Cold Water Shock

This is the first in a series of three about the basics of what can happen to your body when you swim outside. It’s based on years of experience as an outdoor swimmer, coach and wild swim guide. This blog talks about cold water shock, that initial smack in the chops when you get into cold water.

We’ve all experienced cold water shock at some point, even those who’ve never swum outside. Remember that cold swimming pool, the sudden wince as you got in? That’s the monkey. Fine once you’re in and your body’s got used to it but still a little bit of a shock when you thought you were heading for a nice relaxing time in a warm indoor pool.

So what is it?

Cold water shock is an automatic response of your body to cold water. It’s your basic “fight or flight” instinct kicking in. As cold water receptors are triggered on your skin your heart rate increases, your blood pressure increases and you uncontrollably inhale. People generally don’t notice the heart rate & blood pressure increase. Some do feel palpitations and the blood pressure increase can bring on headaches/head tightness/dizziness but this often passes quickly and I’ve seen it only a few times. What people do notice is the gasp response. If it’s not controlled and managed well it can lead to hyperventilation and panic. If the gasp reflex happens when you’re underwater (i.e. you’ve jumped in and are submerged) you can even inhale underwater.

The sudden increase in heart rate and blood pressure is more of a problem for anyone who has existing heart problems and can trigger angina attacks and heart attacks. It’s important to now that it can trigger such incidents in anyone and may bring to the fore previously undiagnosed heart problems. I do emphasise here that such incidents are very rare so please don’t panic you just need to be aware.

The level of shock response varies person to person. I’ve seen people have quite strong shock responses in 20C water others have very little in 5C. Much like every avenue of outdoor swimming there is no simple answer to “will I experience cold water shock”. The bigger the temperature difference between your skin and the water the bigger the shock response could be. Even if you’re well acclimatised to the water, if you’re hot and sweaty 20C water can still create a substantial shock response. Wetsuits do make a difference but don’t completely get rid of the response. It often happens in wetsuited swimmers when water suddenly flushes around the neck and heads and faces go in the water.

Now you know what it is how can you manage cold water shock?

Slowly! Enter the water slowly, wade in, some people splash their faces, chest, arms before submerging to trigger the cold receptors. Allow your breathing to calm down and concentrate on breathing out. Your body will automatically inhale, you need to make sure yo exhale too to prevent hyperventilation. Let your breathing calm to normal before heading off to swim, this generally takes 2-3 minutes. Staying within standing depth until the gasp response has passed prevents you unintentionally inhaling water when your head is closer to the water surface, particularly if it’s choppy.

Everyone’s reactions are different, don’t feel pressure to set off if your breathing hasn’t calmed down. Always swim your own swim. Over time your body can acclimatise to the cold and your cold water shock response can reduce (long term acclimatisation) but always acclimatise on each swim before you set off (short term acclimatisation).

If you decide to put your head in a while after you’ve set off to swim be prepared for a second, albeit usually milder, wave of shock a the cold receptors around your face and had are triggered. I’ve seen plenty of people make this mistake in the middle of a large body of water and have a little panic. By all means get your head in, just be prepared that you might need to control your breathing again.

Parts two and three in this series on swim failure and afterdrop can be found here and here

Happy, safe, swimming folks 😁


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