The Søberg Principle: Should You End a Sauna and Cold Session With Cold?

The Søberg Principle is the advice to end a sauna-and-cold session on cold and let your body rewarm itself. It is a reasonable idea built on real physiology, but it has never been tested directly. The study it comes from compared experienced winter swimmers with non-swimmers in a lab. It did not compare ending on cold with ending on heat, and it did not test a weekly dose such as 11 minutes.

This page summarizes research for general information. It is not medical advice. Cold water can trigger dangerous heart-rate and breathing responses; check with a clinician first if you have heart, blood-pressure or circulation problems, or are pregnant.

Where the idea comes from

Danish metabolism researcher Susanna Søberg described the routine of the winter swimmers she studied on a 2023 Huberman Lab episode. Two to three times a week they alternated short dips of 1–2 minutes with sauna sessions of 10–15 minutes at about 80 °C, starting and finishing in the cold. On the show the host named the end-on-cold habit the Søberg Principle. The reasoning she gave was that letting yourself shiver back to warmth makes your own tissues produce the heat.

That is an expert’s practical advice, reported here as such. It is not a study finding.

What the 2021 study actually did

The Søberg et al. study (Cell Reports Medicine, 2021) recruited 8 young men who winter-swam 2–3 times a week and 8 non-swimmers matched for age, body mass index and fitness; one swimmer’s data were not included, so most results compare 7 with 8. The researchers did not study the swimmers’ own dips. They cooled every participant in the lab with water-circulating blankets and measured brown fat, heat production, shivering and blood markers.

The headline result is real but narrow: the swimmers produced more heat when cooled, and showed a distinct early-morning peak in skin temperature over the collarbone. The authors themselves only went as far as to “propose winter swimming as a potential strategy for increasing energy expenditure.” Because this was a one-off comparison of self-selected swimmers, it cannot show that winter swimming caused any of the differences. After the long lab cooling, the protocol rewarmed participants for 45 minutes at 32 °C.

The 11-minute figure deserves the same care here as on the cold and heat pillar page. It appears in the participant table as the swimmers’ average time in cold water per week (alongside 57 minutes of sauna). It was never varied or tested, so it is a convention, not an established dose.

Why rewarming on your own is plausible

The mechanism behind the advice is sound physiology even if the benefit is unmeasured. Cold triggers a sympathetic surge: in a classic lab study (Šrámek et al., 2000), young men sitting in 14 °C water up to the neck for one hour had noradrenaline rise by about 530 percent and metabolic rate by about 350 percent. A one-hour immersion is far longer than a 1–2 minute dip, so short dips should be expected to produce much smaller responses.

When you get out, you have to make up the heat you lost, using shivering and brown fat. Repeated cold can train that system. In a 10-day cold-acclimation study (van der Lans et al., 2013), adults showed more brown fat activity and more non-shivering heat production afterwards, and reported shivering less. It did not involve cold-water dips or compare ways of finishing a session.

So the logic of the principle is: stepping into a hot shower or sauna supplies heat from outside, so your body has less of its own heat to make. Nobody has measured how big that difference is.

What alternating heat and cold has been tested for

Alternating sauna and cold water has been studied, just not for the question the principle answers.

• Cold breaks change how the next sauna round feels: in a 2026 crossover study, 16 healthy adults did two 15-minute sauna bouts at 85 °C. Between them, they cooled off for 10 minutes in air, either with or without a 90-second whole-body dip in 20 °C water. With the dip, core temperature at the end of the second sauna was 0.48 °C lower and heart rate was 17 beats per minute lower (108 vs 125 bpm), and people felt less hot. The authors concluded that cold water “substantially attenuated thermal and cardiovascular strain” during the sauna. That is about the middle of a session, not how to finish it.
• Contrast water therapy for sore muscles: a 2013 review of 18 trials (Bieuzen et al.) found alternating hot and cold water reduced soreness and strength loss more than passive rest after muscle-damaging exercise. It was not clearly better than cold water alone, warm water, compression or stretching, and every trial had a high risk of bias. None of the trials tested finishing on cold against finishing on warm.

So the parts of a hot-cold routine that have been measured are short-term comfort and recovery. The metabolic payoff from ending on cold, the core of the Søberg principle, has not been measured at all.

The afterdrop: why the minutes after a dip matter

Core temperature often keeps falling after you leave cold water. This afterdrop is the main reason to treat the end-on-cold advice with care.

• How big it can be: in a 2025 field study of 86 military personnel who spent 10 minutes in 1.5 °C water outdoors, core temperature fell a further 1.3 °C on average after they got out, reaching its low about 26 minutes later. That was a long, very cold immersion; a 1–2 minute recreational dip is a much smaller dose.
• Rewarming method changes it: in a 1988 lab study (Romet), 8 men were cooled in 22 °C water and rewarmed three ways. Rapid rewarming in 40 °C water made the core temperature fall faster at first than it had during cooling, before it reversed quickly.

Neither study tested metabolic benefits. Their practical message is that the period after a dip is when you are still cooling, so plan for it.

Practical notes if you try it

These are the conditions under which ending on cold is a low-risk choice, based on the safety literature rather than proven benefit:

• Keep the last dip short: the swimmers Søberg described stayed in for 1–2 minutes. Longer final dips deepen the afterdrop.
• Get dry and dressed fast: towel off, put on a hat and warm layers, and get out of the wind. Passive rewarming does not mean standing wet and cold.
• Light movement is fine: walking around while dressed helps you warm up.
• Know when to stop: confusion, slurred speech, clumsiness or uncontrollable shivering mean it is time to warm up actively and get help.
• Never alone in open water: a review of cold-water immersion (Tipton et al., 2017) covers how the first minutes in cold water can lead to drowning and cardiac arrest.
• Skip alcohol: it impairs both judgment and temperature control.

If your goal is muscle growth, timing matters more than the order of cold and heat; see cold water after strength training. For session lengths and temperatures, see the cold plunge protocol and the sauna protocol.

How strong is the evidence?

A 2022 review of 104 studies (Espeland et al.) of voluntary cold-water exposure found most studies were small and hard to compare, and noted that “Whether winter swimmers as a group are naturally healthier is unclear.” The same caution applies to the Søberg Principle. It is a sensible habit for people who already enjoy sauna and cold dips, as long as the rewarming is done safely, but there is no measured benefit behind it.