When I was in bootcamp, sometimes they would wake us up out of nowhere on a cold night/early am and make us go down to the docks on the lake and jump in and out and then stand at attention over and over again. I think they called them "in and out drills" ( lol
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) They say it is supposed to be good for your heart. Nowadays, if I turn the shower on cold instead of hot on accident, I about have a heart attack!
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I was a cub scout when I was real young, we did those "polar bear" swims, that was actually pretty cool. I liked it, after you got used to being in the water, it wasn't so bad.