FEATURES,  You Ask, We Answer

How to tell if you’re hypothermic when swimming in cold water

You asked

I am a fairly experienced winer swimmer and recently converted to wetsuits in order to get more swimming in. I never shiver and when I measure my temperature it’s below 35 – how do i work out if I’m hypothermic?

We answered

Clinical hypothermia is defined as a core body temperature of less than 35 degrees. However, are you measuring your core temperature? An infrared thermometer used in the ear, for example, is of little use when your skin and ear canal has cooled down, as it only measures the skin temperature, but getting a true core body temperature reading is invasive and probably something you wouldn’t want to do at the side of a lake. As you’re an experienced swimmer, it sounds as if your body has adapted somewhat to cooler temperatures and shivering will probably start at a lower body temperature than for an unadapted person, but it will kick in at some point. When swimming, stay alert of other symptoms of cooling, such as loss of dexterity.

While swimming, you may not know that you are hypothermic, but it will be apparent to people you swim with regularly. They will see changes to your swimming style (change in stroke rate, a less efficient stroke, lower legs) and behaviour (slurred speech, errors you wouldn’t normally make). If your swim buddy or other swimmers start asking what you think are really easy questions, such as who is the prime minster? What day of the week is it? Answer them. All they are trying to do is to establish how cold you are and if they ask you to get out of the water, you should get out – they are concerned for you not trying to ruin your swim.

For swim buddies, if you see a swimmers swimming style deteriorate (they become less efficient at swimming forwards and see their legs drop lower in the water) they are definitely exercising muscle cooling, but may also have a cold deep body. You can ask them simple questions they should know the answer to, such as:

– Who is the Prime minister?

– What day of the week is it?

– What is your (partner’s, child’s, dog’s cat’s) name?

From the way they answer you’ll get an idea of the impact the cold is having on their cognitive function. If they answer correctly, immediately and as you would expect, they maybe starting to fatigue from cold muscles rather than have hypothermia. If they slur their speech are really slow to respond and are vague or argumentative (or otherwise out of character) they are starting to display symptoms of hypothermia.

A few things to remember about hypothermia:

  • Hypothermia can catch you unawares. Not everyone shows the same symptoms. You can often still be able to swim, feed and answer questions despite it, and never complain of being cold or feel excessively cold.
  • It’s not that difficult to swim yourself to a point of total exhaustion. There’s no great will-power involved or mind-over-body heroics. When you get close to your limits your ability to judge where that limit is decreases.
  • “Giving up” shouldn’t be treated as something negative. It’s better to stop too early and go home safely than try to swim too far or for too long.
  • Hypothermia combined with hypoglycaemia is doubly dangerous – and a real risk for swimmers because of the energy you burn while swimming.

If you’ve got a burning question about outdoor swimming, please send it to us: info@outdoorswimmer.com

Stay up to date with The Dip, our free weekly outdoor swimming newsletter.

Outdoor Swimmer is the magazine for outdoor swimmers by outdoor swimmers. We write about fabulous wild swimming locations, amazing swim challenges, swim training advice and swimming gear reviews.