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When it's cold out and you didn't dress for the weather and you're far from shelter, you have a crucial decision to make:
当外面很冷，你又没有穿上适宜天气的衣服，而且你离住处很远时，你就得做一个关键的决定：
should you run (or ski) to try to warm up, or go slow and avoid the cooling effects of wind?
你是应该跑步（或滑雪）来试着取暖，还是应该慢慢走，避免风的降温效应？
When it's cold out and you're not moving, the heat you lose goes to heating up the air around you, forming a slightly warmer protective layer so you don't cool off as quickly.
当外面很冷，你一动不动的时候，你失去的热量会用来加热你周围的空气，形成一个较为温暖的保护层，这样你就不会很快降温。
But if you're moving (or if it's windy), you’re being exposed to some amount of fresh, new, cold air – more of it the faster you go.
但如果你在运动(或者天在刮风)，你就会暴露在一些新鲜的冷空气中——你走得越快，接触的冷空气就越多。
You’re literally running away from the air you warmed and so you cool off faster than if you stayed put.
你实际上是在远离你加热的空气，所以你比待在原地冷却得更快。
Though once you're going fast enough, the protective layer of air will be pretty much entirely gone and you'll basically lose heat at the same rate regardless of how fast you're running.
不过一旦你跑得足够快，空气的保护层几乎就会完全消失，不管你跑得多快，你基本上都会以同样的速度失去热量。
Now, when humans run, we also generate a fair amount of heat inside our bodies.
当人们跑步的时候，我们也会在体内产生大量的热量。
In fact, we produce a roughly constant amount of heat per kilometer traveled, so the faster you go, the more heat you generate any given minute.
事实上，我们每跑一公里产生的热量大致是恒定的，所以你跑得越快，在每分钟内产生的热量就越多。
Because the heat generated by running has a steady increase, while your protective layer of warm air goes away quickly at low speeds,
因为跑步产生的热量稳步增加，而你的暖空气保护层以较低的速度迅速消失，
it turns out that there's a kind of "forbidden range" of speeds where it's not worth walking, or even running slowly, since you’d lose less heat standing still.
事实证明，在某种速度范围内，不值得步行，甚至不值得慢跑，因为站着不动会损失的热量更少。
So what's the minimum speed where the heat you generate running finally balances out the additional heat you lose due to air movement?
那么，当跑步产生的热量最终能够抵消由于空气流动而损失的额外热量时，最小速度是多少？
Well, using some estimations for the surface area and energy generation of an adult human running naked and the effects of wind on heat loss,
通过对一个成年人裸奔时的表面积和发热量以及风对热量损失的影响进行估算，
I found that when it's freezing outside, you need to be able to run roughly a 5-minute mile to be better off moving than staying put.
我发现，当外面很冷的时候，你需要以大约5分钟每英里的速度跑步才能比待在原地更好地保暖。
And faster, if it’s colder out.
外面越冷，就需要越快的速度。
And this wouldn’t even mean you're not losing heat – it's just the point at which you lose less heat running than you do standing still.
这并不意味着你没有失去热量——只是在这个点，你在跑步时比静止不动时损失的热量更少。
Now if 5-minute mile sounds like a challenge, don't worry.
如果5分钟每英里听起来是个挑战，别担心。
All you need to do is put on some clothing – like, enough that you're only losing half as much heat as a naked person –
你只需要穿上一些衣服——比如，足够让你失去的热量只有赤身裸体时的一半——
and a 15 minute mile (basically a brisk walk), will do just fine.
然后走15分钟每英里（基本上就是快步走），就可以了。
So, either stay put, or wear appropriate winter clothing, or run naked very very fast through the snow.
所以，要么待在原地不动，要么穿上合适的冬衣，要么就光着身子在雪地里飞快奔跑。
