Cold water immersion up to the neck is more effective than cold showers for adaptation due to the ability to achieve lower temperatures.

“So the benefit of a cold bath or a cold shower before aerobic activity is that you increase the capacity of your body mass to absorb that excess heat.”

“If you are inclined, it would be wise to try and increase your core body temperature a bit more quickly than it would otherwise if you were to just, you know, shuffle around outside, get your sunlight, maybe read a little bit, et cetera, and there are two main ways you can do that. The first way is to get into cold water of some sort. So this could be a cold shower of anywhere from one to three minutes. [...] And we have light and dark. We already talked about light and sunlight in particular. We've got temperature, food, exercise, caffeine, supplements, and digital tools. Now, once you've woken up and you want to be awake, okay? So this is likely to be early in the day if you're following a more standard schedule. You will also want to leverage not just light, but temperature as a tool.”

“one of the reasons the shower is effective but not nearly as effective as cold water immersion or immersion in ice up to the neck is simply because of the reason you stated before which is that most showers are not going to get that cold you're not going to get down you know into the sub 40s”

“So the benefit of a cold bath or a cold shower before aerobic activity is that you increase the capacity of your body mass to absorb that excess heat.”