Cool runnings: does sprinting or walking conserve more heat in the cold?

06 February 2018

Question

The temperature where I live recently hit -40 degrees. That got me thinking is it better to walk or to run through the cold air? Should you run to reduce the amount of time out in the cold or do the adverse effects of moving faster, like windchill, outweigh the benefits of getting to your destination quickly?

Answer

Izzie Clarke took on Trent's cool question.

Izzie - When you go outside and stand in the cold your body is much warmer than the air around you. Because heat likes to flow from hot to cold, it warms up the air next to your skin and this creates a kind of warm air blanket that slows down further heat loss.

But, if it’s windy, or you start moving then the warmer air molecules are pushed away and you’ll be exposed to new cold air. So running means you lose more heat to the air but we all know running warms us up. The faster you go, the more heat you generate and you get to your warm cosy house much faster.

So what’s the best strategy? It turns out whilst you are generating heat when your run, the air takes away that protective layer rather quickly at slow speeds. So, if you’re not the fastest runner it’s better to walk through the cold than break into a light jog.

Now, there are a few factors to work out the minimum running speed where the heat you generate finally balances out the heat you lose due to air movement. For example, the surface area of an adult human: how much heat do they generate plus the effect of wind on heat loss, but even so, this calculation applies to heat loss of bare skin. I mean we may be the Naked Scientists but we certainly don’t advise running at -40 degrees in your birthday suit.

All jokes aside - clothing’s actually an important factor here. While running slowly through the cold air naked might get rid of your warm air blanket, if you wrap up tight your clothing will trap the warm air  preventing windchill on your skin. So, to sum up, either stay put or where appropriate winter clothing, or run very very fast.

Next time, we’re simmering down to this question from Steve:

Switzerland has now banned boiling lobster live. Do they experience pain; how do we know?

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