Issues such as the poor economy and smaller work forces are leading more people to work longer hours. Many exercise professionals train clients who work in the fields of health, technology, security, medicine, computer programming, food services and transportation, which often require working evenings and/or night shifts. These professions, and many others, may disturb sleep patterns, compromising cognitive performance and leading to serious health consequences.

It has been shown that night-shift workers have poorer sleep, reduced performance and alertness, and higher accident rates compared with those who work during the day (Rajaratnam & Arendt 2001). This article will describe the types and stages of sleep and discuss the deleterious effects of sleep deprivation on cognitive performance and health.

The Main Types and Stages of Sleep

The two main types of sleep are rapid-eye-movement (REM) sleep and non-REM sleep (WebMD 2010). During the night, sleep patterns repeat cyclically, moving sequentially through four stages of non-REM sleep, each of which is followed by REM sleep.

REM sleep, which is about 20% of total sleep, initially lasts about 10 minutes and lengthens with each subsequent cycle, lasting up to an hour in the last phase (WebMD 2010).

During REM sleep the eyes move rapidly back and forth and the body’s muscular contraction activity is minimal. Keenly remembered and very visual dreams occur during REM sleep. Heart rate and blood pressure increase, while breathing rate becomes irregular and shallow. Interestingly, REM sleep increases when people are learning a new task, and REM sleep deprivation will interfere with the learning process (Hobson 2009).

During non-REM sleep, dreams are less emotional and there are fewer visual-impression dreams than during REM sleep. Stage 1 of non-REM sleep is the transition to sleep, which lasts about 5 minutes. This often feels like going in and out of sleep. Stage 1 is also when sleepers experience sudden, jerky movements or muscle twitches, referred to as hypnic myoclonic jerks (WebMD 2010).

Stage 2 of non-REM sleep lasts about 10–25 minutes. During this “light sleep” stage, heart rate slows down, body temperature decreases and brain wave activity slows down as the body prepares for deeper sleep.

Stage 3 of non-REM sleep is often referred to as the first stage of deep sleep. It is during this stage that it is difficult to wake a sleeper, and if awakened, the person will feel disoriented for several minutes. During stage 3, brain wave activity alternates between slow- and fast-wave activity, and blood flow goes to parts of the body needing restorative function.

Stage 4 is the deepest state of sleep. Brain wave activity is mostly delta waves, which are the brain’s slowest-frequency waves (beta, alpha and theta are the other wave categories).

Sleep Deprivation

Most adults average about 7–8.5 hours of sleep each day (Alhola & Polo-Kantola 2007). Alhola and Polo-Kantola add that sleep serves as a restorative process for energy resources, tissue recovery, thermoregulation and cognitive function. Sleep deprivation, which can be either acute or chronic, is the condition of not having enough sleep (see Figure 1 for the signs).

In acute total sleep deprivation studies, subjects are kept awake continuously, generally for 24–72 hours. In chronic partial sleep deprivation research, subjects’ sleep time is restricted over the course of several consecutive nights. Chronic partial sleep deprivation is the more common of the two and is highly associated with real-life conditions for most people.

Sleep Deprivation and Cognitive Performance

Chronic and acute sleep deprivation negatively impact thinking and learning. There is a loss of attention and alertness (Kilgore 2010), which involves a series of lapses or slowed responses, leading to waking-state instability in several cognitive processes, such as working memory (the temporary retention process of holding several pieces of information together in order to solve a problem or do a task) (Alhola & Polo-Kantola 2007).

Kilgore adds that sleep loss appears to affect some aspects of cognition more than others. For instance, creative and innovative mental processing appear to be much more negatively impaired than decision making and planning (Kilgore 2010). Alhola and Polo-Kantola observe that acute sleep loss can also impair reaction time, memory assignments, visuomotor skills and reasoning skills. Rajaratnam and Arendt (2001) note that vehicle accidents peak between 2:00 and 6:00 am, when drivers are more likely to be suffering from acute sleep deprivation (as well as other conditions such as alcohol and drug use).

Sleep Deprivation and Cardiometabolic Disease

Cardiometabolic disease is a cluster of health abnormalities that include insulin resistance, hypertension, atherosclerosis and abnormal cholesterol—conditions that predispose a person to type 2 diabetes and cardiovascular disease (Knutson 2010). In reviewing the research, Knutson found several studies demonstrating that people who get less than 6 hours of sleep a night have a higher association with having or getting these serious maladies.

