REM vs Deep Sleep: What Each Stage Does and Why Athletes Need Both

REM vs deep sleep is a question about two very different kinds of rest. Deep sleep (stage N3, also called slow-wave sleep) is the slow, heavy sleep that dominates the first hours of the night. REM sleep is the active, dream-rich stage that grows longer toward morning. You need both, and you get them at different times of the night, which is why the time you go to bed and the time you wake up both matter.

This guide explains what each stage does, when it happens, what the research actually shows for people who train, and what you lose when you cut sleep short at either end.

REM vs deep sleep: the quick comparison

Light sleep (N1 and N2) fills the rest of the night. Stage N2 is the largest share for most adults, and it matters more than its "light" label suggests, as you will see below.

What deep sleep does

Deep sleep is when your brain shows its slowest, highest-amplitude electrical waves. It is the hardest stage to wake from. If someone wakes you from it, you feel groggy and confused for a few minutes.

Deep sleep and growth hormone

The best-known link is with growth hormone. In a JAMA analysis of 149 healthy men aged 16 to 83, the amount of growth hormone secreted was significantly associated with the amount of slow-wave sleep, independent of age ¹. The same study showed how quickly deep sleep shrinks: it made up 18.9% of sleep in men aged 16 to 25 and only 3.4% in men aged 36 to 50, replaced mostly by lighter stages ¹. Growth hormone output fell in parallel.

Two cautions. First, this is an association in men. It does not prove that more deep sleep causes more muscle growth. Second, growth hormone is only one part of recovery. Tissue repair also depends on protein intake, training load and total sleep.

Deep sleep and sleep pressure

Deep sleep also tracks how long you have been awake. The longer and harder your day, the more deep sleep you tend to get early in the night. A meta-analysis of 66 studies found that a single bout of exercise produced small increases in slow-wave sleep, along with small improvements in total sleep time and time to fall asleep ⁴. The effects were small, so do not expect one hard session to transform your night.

What REM sleep does

During REM sleep your eyes move quickly, your breathing and heart rate become irregular, and your brain activity looks close to waking. Most of your skeletal muscles are temporarily switched off, which stops you from acting out dreams.

REM sleep and emotions

The strongest human evidence for REM sleep concerns emotional processing. A review in Sleep Medicine Reviews concluded that sleep supports the formation of emotional memories and that lack of sleep increases emotional reactivity, with REM sleep likely playing a main role, though some findings are contradictory ⁸. In practice, a short night that cuts your morning REM can leave you more irritable and less resilient to stress the next day.

REM sleep and motor skills: a common myth

You will often read that REM sleep is when you "learn" a new movement. The research is more nuanced. In a well-known Neuron study, a night of sleep improved speed on a finger-tapping motor task by about 20% without loss of accuracy, while the same time awake gave no significant benefit ². The improvement correlated with the amount of stage 2 NREM sleep, especially late in the night. It did not track REM ².

So for skill learning, the late part of the night matters. That part is rich in both stage 2 and REM sleep. Whichever stage turns out to matter most, the practical message is the same: cutting the last 1 to 2 hours of sleep removes the period linked to overnight skill gains.

How deep and REM sleep are spread across the night

Sleep runs in cycles of NREM followed by REM. In a laboratory dataset of 369 healthy people and more than 6,000 recorded cycles, the median cycle lasted 96 minutes, and the first cycle was consistently shorter than later ones ⁷. After sleep deprivation, the first cycle contained more NREM sleep ⁷. That is your body paying back deep sleep first.

The pattern looks roughly like this:

• Early night: long blocks of deep sleep, short REM periods.
• Middle of the night: less deep sleep, more stage 2, REM periods getting longer.
• Late night and early morning: little or no deep sleep, long REM periods and plenty of stage 2.

For more detail on cycle length and why the 90-minute rule is only approximate, read our guide to sleep cycles.

Age changes both stages

A meta-analysis of 65 studies covering 3,577 people found that in adults the percentage of slow-wave sleep and the percentage of REM sleep both decrease with age, while lighter stages increase ³. The JAMA data suggest deep sleep falls first and fastest, between early adulthood and midlife, while REM declines later ¹. If you are 45 and your tracker shows little deep sleep, that alone is normal.

What cutting sleep short costs

Because the stages are spread unevenly, how you lose sleep changes what you lose.

• Going to bed late while your alarm stays fixed: your body still front-loads deep sleep, so you mainly lose later REM and stage 2.
• Waking up early cuts the end of the night, the REM-rich and stage 2-rich part.
• Skipping a night removes everything and raises sleep pressure for the next night.

A 2022 meta-analysis of 69 publications on sleep loss and exercise found an average performance drop of about 7.6% after sleep loss, with effects across strength, endurance, power, high-intensity intervals and skill ⁶. Total deprivation and late restriction (waking earlier than normal) had consistent negative effects. Performance also fell by roughly 0.4% for every extra hour awake before the session, and tasks done in the afternoon or evening suffered more than morning tasks ⁶.

