The dynamics and energetics of locomotion depend on the number of propulsive legs

September 7, 2018, University of Cologne
The number of propulsive legs determines the animal's body dynamics during locomotion Credit: Dr. Tom Weihmann

Although land animals can move in many different ways, most terrestrial creatures use legs to crawl, scuttle, walk and run about. Leg-propelled animals such as mammals, insects, spiders or centipedes, feature a wealth of differently designed locomotor apparatuses and a wide range of leg numbers. In order to cover distances with energy efficiency, many terrestrial animals exploit mechanisms enabling energy recovery. Such mechanisms can comprise repeated interconversion of kinetic and potential energy due to vertical oscillations of the body's centre of mass or the use of elastic energy stores. They typically occur in bouncing gaits—as found in running bipeds or trotting quadrupedal and hexapedal animals.

A current study led by Dr. Tom Weihmann from the University of Cologne's Department of Animal Physiology has now shown that body dynamics in legged animals and robots depend strongly on the number of propulsive legs. The study, titled "Leg force interference in poly-pedal locomotion," has now been published in Science Advances.

In the past, trotting animals have served as models for legged robotic applications. "Scientists and engineers have examined efficiency-enhancing mechanisms, but until now, we knew very little about the effect of different numbers of legs on the ability to recover movement energy and to economize long-distance locomotion," says Weihmann.

His current study shows that growing leg numbers increasingly impede energy recovery because significantly higher degrees of leg synchronisation are required. The results indicate that small changes in leg coordination patterns have a much higher impact on the body dynamics in locomotor systems with many legs than in those with fewer. While animals with only a few walking legs often exploit mechanisms for energy recovery when approaching intermediate to high running speeds, animals with more than three pairs of walking legs are almost unable to achieve the required high level of leg synchronisation.

The revealed mechanisms could also have been a driver for quadrupedal animals like basilisks and other lizards to adopt bipedalism during high-speed locomotion. "Ultimately, these mechanisms could also partly explain the primeval development towards bipedal dinosaurs from their quadrupedal ancestors, which led to the wealth of present-day bird species," adds Weihmann. "And the model may even help to explain one of our own peculiarities: the bipedal human gait."

The new insights also provide strong and reliable scaffolding for emerging neuro mechanical modeling approaches and affect ideas of locomotor systems in general, which may lead to improved control mechanisms of fast-running legged robots.

Explore further: Insights on fast cockroaches can help teach robots to walk

More information: Tom Weihmann, Leg force interference in polypedal locomotion, Science Advances (2018). DOI: 10.1126/sciadv.aat3721

Related Stories

Insights on fast cockroaches can help teach robots to walk

December 8, 2017

Using the example of cockroaches, the Cologne-based zoologist Dr Tom Weihmann and his team were able to show that quickly running insects change their gait at mid-speed. This behaviour has previously only been observed in ...

Six-legged robots faster than nature-inspired gait

February 17, 2017

When vertebrates run, their legs exhibit minimal contact with the ground. But insects are different. These six-legged creatures run fastest using a three-legged, or "tripod" gait where they have three legs on the ground at ...

Study: Long legs are more efficient

March 12, 2007

Scientists have known for years that the energy cost of walking and running is related primarily to the work done by muscles to lift and move the limbs. But how much energy does it actually take to get around? Does having ...

What quails can teach us about the gait of dinosaurs

December 9, 2014

Motion scientists and zoologists of Jena University (Germany) study out the gait of birds. In the Proceedings of the Royal Society B the team published the first detailed analysis of the bipedal gait of quails. The scientists ...

Recommended for you

The taming of the dog, cow, horse, pig and rabbit

November 20, 2018

Research at the Earlham Institute into one of the 'genetic orchestra conductors', microRNAs, sheds light on our selectively guided evolution of domestic pets and farmyard animals such as dogs and cows.

Discovery could neutralize West Nile virus

November 20, 2018

Researchers at Vanderbilt University Medical Center and colleagues have isolated a human monoclonal antibody that can "neutralize" the West Nile virus and potentially prevent a leading cause of viral encephalitis (brain inflammation) ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.