Innate Gear-Shift Gives Cheetahs Their Speedy Stride
Greyhounds and cheetahs have similar body types, but the big cats routinely outrun the dogs. Cheetahs have been recorded running at up to 65 miles per hour - much faster than a greyhound, which, as the fastest canid, is known to reach 43 mph, according to Live Science.
How exactly cheetahs get more speed lies in the number of stride they take, which increases as they run faster, acting like a 'gear shift' that gives them a boost.
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"Cheetahs and greyhounds are known to use a rotary gallop, and physically they are remarkably similar, yet there is this bewitching difference in maximum speed of almost a factor of 2," study researcher Alan Wilson, from the Royal Veterinary College in the United Kingdom.
To find out what gives the cheetah its velocity, Wilson and colleagues laid plates in the ground of an enclosure at the ZSL Whipsnade Zoo outside London to measure the forces exerted on the animals' limbs, their body motion and footfall patterns. They also used high-speed cameras to capture the motion of the animals as they sprinted after a piece of chicken. Measurements on galloping greyhounds in the lab provided a comparison for the researchers.
When the cheetahs ran at the same speed as the greyhounds, the cats' stride was longer but they compensated for that with a lower stride frequency. Unlike the greyhounds who maintained a constant rate of about 3.5 strides per second no matter their speed, the cheetahs increased the frequency of their footfall as they 'shifted gears' into higher speeds.
At 20 mph, the cheetahs took 2.4 strides per second, but at 38 mph, they took 3.2 strides per second. Wilson suspects that wild cats may be able to reach stride frequencies of 4 strides per second, which, in combination with longer stride lengths, may allow them to outrun their captive cousins.
Though the captive cheetahs didn't get up to the speed of wild animals, running at a mere 38 miles per hour compared to the trained greyhounds who topped out at 43 miles per hour, the experiment still showed off the mechanics behind their speed.
"They have lived in a zoo for several generations and have never had to run to catch food. They have probably never learned to run, particularly," Wilson said. "The next stage is to try to make measurements in wild cheetahs in the hope of seeing higher speeds."
The team also analyzed the length of time that each animal's foot remained in contact with the ground - the stance time - and noticed that for some of the cheetah's limbs it was longer, which may be another factor that contributes to the wild cheetah's record performance.
Increasing the stance time reduces the peak loads on the animal's legs, and Wilson says, '[with] a longer stance time the cheetah will get to the limiting load at higher speed than the greyhound'.
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