Let's Get Hot

Heat exposure for health and performance

Photo by Max Vakhtbovycn

Most people taking notice of the health and/or performance spaces would agree that heat is having a moment. Sure ice baths are cool (yup I went there), but heat is where the real benefit lies.

In reading the literature on performance and heat, you’ll likely come across references to upcoming championships being hot (Olympics in Rio, Tokyo or Paris, Football/Soccer World Cup Qatar, Track & Field World Championships in Doha or Rugby World Cup in French Summer including in the South) which poses obvious challenges to health and performance for athletes as well as staff and spectators. In fact I even came across some advice from coaches for crews of events like Western States or Badwater 135 to do some heat training to be prepared and safe whilst crewing.

*A quick safety message; DO NOT DO STUPID THINGS with saunas and risk your health. They can be dangerous - there have been cases of sudden cardiac death associated with sauna. Work with professionals. *

Sauna use for Health Benefits

As is the case with many cultural traditions, the scientific community continues uncover the benefits of the Finnish Sauna. Of course, advocates can be a little overly optimistic at times about the breadth of some of these benefits, with research either yet to catch up or perhaps not supportive of them all. That said, there is solid evidence for improved cardiovascular health, specifically reduced blood pressure, improved cholesterol measures and reduced cardiovascular disease. There is some, much weaker, evidence for sauna’s role for some other ailments like arthritis.

All of this makes sense with the context that heat (and it’s mechanisms of action) are effectively an exercise mimetic (maybe this is the exercise pill everyone has been looking for?).

From Patrick & Johnson

With this knowledge, there should be no surprises as to the diseases that heat can improve. Similarly it is unsurprising that sauna use reduces all cause mortality ie improves longevity.

How Much and How Hot?

This may be the deal breaker for many. The dose is not small as you can see below in the diagrams. Unlike exercise, there seems to be certain thresholds that need to be exceeded to really see improvements. This likely relates to the fact that the cardiovascular system (and physiology in general) is progressively challenged but the rising core temperature unlike exercise where there are other sources of stress (more on this later).

From Henderson et al

From a temperature perspective, these things are HOT. Traditional Finnish saunas and their protocols generally involve short exposures (5−20 minutes) at temperatures of 80°C–100°C (176°F-212°F) with dry air (relative humidity of 10% to 20%). We will discuss some other variants and tradeoffs later.
In terms of how many weeks, some of the blood pressure benefits are quoted as being seen after 8 weeks of regular use.

Interestingly, and somewhat surprisingly, there is research about a multimodal approach including sauna - usually this would be left to inference. That is, there is research on sauna in combination with other lifestyle interventions. Of note, there is a clear impact of augmenting the benefits of sauna when combined with exercise (not necessarily simultaneously - settle down there David Goggins you don’t need to do burpees in the sauna).

For the record; On average, a typical Fin has a sauna at least once a week with the average habitual frequency being 2-3 sessions/week.

Sauna Types

We have already discussed traditional Finnish saunas and what that sort of protocol would look like. In doing this we also mentioned cardiovascular stress being a key variable in dosing, which is to say that, saunas of differing temperatures may need a longer dose to have the same effect (it’s an area under the curve problem for heat stress in essence).

This should liberate you to go forth in search of ‘heat gains’ elsewhere, be it in other saunas or even in really hot baths (these need to be hotter than body temperature, usually quoted as needing to be 40°C/104°F- so they’re unpleasantly warm to say the least).

A note on infrared saunas, there is is very little research on these. Experientially, I would suggest that the thermal load from these in comparison to other saunas is quite low. So any benefits from a cardiovascular standpoint, if available, likely need a large duration. This is not to say there are no benefits and I do love using them - it’s just likely that they aren’t ‘hot’ enough for many of the sauna benefits (just like you can’t boil an egg with lukewarm water).

