Scientists are attempting to discover exactly what makes cheetahs the fastest running animals on the planet.

科学家正试图发现什么使猎豹成为地球上最快的奔跑动物。

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The lure of some string to play with is to difficult to resist

A Royal Veterinary College (RVC) team is using high-speed cameras and a sensitive track to monitor the big cats as they sprint（短距离赛跑）.

Cheetahs can reach speeds of at least 104km/h (64mph) and they can achieve their top speed in just a few paces.

The study is being carried out with North African cheetahs from ZSL Whipsnade Zoo.

Professor Alan Wilson, head of the structure and motion laboratory at RVC, said: "The cheetah is fascinating（迷人的） because it can run 50% faster than any of the other animals we are familiar with, so in terms of understanding what limits how fast you can run, the cheetah is a wonderful animal to study."

Chasing chicken

Just as most domestic cats cannot resist chasing a piece of string, cheetahs also find the temptation of some twitching（颤搐） twine too difficult to ignore - especially if a tasty treat is dangling from the end.

So the research team entice（诱骗，引诱） the zoo's cheetahs to run by attaching some choice chicken pieces - wings and feet are a favourite - to a loop of fast-moving string that is pulled along the enclosure by an electric motor.

And as the cats chase the chicken feast, four high-speed cameras, which record at 1,000 frames per second - compared with 25 frames per second for standard cameras - capture their every move.

Penny Hudson, a PhD student at RVC, said: "We use two cameras on each side of the enclosure（附件，围绕） so we can see the cheetah from both sides.

"When a cheetah gallops（疾驰，飞奔）, it does different things with either side of its body - it has an asymmetric（不对称） gate."

The scientists are also using special plates that are embedded（植入的，内含的） within cheetahs' running track.

Miss Hudson explained: "The plates are like sophisticated weighing scales that are able to measure all the forces going through their legs."

Lightning Bolt

The scientists are going to compare their results with other studies that have been carried out on greyhounds（灰狗，快速船）, which can reach top speeds of approximately 60km/h (40mph).

Miss Hudson said: "Greyhounds are artificially bred by us to be fast, whereas these [cats] have evolved for that.

"But cheetahs can run much faster than a racing greyhound.

"So we're trying to get them running at similar speeds to see what they do that's the same and what they do that makes them go that little bit faster."

In speedy humans - the fastest on record being Usain Bolt who ran 100m in 9.69 seconds (an average of 37km/h or 23mph) - speed is thought to be constrained by leg strength.

While in greyhounds, speed is believed to be limited by how quickly the dogs can swing its legs.

But for cheetahs - the reasons are still unclear - so the data from the experiments will be used to examine the forces and dynamics（动力学） of the cats' legs, their speed, the length of each stride, as well as joint angles and posture.

Miss Hudson added: "We really don't know what it is about cheetahs that make them run so fast - it might be their flexible spines（脊柱）, or it might be their shoulder blades, it could be that they stretch their legs a bit more, but hopefully the data will unravel（阐明，解释） some of those mysteries."