A cold plunge eases soreness but can shrink your muscle gains

Key takeaways

• The popular “11 minutes of cold a week” figure describes the habits of a few Danish winter swimmers in a small 2021 study; no one tested it as a dose.
• A 2025 review of 11 trials found stress scores were lower 12 hours after cold immersion but not at other times, with no clear benefit for mood or immunity.
• A 2012 Cochrane review found less muscle soreness for up to four days after exercise, but its 17 trials were small and low in quality.
• In one small 12-week trial, men who took 10-minute cold baths after strength training gained less strength and muscle than men who did an active cool-down.
• The first minute is the risky part, so enter slowly, keep your head above water, breathe steadily, and never plunge alone in open water.

If you’ve read about cold plunging, you may have met a tidy number: 11 minutes of cold a week.

Here is where it comes from. In 2021, researchers at the University of Copenhagen studied eight young men who swam in cold water through the winter and compared them with eight men who didn’t¹². The swimmers reported spending about 11 minutes a week in cold water, plus 57 minutes in a sauna¹.

That was a description of their habits, not a dose anyone tested. The authors wrote that their design couldn’t show whether winter swimming caused the differences they found¹.

Cold plunging took off anyway. U.S. Amazon sales of ice-bath tubs rose from under 1,000 units in November 2022 to more than 90,000 a year later, according to market data cited by Australian researchers³.

The science has been catching up. It shows a strong, predictable shock to the body, a few modest benefits, a possible trade-off for people building muscle, and some serious risks.

The first minute in cold water is the dangerous one

Mike Tipton, a physiologist at the University of Portsmouth in England, and his colleague Frank Golden coined the term “cold shock” in the 1980s⁵. It describes what happens when cold water hits a large area of skin at once.

First comes a gasp of about two liters of air, followed by fast breathing you can’t control⁵. Heart rate and blood pressure jump as blood vessels in the skin clamp down⁶. These reflexes are involuntary, so willpower can’t switch them off⁶.

If your head is under water during that gasp, you can inhale water. Tipton notes that about 1.5 liters can be enough to drown⁵.

Cold also shrinks how long you can hold your breath. Below 15°C (60°F), the average person manages about a third of their usual breath-hold⁶. In one study at 5°C (41°F), average breath-hold time fell from 45 seconds to 9.5 seconds⁶.

The good news: cold shock fades within about a minute as the skin’s cold sensors adjust⁵. Hypothermia, a dangerous drop in core temperature, takes at least 30 minutes to become fatal⁵. That’s why, in a short plunge, the first minute poses a bigger threat than hypothermia does.

The stakes are real. About 400 people die each year in the United Kingdom from cold-water immersion, and most of them were described as strong swimmers⁵. Those numbers come from all kinds of cold-water incidents, not plunge tubs in particular. But the reflex behind them is the same one you trigger on purpose.

The body does adapt. Tipton writes that six head-out dips of three minutes each can cut the cold shock response roughly in half⁵.

Holding your breath in cold water can confuse the heart

Two reflexes can collide in cold water. Cold shock speeds the heart up. The diving response, set off by cold water on the face while you hold your breath, slows it down⁷.

In 2012, Michael Shattock and Mike Tipton proposed in the Journal of Physiology that firing both at once, which they called “autonomic conflict,” can trigger abnormal heart rhythms⁷. Their review of lab studies found striking numbers:

• When young, fit, healthy volunteers held their breath under cold water, 62% to 82% developed abnormal heart rhythms⁷.
• When volunteers kept their heads out and breathed freely, the rate was about 2%⁷.
• In two studies, about 81% of the abnormal rhythms appeared within 10 seconds of ending the breath-hold⁷.

The bigger concern is for people whose hearts are already vulnerable. The authors listed long QT syndrome, a heart rhythm disorder, along with coronary heart disease and medicines that prolong the heart’s QT interval, including some antihistamines, antibiotics and antipsychotics⁷.

They also note that rhythm deaths usually leave no trace at autopsy and may be recorded as drowning⁷. In one genetic study of drownings with no clear cause, nearly 3 in 10 victims carried mutations in genes that control heart rhythm⁷.

