Cold plunges can improve both REM and deep sleep, but the biggest benefits are seen in deep sleep. By lowering core body temperature and reducing inflammation, cold plunges enhance physical recovery during deep sleep, which is critical for muscle repair and immune health. For REM sleep, cold plunges help regulate stress and boost melatonin production, supporting emotional processing and memory retention.
Key findings:
- Deep Sleep: Gains from better temperature regulation, reduced inflammation, and hormonal balance. Benefits build over 2–4 weeks.
- REM Sleep: Improved by stress reduction and melatonin production. Changes noticeable in 3–7 days.
- WHOOP Insights: Tracks metrics like heart rate variability (HRV) and sleep performance to measure the impact of cold plunges.
Quick Comparison
| Sleep Stage | Primary Function | Cold Plunge Benefits | Recovery Timeline |
|---|---|---|---|
| REM Sleep | Emotional processing, memory storage | Boosts melatonin, reduces stress | 3–7 days |
| Deep Sleep | Physical repair, immune support | Lowers body temperature, reduces stress | 2–4 weeks |
To maximize sleep benefits, aim for 3–4 cold plunges per week at 50–59°F for 5–10 minutes. Use WHOOP to track progress and adjust based on your sleep and recovery data.
REM Sleep vs Deep Sleep Basics
What REM Sleep Does
Rapid Eye Movement (REM) sleep is the phase where your brain gets to work on processing cognitive and emotional information. During this stage, brain activity mirrors wakefulness, helping restore mental function while supporting learning, memory retention, and emotional stability. Ideally, adults should spend about 20–25% of their sleep in REM, equating to roughly 1.5–2 hours during a typical 7–9 hour night of sleep [5].
This stage isn’t just about mental restoration - it also boosts creativity and problem-solving, supports brain development, and contributes to overall mental well-being. REM sleep becomes more prominent in the latter half of the night, so cutting your total sleep short can reduce these benefits. During REM, your body experiences atonia - a temporary paralysis of most muscles except for those controlling your eyes and breathing [4] - and dreams tend to be especially vivid [5].
What Deep Sleep Does
Deep sleep, also called slow-wave sleep (SWS), focuses on physical recovery and repair. During this stage, your body works on healing tissues, repairing muscles, and strengthening your immune system. Adults typically spend 13–23% of their sleep in deep sleep, which translates to about 1 to 2 hours in a 7–9 hour sleep window [5]. This phase is most concentrated in the first half of the night, making those early hours critical for recovery.
Deep sleep offers several benefits, such as stimulating growth hormone production, regulating appetite and stress-related hormones, and clearing out metabolic waste in the brain. It also plays a role in memory consolidation, complementing the mental benefits of REM sleep. Physically, this stage is marked by a significant drop in heart rate - 20–30% lower than when awake - and a slower respiratory rate, which can decrease by up to 15% [6]. Brain waves also slow down dramatically, creating the characteristic slow-wave patterns of this stage [5].
How WHOOP Measures Sleep Stages
WHOOP uses advanced sensor technology to track all four sleep stages - REM, slow-wave sleep (SWS), light sleep, and wakefulness. The device primarily relies on photoplethysmography (PPG), which measures subtle changes in blood flow beneath the skin [1] [2]. Alongside this, WHOOP incorporates a 3-axis accelerometer and gyroscope to collect hundreds of data points per second, enabling it to monitor heart rate, heart rate variability, and respiratory rate. These metrics feed into its sophisticated sleep staging algorithms, which are fine-tuned using polysomnography (PSG) data and machine learning models [2].
Internal testing shows that WHOOP achieves a 99.7% accuracy rate in measuring heart rate and 99% accuracy in monitoring heart rate variability during sleep. This precision improves its ability to classify sleep stages and detect wake periods [2]. By tracking the time spent in each sleep stage, WHOOP provides users with actionable insights into their recovery strategies, including how practices like cold plunges might influence sleep architecture. This detailed tracking makes it easier to explore how cold plunges could uniquely benefit REM and deep sleep.
| Sleep Stage | Percentage of Total Sleep | Duration per Night | Primary Function |
|---|---|---|---|
| REM Sleep | 20-25% | 1.5-2 hours | Cognitive processing, memory, emotional regulation |
| Deep Sleep | 13-23% | 1-2 hours | Physical repair, immune support, hormone regulation |
Understanding the roles of these sleep stages and how WHOOP tracks them lays the groundwork for examining how cold plunges might enhance recovery. Both REM and deep sleep are crucial for overall health, each focusing on different aspects of mental and physical restoration.
