Home heat stress training and cold shower experiment and review of the

Relax Sauna

Conclusion

I would recommend sauna training and this sauna unit in particular to anyone (especially paired with cold showers). It seems to have such wide ranging benefits similar to and is a great addition to the commonly recommended 'core' practices like diet, exercise, sleep, meditation.I think this is pretty exciting as this is a really practical way to do hyperthermic training at home as often as you want even if you live in a small apartment.
The Relax Sauna is probably the best and only realistic option to do hyperthermic heat stress training at home that can replicate (or actually exceed based on my results) the benefits found in studies due to its cheaper competitors being underpowered. Do not waste your time with sub $500 units on Amazon. I have my doubts about Therasage unless someone can provide the same measures I have here. The Sunlighten Solo has a good temperature study showing legitimate heat stress but is weaker, much more expensive, and you have to lie down.
Tracking your temperature in relation to time and heart rate is an easy and effective way to quantify the heat stress dosage and your body's adaptation over time and good for overall safety. If you are healthy some good starting points are 100-101F, 70% HR max, and/or 25 minutes but always listen to your body over biometrics and build slowly.
Tired spells and food comas seem to have been almost banished for me in one week. Cold shower compliance increased greatly after sauna. Sleep and acne greatly improved.

Background

I made a post here giving my thoughts on a more systematic way to evaluate saunas for home use and quantify heat stress training and citing some existing research comparing dry, wet, and infrared saunas. I also noted the sub $300 portable IR sauna I bought on Amazon was a dismal failure and had a new higher end one on the way.

The new one arrived and I followed my own advice and measured both external factors (time, internal air temp) and internal (core body temp, heart rate, weight loss) and will provide these in addition to my results for the cheap sauna to show the difference in training effect. As a bonus I followed up with a cold shower and continued taking measurements.

"Idealsauna" from Amazon

This sauna got pretty decent reviews but I believe mainly because it feels good but does not achieve the heat stress stimulus we are after to reproduce the benefits in the clinical studies on saunas. Subjectively it took a long time to heat up and I only had some moderate forehead sweat around 40 minutes in. The subjective weakness is what prompted me to get out my measuring tools.

First, I used an instant read thermometer hung from the arm hole to measure the internal air temperature. This turned out to be a paltry ~103F, a hot day in my city. Since this is IR, however, I couldn't exclude the chance that the air temperature was low because the IR was depositing the heat directly into my body, a common claim amongst IR sauna makers that I think is somewhat BS to cover for under powered IR panels. To test this I put on my heart monitor (HR increases with heat stress) and a simple under the tongue thermometer. My body temperature never got above 98.1 (I run a little cold). Body temp alone is not a definitive metric either because I could simply be gifted in my body heat regulation abilities. But combined with my HR graph below you can see this sauna provided almost no significant heat stress on me.

Heart Rate Graph

This was the highest rated of the cheap Amazon saunas. Based on this I can pretty confidently say these have zero heat stress training value.

Relax Sauna

After my intense disappointment I started to research the more expensive but seemingly reputable brands in this category. The top two seemed to be Therasage and Relax Saunas clocking in at a much more pricey $800 and $1095. I will list more of the reasons I went with the Relax Sauna below but above all the higher wattage (1500w vs 1000w) is what made me choose the pricer model. The terrible Amazon one claimed to be 900w so the Therasage does not seem that much more powerful or the Amazon one is lying (both equally plausible and I didn't have a watt meter to check). These manufacturers make a lot of claims about the healing power of IR but I'm fairly skeptical about all that and ultimately I think what matters is how many total watts are going into the closed box.

All that said, I was still skeptical of the Relax Sauna but as you'll see below the results exceeded my expectations greatly.

I turned on the sauna at at 2 minutes this thing had reached the 100F mark (rather than 30 minutes in the cheap sauna). At 10-12 minutes I was sweating. After 20 minutes the air temp reached a really surprising 165F. Final reading was around 169F at 25 minutes! For comparison, sources I read say IR saunas are usually around 150F. So even if this sauna's claims about its IR radiation are not true it's still a pretty darn good dry sauna for the form factor.

The internal biometrics are even more exciting. My starting body temp this time was 98.4F. At 25 minutes my temp rose to 101.1F! If you read my previous post this handily beats both the IR and 176F dry Finnish sauna used in the study (176F Finish sauna: +1.62F 100.2F, 136F IR Sauna: +.63F 98.95F). I actually got out at this 25 minute mark as I was not sure going further would be healthy for a first session.

