Sleep is critical to getting in shape.
You always see those advertisements on TV and in magazines for products that let you 'lose weight while you sleep'. Those products are all garbage and a waste of money. Don't buy any of them. The only thing you'll lose is money. However, sleep does play a critical role in getting in shape.
Your body does most of its 'rebuilding' while you are asleep. If you are on a regular weight training program (as you should be) then your muscles are actually growing while you sleep. This means that, obviously you need to get enough sleep to let your body do it's job of rebuilding and growing your muscles. If you do not get enough sleep, your body is not able to grow your muscles adequately. At the same time, if you are on a regular weight training program, this work will burn a lot of your spare energy. What is the only way to recover from this? Sleep! You must get enough sleep to recover the energy you exterted working out.
In today's fast pace society, sleep seems to always be the first thing sacrificed in our lives, in order to get more done. I've been just as guilty of this as anyone else. I always have something to do in the evening. Things like cooking, cleaning, reading technical documentation for work, reading novels, watching TV, writing these blogs, etc. It's a nightly effort for me to force myself to put aside these things for the evening and get to bed. Sometimes I succeed, sometimes I fail, but at least I am conscious of this need and do my best to maintain the proper sleep levels.
Recently, I broke this rule and the results were very noticable. On Wednesday night of last week, I decided to go see the premeire of "Star Wars: Revenge of the Sith" at it's opening time of 12AM. The movie was 2 1/2 hours long. By the time the previews played, the movie played and I got home and got to bed, it was 3:30AM. I had to get up the next day at 7:30AM to go to work. That's a grand total of 4 hours of sleep that night. Literally, for the next FOUR DAYS I was tired, lacking energy and barely able to concentrate at work. It wasn't until last night when I want to bed early (930PM) that I managed to get enough sleep in order to feel back to normal. Many people may not even realize they are tired, since they are out of shape, but it does affect you more than you realize. As you get in shape, you become more in tune with your body and you notice these things.
You must get at least eight hours of sleep a night.