What your heart rate does when you \"totonou\": the Japanese sauna high, on a chart

In Japanese sauna culture, ととのう (totonou) describes a pleasant, settled feeling that some people notice while resting after heat and cooling. Experiences vary: some describe lightness or calm, while others feel nothing distinct at all. It is a subjective expression, not a medical state with a diagnostic heart-rate pattern.

When you totonou, your heart rate has usually done three things: climbed steadily in the sauna, dropped sharply in the cold water, and then kept sliding through the rest until it sits at or below where it started the session. The last part is a parasympathetic rebound, and it is the one piece of the picture that has actually been measured: in a Finnish study, heart rate was below its pre-sauna value after 30 minutes of recovery, and a Japanese field study found that heart rate variability during the rest tracked how "ととのった" people said they felt. The chart shows the setup for the feeling, not the feeling itself.

It also has a shape, and once you have seen it on a chart you can tell a real one from a near miss.

What happens to your heart rate when you totonou?

The climb. In the sauna, heart rate rises steadily from resting to somewhere between 100 and 150 bpm. The skin vessels open to dump heat, blood pressure would fall, and the heart speeds up to hold it. The sympathetic nervous system, the fight-or-flight side, is running the show. A ladle of löyly shows as a small bump. Leaving at the alert, about 75% of heart rate reserve, shows as a clean peak.

The cliff. In the cold bath, heart rate drops off the peak in seconds. There is often a brief spike right at entry from the cold shock response, the gasp and racing heart of the first seconds in cold water, and then a steep fall as the skin vessels clamp shut. In our own session charts the fall is typically 30 to 50 bpm inside a minute, and a 1975 Japanese study described the same sharp drop on cold immersion, sometimes to below resting. Cold water also raises noradrenaline sharply (in one hour-long immersion study it rose more than fivefold while adrenaline did not change), and it does not clear for a while.

The dip. In the rest, the line keeps falling, more slowly, and at some point it can cross below the rate you started the session at. This is the parasympathetic rebound: the rest-and-digest side of the nervous system takes over hard, the heart slows past baseline, breathing deepens, the skin reopens and the warmth comes back. But the noradrenaline from the plunge is still circulating. Deeply relaxed and chemically alert at the same time. That overlap is the feeling.

A dip may appear on some charts, but it does not prove that you did or did not totonou. How you feel and whether you are free of warning symptoms matter more than the shape of the line.

What the research says

The mechanism above is the standard physiological account, and the heart rate part of it has been measured. In a 2019 Finnish study of a single sauna session with a 30 minute recovery, participants' heart rate ended below their pre-sauna value, 68 bpm against 77 before, and heart rate variability had returned to baseline or above, which is the signature of parasympathetic dominance. The rebound is real and it is measurable on a wrist.

The Japanese side has a small field study of its own. A 2023 symposium paper put wrist heart rate sensors on 42 regular sauna-goers through sauna, cold bath, and 外気浴: the vagal HRV index rMSSD fell in the sauna, rose during the rest, and correlated with how strongly people rated their ととのい. Cold water does its part too: after exercise, a few minutes in 14°C water brought vagal HRV indexes back toward baseline faster than passive rest, and a 2025 systematic review found parasympathetic reactivation after cold immersion in every study it included.

What is not well measured is the rest of the popular explanation. Japanese sauna writing usually credits β-endorphin and the "coexistence" of adrenaline with parasympathetic activity. The noradrenaline part is well documented from cold water immersion. The endorphin part is plausible and mostly unmeasured. Treat it as a good story rather than a finding. The chart does not need it: the climb, the cliff, and the dip are enough to explain why the state arrives when it does and why it goes away if you skip a step.

The shape of a real one

On a Furolog session chart a full ととのい looks like this:

• A climb of several minutes ending near the alert line.
• A cliff on entering the cold water, with or without a spike at the top.
• A continued slide through the rest that crosses below your resting rate at some point and holds there. In our own sessions that often happens within the first ten minutes; in the Finnish study above, the group average was below its starting rate by the end of a 30 minute recovery.

