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The Afterdrop phenomenon experienced by cold water swimmers

If you’ve spent time chatting (or chattering!) with open water swimmers during winter you might have heard the term ‘afterdrop’, in fact, if you’ve swum during winter, you may well have experienced the afterdrop yourself.

It’s a common term among cold water swimmers but fear not if you haven’t come across it before because we’ll explain what it is, how it affects swimmers and how to avoid it below. 

What is the ‘Afterdrop’? 

The afterdrop is when the decline in your core body temperature continues after you have already gotten out of the water. In practice, it might mean that when you first exit the water you feel cold, but not freezing, then 10-15 minutes later you start to shiver, and at worst, you feel faint, unwell or become hypothermic.

When you swim in cold water your body tries to protect your vital organs by reducing blood flow to your skin and limbs. This allows your core to stay warm while your skin, arms and legs cool down. This is known as peripheral vasoconstriction.

There are two theories as to what is happening to cause afterdrop.

The first and longest-held theory suggests that once you exit the water the peripheral vasoconstriction ends, this is when the cold blood from your arms, legs and skin returns to your core and mixes with the warmer blood in your core creating your deep core body temperature to drop even if you are rugged up warmly.

The second, and most recent theory puts it down to a side effect of conductive heat transfer. This theory recognises that the cold swimmer cools from the outside in, and, consequently, a heat gradient is established from your relatively warm core to your cool periphery. Until the gradient is reversed, which doesn’t happen immediately, further heat transfer occurs from the warmer core to cooler peripheral tissues, keeping your core cooler for longer.

It has been observed that afterdrop occurs more frequently in swimmers who undergo rapid cooling or rewarming. 

Julie Slattery from the Bay Open Water Swimmers getting a hand to layer up after a cold water mid-winter swim in Port Phillip Bay, Melbourne.

How to best deal with the Afterdrop  

  • Get to a dry and warm location out of the wind
  • Dry yourself immediately
  • Stand on something warm, or in warm water, as you get dressed
  • Get dressed quickly in warm layers, starting with your upper body, then lower body, head, hands, and feet. Have someone help you if you’re finding it hard to do it yourself
  • Find a warm spot to warm up, like in the car with the heater on
  • If taking a shower, make it warm rather than hot to avoid rapid rewarming and increasing the chance of a more sudden and intense afterdrop, or it having an effect on your blood pressure, resulting in you feeling faint and unwell. Waiting until you have warmed up again before your shower is likely to assist with a better outcome
  • Drink or eat something warm
  • Stay with a friend until you warm up and if you start to feel unwell, sit down until it passes
  • If you believe you’ve developed hypothermia, seek medical assistance
Standing on something warm as you dry off and get dressed will help reduce the heat lost through your feet.

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