A brutal cold snap and the water temperature has fallen like lemmings off a cliff. It's well and truly winter swimming season, and, serious face now, it's time to reflect on safety.
The health benefits of cold water swimming are numerous, for our bodies and our minds. But it's not without its risks. Whether you've been winter swimming for years, or you are new to it, considering the risks and taking precautions isn't an option. This isn't a joy-killer, quite the opposite; do it safely, and winter swimming is one of the most joyful activities on earth.
How can we survive cold water?
Freezing cold water can be fatal. And yet, it's possible to swim in water that's below zero degrees centigrade. How?
To start with, it helps to understand the physiology of cold water immersion. But before we start, it's worth flagging up this small but significant disclaimer: there is a lot of contradictory information out there, and the way our bodies respond to being in cold water is still not fully understood.
One thing we do know is that we have a profound cold water shock response. This is what happens in the first 90-120 seconds of being in cold water. Frigid water on our skin is probably the most profound stimuli we'll experience, so the reaction is dramatic too.
Hearts, lungs and blood pressure
First of all, our capillaries and blood vessels close. That means our hearts have to work in overdrive to pump the blood around the body, and that increases blood pressure. There's no downplaying that strain on the heart: it's what can cause a heart attack. At the same time, our respiratory system responds by gasping in-breaths; clearly that's not the moment to have your head under the water, and actually it's people jumping in and then gasping under the water that causes the most drowning accidents. Our breathing rate can increase by tenfold.
Once those first crucial minutes are over, we settle into the water, attenuating the stress response and getting used. This is when you might start to feel numbness or aching in your fingers and toes. Why? It's called 'peripheral vasoconstriction' to give it its proper name. This is when the blood vessels in the skin are reduced in size, limiting blood flow to the surface of the skin so that more of the heat in the blood supply is moved the deep tissues of the body. That means the skin, hands and feet get very cold, but our core stays insulated.
The next response is shivering. Our bodies stimulate the shivering response to increase our core body temperature, and this can happen in the water or 10-15 minutes after we get out. Because shivering is an involuntary contraction of the muscles it makes it hard to swim. But as you get better adapted to cold water, you shiver less. This makes it easier to swim: but be warned, it comes at the expense of greater deep body cooling. That's why it's very important to listen to your body and get out before you get too cold.
The danger zone
As we continue to cool, we slowly lose power, our arms and legs becoming slow and heavy. This is cold incapacitation, and it can cause us to lose coordination as well as strength. Swimmers can then start to become confused and disorientated, and most dangerous of all, lose powers of rational thinking.