Cold water reactions

[Torchwatch]

A recent study has determined 2 distinct reaction to immersion in cold water that can clash and cause trouble for a swimmer.

The first is the involuntary inhale, a adult man will inhale about 1.5l of air if he drops into cold water. Combined with the sudden involuntary inhalation the heart rate rises as the body prepares to exert itself to escape from a dangerous watery environment. You may have stepped or jumped into the water deliberately but unless your body is used to entering cold water you will breathe in and your heart rate will increase.

The second is the mammalian diving reaction, if your face is under water this will stop you breathing in under water, and will lower your pulse rate to enable you to stay under water for longer without drowning.

If you enter cold water and the involuntary inhalation commences as you go underwater then you will inhale water and begin to drown.
If you survive the involuntary inhalation reaction but go underwater signals will be instructing your heart to speed up and slow down simultaneously, this can cause a heart attack.
80% of heart attacks in outdoor triathlons occur close to the start of the swim section.

The study suggests that if you intend to swim in outdoors in cold water you should climb rather than jump in and that you should avoid surface diving until you have adjusted to the water temperature. Swimming every day in cold water will acclimatise your body to it and make water entry less traumatic and safer.