You might remember, if you sea swam as a child, spending a glorious day on the beach, in and out of the waves, running around like a little rocket and then popping back to eat with the rest of the family – if you could find them on a crowded beach. Do you remember the aptly named sandwiches? Sitting wrapped in an oversized towel, shivering? More than likely, that shivering was due to post-swim drop.
When you enter the water, which, even in the summer in the UK, is inevitably colder than the ambient air temperature, your body does a clever thing. It detects the cold water and reduces the amount of warm blood flowing from your core to your peripherals. This protects your core temperature but makes your legs, arms and skin, cool. It has a name – ‘peripheral vasoconstriction.’
Once you leave the water, the reverse happens. Your body knows it is no longer immersed in the cold and peripheral vasoconstriction ends, the colder blood in your peripheries starts to mix with the warmer core blood and hence, even some time after you exit the water, you may begin to shiver as your core temperature drops due to this mixing of different temperature bloods.
There is nothing wrong with shivering but it is very important that you do not become hypothermic which is when you lose heat faster than it can be generated. This is something that can only really be judged by experience and if you are not a regular sea swimmer, it is why it is important to swim with others.
The best way to ensure you do not succumb is to:
- Dress quickly in warm dry, clothes, plenty of layers are best. We also favour taking a flask of hot water and a hot water bottle which I fill (having loosened the tops of both pre-swim) post swim and warm my feet whilst I am changing.
- Hot drinks and cake – being cold and / or shivering are high-energy activities. Flasks are great but the cups are often insulated so if I am ‘flasking’ rather than ‘cafeing’ I try and remember to take a non-insulated mug around which I can wrap my hands.
- Do NOT have a hot shower. When peripheral vasoconstriction occurs it also alters the fluid balance in the body so your core has more than normal – this is why many people tend to pee when in cold water (it’s fine – fish pee in the sea .) When the balance is restored it means there is now less volume in your core and hence your blood pressure lowers – a hot shower can exacerbate this and you can faint. The best thing to do is to potter, do those odd jobs you keep putting off, take a walk IF the weather is conducive!
- If you don’t feel well, DO NOT DRIVE, or ride a bike. Hypothermia can lead to cognitive impairment and it can be as bad as drink driving.
- Keep an eye on your fellow swimmers. It is all too easy to spend too long in the water, particularly if you are with friends, chatting and larking about, not wanting to be the first to leave the water – there is no room for ego in these situations.
- Hypothermia – the signs: shivering, reduced circulation, slow weak pulse, lack of co-ordination, irritability (hard to tell with some people ) or confusion, nausea, slurred speech.
As mentioned, everyone is different and you need to find your own level. Lying in the water is different from swimming where you are generating some heat. People often remark, within our group, that if the water is rough, the effort of wading through the water and maintaining your balance, jumping and splashing in the waves seems to make some people feel less cold than if it is a perfectly flat sea, again, only you know how you feel.
Whatever you do, take it slowly and safely and live to swim another day!
For more information either do a search for ‘after-drop’ or ‘post swim drop’ of take a look at these really helpful articles: