Caffeine & Endurance Performance

Ahhh, coffee. Chances are, you drink it. According to a 2015 Gallup poll, just under 2/3 of Americans drink at least 1 cup a day. But even if you’re not a coffee drinker, you may be taking in caffeine some other way. By far the most common sources of caffeine in the American diet are in the form of beverages, with coffee and tea leading the charge. Caffeine from sodas and energy drinks/drink tablets follow, and caffeine from solid foods (mainly those containing chocolate) makes up the smallest percentage.

The amount of research around caffeine use is huge. In the last few years, the effect of caffeine on athletic endurance – especially during endurance competitions– has been a hot topic. Athletes are always looking to extend duration and delay fatigue. Can caffeine supplementation help? Let’s first take a quick look at how caffeine works.

What does caffeine actually do

We all know caffeine stimulates the brain, but it has several other physiological effects, including a rise in blood pressure, pulse rate, and stomach acid production.  Most interestingly from an endurance point of view, caffeine causes an increase in fat storage breakdown and release of fatty acids into the bloodstream. This is important for endurance athletes, because available fatty acids mean sparing of glycogen.

Glycogen is the main source of energy for working muscles, and once it’s depleted, the body has to rely on another form of fuel. Fat metabolism is preferred at that point, and well-conditioned athletes generally become very efficient at it. Protein metabolism can kick in up to 15% of energy use during the late stages of endurance events, when glycogen is depleted. The bottom line is, the longer you can spare glycogen, the longer you will delay muscle fatigue!

So is that a yes or a no on endurance?

It’s a yes. Studies since the 1970s have consistently shown improvement in athletic endurance and output with caffeine consumption. Runners, cyclists, and cross-country skiers are the usual lab rats for these studies, and besides the measured physiological response, most athletes report feeling stronger and less fatigued for longer.

Note: caffeine has not been shown to have any positive effect on speed and/or strength activities. The performance benefits are strictly over endurance events.

So how much caffeine do you need and when?

Initial studies looked at an intake of 3-6mg/kg of body weight taken an hour before starting the activity (that’s 2-4 cups of coffee for a 150lb athlete!). More recent studies have shown that a much lower intake of 1-2mg/kg of body weight has the same effect (that’s 0.5-1.5 cups of coffee for a 150lb athlete).

Caffeinated gels and drink tablets contain varying amounts of caffeine, so read labels carefully! GU™ gels, for example, have about 40mg each. CLIF SHOT™ can have up to 100mg.

When you take in the caffeine matters, too. Caffeine concentration in the blood peaks around 60-90 minutes after ingestion, meaning you’re the most “caffeinated” about an hour to an hour and a half after taking in the source of caffeine. However, the glycogen-sparing benefit of caffeine kicks in a little later. Intake is suggested 1-3 hours before the event, and/or during the late stages when glycogen stores are depleted.If gels don’t sit well with you, there are several brands of caffeinated gums on the market now, formulated with endurance athletes in mind.

Also keep in mind that the effects of caffeine stay in the system for a long time (up to 12 hours), and “seasoned” users will build up a tolerance (and not experience the same effects as occasional users). It may be wise to avoid caffeine for 3-4 days prior to an endurance event to increase the effect on race day.

Man drinking coffee over blackboard with structure of caffeine molecule

Important things to remember

Caffeine is a drug, and while the FDA recognizes it as “generally safe for its intended use,” it’s important to remember potential side effects:

  • Dehydration, abdominal cramps, and diarrhea are not things you wish to experience during a race! If you choose to use caffeine for endurance, make sure to experiment during training. Don’t do anything new on race day. Ever.
  • Nervousness and tremors can occur. If you tend to be a nervous racer, caffeine may not be the right thing to add to the mix. Again, experiment before toeing the start line.
  • Sleeplessness and long-term sleep deprivation are not helpful in training (or life in general!). Most endurance athletes already fight the clock with early morning workouts or long weekend runs. Habitual caffeine use has been shown to lead to chronic sleep deprivation (that you may not even be aware of).
  • Caffeine increases gastric acid production. If you have a history of stomach ulcers or gastroesophageal reflux disease (GERD), caffeine is a bad idea.
  • If you’re competing on a collegiate or professional level, be aware of drug testing limits. Caffeine is an allowed substance for most competitions, but there is a recognized acceptable threshold. Inform yourself before your event, and keep your intake well below the cut off. Hydration levels, body composition, and many other factors can influence how your body metabolizes caffeine.

Whether to use caffeine to extend your endurance potential is a personal choice. Not all athletes experience the same effect/benefit in performance, and for some the side effects are just too troublesome. In the end, nothing is as valuable to endurance performance as a solid training base – meaning cardiovascular conditioning, proper fueling, and cross-training for injury prevention and strength. Caffeine won’t make up for lack of training, but it can give you that extra little edge you’re looking for.

Marathon running in the light of evening


  1. Drewnowski A, Rehm CD. Sources of Caffeine in Diets of US Children and Adults: Trends by Beverage Type and Purchase Location. Nutrients. 2016;8(3):154.
  2. Eberle SG. Endurance Sports Nutrition, 3E. Human Kinetics; 2013.
  3. Tarnopolsky MA. Caffeine and creatine use in sport. Ann Nutr Metab. 2010;57 Suppl 2:1-8.

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