I can jog, but I can't run. That's hard for me. I like the fact that I can jog for fitness, but to me there's a huge difference between jogging and running.
At the very end of a book I can manage to work for longer stretches, but mostly, making stuff up for three hours, that's enough. I can't do any more. At the end of the day I might tinker with my morning's work and maybe write some again. But I think three hours is fine.
Running through things because you are familiar with them, breeds routine and this is the seed of boredom.