The sauna after training
The sauna after training is a familiar ritual in many gyms and sports clubs. Some consider it the main means of recovery, others an unnecessary strain on the heart. The editorial team looked at what really happens in the body in the steam room, which effects are confirmed by studies, and how to combine the sauna with training safely.
What happens in the body in the sauna
The classic Finnish sauna is dry air with a temperature of about 70–100 °C and low humidity. Skin temperature rises within a few minutes to 40 °C and higher, and body temperature by 1–2 degrees depending on the length of the session. The body reacts in the same way as to heat during exercise: it dilates the skin vessels and increases sweating.
To deliver more blood to the skin, the heart works faster. The heart rate in the sauna often rises to values corresponding to a light or moderate physical load. Cardiac output increases and peripheral vascular resistance decreases, so blood pressure in healthy people usually changes moderately.
Sweating during one session can reach several hundred millilitres, and in people adapted to heat — even more. Together with sweat, sodium and other electrolytes are lost. That is exactly why the weight ‘dropped’ in the sauna is water, not fat, and it returns after drinking.
In parallel, the sympathetic nervous system is activated, the level of noradrenaline rises, and heat shock proteins are synthesised in the tissues — molecules that protect other proteins from damage. The latter are often mentioned in the context of recovery, but their practical contribution in humans has so far been little studied.
The infrared sauna works differently: it heats the body with radiation at a lower air temperature (about 45–60 °C). Subjectively it is tolerated more easily, but most studies on the effect on health have been carried out precisely with the traditional Finnish sauna.
The sauna and endurance: heat adaptation
The most convincing sporting data concern not recovery but heat adaptation. In the study by Scoon and co-authors (2007), runners visited the sauna for about 30 minutes after training over three weeks. As a result, time to exhaustion in running increased by about a third, and blood plasma volume by about 7%.
The mechanism is explained as follows: regular heat stress stimulates an increase in plasma volume, which eases the work of the heart and thermoregulation during exercise. This is part of the classic adaptation to heat, which also includes earlier and more profuse sweating and a lower heart rate at the same workload.
The study was small (six athletes), so the exact figures should not be transferred to everyone. However, the very idea of ‘passive heat adaptation’ later entered the practice of preparing for competitions in the heat. For athletes preparing for events in a hot climate, a regular sauna after training can be an accessible alternative to a heat chamber.
For strength sports there is no similar evidence: hypertrophy and maximal strength do not increase from the sauna. Here the sauna can be a means of relaxation rather than a tool for improving results.
Does the sauna speed up muscle recovery
The popular notion that the sauna ‘flushes out lactic acid’ and removes muscle pain has no scientific basis. Lactate after exercise is utilised by the body within about an hour regardless of the sauna, and delayed-onset muscle soreness is not connected with lactate at all.
There are few studies specifically on the sauna as a means of recovery after training, and their results are ambiguous. Heat subjectively relaxes, reduces the feeling of stiffness and can improve well-being. However, there is no convincing evidence of accelerated recovery of strength or reduced muscle damage.
Moreover, the sauna is an additional stress. Immediately after intense training the body is already dehydrated and overheated, and the sauna intensifies both processes. For athletes who train twice a day or have a further load the same day, this can worsen the quality of the next session.
| Claim | What the data say |
|---|---|
| ‘The sauna flushes out lactic acid’ | No: lactate is utilised on its own and is not connected with muscle soreness |
| ‘The sauna burns fat’ | No: water is lost, which returns after drinking |
| ‘The sauna removes toxins with sweat’ | The contribution of sweat to the elimination of substances is negligible compared with the kidneys and liver |
| ‘The sauna improves endurance’ | Possibly, through heat adaptation; the data are limited |
| ‘The sauna is good for the heart’ | There are observational associations, but not proof of causation |
The observational data from Finland are interesting. In the cohort of Laukkanen and co-authors (2015), men who visited the sauna 4–7 times a week had a lower risk of death from cardiovascular disease than those who visited it once a week. However, this is an association: more frequent sauna-goers may differ in lifestyle, means and health.
