Image copyright Christopher Basu Image caption The researchers hope to understand how the animals evolved to be so "bizarrely long-necked"

Scientists have worked out the anatomical secret to giraffes' long and spindly - but strong - legs.

Researchers from the Royal Veterinary College (RVC) of London found that a supportive ligament is protected by a groove in the animals' lower leg bones.

This groove is much deeper in giraffes than in other animals, and the researchers say this helps the spindly-legged giants support their bodyweight.

The work was outlined at the Society for Experimental Biology meeting.

"Giraffes are heavy animals (about 1,000kg), but have unusually skinny limb bones for an animal of this size," explained Mr Christopher Basu, the PhD student who led the research.

"This means their leg bones are under high levels of mechanical stress.

"I'm interested in how giraffe have evolved from their modestly-proportioned ancestors to these bizarrely long-necked, long-legged animals that we see today," he told BBC News.

This evolution has resulted in an animal with very long legs but relatively little muscle.

"It turns out," explained Prof John Hutchinson from the RVC, "that the suspensory ligament plays an important role".

The team took its measurements from the legs of giraffes that had died in captivity, using a hydraulic press to apply forces to the legs to simulate bodyweight.

This showed that the legs remained upright and stable with no additional support, even when the scientists applied loads slightly greater than a giraffe's body weight.

Image caption Giraffes can support their bodyweight while not engaging too much muscle

Their specialised anatomy, Mr Basu explained, "adds great stiffness to giraffe limbs".

This means that giraffes can support their huge weight without actively engaging as much muscle, which reduces fatigue.

"We're learning new things about giraffe anatomy," Mr Basu told BBC News.

"This is hugely beneficial to today's living giraffes; what we learn here can help to advance medical care for giraffes in zoos."

The findings, the team say, will ultimately help link the anatomy of modern giraffes with their extinct prehistoric ancestors.

"And robotics often draws inspiration from animal movement," said Mr Basu.

"So studies of this long-legged long-necked animal could inspire such oddly proportioned robotic - or even prosthetic - designs."