Training In Cold Water

With winter closing in and water temperatures dropping, if you want to keep up your open water swimming and swimrunnning, then it’s essential to know about how the cold can effect you! 

cold water swimming

One of the risks you face as a SwimRunner or open water swimmer, especially in the colder seasons, is hypothermia. It’s an obvious threat when submerged  in cold water (the body cools 25 times faster in water than it does in air) but is also a possibility when you are running in wet gear. You lose heat much faster when you are wet and when your energy levels get low after exercising, hypothermia is a serious threat.

What is Hypothermia?

There are various states of hypothermia ranging from mild to severe. Hypothermia is caused by a drop in the core body temperature. A small drop of just a 1.5 degrees can cause mild hypothermia – now ‘mild’ doesn’t sound bad but it really is! Cool down further and you are in serious trouble.

It’s important to know that hypothermia does not come on suddenly. Hypothermia due to immersion can often be confused with Cold Shock. Cold shock response is an entirely different thing: it’s the bodies automatic response to sudden exposure to cold, which triggers a gasping reflex, hyperventilation, increase in heart rate, sometimes pain in the extremities, and even cardiac problems. The biggest danger from sudden cold water immersion is the uncontrolled hyperventilation which can leading to inhalation of water – you gasp and breathe water into your lungs and drown. To avoid cold shock it is important to acclimatise to the water temperature slowly – more about that later!

The heat in your body can’t instantly disappear. Hypothermia comes on slowly over time. Your body has enough stored heat that even in zero degree water, it will take around 30mins for an average human to develop severe hypothermia.

How can you spot Hypothermia?

Hypothermia on dry land is easier to spot than when submerged in water so to understand how it can effect the body, lets looks at the basics of hypothermia on land.

So imagine that you’ve been running with a friend in the mountains, it’s a cool day, you’ve been out for a while and you’ve got pretty sweaty. So far your friend has been sure footed, keeping up the pace, and happily chatting with you. A little later you realise that the conversation has died off, you’ve had to slow the pace has they are lagging behind and when you look back you see them tripping over something. You stop to let them catch up and they mumble a grumpy complaint. You suggest they have a bite to eat but they struggle to get into their back pack and you need to help them unwrap the energy bar. You start to pay more attention and see that they look pale and shivering. Your friend is showing classic symptoms of mild hypothermia, the UMBLES: Stumbling, Fumbling, Mumbling and Grumbling.

All these symptoms are relatively easy to spot on the hill, but once you dive in for the next swim and you are submerged in water, it’s much more difficult. For a start, we spend most of the time when swimming with our heads in the water, only really looking at our friend occasionally and briefly to check that they are keeping up. When it’s cold the common sense thing to do is keep moving right? If you do stop for long enough to check on them, properly you might notice some or all of the following (sometimes very subtle) symptoms of hypothermia:

  • Their stroke rate has dropped and they have slowed down.
  • Their position in the water has become more vertical so you don’t see their feet kicking, their kicking will also have slowed.
  • They are splashing excessively due to a deteriorating quality of arm stroke
  • They look pale and have a blank, lost expression
  • They complain of cold
  • Speech is slow and can become labored or slurred. They may have clenched jaws.
  • They mumble and may not be able to answer questions coherently.
  • They have a lack of reasoning and an inability to gauge their own condition saying they can keep going even when it is obvious that they can’t. As blood cools in the body it becomes thicker so less oxygen gets carried to the brain. The resulting confusion means you they unable think clearly.
  • They are shivering (Shivering is the bodies attempt to warm up through exercise, by muscular contraction. A swimmer who is experiencing violent shivering (Moderate stage Hypothermia) should be removed from the water immediately – How do you tell violent shivering from normal shivering? Normal shivering can be stopped voluntarily, violent shivering can’t.)
  • Their teeth are chattering
  • They suddenly start to feel warm again
  • Manual dexterity is reduced, a common symptom is splayed fingers and the inability to keep them together when swimming. 
  • If you get out of the water walking will be difficult, running very hard. They will struggle to even get themselves dressed.

Cold Water Incapacitation

When you remain immersed in cold water your body continues to lose heat, blood shunts to the core to keep organs warm. As a result blood flow to your extremities and limbs is reduced and your muscles begin to lose power, limbs become slow and heavy, you start to feel very tired and swimming becomes increasingly difficult. You will lose your ability to control your hands and keep your fingers together (clawed hands) and the muscles in your arms and legs will eventurally stop working well enough to keep you above water – staying afloat can become very difficult. As soon as you start to notice signs of cold water incapacitation you should finish your swim!


After-drop refers to the decline in your core body temperature when you get out of the water after a swim. When you swim in cold water the body attempts to protect vital organs by reducing blood flow to the skin and limbs so the core stays warm while the rest of the body cools down. The process is known as peripheral vasoconstriction. After you leave the water, peripheral vasoconstriction ends and the cool blood from your limbs and skin begins to returns to your core where it causes your core body temperature to drop. This is why you often only start shivering about 5 minutes after leaving the water, even once you are dressed and in a warm place. You can feel a strange and uncomfortable chilling deep inside you that can make you feel sick and take a while to pass.