How Cold Plunges Affect Your Body
What Happens During Cold Exposure
Stepping into cold water kicks off an immediate chain reaction in your body, designed to protect your core temperature. This exposure creates a stress response that activates your sympathetic nervous system. What does that mean? Your body goes into action - blood vessels tighten (vasoconstriction), your heart starts racing, and blood pressure rises to maintain heat and protect vital organs [3][9].
Within moments, your heart rate can jump by 10–30 beats per minute, blood flow to the brain briefly slows, and your body begins adjusting to the cold [9][10]. After this initial shock, the parasympathetic nervous system steps in, calming things down. Heart rate and blood pressure decrease, and endorphins - your body's natural feel-good chemicals - are released [3].
"Cold-water immersion is an increasingly popular recovery intervention after exercise... This response, in turn, produces indirect beneficial effects throughout the entire body" [9]
But the benefits don’t stop there. Cold exposure has been linked to enhanced immune function. For instance, one study found that cold showers reduced sickness-related work absences by 29% [3]. Another study revealed cold water immersion increased dopamine levels by a staggering 250% [15]. Plus, ice baths are known to reduce muscle damage caused by exercise [7]. Interestingly, a meta-analysis also showed a temporary rise in inflammation markers immediately after and one hour following cold water exposure [8].
These quick, intense reactions in your body might even set the stage for better sleep - something we’ll dive into next.
Cold Plunges and Better Sleep
Cold plunges can help you sleep more soundly by regulating your body temperature and easing stress. Research shows that stress levels drop for up to 12 hours after cold water immersion [8][12]. Even slow-wave sleep - the restorative stage of sleep - gets a boost, increasing by an average of 7.3 minutes during the first two sleep cycles after cryostimulation [14].
Cold exposure also supports melatonin production and activates the parasympathetic nervous system, which is crucial for energy conservation and maintaining balance in the body [13]. This combination creates the perfect conditions for restorative sleep.
Taking a cold plunge in the morning can also indirectly improve sleep by syncing your circadian rhythm. The sharp temperature change helps regulate your internal clock, making it easier to fall asleep at night. If you prefer to plunge in the evening, aim to do so at least 1–2 hours before bed to avoid heightened alertness [11].
Using WHOOP to Track Cold Plunge Results
For those who love tracking progress, WHOOP offers a way to measure the real effects of cold plunges. The device monitors key metrics like heart rate (HR), heart rate variability (HRV), and skin temperature, turning physiological changes into actionable insights [10]. This data can help you understand how your body adapts to stress and improve recovery strategies.
Jayce Love, Founder of Ritual Recovery, highlights the importance of these metrics:
"For biohackers and hybrid athletes, ice baths aren't just about feeling refreshed, they're a measurable tool for nervous system resilience and recovery." [10]
"HR response shows cardiovascular adaptation. HRV response tracks nervous system resilience. Skin temp reveals metabolic efficiency." [10]
A 2019 study published in the Journal of Applied Physiology found that cold exposure increased cardiac vagal activity, which is closely tied to higher HRV [10]. This effect was particularly notable in trained swimmers, as cold water immersion helped restore HRV after intense exercise, showcasing its potential to enhance parasympathetic activity [10].
To get the most out of your WHOOP data, log habits like ice baths, sauna sessions, diet, fasting, hydration, and breathwork in the WHOOP Journal. This way, you can see how each activity impacts HRV and recovery [10]. WHOOP’s features make tracking cold plunge benefits even easier:
| WHOOP Feature | How It Tracks Cold Plunge Benefits |
|---|---|
| Sleep Performance Score | Measures how cold therapy affects deep sleep and REM cycles |
| HRV Tracking Over Time | Monitors nervous system function changes from ice baths |
| Strain vs. Recovery Balancing | Helps decide whether to train or rest based on HRV trends |
| Strain After Cold Exposure | Tracks how quickly your strain score drops post-ice bath, indicating faster recovery |
REM Sleep vs Deep Sleep: Cold Plunge Benefits
How Cold Plunges Help REM Sleep
REM sleep is the stage where your brain organizes emotions, stores memories, and clears mental clutter. Cold plunges activate the parasympathetic nervous system, encouraging relaxation and helping your brain ease into deeper REM cycles [13][16]. This calming effect creates the ideal conditions for restorative REM sleep.
Cold exposure also increases melatonin production, which plays a key role in managing your sleep-wake cycle. Unlike supplements, this natural boost doesn’t carry risks of dependency [16]. With improved melatonin levels, your circadian rhythm becomes more balanced, which can lead to better REM sleep. In fact, studies have shown that heart rate variability (HRV) improves after just three days of consistent cold exposure combined with sauna use [10].
"REM sleep is the time when new learnings from the day are committed to long-term memory" [20].
By creating an optimal environment for REM sleep, cold plunges may enhance your ability to retain new information and solidify memories.
