We get drowsy because of a chemical called adenosine, which is a byproduct of brain activity. When our brains have been in action for a while, and have released a lot of adenosine, the chemical finds its receptors and triggers sleepiness.

Sleep then clears the adenosine, allowing us to wake with more alertness.

Caffeine, it turns out, is not just a stimulant, but also fits into the same receptors as adenosine, but doesn’t trigger the drowsiness response. In effect, coffee’s most important role in keeping us awake is interrupting our brain’s auto shutdown mechanism.

When you preface a power nap with a large, strong coffee, you’re not only clearing adenosine naturally through rest, but also preventing the chemical from finding receptors after you rise. The consequence is greater alertness and better performance on many kinds of tasks.

So next time you start to slow down mid-day, quickly down a cup of Joe and find a spot to relax.