The idea is still a hypothesis, and it’s hard to test⁷. Even so, in a cold plunge, keep your face out of the water and keep breathing. Breath-hold challenges and head dunks add risk without any proven benefit.

A 2025 review found small, short-lived effects

In January 2025, researchers at the University of South Australia published a systematic review and meta-analysis of cold-water immersion in healthy adults³⁴. They pooled 11 randomized trials with 3,177 people³. A randomized trial assigns people by chance to one group or another.

To count, the cold had to be 15°C (59°F) or colder, for at least 30 seconds, at chest depth or deeper³. Showers, ice baths and plunges all qualified. The trials used water from 7°C to 15°C and exposures from 30 seconds to two hours³.

What they found:

• Stress: Questionnaire stress scores in these healthy volunteers were lower 12 hours after cold exposure. There was no change right after, at one hour, or at 24 or 48 hours³.
• Inflammation: Inflammation markers rose right after immersion and at one hour³. The authors suggested this may reflect the body’s metabolic response to cold, such as breaking down stored sugar for fuel³.
• Immunity: The evidence was inconclusive³.
• Mood: One small study of 20 men found no difference³.
• Sleep: One study of men after heat training found slightly better sleep ratings³.
• Quality of life: A small rise at 30 days had faded by 90 days³.

Almost all the women in the review came from a single study. Every other trial enrolled only men³. The authors concluded that many popular claims are not yet backed by good evidence³.

The largest trial in the review tested cold showers. In the Netherlands, 3,018 adults were randomly assigned to end their warm showers with 30, 60 or 90 seconds of cold each day for a month, or to shower as usual⁸. The cold-shower groups had 29% less sickness absence from work, but no fewer days of illness⁸.

People reported being sick about as often, yet missed less work. The outcomes were self-reported, and participants knew which group they were in³⁸. About 79% finished the month, and the most common side effect was a lingering cold feeling, often in the hands or feet⁸.

Brown fat and the 11-minute myth

Brown fat is a type of tissue that burns energy to make heat, which is why it turns up in claims that cold melts fat.

The Copenhagen swimmers were at least into their second winter of the habit and swam about 2.6 times a week, pairing cold dips with sauna sessions¹². At a comfortable room temperature, the controls showed brown fat activity and the swimmers showed none². When both groups were cooled, brown fat activity rose in both, and the swimmers made more heat².

During 30 minutes of cooling, the swimmers burned energy at a rate equal to 3,044 calories a day, compared with 2,560 for the controls¹. Those daily figures were scaled up from a half-hour measurement¹. At a comfortable temperature, the two groups burned about the same¹.

The authors were careful. Brown fat’s fuel uptake didn’t explain the extra heat, and other tissue, such as muscle, may have played a part¹. They also raised the chance that people whose bodies handle cold well are the ones who take up winter swimming¹.

Notice, too, how the swimmers got their 11 minutes. Each dip averaged about 1.4 minutes, with two or three dips per visit¹. The study measured heat production during cooling. It did not measure weight loss.

After a workout: less soreness, possibly smaller gains

For recovery, the strongest evidence is a 2012 Cochrane review by Bleakley and colleagues. Cochrane is an international network that produces systematic reviews. The team pooled 17 small trials with 366 people⁹. Its search ended in November 2011, so newer trials aren’t included⁹.

Compared with resting, cold-water immersion reduced muscle soreness at 24, 48, 72 and 96 hours after exercise⁹. In the few trials that compared them, warm-water immersion worked about as well as cold⁹.

The reviewers rated the trials low in quality, found widely varying results, and noted that most trials didn’t check for side effects⁹.

Now the catch. In 2015, Llion Roberts and colleagues in Australia, New Zealand and Norway tested what regular cold baths do to strength training¹⁰¹¹. Twenty-one active men lifted weights twice a week for 12 weeks. After each session, they spent 10 minutes either in cold water or doing an active cool-down¹⁰.

The active cool-down group gained more strength and more muscle¹⁰. Their fast-twitch muscle fibers grew 17% larger, and a measure of muscle work rose 19%. Neither changed significantly in the cold group¹⁰.

