Melanie Clark (Battaglia), MS, RD, CSSD

Sports Dietitian

How many hours per week do you spend training leading up to an endurance event? As you put in countless hours of training make sure you also have a nutrition strategy as this is a component of race and training success. One example of a race nutrition strategy is caffeine use. Caffeine, when the adequate dose is timed correctly, could improve performance by 2-4%. (1)

How does caffeine work? Caffeine is known to reduce fatigue. Within the brain, caffeine binds to the same receptor as a molecule called adenosine. When adenosine binds to its receptor in the brain, fatigue is triggered. Whereas when caffeine binds to the adenosine receptor, it blocks the adenosine receptor from binding and therefore delays fatigue. Several studies have reported an average 5.6% reduction in ratings of perceived exertion after caffeine consumption, which is likely due to how caffeine works in the brain by blocking the adenosine receptors. (2). Caffeine can also improve reaction time, concentration, and self-perceived energy levels when sleep deprived. 

When should I consume the caffeine? Consume caffeine approximately 40-60 minutes before your race or exercise start to experience the maximal performance benefits. 

How much caffeine should I have before and during a race? 3-6 mg of caffeine per kg of body weight. Up to 6 mg/kg is safe and effective beforehand, though studies have reported that the benefits plateau at doses greater than 3 mg/kg.  A 70 kg athlete following the 3 mg/kg recommendation would need 210 mg of caffeine before the race starts to experience the performance benefits of caffeine. Higher doses greater than or equal to 9 mg/kg body mass are associated with side effects.  

 Is caffeine during the race beneficial? Yes, approximately 1.5 mg/kg to 3 mg/kg doses of caffeine can improve performance late in an endurance race. In a study that assessed low (1.5 mg/kg) and moderate (3 mg/kg) doses of caffeine late in the race found that participants who consumed the low or moderate doses both had significantly faster time trial times compared to the placebo (3). Some theories report that less caffeine is needed when consumed late in the race due increased fatigued and greater sensitivity to the caffeine. Lower doses are recommended for those prone to caffeine side effects. Think about the last race you had. At what time point or mile marker in that race did fatigue set in? For your next race or long training day, take a caffeine source of ~1.5 to 3 mg/kg about 40 minutes before you think significant fatigue will occur to potentially reduce the perceived exertion, pain, and fatigue. For example, mile 11 of my run during 70.3 races is when I feel significant fatigue set in, so I would want to include a caffeine source in my race nutrition plan around mile 7 of the run.

Caffeine sources that can be consumed during a race:

  • Maurten gel (100 mg caffeine)
  • Clif shot energy gel double expresso (100 mg)
  • Science in Sport caffeine energy gel (75 mg caffeine)
  • Military Energy Gum (100 mg)
  • Red bull (80 mg/8 oz)
  • Soda (~50 mg)
  • Run gum (50 mg)
  • GU expresso gel (40 mg)

For more sources and caffeine content of food, supplements, and beverages check out Caffeine Informer.

Non-Responders. There is a chance that the caffeine will not impact your performance and could even worsen it. Caffeine and the performance benefits are influenced by genetics. Some people experience greater performance benefits while others absorb caffeine at a slower rate or experience unbearable side effects. 

Potential side effects: A few examples are, insomnia, headache, nervousness, anxiety, and gastrointestinal problems.

Will caffeine make me dehydrated? One of the most common questions or comments I hear about caffeine is “does coffee dehydrate?” and the answer is no if a low-moderate amount is consumed. A study conducted in 2014 by Killer et al. tested the effect of 4 cups of coffee per day versus 4 cups of water per day on hydration status. There were no changes in body mass, 24-hour urine volume, urinary hydration markers, or hematological hydration markers. It was concluded that coffee, when consumed in moderation, does not dehydrate, but provides similar hydrating qualities as water (4).

Be sure to test out the caffeine during training! A few years ago, I was getting ready for an FTP test at Well-Fit and had just learned all about the role of caffeine and endurance performance. I decided to test out what I had learned about caffeine on my upcoming FTP test. I calculated out exactly how many milligrams of caffeine I would need to consume before the FTP test. Then I went to the grocery store to find something that had the right amount of caffeine in it. I love coffee and decided to check out the cold brews. Conveniently, several brands of cold brew actually list the total mg of caffeine right next to the nutrition facts label. La Columbe cold brew it was!  The morning of my FTP test, I had my usual pre-exercise snack about 30-60 minutes before the workout, which was likely a banana and then the added a serving of the La Columbe cold brew. I finished the FTP test with a 10w FTP improvement and felt great throughout the entire FTP! The improvement could have been the caffeine or the fact that I had worked hard the weeks leading up to the FTP test, but the cold brew has become part of my pre-race nutrition routine ever since! I personally like the Maurten and SIS caffeine gels, and clif bloks for caffeine during races and training. I’ve worked with several marathoners who love the caffeine chewing gums, like Run Gum. Many people also enjoy coke on Ironman run courses, which is beneficial as a source of both caffeine and carbohydrates. I would recommend trying out a variety of caffeine sources during training to see if caffeine is something that could be part of your race nutrition plan!


  1. Guest, Nanci S et al. “International society of sports nutrition position stand: caffeine and exercise performance.” Journal of the International Society of Sports Nutrition vol. 18,1 1. 2 Jan. 2021
  2. Davis JM, Zhao Z, Stock HS, Mehl KA, Buggy J, Hand GA. Central nervous system effects of caffeine and adenosine on fatigue. Am J Phys Regul Integr Comp Phys. 2003;284(2):R399–404
  3. Talanian, Jason L, and Lawrence L Spriet. “Low and moderate doses of caffeine late in exercise improve performance in trained cyclists.” Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme vol. 41,8 (2016): 850-5. 
  4. Killer, Sophie C et al. “No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population.” PloS one vol. 9,1 e84154. 9 Jan. 2014, doi:10.1371/journal.pone.0084154