How Cold Plunges Help Deep Sleep
Deep sleep is when your body gets to work repairing muscles, regenerating cells, and boosting immune function. Cold plunges help by lowering your core temperature, which is essential for entering deep sleep [16]. Research also suggests that keeping your bedroom cool (59–68°F or 15–20°C) can further improve sleep quality [13].
The anti-inflammatory effects of cold plunges contribute to the body’s recovery processes during deep sleep. One study found that regular cold showers reduced sickness absence by 29%, highlighting improved immune system performance [3][17]. Additionally, controlled trials revealed that individuals who practiced cold-water immersion scored higher on sleep quality metrics (3.6 ± 0.5) compared to those relying on passive recovery (3.1 ± 0.5), indicating better physical recovery during deep sleep [17].
Take Shane, for example - a former Australian special forces veteran who saw dramatic recovery improvements after incorporating daily ice baths into his routine. Within a month, his HRV jumped from 16 to 75, and his resting heart rate dropped from 72 to 55 beats per minute [19]. These changes reflect increased parasympathetic activity, which is crucial for high-quality deep sleep.
The table below highlights the distinct benefits of cold plunges for REM and deep sleep, along with recovery timelines.
Side-by-Side Comparison: REM vs Deep Sleep
| Sleep Stage | Primary Function | Cold Plunge Benefits | WHOOP Metrics Affected | Recovery Timeline |
|---|---|---|---|---|
| REM Sleep | Mental restoration, memory consolidation, emotional processing | Boosts melatonin, improves HRV, regulates stress | Heart rate variability, sleep efficiency, recovery score | Visible improvements in 3–7 days |
| Deep Sleep | Physical restoration, muscle repair, immune support | Lowers core temperature, reduces inflammation, decreases stress hormones | Resting heart rate, sleep performance score, strain recovery | Benefits accumulate over 2–4 weeks |
Both REM and deep sleep gain from cold plunges, though the effects develop at different speeds. REM sleep improvements - such as enhanced HRV and emotional balance - often appear within the first week of consistent cold exposure. On the other hand, the benefits for deep sleep, including better temperature regulation and reduced inflammation, tend to build gradually over a few weeks.
For optimal results, aim to take your cold plunge 1–2 hours before bedtime. This timing helps your body transition from the initial stress response to a relaxed, parasympathetic state, promoting both REM and deep sleep [13][16].
WHOOP’s metrics, known for their accuracy (99.7% for heart rate and 99% for HRV during sleep [2]), make it easy to track these changes. The Sleep Performance Score provides clear insights into how cold plunges are improving your recovery. Up next, explore practical cold plunge tips specifically designed for WHOOP users.
Cold Plunge Tips for WHOOP Users
Best Times and Frequency for Cold Plunges
Mornings are generally the best time for a cold plunge. While cold exposure lowers your skin temperature, it can temporarily raise your core temperature as your body works to compensate. This can interfere with the natural drop in core temperature that promotes sleep, making pre-bed plunges less ideal [21].
If evening sessions fit your schedule better, aim to take your cold plunge 1–2 hours before bedtime. This allows your body enough time to return to its baseline temperature and can support both REM and deep sleep. In fact, some swimmers have reported better sleep after a quick five-minute cold water immersion following their workouts [22].
Cold plunges don’t have to be a daily ritual. WHOOP data shows ice baths are among the top five recovery methods, with users seeing an average recovery score improvement of 0.41% [24]. Starting with 3–4 sessions per week is a good approach. Use your WHOOP metrics to adjust the frequency based on how your body responds.
Water Temperature and Time Guidelines
For optimal sleep benefits, aim for water temperatures between 50–59°F (10–15°C) [17]. If you’re new to cold plunging, start with slightly warmer water, around 55–60°F, and gradually decrease the temperature as your body gets used to it [23]. This gradual approach helps your body adapt without feeling overwhelmed.
Duration matters too. Beginners should start with 30 seconds to one minute and slowly work up to 5–10 minutes over several weeks [23]. For example, runners who tried full-body cold exposure reported better slow-wave sleep in the first three hours, fewer nighttime awakenings, and less limb movement [22]. The key is consistency - regular cold plunging has been linked to better sleep, reduced stress, and an overall boost in quality of life [17]. Use your WHOOP data to track how adjustments in temperature and duration affect your sleep patterns.
Getting More from Your WHOOP Data
Your WHOOP app can be a powerful tool for fine-tuning your cold plunge routine. Log each session, noting details like water temperature, duration, diet, and hydration. This helps you spot trends in your recovery data [3].
Pay attention to how your HRV (Heart Rate Variability) responds. A spike followed by a drop during a cold plunge indicates effective parasympathetic activation, which can improve sleep quality. Over time, these changes should reflect positively in your Sleep Performance Score as your nervous system becomes more resilient.