The moment the line crosses below resting is the moment people report the floating feeling. It is not a coincidence. Furolog looks at the depth and timing of this rebound when it classifies the session into one of its five recovery patterns, and the pattern is a decent proxy for whether the session produced the feeling or not.

The shape of a near miss

A chart may show a rise in the sauna followed by a fall during cooling and rest. If the rate stays elevated, possible influences include heat exposure, hydration, alcohol, movement, stress, and sensor error. A chart cannot identify the cause by itself. Why can't I totonou offers practical factors to review without treating them as a diagnosis.

Without a cold bath, heart rate may fall more gradually. That is not a failed session: cold immersion is optional, and a cool shower or ordinary rest may be more comfortable for many people.

How to get the dip more often

• Leave the sauna at the alert, not at the timer. A peak that is too high makes for a slower slide. How many minutes in the sauna.
• Cold bath for about a minute, until the pounding settles. Longer weakens the rebound. Cold plunge: how long.
• Rest for the full ten minutes, lying down if you can. The dip does not arrive at minute two. How long to rest.
• Water between rounds. Dehydration keeps the heart rate up and flattens the dip.
• The second round is often the one. The first round is a warm-up; the second starts from a warm core and produces a bigger swing.
• Not every session. Tired, hungover, or coming down with something, the rebound is blunted. The chart will show it and the honest answer is to go home early.

The whole cycle

ととのう is the reason the cycle has the order it has. Heat first, then cold, then rest, each setting up the next. A first session, in order, is in the beginner's guide.

Read next: Why can't I totonou · Sauna heart rate: what is normal · How long to rest after the sauna

Sources

• Laukkanen JA, Laukkanen T, Kunutsor SK. "Cardiovascular and other health benefits of sauna bathing: a review of the evidence." Mayo Clin Proc. 2018;93(8):1111-1121. https://doi.org/10.1016/j.mayocp.2018.04.008
• Karvonen MJ, Kentala E, Mustala O. "The effects of training on heart rate: a longitudinal study." Ann Med Exp Biol Fenn. 1957;35(3):307-315. https://pubmed.ncbi.nlm.nih.gov/13470504/
• Tipton MJ. "The initial responses to cold-water immersion in man." Clin Sci (Lond). 1989;77(6):581-588. https://doi.org/10.1042/cs0770581
• Mizuta T, et al. "Physiological effect on the body in the sauna bath." Jpn J Phys Fitness Sports Med. 1975;24(3):101-107. https://doi.org/10.7600/jspfsm1949.24.101
• Šrámek P, et al. "Human physiological responses to immersion into water of different temperatures." Eur J Appl Physiol. 2000;81(5):436-442. https://doi.org/10.1007/s004210050065
• Laukkanen T, et al. "Recovery from sauna bathing favorably modulates cardiac autonomic nervous system." Complement Ther Med. 2019;45:190-197. https://doi.org/10.1016/j.ctim.2019.06.011
• Kawahara Y, Ishigami R. "Effects of sauna on heart rate variability (Part 1)" (in Japanese). Proc 47th Symposium on Human-Environment System. 2023;47:93-96. https://doi.org/10.24538/jhesp.47.0_93
• Buchheit M, Peiffer JJ, Abbiss CR, Laursen PB. "Effect of cold water immersion on postexercise parasympathetic reactivation." Am J Physiol Heart Circ Physiol. 2009;296(2):H421-H427. https://doi.org/10.1152/ajpheart.01017.2008
• Galvez-Rodriguez C, et al. "Cold water immersion, heart rate variability and post-exercise recovery: a systematic review." Physiother Res Int. 2025;30(2):e70033. https://doi.org/10.1002/pri.70033

Quick answer

• ととのう is the calm, alert, floating state a few minutes into the rest after sauna and cold water.
• On a chart: heat, cooling, and rest can produce a rise-and-fall pattern, but no curve proves the feeling.
• Why: parasympathetic rebound after a sympathetic push, with noradrenaline from the cold shock still circulating.
• Near miss: a slide that stalls above resting. Usually too long in the heat, too short a rest, or dehydration.