Typical Sleep
Why do we sleep?
• There are many ideas about why we sleep. The truth is, there is no black-and-white answer. However, investigators have proposed that sleep serves as a way to consolidate memories acquired during wakefulness [1] and ward off metabolic harm [2].
Sleep Architecture
• Typical human sleep comprises two states that alternate cyclically: rapid eye movement (REM) when dreaming is common, and non–REM (NREM) sleep characterized by low muscle tone and minimal psychological activity.
• The first episode of REM sleep occurs about 80-100 minutes afterward, and the cycle between NREM and REM sleep repeats every 90 minutes, with REM sleep episodes getting longer throughout the night (Fig. 1).
• Other factors that may alter sleep include previous sleep-wake history, phase of the circadian timing system, environmental factors such as temperature, light, sounds (e.g., a partner’s snoring or teeth grinding), drugs, and sleep disorders.
Figure 1. Average time of each sleep stage.
Age-Related Changes
• Newborns have a shorter sleep cycle (approx. 50 minutes), and REM sleep makes up about 50% of total sleep. After 2 years, REM decreases to be 20% to 25% of total sleep.
• Deep sleep decreases across adolescence by 40%, starting from the preteen years. Recommended sleep for adolescents is eight to ten hours a night, but roughly two-thirds receive less than eight on school nights.
• Poor sleep quality is associated with decreased academic performance and increased risk-taking behaviors [3].
Figure 2. Hours of sleep recommended each night across the lifespan.
Technology Use
• Increased technology use before bedtime is associated with a shorter sleep duration and waking up unrefreshed. Technology use before bed can be a sign of revenge for bedtime procrastination. Other instances of nighttime technology use include being awoken at night by a cell phone, which can lead to daytime sleepiness [4]. For children who use screen technology to communicate or self-regulate, apps that remove high blue light may be helpful.
Sleep and Exercise
• Keep in mind that everybody is different!
• Exercise increases total sleep time, sleep continuity, and sleep efficiency, leading to less daytime sleepiness. Sleep also delays REM sleep onset and reduces REM sleep time.
• While data is relatively inconclusive, exercising earlier in the day may improve the quality of sleep compared to later in the day [5], [6]. Exercising vigorously at night is activating and can potentially keep you awake due to increased body temperature. It may also be helpful to take a warm bath or shower after exercise to wind down.
Figure 3. Positive benefits of sleep and exercise.