Risks and contraindications
For a healthy person the sauna is generally safe if simple rules are followed. The reviews of Hannuksela and Ellahham (2001) and Hussain and Cohen (2018) note that most accidents in the sauna are associated with alcohol, an excessive length of session or existing heart disease.
The main risk after training is dehydration and overheating. A person who has lost 1–2 kg of sweat in the gym and then goes into the steam room without replenishing fluid may face dizziness, a drop in blood pressure, fainting. Especially dangerous is a sharp rise and transition to a vertical position after prolonged sitting in the heat.
A separate risk group is athletes who use the sauna to ‘cut’ weight before a weigh-in. Rapid loss of a few per cent of body weight through dehydration impairs performance and, combined with other methods, can be life-threatening.
- Unstable angina, a recent heart attack, severe aortic stenosis — the sauna is contraindicated.
- Uncontrolled hypertension, arrhythmias, heart failure — only after consulting a cardiologist.
- An acute infection, fever, an exacerbation of chronic diseases — abstain.
- Pregnancy — a decision together with a doctor.
- Taking drugs that affect blood pressure or thermoregulation — consult a doctor.
Alcohol and the sauna are incompatible. Alcohol disrupts thermoregulation, increases dehydration, lowers blood pressure and raises the risk of arrhythmias and injuries. Most fatal cases in saunas described in the Finnish literature are associated precisely with alcohol.
How to use the sauna after training
First — cooling down. After training it is worth giving the body 10–20 minutes to return to normal: drink water, take a cool shower, rest a little. Going into the sauna straight away with a heated and sweaty body is not the best idea.
The duration of a single session for most people is 10–15 minutes, and the total duration up to 20–30 minutes with breaks. Be guided by how you feel: dizziness, nausea, strong palpitations, a headache are a signal to leave immediately.
Replenish fluids. As a guide you can weigh yourself before and after the sauna: each kilogram lost corresponds to about a litre of fluid. The ACSM hydration recommendations advise gradually making up the lost fluid with a reserve after exercise, adding sodium from food or drinks.
Plan the sauna taking the training schedule into account. After the last training session of the day, on a rest day or in the evening before bed it is more appropriate than between two sessions. Some people note that an evening sauna helps them fall asleep, but for others too late a session, on the contrary, is stimulating.
Editorial conclusions
The sauna causes a reaction in the body similar to a light physical load: the pulse quickens, sweating increases, the skin vessels dilate.
A regular sauna can promote heat adaptation and probably endurance, but there is no convincing evidence of accelerated muscle recovery. The myths about ‘flushing out lactic acid’ and ‘burning fat’ are not confirmed.
Safe use means cooling down before the sauna, a moderate duration, replenishing fluids, avoiding alcohol and taking contraindications into account.
We also advise reading our materials on cold procedures and ice baths, on massage for recovery and on an athlete’s drinking regimen.
References
- Scoon GSM, Hopkins WG, Mayhew S, Cotter JD. Effect of post-exercise sauna bathing on the endurance performance of competitive male runners. J Sci Med Sport. 2007;10(4):259–262.
- Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Intern Med. 2015;175(4):542–548.
- Hannuksela ML, Ellahham S. Benefits and risks of sauna bathing. Am J Med. 2001;110(2):118–126.
- Hussain J, Cohen M. Clinical effects of regular dry sauna bathing: a systematic review. Evid Based Complement Alternat Med. 2018;2018:1857413.
- Kukkonen-Harjula K, Kauppinen K. Health effects and risks of sauna bathing. Int J Circumpolar Health. 2006;65(3):195–205.
- American College of Sports Medicine; Sawka MN, Burke LM, Eichner ER, et al. American College of Sports Medicine position stand. Exercise and fluid replacement. Med Sci Sports Exerc. 2007;39(2):377–390.
Andriy Melnyk
A strength-sports coach and author of programs for beginner and intermediate levels. Writes about training planning.
