A good sleep has energy benefits and costs

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A good sleep has energy benefits and costs

Sleep has a regular alternation of non-REM and REM phases consisting of cycles of similar duration. After falling asleep, the subject progressively passes from stage 1 of non-REM sleep to stage 2, then passes to stage 3 or stage 4 slow wave sleep and then, between 70 and 90 minutes after falling asleep, the first occurs.

REM sleep phase that lasts about 15 minutes. At the end of the first phase of REM sleep, the first cycle ends and lasts approximately 80 to 100 minutes. After the first cycle, others follow one another of rather constant duration but where REM sleep tends to increase in duration at the expense of non-REM sleep, in particular stages 3 and 4 (deep non-REM sleep) which become shorter.

During the night, REM sleep ultimately makes up about 25% of the total sleep duration. It is possible that between the various cycles there are moments of wakefulness. The sleep period is represented graphically by means of hypnograms that illustrate the succession of the phases of wakefulness and sleep in relation to time.

The study Energetic costs and benefits of sleep, published on the Current biology, explained: "Energy derived from food is a precious resource to animals. Those finite calories are often well-earned through exhaustive foraging effort, which can dominate waking hours, to support physiological processes (e.g.

body maintenance and growth) and ecological necessities (e.g. predator avoidance and courting) that are pertinent to the production of progeny. So, it is unsurprising to find that animals have evolved strategies to guard against the gratuitous waste of hard-won caloric energy.

Yet, it remains surprising to find such diversity, and elegant creativity, in those solutions. Brief examples of energy-saving innovation could include the very shape of animals and how they move, from streamlined swimming sharks to skyward-soaring seabirds; or the evolutionary appearance of various states of dormancy, such as endothermic animals sacrificing high body temperature through modest (torpor) or se vere (hibernation) curtailments to metabolic heat production. Another reversibly dormant state with energetic benefits is sleep."