Cheetahs Use Hind Limbs to Accelerate

Cheetahs use their hind limb muscles rather than their fore limb muscles to run faster, finds a new study by Japanese researchers.

A team of researchers from Yamaguchi University in Japan studied the muscle fiber distribution of cheetahs to find the secret behind their speed.

Cheetahs are known as the fastest land animals which can cover long distances in short time spans. Recently, a headless robotic cheetah broke its own previous record of 18 mph and set a new world record for the fastest running by a four-legged robot. The robotic cheetah clocked 28.3 mph on a laboratory treadmill breaking the record of the world's fastest man, Usain Bolt, who clocked 27.78 mph in 2009 during a 100-meter sprint, reported the Los Angeles Times.

While the cheetah's ability to run fast is known, the Japanese researchers have found the secret behind their record-breaking speeds. The Japanese researchers compared the muscle fibers of the cheetah with those of the domestic cat and the beagle.

They found that the muscle fibers of both the cat and the cheetah had a very low percentage of Type I fibers, while they had a high percentage of Type IIa fibers. Type I fibers enable slow movement of muscle fibers and help more in slow walking, whereas Type IIa fibers help in faster movements.

They noticed that the hind limb muscles of the cheetah have a high percentage of Type II (Type IIa + IIx) fiber when compared to the muscle fibers of their fore limbs. Type IIx fibers mean that the cheetahs have faster fibers that provide a higher force output which helps in faster acceleration. The cheetahs have both the fibers in their hind limbs that give then a propulsive power to run faster, reported the BBC.

Experts revealed that the cheetah's power to run faster is similar to a rear wheel drive car, where the engine power flows to the rear wheels. Similarly, the cheetah's propulsive power comes from the hind limbs that allows increase in their stiffness while running.

"The fore limb muscles in the cheetah included [the] most Type I muscle fibres of all three animals... while the muscle of hind limb muscles have many Type IIx fibres," Dr Naomi Wada, the study's co-author and Professor in System Physiology at Yamaguchi University in Japan, told BBC.

"The functional difference between forelimb and hind limb is the most remarkable in the cheetah," she said.

Further, in order to monitor how the cheetah takes hold of its high speeds, experts studied the growth of muscle fibers between flexors and extensors of the digits in the cheetah. They found that the digits of cheetah's front legs had more fast fibers, while the digits of the cheetah's hind legs have no such fast fibers.  

This suggested that the cheetah controls its movements by using its fore feet to turn and reduce the speed, Dr Wada explained to BBC.

The findings of the study are published in the journal Mammal Biology.