Sixteen Miles of Cold Water
A physician in New Zealand wrote that he is preparing to swim Cook Strait, the body of water separating the north and south islands of New Zealand, next February. The Strait is 26 km wide (16 statute miles). It may take him anywhere from 8 to 15 hours to swim, depending on tides and other factors. Temperatures range from 14 to 19 degrees Celsius (52-66 F). Body grease is allowed for the crossing, but no wetsuit, just a regular bathing suit. He asked me to call him "Ernie."
Dr. Ernie is 6'2", approx. 190 lbs, on the lean side. He shivers easily. He asked for suggestions about acclimatizing to cold water swimming.
Cold acclimatization means increasing your ability to tolerate cold. Cold acclimatization occurs through regular exposure to cold. People developing cold acclimatization don't need to shiver so soon, and generate more heat without shivering. They may develop ability to both increase and decrease skin temperatures. In some circumstances, skin blood flow increases to keep extremities warm. In other cases, it decreases to reduce heat loss.
Tolerance to cold improves with physical conditioning. A fit person can tolerate a colder external environment and lower internal body temperature than an unfit person before shivering begins, and they can generate more internal heat through shivering. Increased muscle through physical training increases their ability to produce and store heat. Being physically fitter allows you to exercise at a higher intensity to generate more heat. Cold tolerance increases more with exercise in the cold than from exercise alone. For that reason, you need to get out and exercise in the cold.
Dr. Ernie writes, "I've kept up my schedule of working on technique in the pool and have been in Wellington Harbour at least 4 times weekly for 30 minute swims: the temp is about 14-15 Celsius and I can feel myself slowly able to tolerate the cold better -- much less shivering after I'm finished."
A nice fat layer helps maintain warmth and buoyancy for cold water swims. You don't want so much fat that you are slower or unhealthy. I mentioned to Dr. Ernie, that maybe he can stay lean to make the training more effective (difficult) now, then gain the fat closer to time of the crossing when he will want an easier ride.
Ideas? Encouragement? Comment below.
- Information on cold immersion and cold tolerance is in "Diving Physiology in Plain English."
- Read the next update of Dr. Ernie's training for the Cook Straight in Getting Fitter in 50 Degrees.
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