What's the cause of the higher HR?
Is it the body requiring higher circulation to maintain temperature of core?
Is it slower recovery after run due to stress of sauna?

If the raised HR is not driven by oxygen demand, or lactic clearing demand from muscles, but rather temperature management of organs, I'm not sure how that would benefit your fitness. But I'm not up to speed on current sauna use theory.
Unless you were already doing high volumes of training I would think the sauna time would be much better spent running, cycling or swimming, if the main aim is to improve fitness. It may also be useful to define what's meant by fitness in this context! Heat acclimation could be considered fitness but will only be relevant for some races.

In for more hacks.

I am fairly certain it is heat that simulates exercise

Fitness is a higher vo2 max for me.

I just wonder if you could use sauna time as part of your training. I could barely walk after today, but got 20 mins additional higher heart rate.

Why not. If the main point is a higher heart rate. Then an extra 1 hour a week is an extra one hour for free

I thought the base stuff dealt with the "volume" aspect and the hard VO2 stuff dealt with the "how hard it expels" aspect of heart function.

Given we're on the volume end for Z2, I wonder if the muscle still has to work against some kind of resistance in the body at the higher rate in a sauna (or on a bike/run/swim) in Z2 to cause the change.

Just my random thoughts.

The main point is not higher heart rate. Get on your bike.

Commenting from the country that invented the sauna :-)

In Finland it's common to use the Sauna as part of recovery from endurance sport, mainly as one ingredient in a combination of cold/hot treatments that increase muscle relaxation and enhance metabolism. Sauna twice a week is what is recommended in local endurance sport related studies (i.e. Pehkonen S., 2007). If you like it that is.

You should however take into account the skin softening effect of the sauna, as well as the dehydration risk. Skin softening can backlash in the form of chafed feet etc.

That being said, I've never heard of raising fitness through sauna, just as a means for recovery.

Exercise physiology is more complex than simply a higher heart rate, unfortunately. Otherwise our friends in Finland would have been crushing everything for the last 100 years.

Correlation is not causation. Heart rate is a secondary metric that correlates to fitness but is not fitness in itself. There are many reasons why heart rate can be elevated. You might be dehydrated, or nervous, or in a hot room, or working in Z2. The fact that your heart rate is in a particular "zone" doesn't mean you are gaining fitness. It just means your heart rate is in that zone and nothing more. If it's in Z2 because you are running, then you are gaining fitness. If it's in Z2 because you are in a sauna the only thing it means is that you are sweating. You can't hack your way to fitness and HR is a notoriously misleading measurement.

You certainly aren't gaining fitness watching a horror movie while sitting on your butt, even though your HR might be a bit elevated during the scary scenes.

This is where you have gone off the rails. The point is NOT a higher heart rate. The point is to train. Your heart rate can correlate to training, but it is not training in and of itself. Get on your bike.

If the main point was higher heart rate
What about high caffeine intake

Right... Caffeine, scary movies, life stress, bad news, dehydration, overtraining, fatigue, being hot, anticipation, nervousness, all can cause a higher heart rate. None of those things is "training"

1)Not free, its time you could spend actually training. 2) If High HR makes you fitter then maybe you should eat Krispy Kreme for every meal and occlude your arteries, you will be at 100+ just breathing. Those cardiac patients are so fit! Nah, screw that just start doing some bumps of meth on the regular, you will be sub 5 in no time with that fitness!

Sauna has some benefits to your endurance system overall but not even close to efficient use of your training time when you are struggling to crack 20kmh on the bike.

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I have heard there may be some performance gain, though increased blood plasma. To help cooling blood is pumped to the skin so with regular use the body may produce extra blood plasma to aid this.

Increasing blood blood flow may aid recovery as might the activation of heat shock proteins on muscle repair. Otherwise there may be some help in dealing with hot conditions though improved sweat rates etc.

A lot of mights? ;)
And will increased blood plasma increase ability to use the oxygen your blood transports?

Ha ha, no Idea but according to this study "probably" ;) https://www.ncbi.nlm.nih.gov/...om=/25432420/related

As I understand it, one of the primary purposes of low intensity training is to increase mitochondria density. That's stimulated by muscles providing a demand for energy. To produce energy for the muscles aerobically, you need oxygen. That comes from your lungs via your blood to your muscles. Higher demand = higher heart rate. Increased heart rate during exercise is a result of muscle demand for energy. Increase in mitochondrial density is also stimulated as a result of muscle demand for energy. Heart rate does not stimulate mitochondrial growth. Heart rate raises for many reasons as myself and others have already mentioned (heat, cold, stress, drugs, etc...) and it is not in itself "training".

I'm by no means an expert. I think the above is a reasonably accurate simplified overview, but please don't hesitate to correct me if I've gone astray!

ETA:
I meant to also mention capillary density and then forgot. In addition to increasing mitochondrial density, I think aerobic base training is also intended to increase capillary density and function, which IMO is again unlikely to be stimulated by simply elevating your HR via sauna. Although I imagine it's more feasible that capillaries could be effected than mitochondria, perhaps they're also stimulated by need for cooling and recovery as well as oxygen delivery. As before, I'm more than happy to be corrected!

10 min in the sauna didn't do much to my HR after swimming. It was about 120°F in the sauna.

Edit: temps are 140-150 degrees F

I just happened to be wearing my watch and turned it on for kicks. This is where I started at 10 min. I've moved to 20 min but haven't recorded the session since these two. Maybe I'll start again.

https://connect.garmin.com/.../activity/3625003499

https://connect.garmin.com/.../activity/3606138182

Yes increased mitochondria density is a great subject by itself.

Cardio vascular performance I was under the impression is based on
I) how many beats your heart does
II) the amount of blood it pumps per beat
III) the power of the heart can contract

This means more blood being pumped in times of training and thus more oxygen being pumped around the body. However, during the endurance cycle it's fuel + oxygen to create ATP via the mitochondria and more of them would help!

Just to confirm VO2 max is the maximum oxygen consumption. So.. in theory we are talking the same thing. AS more mitro is more oxygen and a stronger cardio vascular performance is more oxygen


so E.G HIIT increases mitro and not cardio performance (https://www.ncbi.nlm.nih.gov/pubmed/20473222)

SO... my theory is that medium heart rates of 65-80% would mean your body adjusts to the situation and creates higher cardio performance... which is the point of zone 2 training... which could lead to more optimised fat burning and a "fitter" heart.

I'll go research

If that involves cycling to the library, great. If not then see posts above. Go and ride your bike and stop trying to skive.

(Said in supportive uncle voice looking over top of specs in a faux wise old man manner.)

Yes Uncle Duncan, my legs are killing me. Haha I dont know how I am meant to increase past 10 hours a week.... but this was just a thought :-p

https://www.foundmyfitness.com/...thermic-conditioning

not crazy. Shall include sauna in my hours

Rhonda Patrick is the queen of being unable to contextualize basic sciences principles. She takes primary studies and extrapolates endpoints that simply aren't there in actual human subjects in the specific area she is talking about. "Sauna increases norepinephrine. Norepinephrine increases focus and clarity." The implication being that sauna will now increase focus and clarity. EXCEPT that it's short lived and has no actual impact other than the few minutes it's elevated. She is maddening to listen to, because she's obviously intelligent and obviously has no idea what she's talking about a lot of the time.

Include sauna all you want. I jump in at the end of most of my workouts because it feels good. But it doesn't replace anything, and there is no objective evidence that it will improve your endurance. Your heart rate theory is ridiculous as has been explained already.

Get on your bike.