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How Caffeine can Improve Endurance Performance

by Laurence Landry 06 Feb 2023
How Caffeine can Improve Endurance Performance

Caffeine is commonly found in daily food and beverages and is so frequently consumed that it is easy to forget that it is a supplement. In fact, it is one of the most popular ergogenic aids, meaning that its use can directly improve sport performance. Once ingested, caffeine binds to adenosine receptors in the body and decreases the perception of effort and increases alertness. These effects are highly beneficial in helping athletes perform for endurance events, such as triathlon.

How to take caffeine for sport performance?

The recommended dosage is 3-6 mg of caffeine per kg of bodyweight, taken either prior to or during training and competition. However, it may be worthwhile for an athlete to initiate caffeine consumption at a lower dose (3 mg per kg of bodyweight). For example, a 60 kg athlete (132 lb) would need between 180-360 mg of caffeine per dose. Here are a few examples of products with their caffeine content:


Caffeine content

¼ bar of dark chocolate 70-85% cacao (25 g)

20 mg

1 cup of green, oolong or white tea (250 mL)

25-45 mg

1 can of cola (355 mL)

37 mg

1 gel (32g) with added caffeine

20-60 mg

1 cup of instant coffee (250 mL)

62 mg

1 shot of espresso (1 oz/30 mL)

64 mg

1 can of energy drink (355 mL)

110 mg

It is worthwhile to note that caffeine takes some time before it reaches its peak effect. General recommendations are to consume caffeine about an hour before it takes full effect. However, this delay varies among athletes, ranging from 45 min to 3 hrs. Thus, athletes benefit from practicing their caffeine intake during training to find the optimal dose and timing that work best for them. Additionally, some studies show that caffeine is best taken with a source of carbohydrate, such as combining caffeine with a fruit, a gel, or a cereal bar.

For example, a 60 kg marathoner could consume:

  • 1 cup of coffee (62 mg caffeine) 90 min before race start
  • 1 caffeinated gel (40 mg caffeine) every hour x 4 hours to complete the race
  • Total consumed: 222 mg caffeine

What are some side effects?

Although caffeine is commonly consumed on a regular basis by the general population, athletes must be cautious and well aware of its side effects, especially those consuming it in great quantities or those with little tolerance.

Caffeine is a stimulant and can increase heart rate and cause anxiety-related feelings. Large doses can also cause nausea, insomnia and restlessness. In some athletes, caffeine can stimulate their digestive system and cause bowel urgency and to some extent, diarrhea. Due to these potential side-effects, testing your caffeine consumption prior to the race is crucial. Knowing how your body responds to caffeine can help you better plan your caffeine intake strategies. 

Is it true that caffeine dehydrates?

Consumption of large doses of caffeine can momentarily increase urine production. However, this increase has no significant influence on an athlete’s overall hydration status. Moreover, tea, coffee and other caffeinated beverages often contribute to many athletes’ daily total fluid consumption and limiting caffeine can significantly alter their hydration strategies. Hence athletes who choose to decrease their caffeine intake should replace its consumption with other fluids, such as water.

Do I need to stop taking caffeine before competition to increase its benefits?

It was historically thought that a period of withdrawal prior to competition was beneficial in increasing the body’s response to caffeine. Later on, many studies showed that withdrawal effects had no significant influence on the body’s response on competition day. In fact, in some cases, coffee withdrawal led to adverse side effects such as irritability, mood swings, and alteration of daily routine, which further outweigh the potential enhanced response to caffeine.

In conclusion, caffeine is a safe supplement proven to be effective in decreasing perception of fatigue and increasing vigilance, making it an interesting option for triathletes looking to enhance their performance. However, due to its potential side effects and delayed peak effect, it is essential that athletes practice its consumption to find their individual optimal dosage and timing. 


Anna Ly, RD, IOC (c) 
(Registered dietitian, IOC Diploma in Sport nutrition) & BRAVA Ambassador 



  • Maughan RJ, Burke LM, Dvorak J, Larson-Meyer DE, Peeling P, Phillips SM, Rawson ES, Walsh NP, Garthe I, Geyer H, Meeusen R, van Loon L, Shirreffs SM, Spriet LL, Stuart M, Vernec A, Currell K, Ali VM, Budgett RGM, Ljungqvist A, Mountjoy M, Pitsiladis Y, Soligard T, Erdener U, Engebretsen L. IOC Consensus Statement: Dietary Supplements and the High-Performance Athlete. Int J Sport Nutr Exerc Metab. 2018 Mar 1;28(2):104-125.
  • Sports Dietitians Australia. Caffeine Fact Sheet. Australian Institute of Sport. 2011 Jun.
  • Dietitians of Canada, Facts on Caffeine, April 26, 2018, - consulted November 11, 2022
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