What happens to the body in cold water? The initial response is the cold-water shock, and that usually lasts for up to five minutes. This results from rapid cooling of the skin following immediate immersion in cold water. It’s when you take a big inhalation, a big gasp and then breathe quite quickly afterwards – what we call a hyperventilation. As your blood rushes towards the centre of the body, you will also experience a sudden increase in blood pressure and heart rate. After that period, you’re going to start cooling the tissues beneath the skin – the superficial nerves and muscle. As they continue to cool, there will be a reduction in contractile capability (strength) and the coordination of the muscle, which will affect your swim stroke and propulsion. With continued immersion, you may start to cool the deeper body tissues, which are typically regulated to 37˚C, give or take half a degree either way. Cooling by 1.5–2˚C or below 35˚C is what we would call clinical hypothermia.
How can we know when it’s time to leave the water during cold water swimming? You obviously want to leave the water before hypothermia sets in. However, it’s important to be aware that our bodies continue to cool after we get out of the water. Some people label this as the ‘after-drop’, but as scientists we prefer to call it continued cooling. Around 30 minutes after you leave the water, your deep body temperature will be much lower than when you were in the water. What we recommend is that you go on the symptoms of any cooling of the superficial nerves and muscles. If you’re starting to get the feeling of numbness in fingers, you’ve got splaying fingers or you can’t coordinate your stroke as well, that’s a definite sign to get out.
What are the signs of hypothermia to look out for in others? When a person becomes hypothermic, they begin to exhibit a change in behaviour. We aren’t necessarily able to see these changes in ourselves, but they are usually evident to other people. The four key things to look out for are: ‘grumbles’, where an individual becomes suddenly insular or develops an unusually low mood; ‘mumbles’, where speech may become slurred; ‘fumbles’, which includes a significant loss of dexterity; and ‘stumbles’, where a person may become uncoordinated or slow in their movements beyond what is normal for them. If you see these behaviours in other people, it’s a good idea to intervene and help them.
What can you do to acclimate to cold water? The best way to acclimatise is by undertaking repeated swims, recovering fully between each one. This means ensuring that you have returned your deep body to its normal temperature, and that you can freely have a conversation and move unimpaired beyond what is normal for you. It is also important to remember that acclimatisation takes time, and that each person’s physiological response to cold water is different. For those looking to take on extreme challenges like an ice mile, it often takes years of practice and experience. If you are looking to acclimatise to cold water and swim through the winter, the best time to start is right now while the water is at peak temperature.
How can a wetsuit assist with your cold-water swimming? Wearing a wetsuit is a valuable tool and for some people it’s the only way to swim outside. For a wetsuit to work, you want it to fit well. The wetsuit traps a layer of water close to the skin, which your body warms up. That layer of water then acts like a barrier, so you start to lose less heat to the water outside of the wetsuit. This is a great advantage to maintaining that deep body temperature, and it means you can stay in the water for longer because you’re not cooling as much. Read more articles about swimming technique and safety in the latest issue of Swim magazine.