( ~36:32)

caffeine is an adenosine antagonist which reduces fatigue and lethargy (verbatim copy of Muhammed's annotation)

It will temporarily park receptors for the sleep inducing neurochemical of adenosine. Kind of making those receptors sleep themselves. Which reduces if not eliminated the influence of that chemical for a while.

36:00 caffeine is an adenosine antagonist which reduces fatigue and lethargy