There are runners who actually run two marathons in a row, separated by a short break (say 30 minutes), and do so willingly. It is all a matter of total lifetime mileage, regularly seeking the limit of your body, finding it's more like a mental barrier, and cross it. That, and lots of easy runs to recover, both mentally and physically.

But then, here's where the analogy breaks down, since I'm told writing your first draft is quite different from running a marathon. In a marathon you want the flow of ideas to stop and focus on the task at hand, in draft writing you want a free flow of ideas, loss focus on details and more attention to the broader picture. I'd say a first edit is more like a marathon than a first draft.