Both men and women need about eight hours of sleep every night, yet the average American adult snoozes for less than seven hours, far less than the amount of sleep that experts suggest is necessary. Sleep happens in progressive stages, referred to as the sleep cycle. The cycle begins with light sleep, followed by the deep, delta sleep of the REM stage. A full night of uninterrupted sleep, with plenty of REM, is needed so that the body can rejuvenate and repair.

The Sleep Cycle

Every night, when you fall asleep, you begin a journey though five stages of the sleep cycle. The deepest stage is called REM, rapid eye movement sleep. While asleep, you may cycle through these stages several times, and with each cycle, you spend more time in deep sleep. Here's what's actually happening when you are catching Zs.

Stage 1: When you first fall asleep, you enter into Stage 1 of the sleep cycle, a state that is very close to waking. This is the stage when your body's beginning to relax. Stage 1 generally lasts about 10 minutes, during which time you have that dozing feeling. If you are awakened, you may not even realize that you've been sleeping.

Stage 2: During the second stage of sleep, your body functions begin to wind down. Body temperature decreases and your heart rate slows. Stage 2 is when your body is preparing to enter deep sleep.

Stages 3 & 4: These are the stages of deep slumber, called delta sleep. The body is nearly motionless, muscles paralyzed, while the brain is extremely active. When in delta sleep, you repeatedly cycle through Stage 3, and the deeper Stage 4.

Stage 5: REM sleep is when you dream, although you may not remember those dreams once you wake up. The muscles of the body don't move, but for small twitches (perhaps to keep you from acting out your dream), and brain activity is intense. Breathing and heart rate speed up and the eyes rapidly move back and forth. REM sleep occurs approximately 90 minutes after you first fall asleep.

The first cycle of REM is short, about 10 minutes, and each time you go through the sleep cycle, the length and intensity of REM sleep increases. That is why the number of hours that you sleep is so important. The fewer hours, the fewer sleep cycles, and the less REM sleep you get. And REM is important to your health and well-being. This is the stage of restorative sleep, and people who are deprived of REM have difficulty with memory and learning.

So boost your brain power and feel rested tomorrow by allowing yourself enough time to 'go cycling' tonight.

For more information on the science of sleep, see: