Water temperature and the effects on your body

Do you really know how your body reacts to cold water when swimming in open water? Nobody knows for sure. So our safety team, physiologist Jonny Hisdal and safety director Jørgen Melau, have started a research project to find out more. What better place to start than Norseman, where the water temperature in the Hardanger Fjord is a hot topic among triathletes worldwide?


They have been testing the water on the Norseman swim course for several days now. Water temperature is measured daily at different times and at different locations on the swim course. But then they go deeper. They aim to find out how water temperature affects a swimmer’s core temperature. But how?

The answer was to go James Bond style. You’ve seen the character ”Q” in James Bond, the man with all the gadgets? Well, Jonny and Jørgen have a sensor that Q himself would be proud of – they’ve got a pill to swallow, and this pill measures and constantly send their core temperature to a receiver in a vest under their wet suit.

The magic sensor pill, ready to go to work

The magic sensor pill, ready to go to work

This year the two researchers are carrying out this study on themselves as a pilot for a larger study of Norseman athletes in the future.

Jørgen said, ”this year we’ll do a study with a very small ‘n’ – so that means we need to be a little bit careful about making generalizations from our results. But, it will give us some pointers about how the water temperature affects the body, and how to arrange a larger study in the future”

Jonny and Jørgen offered the following observations after swimming the full distance in Eidfjord today, where the water temperature was measured at around 11°C: “As expected, hyperventilation was observed the first minutes in the cold water. We both used standard equipment today with an ordinary swimming cap and no neoprene socks to make the test as realistic as possible.

An "upgraded" pulse belt.

An “upgraded” pulse belt.

Total duration in water was 1 hour, 33 min.  A gradual drop in skin temperature at the chest to approximately 27.5 °C was observed in the first 20 minutes. After that skin temperature stabilized at that level for the rest of the swim, indicating that the wetsuit works as intended. Interestingly, the core temperature started at 37.2° C and ended at 37.7 °C. The lowest core temperature at around 36.9 °C was observed approximately 15-20 min after the swim. This is due to redistribution of the cold blood from the skin and extremities to the core.”

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Figure 1 shows how the temperature tracked over the duration of the swim. Jonny and Jørgen said the results from their pilot didn’t reveal any drop in core temperature after their swim of 3800m for 1 hour, 33 min in water temperature around 11°C. Watch this space – we plan to keep you posted on what their project shows us as it goes along.