I think I’m made of iron filings, in fitness and in general terms, but actually I’m a physical coward. I think a lot of people are like this, but maybe that’s just a thing that cowards think. So I gave open-water swimming a shot in late October – the first hint of a cold snap – in a regular swimsuit, and gave up somewhere around my ankles. I didn’t rear up against the discomfort; I genuinely thought I might die. The most likely outcome was a heart attack.

I got a wetsuit from affordable sports brand dhb and tried again, every day, for the first week of November. I chose a beach on the Isle of Wight, but nothing – not the instructions, not the white-coated gloves it comes with – prepared me for the arduousness of getting into this garment. Squidging my legs in like sausages, bouncing around to zip it up: it was like being a teenager again, having to wear a dress that you’d bought with all your money in the world before you’d figured out what size you were. So I did all this in the house, and wandered down the street like a futurist Navy Seal overlord.

The insulation, for the first 20 seconds, was incredible. No prospect of a myocardial infarction at all; more like getting off a bus in bracing weather. Feet and hands, sure, do your worst: but my core temperature stayed stable for at least two yards. Then the water gets into the suit, and the freeze begins, and my first experience of this entirely predictable physical event shooed me out of the water immediately. It wasn’t that I’d misunderstood the principle – a thin layer of water gets trapped between your body and your suit, warms up under contact and then keeps you warm – more that I didn’t believe in it. The next day, I gave it longer, but still not as long as two minutes.

There is another principle: that you have to work up to the cold. Yet this doesn’t work like running, where you work up to 20 minutes by doing shorter runs for progressively longer. It’s more the way you adapt to the weight of a toddler, by growing your muscles imperceptibly as the kid grows: better to swim through the mild autumn into the start of winter, and build a tolerance with the season. It doesn’t work if it gets suddenly cold; so I stayed focused purely on advancing chunks of seconds. Even running, out of shape, for 90 seconds and feeling the mournful weltschmerz, of how much you’ve let yourself go, cascading over the wheeze of your sorry lungs doesn’t hold a candle to this discomfort.

On the plus side: it burns a lot more calories, if you can take it, than regular swimming; it’s good for your libido, apparently (though seeing me climbing into the wetsuit did nothing for my Mr’s libido); and you sleep better. But that could have been the trauma.

What I learned

Body heat is lost 25 times faster in water than in air. For me, the wetsuit isn’t a nice-to-have, it’s essential.