Muscle building can suffer too. In a small randomized crossover study of 13 young adults, one night without sleep reduced muscle protein synthesis by 18%, raised cortisol by 21% and lowered testosterone by 24% the next day ⁵. That was total deprivation in a small group, so treat it as a mechanism rather than a precise number for your own training.

Can you get more deep sleep or REM sleep?

You cannot target one stage reliably with a supplement or a gadget. What works is protecting total sleep and its timing:

1. Keep a regular wake time. It anchors your body clock and stabilizes when deep and REM sleep occur. See how your circadian rhythm works.
2. Give yourself a long enough sleep window. Most of your REM sleep lives in the last hours. To find your number, read how much sleep you need or use the sleep calculator.
3. Train regularly. Exercise has small positive effects on deep sleep and moderate effects on overall sleep quality ⁴.
4. Watch caffeine timing. Late caffeine can push back sleep onset. The caffeine cutoff tool helps you set a limit.
5. Limit alcohol near bedtime. It is widely reported to disturb the second half of the night, where REM sleep sits.

Should you trust your tracker's deep and REM numbers?

Consumer wearables estimate sleep stages from movement, heart rate and heart rate variability. They are reasonable at total sleep time and less reliable at telling deep sleep from REM sleep on a given night. Use trends over weeks rather than single nights, and do not chase a deep sleep score. Our article on sleep tracker accuracy covers the details.

Common mistakes

• Treating deep sleep as the only "good" sleep. REM and stage 2 sleep carry their own benefits for emotions and skill learning.
• Cutting the morning to train early. A 5 a.m. alarm before a morning session removes REM-rich sleep. If you train early, move bedtime earlier too.
• Worrying about low deep sleep as you age. A decline from your twenties is expected ¹³.
• Relying on one long night. Recovery sleep helps, but a regular schedule beats catch-up.

The bottom line

Deep sleep is front-loaded and tied to growth hormone and sleep pressure. REM sleep is back-loaded and tied to emotional processing, while overnight skill gains have been linked to late-night stage 2 sleep. Losing either end of the night has a cost. For people who train, the simplest strategy is a consistent wake time and a sleep window long enough to finish the final cycles. That is where your training block gets its chance to turn into supercompensation.

Frequently asked questions

Is REM or deep sleep more important?

Neither is more important overall. Deep sleep is tied to growth hormone release and recovering from sleep pressure, while REM sleep is tied to emotional processing. Lighter stage 2 sleep, which surrounds REM late in the night, has been linked to overnight motor skill gains. Since the stages come in a set order across the night, the best way to get enough of each is to get enough total sleep at a consistent time.

How much deep sleep should I get per night?

There is no single target. In lab data, deep sleep made up about 19% of sleep in men aged 16 to 25 and only about 3% in men aged 36 to 50. It declines with age in healthy people, so a low number on your tracker is not automatically a problem. Focus on total sleep, a regular schedule and how you feel and perform rather than a deep sleep percentage.

How much REM sleep is normal?

REM sleep takes up a substantial share of the night in healthy adults and decreases slowly with age. Most of it happens in the last third of the night, so the amount you get depends heavily on how long you sleep. If you routinely wake early with an alarm, you are likely trimming REM. Wearables estimate REM only roughly. A lab sleep study is the only precise measure.

Does exercise increase deep sleep?

Slightly. A meta-analysis of 66 studies found that a single exercise session produced small increases in slow-wave sleep and small improvements in total sleep time and time to fall asleep. Regular exercise improved overall sleep quality moderately. The effects are real but modest, and very hard or late sessions can make it harder for some people to fall asleep.

Why do I dream more in the morning?

REM sleep, the stage most associated with vivid dreams, gets longer with each sleep cycle. The final cycles before you wake contain the longest REM periods, so you are more likely to wake from or near a dream in the morning. Waking during REM also makes it easier to remember the dream.

Sources

1. Van Cauter E, Leproult R, Plat L (2000). Age-related changes in slow wave sleep and REM sleep and relationship with growth hormone and cortisol levels in healthy men. JAMA.
2. Walker MP et al. (2002). Practice with sleep makes perfect: sleep-dependent motor skill learning. Neuron.
3. Ohayon MM et al. (2004). Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep.
4. Kredlow MA et al. (2015). The effects of physical activity on sleep: a meta-analytic review. Journal of Behavioral Medicine.
5. Lamon S et al. (2021). The effect of acute sleep deprivation on skeletal muscle protein synthesis and the hormonal environment. Physiological Reports.
6. Craven J et al. (2022). Effects of Acute Sleep Loss on Physical Performance: A Systematic and Meta-Analytical Review. Sports Medicine.
7. Cajochen C et al. (2023). Ultradian sleep cycles: Frequency, duration, and associations with individual and environmental factors. A retrospective study. Sleep Health.
8. Tempesta D et al. (2017). Sleep and emotional processing. Sleep Medicine Reviews.