A second experiment with nine men took muscle samples after exercise. Satellite cells, the muscle stem cells that help repair and build fibers, responded less after cold water, and so did a key growth-signaling enzyme¹⁰.

Roberts advised people chasing strength or size to skip ice baths, though he said they could still be used in stretches when recovery matters more than building muscle¹¹.

This is one small trial, so treat it as a warning sign rather than a settled rule.

Still, a sensible pattern follows. If you have games or races on back-to-back days, a plunge may help you feel fresher. If you’re lifting to get stronger, keep it away from your training sessions. No study we found has pinned down how long to wait.

An evidence map for cold plunge claims

This table uses four levels: strong evidence, promising but early, not enough evidence, and evidence says no (or unsafe).

Claim	Evidence level	What the research shows
Less muscle soreness after exercise	Promising but early	Cochrane review: lower soreness up to 96 hours; 17 small, low-quality trials; warm water did about as well9
Lower stress scores in healthy adults	Promising but early	Pooled trials: lower questionnaire scores at 12 hours only, mostly in men3
Better sleep	Not enough evidence	One small study in men3
Better mood	Not enough evidence	One small study found no difference3
Stronger immunity	Not enough evidence	Immune markers inconclusive; cold showers cut work absence but not illness days38
Burning fat through brown fat	Not enough evidence	One small study of trained swimmers measured heat output, not weight loss1
Calming inflammation soon after a plunge	Evidence says no	Pooled markers rose, rather than fell, right after immersion and at one hour3
Building muscle by plunging right after lifting	Not enough evidence	Only one small trial has tested it, and it pointed the other way: 21 men gained less strength and muscle than with an active cool-down10
Breath-hold or head-under plunges	Evidence says no, or unsafe	Breath-hold cold submersion caused abnormal rhythms in most healthy volunteers7

Talk with a clinician first if any of these apply

The trials above enrolled healthy adults, and one review excluded people with chronic illness³. Ben Singh, one of its authors, put it plainly: “people with pre-existing health conditions should take extra care”⁴. His reason was the early rise in inflammation, which could do harm⁴.

Check with a doctor before you plunge if you have:

• Heart disease or a heart rhythm problem, including long QT syndrome, or a family history of sudden death or unexplained drowning⁷.
• High blood pressure or a past stroke. Cold sends heart rate and blood pressure up fast, and vulnerable people face a higher risk of heart failure and stroke⁶.
• A daily medicine that affects heart rhythm. Ask your pharmacist whether any of yours prolong the QT interval⁷.
• Raynaud’s phenomenon, where fingers and toes turn white or blue in the cold. The National Institutes of Health names getting cold as the most common trigger and stresses keeping your whole body warm¹².
• Pregnancy, or plans to plunge with a child. The research reviewed here offers no safety data for either.

A safety-first plunge routine

This routine draws on cold-water safety research. It’s a starting point for healthy adults, not a prescription.

1. Never plunge alone. In open water, wear a life jacket. It keeps you afloat while your breathing is out of control⁶.
2. Check the temperature. The trials used 7°C to 15°C, about 45°F to 59°F³. Colder isn’t proven better, and below 7°C severe pain adds to the strain⁶.
3. Ease in. Tipton advises entering slowly rather than jumping or running in⁵.
4. Keep your head out and breathe. Skip breath-holding contests and face dunks⁷.
5. Ride out the first minute. Sit still or hold on, and let your breathing settle. The shock usually passes within about a minute⁵.
6. Keep it short. Some trials used just 30 seconds³, and the Danish swimmers averaged about 1.4 minutes per dip¹.
7. Stay sober. Cold already clouds thinking and can bring on panic and poor judgment⁶. Don’t add alcohol.
8. Get out at the first warning sign. Leave for chest pain, dizziness, confusion or breathing that won’t calm down.
9. Rewarm gently. Dry off, dress in warm layers, and give your body time before you drive.

When to get help. Call 911 if someone has chest pain, faints, becomes confused or struggles to breathe during or after a plunge. Report a tub or chiller that shocks, burns or injures someone to the Consumer Product Safety Commission at SaferProducts.gov. Report misleading health claims to the FTC at ReportFraud.ftc.gov.

