While you're asleep the body is repairing, rebuilding and strengthening. Your muscles are adapting to the stress of exercise and replenishing depleted energy stores and fixing damaged tissues.
More after the break
But how long does this process take? How much sleep do you need to recharge your batteries?
Tony Strudwick, Manchester United's head of sport science, is the man responsible for making sure the Red Devils' multi-million stars get the right amount of shuteye.
To find out what he has to say about sleeping yourself sharp for football watch this video.
Tony Strudwick was talking at Leaders in Performance, part of Leaders in Football. For details on 2011’s conference, click here.