Cold acclimatisation is partly about what you are happy to tolerate. We can all develop a barometer of what’s right for us and may learn from how awful we feel after getting out what counts as having ‘over- done it’.
Anyone looking to push themselves to extremes may be interested to learn that science’s answer to the question ‘can I tell if I’m too cold?’ is surprisingly ‘no’. There is a poor correlation between thermal perception (how cold you feel) and thermal status (how cold you are), and cold acclimatisation makes this already poor relationship worse. Not only do acclimated swimmers not shiver, paradoxically they feel more comfortable as their deep body temperature falls.
Two of the first physiologists to look at cold water immersion were Griffith Pugh and Otto Edholm. In the early 1950s, they put two people in 16 °C water in a cold immersion tank and measured their core temperature and responses. One of these men was Pugh himself, while the other was a leading endurance swimmer of his generation, Jason Zirganos, who had crossed the Channel three times. Where Pugh was tall, lanky and unacclimatised, Zirganos was stocky and acclimatised, and 20 kilos heavier than Pugh despite being 19 centimetres shorter.
The authors measured the discomfort and the core temperature of the two men in their tanks. Mike Tipton (a consultant in thermal and survival medicine from the University of Portsmouth) told me that he found out more about the study in private correspondence with the researchers: they discovered that while Zirganos grew dangerously cold on a core temperature level, he neither shivered nor reported discomfort – in fact, he sat there happily, reading his newspaper. At the same time Pugh, thinner, taller and unacclimatised, was in an adjacent immersion tank ‘cooling at about the same rate but desperately uncomfortable and almost tetanic with shivering’. (Tetanic means having spasms or contractions).
What the study showed was that Zirganos lacked insight into his thermal state, a phenomenon Tipton dubs ‘undetected hypothermia’, understanding cold where people drift into unconsciousness on a swim. Zirganos drifted into unconsciousness in 1953, in a four-hour swim in the 8 °C Bosphorus, and again a few years later as he attempted to swim the 22-mile North Channel of the Irish Sea. He did not feel cold prior to this. He was hauled from the water and pronounced dead at the scene. A tragic and cautionary tale – and one which isn’t, according to Dr Heather Massey, a sports scientist, physiologist and ice swimmer at the University of Portsmouth, wholly uncommon.
This is an extract from The Outdoor Swimmers’ Handbook, by Kate Rew, pictured here with her lips going blue.