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Pretty much everyone over the age of four has heard that cheetahs are the fastest land animal.
几乎所有四岁以上的人都听说过猎豹是陆地上跑得最快的动物。
These long, lean cats can accelerate from zero to 72 kilometers per hour in 2.5 seconds, which is ridiculously fast. Faster than a lot of cars.
这些体型修长的猫科动物可以在2.5秒内从0加速至72公里每小时，简直快得离谱，比很多车速都快。
But if you stop to think about it, it kind of seems like a bigger animal ought to hold the land speed title.
但如果你停下来想一想，似乎一种更大型的动物应该拥有陆地速度的头衔。
PIT's Tyrannosaurus Rex against a cheetah, and wouldn't the T. rex leave the cheetah in the dust?
霸王龙对比猎豹，难道不是霸王龙把猎豹甩到尘埃中吗？
The T. rex had longer legs and more muscles than a cheetah, so it seems like the cheetah would lose the race and get devoured at the finish line.
霸王龙比猎豹的腿更长，肌肉更多，所以似乎猎豹会输掉比赛，并在终点被吃掉。
But alas, T. rex was probably as useless as a sprinter as it was at playing piano with those tiny little arms.
但霸王龙可能会像短跑选手，像用它的迷你小手手弹钢琴一样没什么用。
And that has to do with the way muscles work.
这与肌肉的运动方式有关。
Skeletal muscles are made of bundles of fibers, and those fibers come in two kinds: slow twitch and fast twitch.
骨骼肌由纤维束组成，这些纤维分为两种：慢肌纤维和快肌纤维。
Slow twitch muscle fibers contract slowly, and are used by the body for activities that require endurance.
慢肌纤维收缩缓慢，被身体用于需要耐力的活动。
Fast twitch muscle fibers contract more quickly, and are good for rapid actions like jumping or sprinting.
快肌纤维收缩迅速，擅长需要速度的动作，如跳跃或短跑。
Slow twitch muscle fibers can keep doing their thing for a long period of time,
慢收缩肌纤维可以长时间保持运动，
while fast twitch muscle fibers tend to get fatigued pretty quickly and use up a lot of energy.
而快肌纤维往往很快就会疲劳，并消耗大量能量。
Big animals have more muscle mass, and therefore more fast twitch fibers.
大型动物有更多的肌肉，因此有更多的快速收缩纤维。
So logically, big animals should be faster than smaller animals, but there's a catch.
所以逻辑上，大型动物的速度应该比小型动物更快，但有个问题。
The fast twitch muscles of larger animals run out of fuel a lot more quickly than muscles of smaller animals.
大型动物的快肌纤维消耗能量的速度比小型动物的快的多。
Because their mass makes them heavier, it takes longer for a large animal to accelerate.
因为它们的肌肉让它们更重，大型动物加速所需时间更长。
So some biologists think large animals are simply incapable of reaching their potential top speed because they use up all their fuel before they can get there.
因此一些生物学家认为大型动物根本无法达到它们潜在的最高速度，因为它们在此之前就已经消耗掉了自己所有的能量。
So in terms of speed, it's not the big animals that rule, and it's not the small ones, it's the medium-sized ones.
就速度而言，获胜的不是大型动物，也不是小型动物，而是中等体型的动物。
In fact, in 2017 researchers hoping to answer this question published a model for predicting maximum speed in the journal Nature Ecology and Evolution.
实际上，在2017年，希望回答该问题的研究人员在《Nature Ecology and Evolution》杂志上发表了一项预测最大速度的模型。
The model uses body size alone to make predictions about animal speed, and it's accurate not just for land animals, but for birds, insects, and fish too.
该模型根据体型对动物速度做出预测，能够准确对陆地动物、鸟类、昆虫类和鱼类做出预测。
They developed this maximum speed model to answer questions about why there seemed to be an upper limit to animal movement,
他们开发了这个最大速度模型以回答为什么动物运动似乎有一个上限，
and what the consequences of those limits were for individual species.
以及对于个别物种而言，这些限制有什么影响。
In other words, the model can help us understand more about why some animals traded speed for size, and vice versa.
换句话说，该模型可以帮助我们更多的了解，为什么一些动物用速度换取体型，而一些则相反。
The relationship between size and speed was so robust, they can even use it to predict the speed of extinct species, even though we'll never see them in motion.
体型和速度之间的关系是给牢固，他们甚至可以利用这种关系来预测灭绝物种的速度，尽管我们永远看不到运动中的它们。
Like Velociraptor, which it predicts would have been roughly twice as fast as T. rex.
比如伶盗龙，预测其速度可能是霸王龙的两倍。
Cheetahs are the clear winners of the modern land speed game, even though they are roughly the same size as some other slower animals, like the leopard.
猎豹显然是当代陆地速度游戏的赢家，即便它们的体型和一些其他速度较慢的动物差不多，比如美洲豹。
The difference between cheetahs and their slower cousins can be found in certain physical characteristics that give them an edge.
猎豹和美洲豹之间的差异可以在某种身体特征上看到，这种特征给了它们优势。
For example, the cheetah's spine is longer and more flexible than the leopard's — or any cat species — which lets it maximize the length of its stride.
例如，猎豹的脊椎比美洲豹的更长更灵活——或者任何猫科动物——使它能够最大幅度地伸展它的步伐。
Other physical characteristics, like paw pads that provide traction, a large heart, liver, and adrenal gland, an aerodynamic body,
其他身体特征，比如提供抓地力的爪垫，大心脏、肝脏以及肾上腺，流线型体型，
and swiveling hips give it the edge it needs to claim the "fastest land animal" title. So a cheetah could definitely outrun a T. rex, but take heart.
以及能够扭转的臀部，这些给了猎豹获得“最快陆地动物”头衔的优势。所以猎豹绝对能跑赢霸王龙，但需要振作精神。
If you put the two species together in an ultimate fighting ring, the T. rex would win every time.
如果你把这两个物种放在一起进行一场终极格斗，霸王龙每次都是赢家。
Just as long as it doesn't have to outrun anyone. Or play the piano. Thanks for asking, and thanks to our patrons for bringing you this answer.
只要不是跑步或者弹钢琴。感谢提问，感谢我们赞助人带来的这个答案。
We are so grateful to have the coolest community of supporters out there. If you'd like to join them, check out patreon.com/scishow.
我们非常感谢有这么多最酷的支持者。如果你想加入他们，请登录patreon.com/scishow。
