PREVIEW

As the old adage says, when cats fall, they almost always land on their feet.

This remarkable ability to right themselves before hitting the ground has puzzled scientists for decades.

Now researchers at Yamaguchi University in Japan say they have uncovered the reason. Their study, published in the journal The Anatomical Record, suggests the secret lies in the unique flexibility of a cat’s spine.

The so-called air-righting reflex allows cats to twist their bodies in mid-air so that their feet face downwards before they land. At first glance this appears to defy the laws of physics, because an object in free fall should not be able to rotate without pushing against something.

To investigate how the manoeuvre works, the researchers first examined the spines of five deceased cats. They separated the thoracic spine – the upper and middle section of the back – from the lumbar spine in the lower back.

“The thoracic and lumbar spine regions exhibited marked differences in torsional mechanical properties,” the researchers, led by Yasuo Higurashi wrote. “The thoracic region exhibited a larger range of motion, a larger neutral zone, and lower stiffness than the lumbar region, indicating greater torsional flexibility.”

Each section was then subjected to controlled twisting forces to measure its flexibility, strength and resistance to rotation. The tests were designed to reveal how much each part of the spine could move.

The team also used high-speed cameras to film two healthy cats being gently dropped on to a soft cushion. Markers were placed on the animals’ shoulders and hips so the scientists could track how different parts of the body moved during the fall.

The study found that a cat’s spine is not uniformly flexible. Instead, different sections perform different roles during the fall.

“These results suggest that trunk rotation during air-righting in cats occurs sequentially, with the anterior trunk rotating first followed by the posterior trunk, and that their flexible thoracic spine and rigid lumbar spine in axial torsion are suited for this behavior,” they added.

The thoracic spine proved to be extremely flexible. It contains what scientists call a “neutral zone” – a range in which it can twist almost freely, reaching close to 50 degrees of rotation with very little effort.

By contrast, the lumbar spine is significantly stiffer and acts more as a stabilising structure.
This difference allows the front and back halves of the body to rotate at different times. As a cat begins to fall, it first turns its head and front legs towards the ground. Because the thoracic spine is flexible and the front of the body is relatively light, this section rotates quickly.

The back half then follows. The firmer lumbar spine provides a stable anchor point, allowing the cat to swing its front half around without the entire body spinning uncontrollably.

According to the researchers, the movement happens in stages. The front part of the trunk rotates first, followed by the rear section, until both halves of the body face upwards and the paws are positioned to absorb the landing.

The authors say the findings may have wider applications beyond explaining a familiar feline trick. They suggest the results could help refine mathematical models of animal movement, improve veterinary understanding of spinal injuries, and even inform the design of more agile robots.