A study led by the UK's University of Manchester shows that unlike most quadrupeds, elephants move by a form of 'four-wheel drive'. The research, which is published in the Proceedings of the National Academy of Sciences (PNAS), also reveals that elephants' knees are more flexible than previously thought. The findings could lead to improved treatment for animal diseases such as arthritis and may even throw light on how the dinosaurs moved around.
Whereas most four-legged animals use their front legs to stop and their back ones to propel themselves forward, elephants share the work more evenly. 'There's no obvious division of labour,' said lead author of the study Dr Lei Ren of the University of Manchester. 'They all work together to achieve the same goal.'
The researchers found that while elephant legs look heavy and stiff, they are in fact more flexible than those of a horse. If an animal's legs are like stiff columns, this means less work for its muscles, explained co-author of the study, Dr John Hutchinson of the Royal Veterinary College in London, UK. 'If you lock your knees, your leg turns effectively into a pillar. You don't need a lot of force from your muscles at all. If you bend your legs you can feel your muscles exerting more force.'
Previous research has shown that the larger an animal is, the heavier and stiffer its legs are. With the help of expert elephant handlers, the team carried out tests on six Asian elephants at the Thai Elephant Conservation Center in Lampang, Thailand. They wanted to find out whether the elephants naturally stand and walk with their legs straight or bent.
One reason why this kind of research had not been carried out before was the sheer size of the undertaking. At the Conservation Center, 16 custom-made force platforms (like vast bathroom scales) were placed in the ground. Reflective disks were positioned at key points on the elephants' bodies and infrared cameras recorded their movements as they walked over the platforms.
The team used the data from the cameras and the platforms to analyse the elephants' movements and see how hard their muscles work to propel them forward. The results demonstrated that the animals' muscles provided only one-third of the power that computer models had predicted. This indicates that the elephants' legs were supple and flexible enough to be able to propel them forward easily.
The team also noted that the elephants' leg muscles worked harder as they shifted from walking to running, perhaps explaining why they prefer walking to running in the wild. Further three-dimensional (3D) evidence of the elephants' movements showed that they used all four legs to stop and go – unlike other four-legged animals which mostly use their back legs to propel themselves forward and their front legs to stop.
The team is now focusing on building computer models of the contribution each muscle, tendon and bone makes to an elephant's movements, hoping that the models will help problems such as arthritis in elephants.
'There's got to be some weak link in the limb that prevents elephants from moving any faster than they do,' said Dr Hutchinson. 'If we can figure it out for elephants it can help for other species as well.'