elite athletes) per hour	Multiple transportable carbohydrates (2:1 Glucose:Fructose ratio or Cyclodextrin)

📌 HSN Tip: The intestine has a limited absorption capacity. If your goal is to tolerate more than 60 g/h without gastrointestinal discomfort, consider advanced formulations that combine different absorption pathways, such as amylopectin or cyclodextrin with fructose (2:1 or 1:0.8 ratio).

Hydration and electrolytes: Before and during the event

Starting exercise in a dehydrated state is just as detrimental as overhydration (which may lead to hyponatremia). Sweat losses should be replaced, limiting body mass loss to no more than 2–3%.

Pre-hydration: Drink between 5–7 ml/kg of body weight gradually about 4 hours before the start.
During exercise: Consume fluids containing electrolytes, especially sodium, to promote water retention and improve carbohydrate absorption through the intestinal wall.

Caffeine as an ergogenic aid for endurance performance

Caffeine has the highest level of scientific evidence (Level A) as a performance-enhancing aid. It not only acts at the metabolic level but also reduces the perception of effort (RPE) through its effects on the central nervous system.

Suggested supplementation protocol:

Dose: Between 3 and 6 mg per kg of body weight.
Timing: 45–60 minutes before the event, or strategically during the second half of a long race to counteract mental fatigue.
Format: Can be consumed as a standalone supplement or included in sports drinks and energy gels.

Key takeaways for endurance athletes

To cross the finish line performing at your best, don’t leave your nutrition to chance. Follow these three key principles:

Start the event with fully stocked glycogen stores.
Consume carbohydrates consistently throughout the event (30–90 g/h), after training your digestive system to tolerate them.
Follow a structured hydration plan that includes adequate sodium replacement.

Developing an individualized nutrition strategy is essential. Explore the Energy & Endurance ingredients category to formulate the drink or nutrition plan that best matches your intestinal tolerance and energy requirements.

References

Asker, E. J. (2011). Nutrition for endurance sports: Marathon, triathlon, and road cycling. Journal of Sports Sciences; 29(S1): S91–S99.
Burke, L. M., Hawley, J. A., Wong, S. H. S., & Jeukendrup, A. (2011). Carbohydrates for training and competition. Journal of Sports Sciences.
Cox, G. R., Desbrow, B., Montgomery, P. G., Anderson, M. E., Bruce, C. R., Macrides, T. A. et al. (2002). Effect of different protocols of caffeine intake on metabolism and endurance performance. Journal of Applied Physiology, 93, 990–999.
Hargreaves, M., Hawley, J. A., & Jeukendrup, A. (2004). Pre-exercise carbohydrate and fat ingestion: Effects on metabolism and performance. Journal of Sports Sciences, 22, 31–38.
Jeukendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20, 669–677.
Jeukendrup, A. (2008). Carbohydrate feeding during exercise. European Journal of Sport Science, 8, 77–86.
Jeukendrup, A. E., & Chambers, E. S. (2010). Oral carbohydrate sensing and exercise performance. Current Opinion in Clinical Nutrition and Metabolic Care, 13, 447–451.
Rodriguez, N. R., Di Marco, N. M., & Langley, S. (2009). American College of Sports Medicine Position Stand: Nutrition and Athletic Performance. Medicine and Science in Sports and Exercise, 41, 709–731.
Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). American College of Sports Medicine Position Stand: Exercise and Fluid Replacement. Medicine and Science in Sports and Exercise, 39, 377–390.
Smith, J. W., Zachwieja, J. J., Horswill, C. A., Pascoe, D. D., Passe, D., Ruby, B. C. et al. (2010a). Evidence of a Carbohydrate Dose and Prolonged Exercise Performance Relationship. Medicine and Science in Sports and Exercise, 42 (5), 84.