‘One minute per degree’ is a rule often touted among cold-water swimmers, but is it a reliable guideline? Heather Massey and Mike Tipton of the Extreme Environments Laboratory at the University of Plymouth investigate.
There is an inverse relationship between water temperature and rate of cooling (the colder the water, the faster your tissues cool). So, the idea that in-water duration is reduced as water temperature cools in winter and spring is not a bad starting point.
But the nature of the relationship between water temperature and deep body cooling rate varies hugely between individuals.
Also, focusing on this relationship ignores more important issues. Hypothermia is not the only problem associated with cold water immersion. Fixing the time in specific water temperatures isn’t helpful. This ‘guideline’ doesn’t address many situations.
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