Chronic sleep loss will activate the body’s sympathetic nervous system, which can lead to increases in blood pressure and cortisol secretion (Alhola & Polo-Kantola 2007). Cortisol has been shown to stimulate appetite and activate lipoprotein lipase, the enzyme that facilitates the deposition of fat, thus leading to weight gain (Björntorp 2001). >>

Alhola & Polo-Kantola add that chronic sleep loss may impair immune function as well. The immune system has many different types of cells and proteins designed to protect the body from foreign substance invaders, such as colds and the flu. However, with sleep deprivation the immune system may function improperly, making the body more vulnerable to these ailments. Figure 2 shows the effects of sleep loss on health.

Final Thoughts

The importance of quality sleep should be part of the exercise professional’s common message to clients attempting to achieve optimal health. Good sleep can help clients effectively solve problems, be innovative and creative, cope successfully with stress, impede the onset of weight gain and be more alert and productive during the waking day.

Sources: Figure 1:; Figure 2: Adapted from Knutson 2010.

10 Popular Questions About Sleep

1. Will getting 1 hour less of sleep per night affect daytime functioning? Yes, it will compromise a person’s thinking and responding abilities, in addition to impacting cardiovascular health, energy balance and immune function.

2. Does the body adapt easily to different sleep schedules—for example, during travel across several time zones? No, it can take more than a week to adjust when traveling across several time zones. However, most people can easily reset their sleep pattern when experiencing a 1- to 2-hour time zone difference.

3. How long does it take to adjust when switching to a night-shift job? About 1 week.

4. What is the cause of excessive daytime sleepiness? In addition to self-imposed sleep deprivation, insomnia is a main cause of daytime sleepiness. Other causes include some sleep disorders, such as sleep-disordered breathing, restless leg syndrome and narcolepsy (a neurological disorder characterized by disabling sleepiness).

5. Can you make up for lost sleep during the week by sleeping more on the weekend? Not a good strategy, although many people take this approach. Sleeping later on weekends will affect your sleep-wake cycle and potentially make it harder for you to go to sleep on Sunday evening and to get up on Monday morning.

6. Are there differences in sleep disturbances between men and women? Yes, women of all ages report more sleeping problems than men.

7. What happens to sleep patterns as a person ages? Sleep efficiency and slow-wave sleep decrease with age (≥52 years). A person’s circadian rhythm (the body’s 24-hour cycle for biochemical and physiological processes) also alters, which may hinder sleep.

8. Will caffeine intake affect sleep? Caffeine (found in soft drinks, coffee, tea and chocolate) alters chemical reactions in the brain, causing those who consume it to feel more energetic and alert. It may delay sleep onset, reduce total sleep time and decrease the overall quality of a person’s sleep. However, such alterations depend on the time of day the caffeine is consumed, the amount consumed and an individual’s sensitivity to caffeine.

9. Do infants and teenagers need more sleep than others in each 24-hour cycle? Yes, infants need 14–18 hours of sleep per cycle, and teenage boys and girls need about 9 hours of sleep per cycle.

10. Are short naps beneficial after a night of sleep loss? Yes, a short nap (<15 minutes) in the mid-afternoon after an evening of restricted sleep will result in fewer major and minor driving accidents. This has been demonstrated in car-driving simulator studies.

Sources: Alhola & Polo-Kantola 2007; WebMD 2010;;


Alhola, P., & Polo-Kantola, P. 2007. Sleep deprivation: Impact on cognitive performance. Journal of Neuropsychiatric Disease and Treatment, 3 (5), 553–67.
Björntorp, P. 2001. Do stress reactions cause abdominal obesity and comorbidities? Obesity Reviews, 2, 73–86.; retrieved Nov. 22, 2011.
Hobson, J.A. 2009. REM sleep and dreaming: Towards a theory of protoconsciousness. Nature Reviews: Neuroscience, 10, 803–13.
Knutson, K.L. 2010. Sleep duration and cardiometabolic risk: A review of the epidemiologic evidence. Best Practice & Research: Clinical Endocrinology & Metabolism, 24 (5), 731–43.
Killgore, W.D. 2010. Effects of sleep deprivation on cognition. Progress in Brain Research, 185, 105-29.
Rajaratnam, S.M.W., & Arendt, J. 2001. Health in a 24-h society. The Lancet, 358, 999-1005.
WebMD: Coping With Excessive Sleepiness.; retrieved Nov. 22, 2011.

Len Kravitz, PhD

Len Kravitz, PhD is a professor and program coordinator of exercise science at the University of New Mexico where he recently received the Presidential Award of Distinction and the Outstanding Teacher of the Year award. In addition to being a 2016 inductee into the National Fitness Hall of Fame, Dr. Kravitz was awarded the Fitness Educator of the Year by the American Council on Exercise. Just recently, ACSM honored him with writing the 'Paper of the Year' for the ACSM Health and Fitness Journal.

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