After we’ve completed that workout and let our maintenance crew do their jobs, eventually morning arrives.
After That Workout, I'm Going To Need More Than Just A Protein Shake
After all that talk about intense workouts, lactate and the punishment we subject our knees to, there is one rather obvious question left.
Our eyes open, the alarm goes off, and we drag ourselves out of bed to begin another day. For many of us, the next step is almost automatic: reach for a coffee and try to convince our brains that we’re fully awake and ready to rumble. We think it’s all about the caffeine.
So why does coffee work, and what exactly is it doing inside our brains?
The answer begins with a rather interesting molecule called adenosine.
Adenosine is produced naturally as our cells carry out their normal activities. In the brain, its signalling is closely associated with the accumulation of sleep pressure. Sleep pressure describes the biological drive to sleep, which is higher when we have stayed awake for longer. Research has shown that adenosine signalling increases during prolonged wakefulness and contributes to the sleep-inducing effects of being awake for extended periods.
As it is with many other biochemicals involved in biological signalling within our bodies, adenosine binds to specific receptors in our brains, where it can influence the activity of our neurons.
Now, the chemical structure of caffeine is similar enough to adenosine that it can fit into those same adenosine receptors too.
That’s when the problem starts.
Caffeine can occupy the receptor without activating it in the same way that adenosine does. In other words, it effectively gets into the parking space that adenosine was supposed to use, but then refuses to do the job that adenosine was there to do.
That’s a somewhat similar idea to how non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen interfere with inflammatory signalling — although NSAIDs act by inhibiting cyclooxygenase (COX) enzymes rather than blocking inflammatory receptors.
But that’s another story for another time.
Would you like me to do a deep dive into how NSAIDs actually work?
But back to the caffeine first.
With caffeine blocking the adenosine from reaching those adenosine receptors, the result is that the brain becomes less responsive to the sleep-promoting signal from adenosine.
And suddenly, we feel more awake.
The rather amusing part is that the adenosine hasn’t actually gone anywhere.
It is still there, waiting for an opportunity to bind to its receptors, but caffeine has simply interfered with the binding process. That morning cup of coffee isn’t necessarily giving our brains a magical injection of energy. It is, in effect, interfering with our ability to hear one of the chemical signals telling us that we are tired.
So caffeine has occupied the adenosine receptors.
So what?
Well, this is where the biology gets rather sneaky.
Adenosine normally acts as one of the chemical signals contributing to sleep pressure. As it binds to its receptors, it influences neuronal activity in ways that make us progressively less alert and more inclined to sleep.
But if caffeine is sitting in those receptors instead, adenosine has fewer opportunities to deliver that message.
The brain therefore becomes less responsive to the signal that says:
“You’ve been awake long enough. It’s probably time to go to bed.”
And that is why we feel more alert after drinking coffee.
Caffeine hasn’t necessarily given us a fresh supply of energy. It has temporarily interfered with our ability to perceive one of the signals telling us that our energy and alertness are running low.
This interference is just hiding the fact that adenosine is still there and waiting to do its job. It is simply being blocked from doing its job.
Caffeine isn’t really telling our brains to stop being tired. It is telling our brains to ignore the tiredness notification.
Once caffeine is metabolised and exits those adenosine receptors, those adenosine receptors become available again.
And the adenosine, which has been patiently waiting outside those “parking lots”, now have no competition for the parking space. They go right back in, and in doing so, proceed to apply the sleep pressure back on the body, which can eventually contribute into what people feel as a “caffeine crash”.
Moral of the story? We can’t cheat on sleep.
We can drink coffee. We can block the adenosine receptors. We can tell our brains to ignore the tiredness notification for a little while.
But eventually, the caffeine wears off, the adenosine gets its parking spaces back, and the sleep pressure comes knocking again.
The maintenance crew still needs to clock its hours and complete its shift.
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