In most of the world – anywhere where water is cooler than body temperature – swimmers can achieve hypothermia at any time of year, it’s just a matter of how long it will take. Knowing what hypothermia is, how it develops and how to treat it is will help keep you, and people you swim with, safe, and it all comes down to being able to answer these simple questions.
“Cold is feeling cold, hypothermia is defined medically as a core body temperature drops below 35 ˚C, but your swimming performance is likely to be affected when it drops below 36˚C,” says OSS’ expert medical advisor Dr Mark Harper of Brighton and Sussex Medical School.
Hypothermia can be classified as:
Hypothermia creeps up on people gradually, and “most of the symptoms found in mild hypothermia can be found in any temperature below normal body temperature (36.5 degrees C),” says Harper.
Signs that you could be becoming hypothermic include:
The only way to recognise your own limits is to get to know them, through experience. Whether it’s summer or winter, start with short immersions close to the shore and build up your swim time. Notice that you are colder 10-40 minutes after you get out than you are when you exit (a phenomenon called ‘afterdrop’, covered below). Notice that your body is not a machine (so don’t use x degrees = x minutes in the water) – on days with wind chill, or when you are tired, hungry, stressed or hungover, you will likely get cold faster.
A dangerous aspect of hypothermia is that thought processes slow down and people are not able to gauge their own condition. With more severe hypothermia swimmers can even start feeling warm, which is a big danger sign if they’re in the water.
Any of the signs of growing cold listed above are possible to witness in another – shivering, a change in swimming technique or speed, being unable to speak, growing more vertical in the water, fingers becoming splayed. When blue appears around the lips that it also a sign someone is cold. These signs suggest someone should get out of the water as quickly as possible.
Marathon swimmers refer to ‘The Umbles’ as a way of remembering what to look for. A hypothermic person shows some or all of the following (and might appear drunk):
The key is to get warm and dry as fast as possible:
Shivering is not a reliable sign of whether a cold swimmer is okay. Shivering is a way that a body can warm itself up: the involuntary muscle movement is your body’s natural response to getting colder and trying to warm up.
It is not a reliable sign of how cold a person is – people shiver less when they are older, some people can suppress the shiver response, and the response can be attenuated or repressed in experienced cold water swimmers.
What we do know is that shivering is a sign of getting cold, while violent shivering and shaking which you cannot stop – in or out of water – is a symptom of moderate hypothermia. And that stopping shivering can be a sign of severe hypothermia as well as getting warm again.
No, do not try to measure your temperature. Oral and rectal thermometers are the most reliable guides to internal body temperature but are difficult to use effectively in an outdoor situation (it is likely to be difficult to keep a thermometer under the tongue in place long enough whilst shivering). Infrared thermometers will just be reading skin temperature, which will be misleading.
Instead, know and look out for signs of cold and err on the side of caution: put efforts into getting the cold person warm earlier rather than later.
Yes. Getting cold is an inevitable result of swimming in natural temperature water in temperate climates, and, outside the tropics, it is possible to become hypothermic in summer as well as winter.
Avoid peer pressure, and avoid self pressure. What is there to prove? Cold talented people may tell you that “cold is in the mind”, but it does also exist in the body. In physiological terms there are fast coolers and slow coolers. Just as there are people who can run marathons in the desert and people who feel unwell when the weather is still in the 20s, people arrive at cold swimming with different baselines.
Your own baseline will also change: lack of sleep, food, hangovers and external factors such as the weather and temperature will all affect how long you can swim before you become hypothermic.
The best way to avoid hypothermia is to be cautious, and when the signs of getting cold appear, get out of the water, get quickly back into clothes and warm up.
Yes. “Exposing ourselves to cold water is a good and healthy thing, if done with care,” says Mark Harper. “I believe it may have health benefits in assisting with anxiety, depression, inflammatory conditions such as arthritis, easing of unwanted menopausal symptoms and maybe even dementia. But the body functions best over a very small range of temperatures, with any deviation impairing physiological functioning, and can – in extreme cases – lead to problems that include unconsciousness, heart attacks and death.”
Acclimatisation is the process of becoming better able to deal with cold, and is seen across sports – for example, in mountaineers and polar explorers, as well as endurance swimmers, channel swimmers and winter swimmers. It is achieved by consistent, increasing exposure to cold. The committed also avoid its opposite – being too warm – by wearing less, sleeping in cooler rooms and so on.
“Acclimatisation just requires exposure to cold, but not so much exposure that you experience hypothermia,” says Harper.
Timings are so individual that it’s impossible and unhelpful to apply a formula. It’s best to err on the side of caution. “Staying in longer does not bring any extra health benefits,” says Harper. “In fact quite the opposite, it’s more likely to be detrimental to your wellbeing.”
Yes, it’s quite safe to wear these if you choose, as they will stop or reduce the pain of cold and protect sensitive areas. They won’t stop you getting hypothermia, though.
Yes and no. It will delay the onset of hypothermia but not prevent it.
It is continued cooling, after the swimmer exits the water, as heat flows out of the body into the cold water.
Once you exit the water, you continue to cool for up to 30 minutes. This means that your deep body temperature may be cooler 30 minutes after your swim than you were when you got out of the water. This is why warming up immediately after your swim is vital. See Afterdrop & the subtle art of warming up
This is contentious. As long as you are not hypothermic, you can use warm (not hot) showers or baths to warm up. Be careful if you feel dizzy – if you do, you should sit on the floor straight away, or you can use a chair in the shower.