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Various sources (mostly TV stations, at least in my region) are constantly warning about the danger of cold shock response, if someone goes to water too quickly.

But on the other hand, Bear Grylls is famous for not passing any occasion of jumping naked into ice-cold water. The sudden heat loss by swimming in such cold water (near 0 degree) must be immensely greater that when you go from heat air into c.a 20 degree water in summer. And I've never heard of him having cold shock response.

So, is the cold shock response a real danger for someone used to cold water? Or it's just a problem for people who never take cold showers and swim only in summer? Or it's just an urban myth, popularized by media in cucumber season?

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up vote 2 down vote accepted

According to this article, Avijit Datta and Michael Tipton: Respiratory responses to cold water immersion: neural pathways, interactions, and clinical consequences awake and asleep,

A fall in skin temperature elicits a powerful cardiorespiratory response, termed “cold shock,” comprising an initial gasp, hypertension, and hyperventilation despite a profound hypocapnia. ... The respiratory responses to skin cooling override both conscious and other autonomic respiratory controls and may act as a precursor to drowning.

Now about the getting used to it:

Recent evidence from our laboratory suggests that there is also a marked and modifiable psychological component to the breath-hold component of the cold shock response

They had a case-control study with one group getting a psychological training, the others not. The ones with psychological training got basically back to normal breath holding times (one week later), the ones without stayed at less than half of the normal breath holding time.

However, for other reactions in the cold shock, the psychological training didn't help:

A corresponding change was not seen with the heart rate response before or during immersion

How long does it take to get used?

The initial respiratory responses to immersion in cold water can habituate. As few as five 3-min immersions in cold water can reduce these responses by 50% (74), with the response still being reduced by 25% 14 mo later (75).

They also have a section on cardiac arrhytmia, but for that I recommend reading the paper - this is more complicated it seems: there's a "diving reflex" that plays a role as well, and the arrhytmia seems to be connected to the gasping.

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I do believe cold-shock is a real threat, but the reaction is a combination of physical and psychological reactions. As being dropped in near freezing water is a horrendous experience, even for the more hardy of us. The mind goes into full panic, only wanting to get up out of the water, often flailing and thrashing to do so.

The physical effect just pours gasoline on the fire created by our paniced mind, shortness of breath, muscles getting sluggish, cramps etc. just creates more panic. If you have undergone some cold water training, you know that it is very important to keep your cool(no pun intended), and to focus on staying afloat and to not panic. Easier said than done.

Conclusion: If you are used to cold water, I don't believe cold-shock is as much of a danger as if you are untrained. Just as you stay in control of the situation, and try to get up, safely and quickly.

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