There's always something to think about while, say, running.
Is my posture correct? Are my feet hitting the ground well? Is this a good pace? And lots and lots of self talk about not shirking the next effort (30s hard running, hill run etc etc).
Boring doesn't mean nothing to do. It means no interest in what is there.
Not shockingly, people good at setting somewhat mundane objectives and iterating on them are good at both intelligence and exercise. They probably feed each other. :)
