I'm a relative newby, about ten weeks in. Last week I started getting into a local river; now about 7 min, with current, 39 degrees F. After I get out, I do about five rounds of the "brown fat activation" technique from the course - 15 very quick chest breaths followed by a breath hold on the inhale, 20 seconds or so, while tensing up the core, chest, shoulders, arms, followed by horse stance breathing for several minutes. After around ten minutes or so, some pretty vigorous shivering starts up. I crank the heat on the way home, about 20 minutes, sometimes hop in a hot shower. I've looked at the "stages of hypothermia" and see that corresponds with Stage 1 Hypothermia - vigorous shivering plus alert, 90-95 degrees. I just ordered an ear thermometer, which ought to be interesting to play with. Thoughts, insights welcome. Cheers. Keep on Hoffing.