Heat Training and Sauna for Performance

The first thing I would note here is that ‘performance’ is a broad term to say the least. Similarly, the temptation (and I will yield to this for ease) is to split performance into a strength/power type of realm and an endurance type realm. This does no favours to hybrid types of performance such as Crossfit or Hyrox. That said, the easiest way to consider where a useful line in the sand is for these hybrid events may be via duration. Arbitrarily, the 10-15 mins timeframe probably encompasses the line between where we can group events within these hybrid types of performance (so obviously Hyrox falls on the endurance side where as something like the “Fran” Crossfit workout falls on the strength/power side).

Strength and Power

Anecdotally and having talked to many athletes in the space, many agree that moderate to warm temperatures (intentionally subjective here) probably help strength and power activities. There is some evidence to this effect too, but it is far from conclusive. Similarly there seems to be some evidence in the opposite direction, that is, performance of these types of activities is impaired when feeling cold.

Similarly, there is some thought that warmer temperatures positively impact hypertrophy, though this is quite speculative.

There may also be a role for sauna in some of these strength and power athletes who are allergic to any form of endurance work (I’ve legitimately met some who consider reps of 5 ‘cardio’). These athletes often see benefits of improved cardiovascular fitness when it comes to work capacity and recovery (between sets and between days) but given their allergy to endurance work, the sauna may provide some of this stimulus without the need for extra training.

Endurance

Few, if any, readers would be surprised to hear that heat is detrimental to endurance performance (for the record the quantification of this decrement is 6%–16% or 0.3% to 0.4% for every 1 °C WBGT outside of 7.5–15 °C). Similarly, most would intuitively understand that preparing for the heat would help limit some of this performance impairment.
However, the real interest is in the mechanisms of improvement as a result of some heat adaptation. There’s an old adage in the endurance world:

Heat is the poor man’s altitude

and ironically, as happens from time to time, this has been largely proven to be true. There is an unsurprising fascination with heat training given the aforementioned hot championships. As such the impact of both heat on performance and ways to prepare for it have been extensively investigated. The upshot; many of the same sorts of adaptations you see from altitude. These include; increased haemoglobin mass (total haemoglobin, NOT concentration as is commonly measured - haemoglobin is what carries oxygen in the blood for the record) and increased plasma volume (more blood). Adapting to the heat will also cause a range of changes to sweating including an increased rate, sweating earlier and a change in the electrolyte concentration in the sweat.

One of the most interesting things to come from all this literature (and maybe not surprising given the adaptation) is that heat training can improve performance in the cold too!

From Esh et al

How Should Athletes Acclimatise to the Heat

This stuff can get quite complicated, and swiftly. I’ll do my best to keep this high level, and brief (the literature really breaks up the nuances nicely so scope out the reference list if you’re interested). Training in the conditions you will race in makes the most sense and is simplest (though you sacrifice some speed training in the heat). This is known as ‘acclimatisation’ but isn’t realistic for many who aren’t racing their local races.
The next set of possible interventions all hinge on getting core temperature up and keeping it there, which can be done via active (training), passive or mixed methodologies (known as ‘acclimation’ for the record).
Training, of course, raises core temp which can be a great way to kickstart things for athletes; they’re training anyway so why not use this then hop into some heat afterwards (sauna or hot bath). Those living in climates not conducive to raising core temperature much (or quickly) often use methods of ‘overdressing’ - this is as bad as it sounds, one paper’s overdressing setup included “wearing clothing that limited heat loss, consisting of a wool layer on both the upper and lower body, a wool hat, nylon rain jacket, down jacket and nylon pants with poor evaporative capacity.”

So in essence, get warm, keep the core temp up and adapt. Do it using a mix of the climate and excessive clothing. You can augment this (to prevent impacting training too much) by doing some passive heat afterwards, or indeed do only passive heat if this is your fancy.
Given the smorgasbord of options, and brevity, I won’t detail specifics but the reference section is your friend here. Most protocols last at least 10 days, though significant adaptation occurs in the first 5 days or so.

A quick note, the quoted decay rate of these adaptations is about 2.5%/day, so top up work is needed roughly every second or third day.

