For sure you can use the sauna but accourding to how we were trained ideally you need to lay down, with knees up and put a cool towel over your head making sure the back of your neck is cool. Sauna’s can really suck the life out of you so you need to be careful in a way that is different than the properties of how water works. As for cortisol , pain for sure raises your levels and I believe some people do not benefit from hot and colds the way others do. Ben did them but hated them and I can’t say that I know of Lindford or Desia or many of the Carribean guys if I could steriotype. Don’t forget that most of these athletes had a multitude of therapies at their disposal towards their late careers and massage was the primary thing done by Charlie early on.
One reason I am an big promoter of hot and colds? They really work for me and I have needed them in a big way to keep my back loose due to almost one inch leg difference. But my tissue is different than anothers and my ancestory is from more northern climate etc and well I also believe that regeneration is as individual as ones response to training methodology.