How does caffeine work?

Caffeine is both a drug and a nutrient. A cup of coffee in the morning is used to wake up a cup in the evening is often used to work or study late. Athletes often use it to improve endurance performance, but it is also used in power sports for explosive power. There is a substantial amount of evidence that caffeine has ergogenic effects, especially for endurance performance but how exactly does caffeine work?

Three mechanism by which caffeine might work. Most evidence indicates a central effect.

There was a theory that caffeine improves fat metabolism but is that really the way it works? The short answer is no. There is little evidence that the small effects that caffeine may have on fat metabolism in some situations is responsible for the performance effects. So, what is the true relationship between caffeine and athletic performance?


What are the proposed mechanisms?

Caffeine has been thought to improve performance in a variety of sports and exercise types through three possible main mechanisms:

  1. Blocking adenosine

  2. Increased muscle calcium release

  3. Effects on catecholamines

We will discuss each of these mechanisms briefly below. First we will describe the mechanism, then we will discuss the evidence for each.


Blocking adenosine: how does caffeine affect the brain?

Caffeine has a chemical structure that is similar to a molecule called adenosine. This molecule is produced naturally in the body and is responsible for feelings of tiredness, fatigue and even pain sensation when it binds with its receptors in the brain. Simply put: more adenosine means more fatigue. Because of the structural similarities between caffeine and adenosine, caffeine can stop adenosine from binding to these receptors, reducing the sensations of both tiredness and pain. This effect of caffeine is often referred to as a central effect: an effect on the brain.


Because of the structural similarities between caffeine and adenosine, caffeine can stop adenosine from binding to these receptors, reducing the sensations of both tiredness and pain.

Caffeine increases calcium release from muscle cells

Caffeine increases the release of calcium in muscle cells. This release is responsible for the contraction of muscle. It was thought that caffeine supplementation might be able to increase the force production of muscle because of this.


Caffeine may affect catecholamine levels

The early theory of how caffeine improved exercise performance was that caffeine stimulated fat metabolism and spared muscle glycogen. Now we know that this is unlikely the main explanation. Although caffeine may have small effects on fat metabolism (at least in some situations), this is not the reason for the performance effects. Caffeine may stimulate the breakdown of triglycerides (the storage form of fat). The fatty acids that are released can be used for energy. In addition, caffeine can cause an increase in the family of hormones called catecholamines, which includes the ‘fight or flight’ hormone adrenaline (also called epinephrine). The increase in catecholamines can also increase the breakdown of fat. If the condition are right and more fatty acids are available, they will be used for energy during exercise (but not in all situations). If more fat is used this could lead to reduced breakdown of glycogen – the stored form of carbohydrate in the body – meaning it is available for energy later, perhaps delaying fatigue or exhaustion and leading to improved performance.


What is the