Q: How much sleep is needed for someone who does 4 days of heavy lifting?

A: Try for at least 8 hours a day! Rest, along with nutrition, is just as important as hard workouts. Without sufficient sleep your body will not be able to repair damage inflicted at the gym (remember -- you damage the muscles at the gym and rebuild them outside the gym!). Equally important, your nervous system will suffer as well. Your nervous system is responsible for efficiently recruiting the fibers of your muscles to lift the most possible weight. If your nervous system doesn't get enough rest through sleep, your gym performance will decline.

If for whatever reason you cannot get much sleep for a few weeks or longer, tone down your workouts accordingly -- do fewer sets than usual, don't go to failure on every set, add an extra day of rest here and there, etc.