We’ve talked a lot about coldwater immersion and whole body cryotherapy, and cold packs, and hibernation, and everything in between in an effort to be comprehensive and see where we can make inferences. However, what we have not done is more directly try to compare whole body cryotherapy and coldwater immersion. In terms of application, this is actually a really important point. So here’s the million dollar question: is whole body cryotherapy the same as coldwater immersion? The answer is probably not. If we dive into the science we can see that there are three factors that really differentiate whole body cryotherapy from coldwater immersion and all of them have to do with how effectively each technique lowers body temperature. But I also want to point out that in addition to these three factors, which we will discuss in a minute, is the fact that people can remain in cold water for longer durations than cold air cryochambers and this may affect how robust the cold shock response is.
These factors are…
1.) Thermal conductivity. This is essentially how well heat is extracted from the body.
2.) How much of the body is exposed to the cold (surface area).
3.) Temperature gradient
Each of the mediums (ice, water, and air) have different properties that affect how well heat is extracted from the body. Starting with the first factor, thermal conductivity (how well heat is extracted from the body). Ice has the greatest capability to extract heat from the body, followed by cold water, and finally air. Cryotherapy is slightly less effective at heat transfer since it only uses air. The second factor, surface area, also plays a role in cooling the body. In the case of coldwater immersion the surface area of cold water covering the body really depends on the protocol and can vary from submerging just the legs or can involve submersion all the way up to the shoulders.
In any case, your head will usually not be submerged. This is different from a cryotherapy chamber where the entire body including the head is exposed. Although some cryo tanks do not expose the head to cool air. Finally, the third factor is the temperature gradient which is the actual temperature difference between your body temperature (98.6ºF or 37ºC) and the modality being used to suck the heat right out of you. This is really where cryotherapy shines because the air temperature can be as low as 289°F (178°C). That is cold. Lastly, another important factor to consider when comparing coldwater immersion differences with exposure to cryogenic temperatures in the air is that fact that people can stay submerged in the cold water for much longer time periods than cryotherapy air temperatures. So what’s the final word? Well, what is clear is that there is a very robust release of norepinephrine in the brain and the body that is consistent with both coldwater immersion and whole body cryotherapy. There have even been studies comparing the norepinephrine response to coldwater immersion (whole body submerged for 20 seconds in 40°F) with whole body cryotherapy (2 min at 166°F) and found they are more or less identical, at least in that respect. Now, if you were to stay submerged in that cold water for an hour as opposed to just 20 seconds we know that norepinephrine would increase 5fold. Which brings us back to the point that exposing the body to cold for prolonged periods may have a more robust effect. Other than that…
I’ll leave it as an exercise to the reader (and listener) to make their own value assessment based on the information at hand. It’s probably not worth overthinking too much at this point.