What makes a cheetah run so fast?

Any animal that can go from zero to 40 mph in three strides must have a very specialized body. The cheetah is so built for speed, it really can't do much else.

A cheetah's speed starts with aerodynamics. Its slender body, small head, flattened rib cage and long, thin legs minimize air resistance. It typically only weighs about 125 pounds (57 kg), so its muscles don't have that much weight to carry.

Everything about a cheetah contributes to its superlative running skills. An oversized, powerful heart pumps huge amounts of blood; large lungs and nostrils allow for fast and deep air intake. A cheetah's eyes are extra long so they can get a fast, wide-angle view of their surroundings even at top speed. It has an extra flexible spine that curves with each stride, acting something like a spring for the back legs. The large tail is both a rudder and counterweight to a cheetah's body so it doesn't spin out during fast turns.

It's the stride, though, that makes most people gasp. The flexible spine, combined with unique leg muscles that give a cheetah's legs incredibly broad swing range, allow the animal to achieve a stride of 25 feet (7.6 meters) [source: Cheetah Conservation]. It's more like a bound at that speed, completing up to three strides per second, with only one foot on the ground at any time and several stages when feet don't touch the ground at all. Hard, ridged foot pads and blunt, nonretractable claws maximize traction with the ground.

Because a cheetah's heart rate accelerates so quickly to achieve that speed, the cat can only maintain the chase for about 600 yards (550 meters) [source: Cheetah Conservation]. Then, it's too hot and too tired to run anymore -- at which point it becomes easy prey for a larger, more aggressive animal. A cheetah is so hot and winded at the end of a chase, it nears the point at which brain damage could occur [source: Blue Lion]. Cheetahs often lose their kill to a larger animal because they need to rest before eating.

That need to rest is one of the drawbacks of speed. Being the fastest animal on land can be a curse. Accelerating to 70 mph in several seconds puts serious strain on the heart, but there's more to it. The small, slender head and short muzzle that increase aerodynamics also means a cheetah has weaker jaws and smaller teeth than other predators. Cheetahs can't fight back if a larger animal attacks them or their young. If confronted, a roughly 125-pound cheetah will always run rather than fight -- it's too weak, light and thin to have any chance against something like a lion, which can be twice as long as a cheetah and weigh more than 400 pounds (181.4 kg) [source: Wild Habitat].

A cheetah's intense specialization for speed has taken its toll. Cheetahs' inability to defend themselves, along with habitat loss to humans, has shrunk the population so much that inbreeding has become a survival problem, too.

Once all over Africa, Asia and India, cheetahs now are limited to only small parts of Africa and Iran. The wild population has shrunk from 100,000 in 1990 to about 10,000 today [source: Defenders of Wildlife]. It's possible that cheetahs are an example of over-specialization -- such extreme adaptation for a single skill that a species no longer has the other skills it needs to survive. Overspecialization can result in extinction, and experts don't rule that out for cheetahs. The hope is that if cheetahs go extinct in the wild, conservation efforts will at least ensure their survival in captivity.

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