What is an after drop?
Soon after a cold water swim, you may experience what’s called an “after drop”.
This is when your blood vessels expand (vasodilation) allowing for the warm blood, which had been concentrated around your core, to flow evenly throughout the body once again. When cold blood from the extremities (hands and feet) re-circulate to the torso, a sudden drop in temperature may be felt. This is followed by a shivering response which generates heat and gradually restores a core temperature of 36.5 - 37.5°C.
How long does the after drop last?
The length of time is takes for your core temperature to be restored to normal levels depends on:
a) The temperature of the water
b) The length of time that was spent in the water
c) Your adaptation to cold water
The after drop may last from a few minutes to about 45 minutes in extreme cases, such as being exposed to ice water. During this time it is normal to experience shivering as your body heats itself up.
The best way to warm up after a cold swim:
Remove wet clothing as soon as possible and dress into dry, warm clothing
Cover areas prone to heat loss (head, neck, arm pits, groin). This can be done by wearing a beanie, scarf, and warm jacket, for example.
Next, it's best to warm the body from the inside out. Drink a luke-warm, energy-rich drink such as hot chocolate.
In extreme cases, gradual external heat can also be provided, such as using heaters and hot water bottles (be careful not to burn the your skin).
The swim itself is only a part of the challenge – the real challenge is the recovery. Be sensible and responsible when taking part in open water swims. Have a tough mind, but be smart enough to listen to your body and to stay safe during your open water swim.