When you sleep, your body rests and restores its energy levels. However, sleep is an active state that affects both your physical and mental well-being. A good night’s sleep is often the best way to help you cope with stress, solve problems, or recover from illness.
What Happens During Sleep?
Sleep is prompted by natural cycles of activity in the brain and consists of two basic states: rapid eye movement (REM) sleep and non-rapid eye movement (NREM) sleep, which consists of Stages 1 through 4.
During sleep, the body cycles between non-REM and REM sleep. Typically, people begin the sleep cycle with a period of non-REM sleep followed by a very short period of REM sleep. Dreams generally occur in the REM stage of sleep.
What Is Non-REM Sleep?
The period of NREM sleep is made up of stages 1-4. Each stage can last from 5 to 15 minutes. A completed cycle of sleep consists of a progression from stages 1-4 before REM sleep is attained, then the cycle starts over again.
- Stage 1: Polysomnography (sleep readings) shows a reduction in activity between wakefulness and stage 1 sleep. The eyes are closed during Stage 1 sleep. One can be awakened without difficulty, however, if aroused from this stage of sleep, a person may feel as if he or she has not slept. Stage 1 may last for five to 10 minutes. Many may notice the feeling of falling during this stage of sleep, which may cause a sudden muscle contraction (called hypnic myoclonia).
- Stage 2: This is a period of light sleep during which polysomnographic readings show intermittent peaks and valleys, or positive and negative waves. These waves indicate spontaneous periods of muscle tone mixed with periods of muscle relaxation. The heart rate slows and the body temperature decreases. At this point, the body prepares to enter deep sleep.
- Stages 3 and 4: These are deep sleep stages, with stage 4 being more intense than Stage 3. These stages are known as slow-wave, or delta, sleep. If aroused from sleep during these stages, a person may feel disoriented for a few minutes.
During the deep stages of NREM sleep, the body repairs and regenerates tissues, builds bone and muscle, and appears to strengthen the immune system. As you get older, you sleep more lightly and get less deep sleep. Aging is also associated with shorter time spans of sleep, although studies show the amount of sleep needed doesn’t appear to diminish with age.
What Is REM Sleep?
Usually, REM sleep occurs 90 minutes after sleep onset. The first period of REM typically lasts 10 minutes, with each recurring REM stage lengthening, and the final one may last up to an hour. Polysomnograms show brainwave patterns in REM to be similar to that recorded during wakefulness. In people without sleep disorders, heart rate and respiration speed up and become erratic during REM sleep. During this stage the eyes move rapidly in different directions.
Intense dreaming occurs during REM sleep as a result of heightened brain activity, but paralysis occurs simultaneously in the major voluntary muscle groups. REM is a mixture of encephalic (brain) states of excitement and muscular immobility. For this reason, it is sometimes called paradoxical sleep.
The percentage of REM sleep is highest during infancy and early childhood. During adolescence and young adulthood, the percentage of REM sleep declines. Infants can spend up to 50% of their sleep in the REM stage of sleep, whereas adults spend only about 20% in REM.
How Much Sleep Do You Need?
The amount of sleep a person needs depends on the individual. The need for sleep depends on various factors, one of which is age. Infants usually require about 16-18 hours of sleep per day, while teenagers need about 9 hours per day on average. Most adults need about 7-8 hours of sleep per day.
The amount of sleep a person needs also increases if he or she has been deprived of sleep. People do not seem to adapt to getting less sleep than they need.
What Are the Consequences of Too Little Sleep?
Too little sleep may cause:
- Impaired memory and thought processes
- Decreased immune response
- Increased pain
Sleep deprivation also magnifies alcohols effects on the body, so a fatigued person who drinks will become much more impaired than someone who is well-rested. Sleep deprivation also increases pain perception on pain simulation testing. Caffeine and other stimulants can temporarily overcome the effects of severe sleep deprivation, but cannot do so for extended periods of time.
It’s all too tempting to hit the snooze button when the alarm goes off in the morning. Don’t do it: You might think the extra few minutes will give you time to wake up, but it does more harm than good. The video below explains why:
You might experience a number of negative effects if you do not regularly get a full night’s sleep. Sleep deprivation makes you feel lazy and less motivated, which makes you less likely to grab your exercise gear and go to the gym or for a jog. A lack of sleep also can affect your concentration and impair your memory, which can make it more difficult for you to chart your progress and stay on track at the gym.
Not getting enough sleep might cause you to gain weight, which can thwart any weight-loss goals you set with you exercise routine. Sleep deprivation decreases your body’s levels of leptin, a hormone responsible for making you feel full, according an October 2010 article in the journal “Best Practice and Research: Clinical Endrocrinology and Metabolism.” Not sleeping enough also increases your levels of ghrelin, which increases your appetite and makes you want to eat more.
Not getting enough sleep can affect your performance when you exercise in a couple of ways. Sleep deprivation can decrease your energy levels, which makes it harder for you to get a good workout. A May 2003 study published in the “European Journal of Applied Physiology” examined the energy levels of men who had a normal night’s sleep and men who did not sleep. The men who did not sleep showed lower maximum and average energy levels.
Muscle and Bone Repair
You might limit your progress with exercise if you do not get enough sleep each night. Your body releases growth hormone while you sleep, which helps strengthen your bones and muscles. So not getting enough sleep might limit your body’s ability to recover from an intense workout or make your muscles and bones stronger. Not getting enough sleep might be particularly limiting if you strength train, as you depend on the growth hormone your body secretes at night to make your muscles stronger to allow you to recover and lift more weight.