How does caffeine’s stimulatory effect fit into the world of endurance sports?

How does caffeine’s stimulatory effect fit into the world of endurance sports?

by Alister Gardner

If you’re anything like me, it can be a daily struggle to not drink too much coffee. I love it so much; the smell of roasted beans, its warm bitter taste and above all, the stimulating effects of methyl xanthine alkaloid, the compound in coffee better known as caffeine.

I do well to stick to 2 cups on most days; 1 to help me wake up in the mornings and a second 1 to perk me up again mid-afternoon. I am no doubt not alone here. Some of you may even drink a few cups more...

Caffeine and endurance sports?

Let’s start with how it works: Caffeine stimulates the central nervous system. It does so by temporarily blocking the adenosine receptor and the onset of drowsiness caused by adenosine.

Caffeine also stimulates parts of the autonomic nervous system, which controls our automatic functions like breathing, heart rate and digestion. It may also facilitate the signals between the nervous system and muscles.

When does caffeine "kick in"?

Once ingested, we tend to feel the effects of caffeine within ten to fifteen minutes, peaking after about 30-60 minutes and lasting for around 3 hours.

Research shows that these stimuli can in turn reduce fatigue and drowsiness (1), and increases alertness, especially during sleep deprivation (2). Caffeine has been proven to help in both high intensity and endurance sports; improving anaerobic performance like sprinting and Wingate tests (3, 4) and reducing perceived and time to fatigue effort in endurance sports (5, 6).


Drink (250 ml)

Caffeine (mg)

Brewed coffee


Brewed, decaf








Black tea


Brewed green tea


Bottled tea




Red Bull



Given these amazing benefits, why not just knock back a tasty caffeine source every time you train?!

Firstly, our bodies are able to build a tolerance to caffeine, and so over time, it will take higher doses to get the same benefit. 

Secondly, there are some adverse effects associated with caffeine:

It can increase blood pressure and affect gastrointestinal motility (yep, it can make us need to go to the loo sooner).

In postmenopausal women, high caffeine consumption can accelerate bone loss. It can also cause jitteriness, increase anxiety and insomnia.

While moderate amounts of caffeine do not have a diuretic effect, however large doses of typically more than 300 mg (2-3 cups of coffee or 5-8 cups of tea) can have a diuretic effect.

So it is best to pick your caffeine dosing wisely. For example, specifically during races, early morning trainings or bigger training sessions.

It is only through comparative studies that we can really measure the benefits of caffeine, but in my own experience it seems I can push harder, and for longer, following a pre-training coffee (interval training especially).

Some personal experience while racing - the good

Competition-wise, earlier this year I achieved a PB on the half marathon (1:10:42, Banque Scotia 21K de Montreal) with just 1 XACT ENERGY blackcurrant before the race, then another PB on the marathon (2:31:50, Ottawa Marathon) with three XACT ENERGY blackcurrant during the race.  So I am a big fan of caffeine and consider it a part of my race kit.

... And the ugly 

But getting the right dose can be a fine balancing act: During the CCC 101 km ultra-race in Chamonix  I drank 3 cans of Red Bull and hydrated mostly on a caffeinated drink we (XACT) were testing. Again I ran the race well, however towards the end and afterwards, my head was jittery and it wasn’t easy to sleep despite the exhaustion! 


A few tips to get the most out of caffeine:

  • For any event lasting less than 90 minutes:
A pre-race coffee or gel will be sufficient. For example, a XACT ENERGY blackcurrant 15 minutes ahead of the race will mean the caffeine will kick at the start line and last you through your race. For me, a quick espresso before heading for interval training is a low volume shot of caffeine I can enjoy while I finish up work for the day.
  • Longer endurance events (marathon/ultramarathon/Ironman):

Here you need to think about regular dosing, for example a XACT ENERGY blackcurrant or XACT ELECTROLYTES with caffeine every second or third gel or tab. The key is too not overdose but remain consistent.
For longer ultra-races that can last a up to a day or more, there will be times during the race that are harder than others. For example, having run a whole night during an ultra, early morning can be taxing due to lack of sleep and so a caffeine boost can help to reduce that type of fatigue. A hot tea or coffee at the aid station can also help, similar to the usual morning cuppa.

  • Post workout:

There is some research showing that when combined with carbohydrates caffeine helps refill glycogen reserves faster. This is hugely beneficial to folks who train more than once a day, or still have a busy day following their training. So enjoy a XACT ENERGY blackcurrant along with your post workout XACT PROTEIN wafer. An interesting recipe I learned was to add a shot of espresso to my alredy made chocolate soy milk and banana smoothie, it adds a delicious twist of warm and bitter mixed with sweet, cold and creamy).

So don’t wait until the last thirty minutes of your marathon before taking you caffeinated energy gel or XACT ENERGY. Instead, take it early or even before your race, and get the most out of your caffeine dose!


  1. Nehlig A, Daval JL, Debry G (1992). "Caffeine and the central nervous system: mechanisms of action, biochemical, metabolic and psychostimulant effects". Brain Research. Brain Research Reviews.
  2. Snel J, Lorist MM (2011). "Effects of caffeine on sleep and cognition". Progress in Brain Research.
  3. Pesta DH, Angadi SS, Burtscher M, Roberts CK (December 2013). "The effects of caffeine, nicotine, ethanol, and tetrahydrocannabinol on exercise performance". Nutrition & Metabolism
  4. Grgic J (March 2018). "Caffeine ingestion enhances Wingate performance: a meta-analysis". European Journal of Sport Science.
  5. Doherty M, Smith PM (April 2005). "Effects of caffeine ingestion on rating of perceived exertion during and after exercise: a meta-analysis". Scandinavian Journal of Medicine & Science in Sports.
  6. Southward K, Rutherfurd-Markwick KJ, Ali A (August 2018). "The Effect of Acute Caffeine Ingestion on Endurance Performance: A Systematic Review and Meta-Analysis". Sports Medicine.