Where the weekly goal presets come from

The presets could have been 30, 60 and 90 minutes. They are 20 and 4, 60 and 11, 100 and 20, and every one of those numbers has a paper behind it. Awkward figures with provenance beat tidy figures without.

The three presets

Custom runs from 10 to 180 minutes of heat and 1 to 30 of cold. Heat counts sauna, hot baths and hot showers; cold counts plunges and cold showers. The rings on the Analysis tab and the 12-week chart underneath both measure against whichever you pick.

The heat figures, and the cohort behind them

Two Finnish studies set the range.

The 2015 cohort followed 2,315 middle-aged men for a median of 20.7 years. The typical user went 2.1 times a week for 14.2 minutes — about 30 minutes a week. Against once a week, four to seven sessions was associated with lower sudden cardiac death, hazard ratio 0.37 in those men, and sessions over 19 minutes went with lower risk than sessions under 11.

The 2018 sample added women and reported a median of 30 minutes a week. More than 45 minutes a week went with lower cardiovascular death than 15 minutes or fewer, hazard ratio 0.57.

So Beginner’s 20 minutes sits just below the typical Finnish user. Intermediate’s 60 clears the 45-minute line comfortably. Advanced’s 100 sits inside the most frequent group in those studies rather than beyond it, which matters — there is no evidence that more is better without limit, and the app does not offer a preset that implies there is.

The cold figures, and the gap in the evidence

Here is the part the app says outright on the metric page: no study ties a weekly cold total to long-term health. There is no cold equivalent of the Finnish cohorts. Anyone presenting a weekly cold target as evidence-based is extrapolating.

What exists is narrower and worth knowing precisely.

Beginner’s 4 minutes comes from a randomised trial of cold showering. Participants took 30, 60 or 90 seconds of cold at the end of their daily shower for 30 days. Sickness absence fell 29% in that group, and 79% of them kept the habit up afterwards. Thirty to ninety seconds a day lands around 4 to 10 minutes a week.

Intermediate’s 11 minutes is a description of what a particular group of people do. Eight experienced Danish winter swimmers reported roughly 11 minutes of cold water and 57 minutes of sauna a week, in water of about 1 to 9 °C, across two or three visits. That study measured brown fat and cold-induced thermogenesis in young healthy men; it is a description of a routine, not a tested dose, and eight people is eight people.

Advanced’s 20 minutes has no single study behind it. It is the top of the range the app offers, and it is still under a minute a day averaged out.

Separately, the habituation literature gives a shape rather than a total: the cold shock response settles after about four to six short immersions and stays settled for months. That is about frequency early on rather than minutes per week.

Why the presets are called starting points

The app’s own wording is starting points, not prescriptions, and the reason is in the limits paragraph of the metric.

The sauna studies are observational. They asked about habits once, at the start, in mostly middle-aged Finnish men using traditional saunas at about 79 °C. They show association rather than a dose that causes benefit — people who use a sauna four times a week may differ from people who use one once a week in a dozen ways nobody measured. The authors themselves caution against applying the results to steam rooms, infrared or cooler saunas.

And the heat total treats an 80 °C sauna minute and a 40 °C bath minute as equal, because nobody has run the trial that would let anyone convert between them.

The risk side, stated plainly

Cold water is riskiest in the first minute, when the gasp reflex peaks. Very cold water can make it hard to move within about ten minutes, and your body temperature keeps falling for a while after you get out. A weekly minutes target says nothing about how those minutes should be distributed, and twenty minutes in one go is a different proposition from four five-minute dips.

Sauna is well tolerated by most healthy adults. Unstable angina, a recent heart attack and severe aortic stenosis are reasons to avoid it, and alcohol raises the risk of low blood pressure and arrhythmia.

What the rings actually do

They fill. They do not congratulate, there is no streak, nothing turns green, and no notification asks where you have been.

The 12-week chart under them is the more useful view, because a weekly total is noisy and a quarter of them is a habit. It splits each week into sauna, bath, hot shower, plunge and cold shower, with your goal drawn as a reference line, so a week that missed the target because you travelled looks different from a month of drift.