Cats fall and land on their feet. This uncanny ability to right themselves before hitting the ground has long puzzled scientists. Now, a team from Yamaguchi University in Japan has provided the answer, detailing how the thoracic spine is more flexible than the lumbar spine in a study published in the journal The Anatomical Record.
The key is a highly flexible thoracic spine in the middle of the back. It is nearly three times more flexible than the lumbar spine in the lower back, which acts more like a stabilizer. The arrangement enables rapid, almost unresisted rotation of the upper body of up to about 50 degrees. This lets a cat bring its paws toward the ground within milliseconds.
The discovery resolves a physics conundrum that has intrigued researchers for three centuries. A scientific debate sparked by Étienne-Jules Marey's motion studies in the 1890s has continued among physicists and physiologists for over a century. The question boils down to this: if cats have nothing to push off of, how can they manage to turn midair? Classical physics says a spinning object needs an external force to change direction. Cats appear to violate that rule.
The team, led by Yasuo Higurashi at Yamaguchi University, examined the spines of five cat cadavers. They separated the thoracic spine (upper and middle back) from the lumbar spine (lower back) and mechanically tested them under twisting forces to measure flexibility, strength and resistance to rotation. They also filmed live cats performing their famous aerial rotation.
What researchers observed was elegantly simple: when cats tumble through the air, the front half of the body rotates first, followed by the rear half. The head and front paws begin to turn toward the ground, helped by the lighter front of the body and the superior torsional flexibility of the thoracic spine. The stiffer lumbar region anchors the motion while the thoracic region supplies the twist. As the anterior segment rotates and orients the forelimbs downward, the posterior follows in quick succession, with the hind legs aligning for landing.
By showing that an internal redistribution of twist—rather than a single-body spin—drives the reflex, the study explains how cats reorient without violating conservation of angular momentum. The two halves of the spine rotate in opposing directions but at different speeds, cancelled out by their different sizes and weights. It is, in essence, an internal balancing act that requires no external contact.
The righting reflex can take less than a second and a cat needs at least two and a half feet to stick the landing. Falls from too short a height leave insufficient time; falls from certain medium heights can be more dangerous than very high falls, since gravity gives the cat more time to deploy protective measures. Falls from the seventh or higher stories are associated with more severe injuries and with a higher incidence of thoracic trauma, though cats land with less impact when they fall from higher than the seventh floor than from lower heights, mostly because of air resistance, which slows the cat's body enough to allow it to turn.
The findings may do more than just explain a curious pet trick. The research could improve mathematical models of animal movement, help vets treat spinal injuries and even lead to more agile robots. In the late 1960s, NASA became interested in cat-righting because astronauts needed to learn how to turn over in weightless environments. Engineers at Stanford University used computer simulations to refine understanding of the motion. Today, roboticists continue to study the reflex as inspiration for machines that can recover from falls.