The strain versus recovery balance feature in the WHOOP app can guide your timing. For example, if your HRV is trending downward or your recovery score is low, a gentle cold plunge might help reset your system. But if you’re already highly strained, skipping the session could prevent adding unnecessary stress.
Long-term WHOOP tracking can reveal broader trends. For instance, while recovery methods like meditation and massage therapy show average impacts of 1% and 0.82% respectively, ice baths consistently contribute about 0.41% to recovery metrics [24]. Over time, the cumulative effects on sleep - such as improved REM cycles and deeper slow-wave sleep - become more noticeable when you review your data regularly.
Conclusion
Main Findings and Recommendations
Research and data from WHOOP highlight how cold plunges can significantly enhance both REM and deep sleep, with the most noticeable improvements seen in deep sleep. This is due to the release of norepinephrine and dopamine, which boost slow wave (N3) activity, making deep sleep more restorative [25].
Cold plunges also activate the "diving reflex", which helps lower heart rate and blood pressure, preparing the body for restful sleep [25]. A study by the University of South Australia found that participants who engaged in cold-water immersion scored higher on sleep quality measures (3.6 ± 0.5) compared to those in passive recovery groups (3.1 ± 0.5). The researchers concluded:
"Cold-water immersion may improve sleep quality, lower stress, and boost quality of life." [17]
For REM sleep, cold plunges regulate core body temperature and encourage melatonin production, a hormone essential for maintaining healthy sleep-wake cycles [25].
Tracking your progress with WHOOP is a game-changer in optimizing these benefits. As Jayce Love, Founder of Ritual Recovery, explains:
"What gets measured, gets managed, and the Whoop is an incredible tool to track your daily activities and recovery modalities to see how they affect you." [18]
WHOOP users often rank ice baths among the top five recovery methods, emphasizing the value of personal data to fine-tune your cold plunge routine. Use WHOOP's sleep tracking features to ensure you're meeting the recommended 15–20% deep sleep and 20–25% REM sleep [26].
Find Quality Cold Plunge Equipment at ColdPlungeTubs.com
With the proven benefits of cold plunges backed by research and WHOOP data, now is the time to take action. ColdPlungeTubs.com offers expert reviews, guides, and comparisons to help you choose the right cold plunge tub for your needs. Whether you’re aiming to improve muscle recovery, strengthen your immune system, or enhance sleep quality, the right equipment can make all the difference.
Head to ColdPlungeTubs.com today to explore our curated selection and expert advice on cold therapy. Start optimizing your recovery and unlock the health benefits of cold exposure today.
I Did Ice Baths for 30 Days - The Cold Plunge Protocol That Transformed my Sleep & Recovery!
FAQs
How does WHOOP track the effects of cold plunges on REM and deep sleep?
WHOOP keeps track of how cold plunges affect your sleep by analyzing key biometric data, such as heart rate, heart rate variability, and movement. With this information, it can automatically determine when you fall asleep, wake up, and how your sleep breaks down into stages like REM, deep, and light sleep.
By studying these patterns, WHOOP offers insights into whether cold plunges might boost recovery, improve sleep quality, and contribute to your overall well-being. This data helps you see how your body reacts to cold therapy and fine-tune your routine for better outcomes.
How often and how long should I do cold plunges to improve my sleep?
To improve your sleep, experts suggest cold plunges lasting anywhere from 2 to 10 minutes, depending on your experience. If you're just starting out, try keeping it short - around 30 seconds to 1 minute - and gradually work your way up as you get used to it. Consistency matters here, so aim for 3 to 4 sessions per week to see noticeable results.
Cold plunges are known to help with relaxation, ease inflammation, and aid recovery - all of which can lead to better sleep. Pay attention to how your body responds and adjust the length and frequency of your sessions to align with your comfort level and personal goals.
Can cold plunges negatively impact sleep if not done properly?
Yes, cold plunges can negatively impact your sleep and overall health if not done properly. Spending too much time in cold water or exposing yourself to extreme cold can result in hypothermia, added stress on the heart, or even irregular heartbeats. For those with existing heart conditions, the risks can be more severe, potentially leading to a heart attack in extreme situations.
To stay safe, it’s important to follow a few guidelines: keep your time in cold water short, pay attention to how your body reacts, and consult a healthcare provider if you’re unsure about whether cold plunges are right for you. The key is moderation - this allows you to enjoy the benefits without putting your health at risk.
Related posts
- The Science of Deep Sleep: How Cold Plunges Impact WHOOP SWS Scores
- A Guide to Improving WHOOP Sleep Performance with Cold Water Immersion
- How to Time a Cold Plunge for Optimal WHOOP Sleep Stage Results