The Sleep Stages & How They Affect Your Energy Levels
Even though there are varying differences with circadian rhythms and sleep styles, we all have one thing in common - we need good sleep to be energetic, to be alert, and to stay healthy. Sleep is made up of distinct stages with specific characteristics defined by brain waves, eye movements, and muscle tension. In a sleep lab, these stages are recorded by electroencephalography (EEG), electrooculography (EOG), and electromyography (EMG). The two broad categories of sleep include rapid eye movement (REM) sleep and nonrapid eye movement (NREM) sleep.
During REM sleep, there are small, variable-speed brain waves, rapid eye movements like those of eyes open wakefulness, and no muscle tension. It is during REM sleep that you have most of your dreams. (When you are aroused from REM sleep, you may have recall of vivid imagery.) NREM sleep is composed of four different levels or stages - 1, 2, 3, and 4 - characterized by different combinations of brain waves, eye movements, and reduced but not absent muscle tension.
Different Stages of Sleep
Stage 1 - light sleep
Stage 2 - moderate sleep
Stages 3 and 4 - deep or delta sleep
Your sleep intensity or quality is reflected by the amount of delta sleep you get each night. Delta sleep (stages 3 and 4) is the deepest level of sleep, a regenerative period during which your body heals itself. Growth hormone secretion is highest during delta sleep, and some researchers believe that this is important for growth and repair of body tissue.
Delta sleep occurs mostly in the first third of the night and makes up about 10 to 20 percent of total nighttime sleep in normal young adults. REM sleep takes place mostly during the last third of your night's sleep and comprises normally 25 percent of the sleep period.
The percentage of delta sleep is affected by age, amount of prior sleep, and various diseases. As a rule, delta sleep decreases with age and may be brief in healthy, elderly males. If you do not get enough delta sleep, you will feel tired and groggy the next day.
Not surprisingly, young children have particularly large proportions of delta sleep, which increases if they are sleep deprived. This explains why trying to wake up a young child may be difficult. Elderly people have smaller proportions of delta sleep, which is why they can be easily aroused by environmental noise. Medical problems such as obstructive sleep apnea, periodic leg movements during sleep, or fibromyalgia (an arthritis-like syndrome) may affect both the quantity and the quality of delta sleep. This, in turn, probably accounts for the feeling of fatigue experienced by people suffering from these ailments.