After a long week of work, there's nothing that feels better than sleeping in on the weekend. And yet when you open your eyes Saturday morning, it's only 8:00 a.m., and you're ready to start your day. If you're unable to sleep in during the weekends, we now know why.
To put it simply, your body's just too used to your work schedule. While your alarm clock may be turned off, your body clock is still stuck in the same rhythm as during the week. When your body prepares to wake up, it begins to raise your blood pressure, body temperature and cortisol levels about an hour beforehand. So basically your body prepares itself to wake up and begin the day. So even if you want to sleep in until noon, if your body begins preparation at 7:00 a.m., you're going to wake up at 8 whether you like it or not.
It also doesn't help that your body doesn't need to sleep as much as it used to. Babies require about 16 to 20 hours of sleep per day. Teenagers require about nine hours every night. But adults only need eight hours per night, and your body basically doesn't need anything more after that amount of time. It's basically like filling a bucket. Once you get those eight hours, the bucket's full so your body doesn't need to put anything else in so it wakes you up.
There is a way to force your body to sleep in on the weekends: Deprive yourself of sleep during the week. If you only get six or seven hours every night Monday through Friday, your body will need a few extra hours on the weekends just to make sure everything is in balance.
So either you can just accept you're never sleeping until noon again, or you can torture yourself during the week.
(h/t Mental Floss)