Medical residents routinely do close to 80 hours, and I would argue on average a small single digit number of those hours are unproductive. My SO is an OB resident and worked over 90 hours last week, and probably 75 of that was either in surgery, reading, studying, or giving a presentation of one form or another. About half of her weeks are above the 80 hour limit.

It's definitely possible. Just because we don't want to do it (I don't either!) or that it has negative long-term consequences doesn't mean it's not possible.