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It's one of those basic ideas you hear scientists repeating all the time: correlation does not imply causation.
科学家们一直在重复的基本观念之一：相关性并不意味着因果性。
Just because two things happened together doesn't mean one caused the other.
两件事情的同时发生并不意味着一个是因，另一个是果。
Well, back in the 1920s, they ignored their own advice.
好吧，回到上世纪20年代，他们忽略了他们自己的建议。
And the result was a major misconception that's still around today.
其导致的结果是一个至今仍存在的误解。
Because, despite what you probably were taught in high school,
因为，不管高中老师怎么说
lactic acid does not make your muscles hurt when you exercise.
乳酸不会让你在运动时产生肌肉疼痛。
In fact, it might actually help. It all started around 1920, with a German biochemist named Otto Meyerhof.
事实上，它还能有所帮助。这一切都要从1920年左右的一名德国生物化学家奥托·迈尔霍夫说起。
He helped figure out many of the steps of glycolysis,
他帮助计算出了糖酵解的很多步骤，
which is the series of chemical reactions that cells use to make energy from glucose or sugar.
这是一系列化学反应，细胞可以用此从葡萄糖，即糖中制造能量。
He also kind of fit the "mad scientist" stereotype.
他也有些符合“疯狂科学家”的标准。
If you've ever seen a scientist in a movie electrifying disembodied frog legs, well, Meyerhof did that in real life.
如果你曾在电影中看到过一名科学家给没有身体的青蛙腿充电的话，迈尔霍夫也做过这种实验。
He took frog legs — just the leg parts — and he gave them electric shocks, making them jump and twitch.
他截取了青蛙的腿—只有腿部—并电击它们，让它们蹦跳抽搐。
But, after a while they stopped jumping, Meyerhof found that the legs were full of lactic acid
但是，在它们停止跳跃一会儿后，迈尔霍夫发现青蛙腿中充满了乳酸
or, more accurately, lactate, which is lactic acid minus a proton.
或者更准确的说是乳酸盐，即乳酸减去一个质子。
He and another scientist, Archibald Hill, correctly figured out the steps of glycolysis that led to higher levels of lactate in the muscles.
他和另一名科学家阿奇博尔德·希尔争取的计算出了糖酵解（造成肌肉乳酸盐含量更高反应）的步骤。
But Meyerhof also assumed that the lactate buildup contributed to muscle fatigue, stopping the frog legs from jumping around.
但迈尔霍夫也认为乳酸盐积累促成肌肉疲劳，让青蛙腿停止跳动。
When you exercise, your body uses up its main source of energy, ATP, within a few seconds.
当你在运动时，你的身体在几秒钟内便耗尽了其能量的主要来源，三磷酸腺苷（ATP）。
Then it starts to make more, using a bunch of different chemical reactions.
然后身体利用很多不同的化学反应开始制造更多的ATP。
And during a hard workout, your muscles start to rely more heavily on reactions that also produce more lactate.
在进行高强度运动时，你的肌肉开始更多的依赖于也能够产生更多乳酸盐的反应。
When you exercise, the pH in your muscles goes down, meaning they become more acidic.
运动时，肌肉中的酸碱值（pH）下降，意味着它们变得更具酸性。
That's called appropriately muscle acidosis, and the drop in pH may be part of what causes the famous burn while you're exercising.
这被相应地称为肌肉酸中毒，并且pH值的下降可能是导致运动时肌肉燃烧的部分原因。
There was a clear correlation between the lactate buildup and acidity in the muscles,
乳酸盐积累和肌肉酸度之间有着清晰的相关联系，
and Meyerhof assumed causation, too: that lactate was responsible for lowering the PH in muscles.
迈尔霍夫也认为有因果联系：乳酸盐要为肌肉中pH值的下降负责。
This became a generally accepted hypothesis, and you still see it all over the place today.
这成为了被普遍接受的假说，并且至今仍随处可见。
Unfortunately, as we all know, assuming causation can be risky. And in this case, Meyerhof was wrong.
不幸的是，众所周知，假设因果关系是有风险的。在这一情况中，迈尔霍夫是错的。
Even though the lactate idea was well-accepted, there wasn't much empirical evidence for it,
虽然乳酸盐的想法被普遍接受，但其中并没有很多实验性证据证明，
and over the years researchers started to question whether it was accurate.
多年来，研究人员们开始质疑这一假设的正确性。
Around the second half of the 20th century, they started to pick apart what was really going on.
在20世纪下半叶左右，他们开始彻查真相。
One important clue was the fact that unlike lactic acid, lactate isn't an acid.
一条重要的线索是，和乳酸不同，乳酸盐并不是一种酸。
That missing proton means it's a base — it accepts, rather than donates, protons.
缺少质子意味着它是碱性的—它接收而不是奉献质子。
Meyerhof's idea assumed the reaction that produced lactate also produced a proton at the same time,
迈尔霍夫的想法是假设这种反应可以同时产生乳酸盐和质子
making the muscles more acidic overall. Turns out, it doesn't.
让肌肉总体更酸。事实证明并非如此。
The series of reactions that generate more ATP in muscles do produce extra protons, which lowers the pH in your muscles.
肌肉中形成更多ATP的系列反映确实产生了额外的质子，降低了肌肉中的pH值。
But the extra protons don't come from the step that generates lactate.
但额外的质子并不是来自于产生乳酸盐的步骤。
And, in fact, lactate bonds with some of those protons, making the muscles less acidic.
事实上，乳酸盐和其中一些质子相结合让肌肉没那么酸。
Lactate also isn't involved in delayed onset muscle soreness — the pain you feel a day or two after a hard workout.
乳酸盐也并没有参与延迟性肌肉酸痛—你在运动完一两天后会产生的痛感。
Scientists think that comes from microscopic tears in your muscles, although they are still investigating that.
科学家们认为这源于肌肉中的微小撕裂，虽然他们仍在对此进行调查。
It's weird that we don't 100% know, but we don't.
很奇怪我们不是百分百了解，但是我们确实不知道。
So, despite what you hear from personal trainers everywhere and sometimes even see in textbooks,
所以不管别处的私人教练怎么说，教科书里怎么写，
there's no reason to be so hard on lactate. It's just trying to help.
也没有必要为难乳酸盐啦。它只不过想帮帮忙而已。
Also, a side note here: you're gonna want to tell people about this. When they say "ah, the lactic acid!"
还有一条旁注：你要将这一点告诉所有人。当他们说“啊，乳酸！”
Do it - but try to be in the least pedantic way possible. We have to be accurate. But don't be condescending!
当你这么做时，请尽可能不要太过卖弄。我们必须要精准，但是不要表现出优越感！
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感谢提问，特别感谢Patreon社区，有你们的支持才有我们的回答！
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