What are Sleep Stages and Sleep Cycles?

Sleep is segmented into four stages (Slow Wave Sleep, REM Sleep, Light Sleep, and Wake), each of which serves a unique purpose.

Slow Wave Sleep (SWS) is an intense, active phase of sleep. In it, the body repairs and regenerates tissues, builds bone and muscles, and strengthens the immune system. Because of its role in muscle and bone repair, this is a particularly important sleep stage for athletes. It is common for SWS to occur more, and in longer bouts, at the beginning of the night than at the end. Over the course of the night, SWS accounts for 25-30% of total sleep time.

REM Sleep is the sleep stage in which memory consolidation and dreaming occur. REM periods increase in length as the night progresses. The first REM period usually occurs about 90 minutes after you first fall asleep, and lasts only 10 minutes. For young, healthy athletes, a normal amount of REM sleep is 60-100 minutes, or roughly 20% of the night.

Light Sleep typically accounts for 50% of the total sleep time. Light Sleep primarily serves as a transition stage between Slow Wave Sleep and REM.

Wake comes in two forms – Sleep Latency is the time it takes you to fall asleep. Normal sleep latency is roughly 5-35 minutes. Sleep Disturbances are short periods of wake throughout the sleep episode. For athletes, anywhere from 3 to 7 disturbances per hour is normal. Most people experience more frequent disturbances as time in bed increases. In total, Wake (not including sleep latency) accounts for about 5% of the total time in bed.

A Sleep Cycle is a complete set of Sleep Stages, in which our bodies cycle from Light Sleep, to Slow Wave Sleep, to REM Sleep. A night’s Sleep typically consists of 3-5 complete cycles.

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