Nutrition, Podcast, Science

Caffeine and Endurance Performance with Ajmol Ali, PhD | EP#234

 May 18, 2020

By  Mikael Eriksson


In this Episode you'll learn about:

  • The background on caffeine in endurance sports, including the time on WADA's prohibited substances list
  • The differences between the meta-analysis conducted by Dr. Ali and previous reviews and meta-analyses, including the specific inclusion criteria and reasons behind them
  • The findings: 2-3% improvement in endurance performance longer than 5 minutes when ingesting 3-6 mg/kg bodyweight prior to the event
  • Responders and non-responders: how factors such as caffeine metabolism and sensitivity (determined by specific genes) may impact the effect each individual gets from caffeine
  • Washout period: do you need to taper off your coffee consumption before an event to get the benefits of caffeine supplementation on race day?

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History of caffeine as an endurance performance enhancing substance

05:10 - 

  • It was the Ethiopians who were first to discover that caffeine has a positive impact on endurance performance.

    They started to take in caffeine before long marches, which they found enhanced their physical ability.
  • During the early 1900s, the first academic reports were published that investigated caffeine as a potential performance enhancing agent and the effect could immediately be demonstrated.

    Consequently, the World Anti-Doping Agency (WADA) put in a restriction on the amount of caffeine allowed in urine in athletes.

    This restriction was later removed as caffeine did become so widely used by the majority of the world’s population.

    In more recent years, a Spanish study investigated the amount of caffeine in elite runners during competition and found that the majority of the athletes had more caffeine in their urine than the old WADA guidelines would allow.

    The use of caffeine among athletes is largest within endurance sports.

Caffeine metabolism

10:00 -

  • The prevailing consensus in regards to caffeine’s effects on the body and performance is that it works as a so-called ”antagonist” to adenosine.

    Adenosine is a substance involved in phosphate metabolism and has a key role for controlling the feeling of tiredness and the sleep cycle, the substance is gradually building up during the day and the higher the amounts of accumulated adenosine, the more tired we feel.

    The caffeine molecule mimics the structure of adenosine but has the opposite effect, accordingly counteract tiredness.

    Caffeine also affects the transmission between neurons by inhibiting pain signals as well as the feeling of tiredness and exertion, and these effects are regarded as primary to why caffeine enhances endurance performance.


12:20 -

  • In terms of doses of caffeine, what’s interesting is how much caffeine is taking in per kg body mass.

    A moderate caffeine user (global average) takes in around ~3mg caffeine/kg body mass a day (one cup of coffee is approximately 100-120mg caffeine).

    A heavier caffeine user takes in between 5-6mg of caffeine per kg body mass a day and in research investing the potential performance enhancing properties of caffeine, this is also the most typically amount of caffeine studied, which in these studies normally is taken in around 1h pre exercise.

How big of a performance benefit can one expect from caffeine?

17:35 -

  • In the recent meta analysis that we performed, we implemented some really strict inclusion criteria including solely looking at caffeine taking in on its own (i.e. as caffeine tablets and not for instance as a part of coffee or energy drinks) and without simultaneously taking in carbohydrates, we also only included studies where the participants did take in more than 3 mg of caffeine per kg body mass and studies with a performance relevant outcome measurement (i.e. not ”time to exhaustion”).
  • In total, we found 44 studies (~1000 subjects) that met these inclusion criteria and the vast majority of these studies were cycling studies (probably because it’s the easiest modality to look at).

    On average, the included studies investigated the effect of 5 mg of caffeine per kg body mass that had been taking in 60 min before exercise.
  • Pooling all the 44 studies together, our key finding was a 2.52 % improvement in overall performance by taking in ~5mg caffeine/kg 60 mins prior to exercise, which may not seem like a lot but within exercise physiology this is actually a rather big improvement.
  • We also did some additional analysis to investigate if the caffeine effect was limited to a certain fitness level (elite vs recreational athletes) or male and female but no such distinctions could be found.

    The conclusion is therefore that no matter how well trained you are or if you are a male or female, one can expect a 2.5 % improvement in overall performance by the above stated dosage of caffeine.

Limitations of the study/remaining question marks

32:45 -

  • In some of the included studies, some subjects did not seem to respond to caffeine (no performance gains were seen in these individuals) or caffeine even had negative effect in their performance, and such findings always raise many question marks.

    Several theories regarding this do however exist, for instance, we know that the caffeine metabolism is affected by age (decreases with age), menstrual cycle, brit control pills, smoking, genetics among others.
  • One also needs to point out that the studies included in the meta analysis did not include subjects belong to the absolute world class in their sport, we know that these athletes differ physiologically in several aspects from recreational or even well trained amateur athletes and this could potential influence their response to caffeine.
  • Moreover, the larger degree of fatigue or tiredness in the athlete, caffeine seemed to have a larger influence on performance.
  • One cannot either ensure that caffeine may have a larger benefit in certain sports compared to others even though this meta analysis suggested that.
  • Additionally, since caffeine is such a commonly ingested substance, this makes it fairly difficult to standardize a study population in terms of how habituated they are to caffeine and to make sure that they have not taken in any additional amount of caffeine prior to the study (caffeine is a very common additive in plenty of other food and drinks than coffee, coca-cola or energy drinks).
  • In terms of genetics, some studies demonstrated a higher response to caffeine in people who genetically metabolize caffeine faster.

    There are also genetic differences in the uptake of caffeine into cells (especially the brain cells) and how it reacts within the cells, which some studies also suggest affects the overall response to caffeine
    in an individual.

Taper off caffeine in order to get the performance enhancing effect

50:00 -

  • One can divide the world’s population into three main groups based on caffeine intake: the ”naive user group” who drinks nothing or very little caffeine, the ”moderate user group” (~3 mg of caffeine/kg/day) and the ”heavy consumer group” (> 5-6mg/caffeine/kg/day).

    In order to get the performance gains that can be seen from caffeine, generally the ”heavy consumer group” needs to completely stop taking in caffeine for 2-3 weeks in order to be able to expect the performance enhancing effects similar to these seen in the meta analysis.

    The ”moderate group” typically just needs to reduce their intake a bit in the weeks leading up to the event where they would like to see the desired performance enhancing effect.

    The ”naive user group” on the other hand doesn’t need to change anything in their caffeine intake behavior prior to an event where they would like to use the performance enhancing properties of caffeine.

Genetic testing for caffeine response related genes

54:05 -

  • Since the knowledge of the genetics behind of caffeine and caffeine response is still rather unexplored, especially when it comes to how to implement genetic testing, I would start by recommending athletes to experiment what works best for you on an individual level.

Rapid fire questions

1:03:50 -

  • What is your favorite book, blog or resource related to endurance sports? I rarely read sport books but lately I have read a lot of books about mindfulness, which has helped me a lot and I could strongly recommend.
  • What is a personal habit that has helped you achieve success? Perseverance and dog headiness to get the job done.
  • What do you wish you have known or done differently in your career? From my sporting perspective I neglected recovery and flexibility training for a too long time.


Mikael Eriksson

I am a full-time triathlon coach, founder of Scientific Triathlon, and host of the top-rated podcast That Triathlon Show. I am from Finland but live in Lisbon, Portugal.

Please contact me if you have feedback on the podcast or want to make suggestions for improvement or send in a question for a Q&A episode.

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