Caffeine use in endurance sport

Caffeine is found in drinks such as colas, tea, coffee and hot chocolate. It has been used over the years as a pick-me-up, and is consumed in generous proportions by many people. In Ironman Triathlon and other endurance sports its use was banned above certain limits until 2004, when the world anti-doping agency removed its prohibition. Caffeine is present quite commonly in the form of caffeinated gels, occasionally as caffeinated drink mixes and often as colas, typically on the run sections of triathlons. In other words a lot of caffeine is being consumed in endurance sports. What we need to know is, are these competitors using caffeine gaining an advantage, and if so, could they use the caffeine more effectively by optimising the timing and amount of their intake?

Caffeine the fat burner.

There is good evidence that caffeine leads to breakdown of fat (known as triglycerides) in your fatty tissues into free fatty acids1,2. Some of these free fatty acids then get burnt as fuel, the rest are restored as triglycerides. It all depends on the type of exercise you are doing after ingesting the caffeine. Caffeine seems to increase fat burning in two ways. Firstly by boosting adrenaline levels and secondly by activating lipase, the hormone that breaks down fat.

One study suggested that the adrenaline mechanism is the only effective way that caffeine improves performance3. However, having looked at the details it seems that the study demonstrates rather effectively that beta-blockers are particularly bad for endurance sport - they drastically reduce the time that high efforts can be maintained. This study compared beta-blockers alone with caffeine and beta-blockers together. There was a slight improvement with caffeine, but the effect of the beta-blockers was in my opinion too strong to draw any firm conclusions about the workings of the caffeine. 

The effect of caffeine on fat burning depends on the amount and timing of the caffeine intake. Many studies have used an amount of 6mg/kg body weight to cover an exercise period of typically 2-3 hours. In other words a 70kg man would take 420mg and a 60kg woman 360mg for a 3 hour exercise bout including some intense efforts. Some other trials have experimented with about half that amount, where some ergogenic (enhancing physical performance) effects were found, but not as much as with the greater amounts. There is however a limit to how much caffeine you can take and still improve performance. It varies between individuals, but the main message from the studies is that there is some optimal amount that will boost your performance and that for many this will be below the level that could cause any side effects on health such as heart palpitations or anxiety.

Caffeine the motivator?

Another way that caffeine can affect athletic performance is by reducing our perception of effort. A lot of studies have demonstrated this effect4,5, which gives competitors taking caffeine the ability to push themselves harder and for longer. The first of the studies I looked at, showed an increase of 12% in the amount of work that could be done for the same perceived effort, on a 30 minute indoor cycling trial. The 2nd study which was a meta-analysis looking at 21 studies found that exercise performance improved by about 11% and that one third of this improvement probably related to changes in perception of effort. These studies used a measure of perceived effort called the Borg scale6 which measure effort levels between 0 - no effort and 20 - maximal effort.

It seems likely that a performance benefit during racing is likely from caffeine supplementation. Quantifying this is difficult, but it will certainly vary between different individuals and will probably become more significant the longer the endurance event.

How much caffeine?

One problem with caffeine supplementation in anything other than pill form is that amounts are often highly variable. Amounts of 200mg are often taken in pill form, which is equivalent to a strong cup of coffee.

When it comes to coffee, amounts of caffeine vary considerably depending on a number of factors such as:

  • Brewing time. The longer coffee brews the stronger it is, so coffee left to brew for 5 mins in a cafetiere will be stronger than coffee created by pouring boiling water onto instant coffee.
  • When the coffee was ground. Often more recently ground coffee is stronger, so coffee ground from beans a few minutes ago is stronger than instant coffee from a jar.
  • The type of coffee bean and how long it is roasted for. The longer a bean is roasted the stronger it is.
  • How much of the coffee are you going to drink?

In general a typical instant coffee of 250ml will contain 30-160mg of caffeine. A big variation! A coffee ground on the premises in a reputable coffee shop will often be a bit stronger, containing from 90-200mg7 of caffeine. I understand that Starbucks coffee tends to be weaker (and not as nice in my opinion), while Cafe Nero and Costa Coffee are quite a bit stronger. When you get served up a large volume, as seems increasingly common then you could easily be consuming up to 400mg of caffeine in one hit. This is enough for some people to get palpitations, while some will feel only slightly stimulated.

When it comes ot products typically used in an endurance event such as an Ironman, the amounts are as follows:

  • Caffeinated sports gels such as Powerbar, SIS or High5 contain 40-50mg per sachet. That means that 8 sachets should give most people a substantial (400mg) boost.
  • Colas tend to contain 1mg per 10ml of fluid, so a few swigs from a typical plastic cup 1/2 fill (120ml) should yield about 12mg. Not as effective a boost as caffeinated gels, but still adding to your caffeine load.

Some studies have shown cola to be more effective than you might expect given the amount of caffeine it contains. this could be due to the type of sugars in the drink, how effectively they are absorbed and even the taste qualities.

When should I supplement?

It takes at least 50 minutes for levels of caffeine to peak in the bloodstream after a drink. This peak may last for up to 3 hours. So for shorter events caffeine is likely to be effective when taken prior to the race start. For longer events such as Ironman it is best to start taking caffeine on the bike, probably in the form of gels. When you reach the run your need for a boost is likely to peak and it would be prudent to continue with some form of caffeine supplementation for at least the first 2 hours. In practice this will often be in the form of coca cola, which if drunk regularly should improve your Ironman marathon performance.

What are the dangers of supplementing caffeine?

Caffeine is known to have some side effects.

  1. Caffeine can act as a diuretic, causing you to lose more fluid in your pee. However, people who regularly consume caffeine seem to become less affected by this than those who are not used to it. In a long distance endurance event it is worth being aware that caffeine may make you more thirsty and that this extra fluid is probably needed.
  2. If you supplement with creatine, caffeine may restrict the effect the creatine has on improving your ability to accelerate in short bursts. Normally using creatine for long distance endurance events would be unlikely to improve performance in my opinion, so sticking to the caffeine is much more likely to be effective.
  3. Despite raising blood pressure in the short term, it appears from a number of studies that regular caffeine use does not damage cardiovascular health8.
  4. In order to prevent negative side effects there was until 2004 a limit on the amount of caffeine that could be detected in the urine of elite competitors. This was set at 12mg per litre of urine. Of course there is quite a bit of individual variability as to how much caffeine you pee out. Nevertherless it was said to equate to roughly 8 cups of coffee or in excess of 1000mg of caffeine.


There is very little doubt that for a large number of athletes caffeine use can improve performance. It is important that those that use caffeine try to do so in a way that maximises the benefits, while avoiding any of the possible negative health ef