Treating hypothermia

The most important and immediate step is to try and reduce further heat loss:

  • Get the person out of the water AND sheltered from the wind. If you can’t get them indoors and into the warm it is more important to get them covered and removed from wind exposure than dry. So just get them covered in blankets or what ever you have, even newspaper, covering as much of the person as possible, including head and hands. If further heat loss can be stopped, a person will rewarm themselves at a rate of about 2ºC per hour.
  • Remove wet clothing/wetsuit and get the person dry as quickly is possible. They may be unable to dress themselves so help them carefully.
  • DON’T try to warm them using vigorous rubbing, instead pat them dry.
  • Watch for the After-drop effect (see below)
  • Apply a gentle heat source such as a warm hot water bottle or shared body warmth. No heat source should be placed directly on the skin. DON’T get into a hot bath or shower straight away.
  • Give fuel through high energy food and/or a warm drink. Do NOT give alcohol or caffeine: Alcohol expands the veins so cold blood from the exterior will flow into the core quicker. Caffeine slows the flow of warm blood from the core.
  • Once they have been fed and show signs of improvement (no more shivering) get them moving gently. Shivering itself is the bodies attempt to rewarm through physical movement. It is a good thing. DON’T try to suppress shivering and DON’T force someone to move who can’t. Shivering uses up a lot of energy so keep giving high energy food.
  • If they are not feeling better after a short time, get help, call 999 or get to A&E

The prevention is better than cure.

Stay safe and take precautions while swimrunning to help prevent, or at least stave off cold related illnesses:

  • Wear a wetsuit (full suit in cold weather), silicon or neoprene cap (or both!), neoprene socks inside trainers (or neoprene boots) and gloves. Thermal rash vests and close fitting fleeces give a lot of extra warmth under a wetsuit.
  • Eat high energy foods before you go out allow time for digestion. Hydrate properly.
  • Keep eating during your SwimRun to keep energy levels up.
  • Swim close to the shore
  • Use a tow float and carry emergency high energy food, warm clothing and a phone.
  • SwimRun with a friend and regularly check on each other for symptoms of hypothermia.
  • Ask someone to keep an eye on you from the shore when swimming
  • Acclimatise to cold water swimming (see below)
  • Know the symptoms of hypothermia
  • Know your own limits and don’t stay in the water too long. Make sure the runs are long enough inbetween the swims that you can rewarm sufficiently.
  • When you start to run again take it easy and be aware of After-drop (see below) which can make you feel unwell.
  • Don’t set strict time or distance goals for your route, use your head, not a watch! Finish your swimrun when you start to feel uncomfortable or notice any of the signs of hyperthermia listed above.


To avoid the initial dangers of cold water shock you need to ease yourself into cold water. Give yourself a couple of minutes getting in gradually and staying in you’re depth until the gasp relief has passed and you can control your breathing. This can take a few minutes. The secret to acclimatising (getting your body used to the effects of cold water) is just to swim in cold water often – at least once a week, preferably two or three, gradually extending the time that you stay in the water. Eventually your body learns not to react to the cold so severely and you will be able to get in and swim much quicker. will get less It is easier to start swimming outdoors in summer, when water temperatures are at around 16 degrees, and then keep on swimming regularly as the temperature drops.

Protect Your Extremities

Getting into very cold water (typically less than 10ºC) can cause numbness and pain, particularly in the extremities, such as the hands and feet. Neoprene socks and gloves can help protect your hands and feet and will dull the cold shock response. Wearing more neoprene will extend the time you feel comfortable in the water, but still take care to notice other signs of hypothermia setting in. do some great neoprene accessories.

Food and hypothermia

We need fuel to stay warm. In cold environments we need extra food to help keep the body temperature up. The human body can adapt and deal well with cold (a few people even happily swim in speedos in the Arctic!), however, as soon as our energy levels get low, we just don’t have enough fuel stored to keep up physical activity as well as keep the body functioning normally, including keeping warm. As blood sugar levels drops something has to give – the fuel tank is on empty and problems start to occur. Our bodies use the energy we get from food to do some important things, these include; keeping us warm, powering our muscles and feeding our brain. The food we eat contains carbohydrates which we use for fuel. These are split into two categories, Simple and Complex. Simple carbs are sugars and are easy for our muscles to use and provide a quick spike of energy – sugars are the ONLY type of fuel our brain uses. Complex carbs are more difficult for our muscles to access, so they provide a slower releasing source of energy that will keep you going for longer. When you swimrun or swim longer distances make sure you keep taking on food with both simple and complex carbs to fuel your body and brain through your work out – flapjack is a good example.

Happy Swimrunning! 

Stay safe out there, keep fueled up and keep warm. If you follow the tips above you can keep SwimRunning and open water swimming through the winter!

Take some inspiration from this guy!…

Written by Jonny & Chloë, Love SwimRun Organisers, Updated 13/11/20
Chloe is an STA Level 2 Open water swimming Coach. Jonny Collins is an experienced REC First Aid trainer at