Take Home Messages

Firstly, it would be remiss of me not to remind readers to focus first and foremost on the big rocks. The best thing to be able to cope with the heat (and for health) is to be fit.

Secondly, don’t overcomplicate things, there’s lots of flexibility and freedom in protocols meaning they can be adapted to your situation and needs. A mix of active and passive methods is completely fine (and maybe better, who knows). This applies to both health and performance, daily saunas of 60mins may not be possible, but perhaps finishing your cardio for the day and then doing 30mins in the sauna is feasible on some days.

Thirdly, stack behaviours to augment them, your performance or health improvement will be greater if you are ticking all the boxes, not just doing some sauna (so get your training/exercise, nutrition, sleep etc in order too). That said, on days where training is just too much maybe some extended sauna helps ticking a few boxes.

References

1. Esh, C.J., Carter, S., Galan-Lopez, N. et al. A Review of Elite Athlete Evidence-Based Knowledge and Preparation for Competing in the Heat. J. of SCI. IN SPORT AND EXERCISE (2024). https://doi.org/10.1007/s42978-024-00283-y

2. Laukkanen JA, Laukkanen T, Kunutsor SK. Cardiovascular and Other Health Benefits of Sauna Bathing: A Review of the Evidence. Mayo Clin Proc. 2018 Aug;93(8):1111-1121. doi: 10.1016/j.mayocp.2018.04.008. PMID: 30077204.

3. Patrick RP, Johnson TL. Sauna use as a lifestyle practice to extend healthspan. Exp Gerontol. 2021 Oct 15;154:111509. doi: 10.1016/j.exger.2021.111509. Epub 2021 Aug 5. PMID: 34363927.

4. Kunutsor SK, Laukkanen JA. Does the Combination of Finnish Sauna Bathing and Other Lifestyle Factors Confer Additional Health Benefits? A Review of the Evidence. Mayo Clin Proc. 2023 Jun;98(6):915-926. doi: 10.1016/j.mayocp.2023.01.008. PMID: 37270272.

5. Henderson KN, Killen LG, O'Neal EK, Waldman HS. The Cardiometabolic Health Benefits of Sauna Exposure in Individuals with High-Stress Occupations. A Mechanistic Review. Int J Environ Res Public Health. 2021 Jan 27;18(3):1105. doi: 10.3390/ijerph18031105. PMID: 33513711; PMCID: PMC7908414.

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16. Casadio, Julia R.; Kilding, Andrew E.; Cotter, James D.; Laursen, Paul B. (2016). From Lab to Real World: Heat Acclimation Considerations for Elite Athletes. Sports Medicine, doi:10.1007/s40279-016-0668-9

17. Sawka MN, Leon LR, Montain SJ, Sonna LA. Integrated physiological mechanisms of exercise performance, adaptation, and maladaptation to heat stress. Compr Physiol. 2011 Oct;1(4):1883-928. doi: 10.1002/cphy.c100082. PMID: 23733692.

18. Racinais, S., Alonso, JM., Coutts, A.J. et al. Consensus Recommendations on Training and Competing in the Heat. Sports Med 45, 925–938 (2015). https://doi.org/10.1007/s40279-015-0343-6

19. Ely, Brett R.; Blanchard, Laurie A.; Steele, Jared R.; Francisco, Michael A.; Cheuvront, Samuel N.; Minson, Christopher T. (2018). Physiological Responses to Overdressing and Exercise-Heat Stress in Trained Runners. Medicine & Science in Sports & Exercise, (), 1–. doi:10.1249/MSS.0000000000001550 

20. Rønnestad, Bent & Urianstad, Tomas & Hamarsland, Håvard & Hansen, Joar & Nygaard, Håvard & Ellefsen, Stian & Hammarström, Daniel & Lundby, Carsten. (2022). Heat Training Efficiently Increases and Maintains Hemoglobin Mass and Temperate Endurance Performance in Elite Cyclists. Medicine & Science in Sports & Exercise. Publish Ahead of Print. 10.1249/MSS.0000000000002928. 

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