Cold water is a natural stress. Respect it like one

Many natural-health readers like practices that train the body to adapt, and cold water does that. Tipton’s work shows the gasp reflex weakens with repeated short dips⁵. The Danish swimmers had smaller jumps in pulse and blood pressure when their hands were put in cold water².

That adaptation is real, but it’s not magic. The measured benefits so far are modest and short-lived³⁹. The biggest proven effect, the shock itself, is also the main danger⁵⁶.

Treat a plunge the way you would a strong herb: start small, respect the dose, and know who should skip it. If you enjoy the bracing feeling, that’s a fine reason to do it. Just don’t let a tub, an app or a seller promise more than the research does.

Questions readers ask

The bottom line

A cold plunge is a strong jolt to the body with a short list of proven payoffs: some relief from post-exercise soreness and a brief dip in stress scores. Claims about immunity, mood and fat burning are well ahead of the research, and one trial suggests regular plunges right after strength training may cost you gains.

The real risks come in the first minute. Ease in, keep your head up, breathe, keep it short, and never go alone in open water. If you have a heart, blood pressure or circulation condition, or take medicines that affect your heart rhythm, talk with a clinician first.

Related reading

• The famous sauna longevity study used Finnish saunas, not infrared cabins
• Red-light therapy’s strongest evidence is for cancer mouth sores, not wrinkles
• The symptoms that mean call 911 now
• Most health products aren’t scams, but many just haven’t been proven
• Six questions to ask before you buy anything for your health

Sources

1. Søberg S, Löfgren J, Philipsen FE, et al. “Altered Brown Fat Thermoregulation and Enhanced Cold-Induced Thermogenesis in Young, Healthy, Winter-Swimming Men.” Cell Reports Medicine, 2021. pmc.ncbi.nlm.nih.gov
2. University of Copenhagen, Faculty of Health and Medical Sciences. “Winter-Swimming Scandinavian Men Can Teach Us How the Body Adapts to Extreme Heat and Cold.” University of Copenhagen, 2021. healthsciences.ku.dk
3. Cain T, Brinsley J, Bennett H, Nelson M, Maher C, Singh B. “Effects of Cold-Water Immersion on Health and Wellbeing: A Systematic Review and Meta-Analysis.” PLOS ONE, 2025. journals.plos.org
4. University of South Australia. “The Big Chill: Is Cold Water Immersion Good for Our Health?” Newswise, 2025. newswise.com
5. Tipton M. “As Heat Waves Hit Worldwide, a Reminder That Diving Into Cold Water Can Be Deadly.” PBS NewsHour (from The Conversation), 2019. pbs.org
6. National Center for Cold Water Safety. “Cold Shock.” National Center for Cold Water Safety. coldwatersafety.org
7. Shattock MJ, Tipton MJ. “‘Autonomic Conflict’: A Different Way to Die During Cold Water Immersion?” Journal of Physiology, 2012. pmc.ncbi.nlm.nih.gov
8. Buijze GA, Sierevelt IN, van der Heijden BCJM, Dijkgraaf MG, Frings-Dresen MHW. “The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial.” PLOS ONE, 2016. journals.plos.org
9. Bleakley C, McDonough S, Gardner E, Baxter GD, Hopkins JT, Davison GW. “Cold-Water Immersion (Cryotherapy) for Preventing and Treating Muscle Soreness After Exercise.” Cochrane Database of Systematic Reviews, 2012. pubmed.ncbi.nlm.nih.gov
10. Roberts LA, Raastad T, Markworth JF, et al. “Post-Exercise Cold Water Immersion Attenuates Acute Anabolic Signalling and Long-Term Adaptations in Muscle to Strength Training.” Journal of Physiology, 2015. pubmed.ncbi.nlm.nih.gov
11. University of Queensland. “Are Athletes Approaching the End of the Ice Age?” UQ News, 2015. news.uq.edu.au
12. National Institute of Arthritis and Musculoskeletal and Skin Diseases. “Raynaud’s Phenomenon.” National Institutes of Health. niams.nih.gov