How does caffeine work?

Caffeine is a stimulant that mainly works by blocking adenosine receptors (adenosine is an organic compound that plays a role in mediating sleep pressure and drowsiness) and inhibiting phosphodiesterases (a group of enzymes that mediate sympathetic nervous system activity) (1).

The use of caffeine to enhance exercise performance is common amongst athletes and exercise enthusiasts alike. Its exact mechanisms of action as an ergogenic aid, however, are still somewhat unclear and the supporting literature is mixed.

The positive and negative effects of caffeine during exercise

Caffeine ingestion is often shown to significantly improve exercise performance, both submaximal exercise (2) and high-intensity exercise (3). However, the body of literature on this subject is mixed and the underlying mechanisms behind these results are still relatively unclear.

Caffeine may affect physiological factors such as lung function, blood glucose and lactate levels during submaximal exercise (1), however, caffeine’s main performance-enhancing effects are more likely to be psychological, such as increased alertness and arousal, raising individual’s pain threshold and tolerance to fatigue, all of which can reduce the rate of perceived exertion (RPE) in response to a bout of exercise (4).

How much caffeine should you consume before exercise?

Safe and effective doses of pre-workout caffeine range from 3-6mg/kg of body weight (5). This works out to 240-480mg for an 80kg person. For context, a shot of espresso contains about 210mg of caffeine. Take caffeine at least 15mins before your workout to allow it to take effect.