Wim Hof is a Dutchman who has set numerous world records for resisting extreme cold, including climbing to 22,000' on Everest wearing only shorts and shoes and sitting in a bath of ice for over 90 minutes without change in core temperature or heart rate. He accomplishes this via a breathing technique that he created a 10 week online program for. Here's a sample video of him leading some students up a snowy mountain in only shorts and shoes.
I just signed up for it and will be posting on my progress as I go through the course. Today I did the first two benchmarks he has you do at the beginning - 1) hold your breath with full lungs and 2) pushups till failure. They are done separately with full rest. I was able to hold my breath for 1:40 with the last 30s being very painful, though I could probably have lasted at most another 10-20s before total failure. I was able to do 28 pushups.
Although I'm not officially starting until tomorrow, I reviewed all the videos and workbook so I will be ready. One of the breathing exercises finishes by holding your breath with lungs fully exhaled. Within the first 15 minutes of the video I was able to comfortably hold my breath (again, lungs empty) for 1:47. One key point is he clarifies you only hold until you feel the impulse to breathe, not until you need to. So I had some more time available before I actually needed to breathe again. The daily training also includes simple exercises and a cold shower. I'm really excited to see where this goes, and in the middle of winter in North Carolina is a great time to train.