Body Temp and Air Temp

Second, my heart rate went from 90bpm to 133bpm (it was already elevated from a light workout) a 47% increase (from elevated). This is higher than the dry and wet sauna in the other comparison study (+21.2% for wet). My resting is around 60 and 133bpm is in my steady state aerobic training zone according to my Polar app (70-80% HR max), so by the end this was working my heart equivalent to a moderate cardio workout.

My Heart Rate Graph

I was in until the 25 minute mark. The second half is the cold shower portion of the experiment.

Finally, I weighed myself and lost 2lbs (+/- 0.5lbs). This beat the 45 minutes in the dry sauna in the third study (1.59lbs) (was done in three 15 minute segments with 5 minute breaks) in one unbroken 25 minute session.

5 minutes after getting out my body returned back to 98.8F. It's remarkable how quickly it re-established. You can also see my heart rate remained elevated for another 6+ minutes.

Subjectively the heat felt great. It was not harsh or uncomfortable at all like many wet and dry saunas I've been in. Head being out is really nice. I could really feel my heart going by 25 minutes.

I'm thoroughly impressed with this unit and even more amazed as I write this up and am comparing my numbers to those in the studies. It's even more impressive it was able to accomplish all this even with my head out. Of course I am N=1 and I may simply respond aggressively to heat, but my lack of response to the cheaper model suggests it can't all be explained by that. The fact that it beat saunas in all three categories suggest to me that this sauna is working both through IR and air temp, inducting heat both at the skin and deeper at the same time. Tradition larger wooden IR boxes don't get the same air temperatures because there is much more space to heat.

Edit: Since starting this writeup I found a great core temperature study by Sunlighten which makes large wooden IR saunas and a lying down dome style personal sauna called the Solo which costs $700 more than the Relax. http://www.sunlighten.com/pdfs/manuals/solo-test-results.pdf This is great because you can see the exact temperature every minute and the subject topped out at 100.32F. This is no doubt better than the cheap Amazon sauna but the cheaper Relax seated sauna handily beats it with 101.1F at 25 minutes. There is a chance this could be individual variation but I am a heavy sweater which means I had a higher increase despite shedding off a lot of heat with sweat.

Is this model the best choice

I would have loved to have come here and said the $250 Amazon model is great and we can all enjoy the benefits of heat stress daily at home with a low bar of entry but I believe this is the cheapest viable option right now. Compared to the next step up the full size wood saunas, this is still a good deal and my results above suggest this actually performs better than those large multi-thousand dollar models (which also consume more space, electricity, and warm up time). The Therasage is the only other option at a lower $800 (they have spiked their price recently I believe due to the big sauna popularity increase) but with 1/3 less wattage I would say just spend the extra few hundred and get the Relax. Their wattage is closer to the Amazon sauna than the Relax Sauna's so I don't expect it to do that much better and they refused to tell me the air temp it can reach instead giving me some BS explanation about how it doesn't matter because the heat goes directly into your body not the air which makes me extremely skeptical of the product. The Sunlighten Solo looks more legit and has demonstrable changes to core temperature but is more money and doesn't seem as strong. I believe these three models are good from a low EMF standpoint. Infrared blankets are another possibility but I can't comment on their effectiveness and they have very mixed review on Amazon.

In addition to my results some other things going for the Relax Sauna are 1) the IR heat generators are actual FDA registered devices and emit low emf, you can see on his YouTube he is able to present at medical conferences because of this 2) the volume of video testimonials is quite impressive, many from actual doctors, but most impressive is this one in particular by Dr. Roger Billica who was the medical director for NASA (I did a double take, too) and uses them in his clinical practice now.

Also, Relax has a comparrison testimonial posted from someone that's tried both the Therasage and Relax. I was skeptical because it's published by Relax but after my measurements and seeing the heat ramp up of the radiator design compared to the heat panel design of the cheaper unit I believe this comparison.

Whether or not it's worth the $1000+ is up to you. I would review Rhonda Patrick's post/video on sauna benefit studies and ask if those are worth $1000. I believe this unit is capable of reliably reproducing those benefits based on the above. If you have a great sauna at your gym this post probably isn't as relevant to you, but if you are interested in making this a daily training stimulus on the in between days then it's still worth considering. My feeling is that the price is right on considering this is better in many ways than full size $2000-4000 units (portable, head out, faster warmup).