Originally Posted by Mariedut
After a DNF halfway in a 10 km swim due to hypothermia in the 11 degree water, I tried to work out why it happened because I was not feeling the cold and was actually enjoying the swim a lot when I suddenly was dead tired and just wanted to turn on my back and drift for a while. (Not thinking straight any more?)
One of the causes might be not breathing enough and getting enough oxygen. I breath occasionally to the left (on every 3) and then to the right on every 4 strokes- more frequently the latter pattern. I take about 56 strokes per minute so have a long slow stroke.
Another mistake I made was to speed up my stroke rate thinking I could increase my metabolism and stay warm in the extreme cold conditions. This apparently might also have been a mistake
That was a life saving move you made getting out when suddenly fatigued set in, although you felt very good up until that point. We are really unaware of when we go hypothermic. There was a young swimmer (36 yo) crossing EC a couple of years ago, 14 hours in the water and just a mile from the French shoreline. Which really means another 4-5 miles with lateral ebb. She rolled on to her back to recover for a few minutes, then rolled back face down and collapsed. They could not revive her. The Med Examiner reported respiratory failure due to exposure (hypothermia).
A couple of years ago, swimming a 10k in SF Bay, they pulled a swimmer out just after an hour (he was wearing a wetsuit). I heard he was swimming in circles. Support crew asked him what he was sighting on, he wasn't sure but noted the Golden Gate Bridge - which was in the opposite direction our destination. Oakland Bay Bridge was the finish. He felt fine and didn't want to get out. His body temp 94 degs, hypothermic.
In any case, very good move getting out when sensing sudden change, especially in 11 deg (52f) water.