You can't. Eventually it will do you in. When I was 29 I spent 4.5 months coding 100 per week and once we shipped I wound up in the hospital. Never again.
I've been doing this for 11 months and still going strong. I'm still getting a reasonable amount of sleep every night (about 6 hours) which I'm sure helps, and I make sure to recover when I need to.
I seriously believe that you have the wrong attitude here. You should be looking to reduce the amount of hours and instead focus on decent, solid and productive hours.
There is no way you can be at 100% after 11 months of 80 hour weeks.
