I think it's more that after 8 exhausting hours, I don't have energy anymore for anything. The 8 exhausting hours would be a day full of meetings, after which my brain is a mush and doesn't work anymore.
But it may start out feeling like a diet for the mind, that I am willing to believe. But like with a healthy diet you’ll benefit immensely over time. But it requires discipline.
Pushing the limits of a body is sitting in a chair for 8 hours, barely moving, in stead of walking around doing stuff with your hands, taking a swim, climbing a tree picking some nuts.
We should make no mistakes about what the natural actions and states of our minds and bodies are.
I slept pretty well and feel healthy and energized today and doing the dishes was easy this morning, but it's totally contrary to my entire life experience to claim that doing something physically tiring gives you more energy afterward.
Not that doing nothing all the time feels good— humans just don't have unlimited capacity for output. Taking a leisurely morning walk (or a moderate-distance bike commute) certainly gets my day started on the right foot, but going harder faster longer at physical activity makes me physically tired and less capable of doing other things.
A great exercise would be to find some causality from Strava data and git commit, both of which I have fairly extensive data on.
Exhausted or not, you’re probably more likely to come across something unexpectedly and write it down than remember them all and offer up something fitting from memory.