Most of that work isn't that cognitively demanding though. If you're reading research papers or textbooks most of the time the really hard parts have been done for you. You just need to follow along.
Also, with most work there's lots of things that need to do that require relatively little concentration once you've made the cognitive shift.
I think the four hour limit applies to design/creative work or work that requires immense attention to detail.
I'd say most people have little in a day that actively drains this reserve in more than a trickle.
If reading research papers is not cognitively demanding, that just means that you're not reading fast enough, or you're not truly absorbing the content. Or are you saying that the speed at which you read research papers is limited by the speed at which your eyes can move?
Also, with most work there's lots of things that need to do that require relatively little concentration once you've made the cognitive shift.
I think the four hour limit applies to design/creative work or work that requires immense attention to detail.
I'd say most people have little in a day that actively drains this reserve in more than a trickle.