People: John Hutchinson

Why do elephants move so strangely? — A mystery dating back to the dawn of cinematography

Researchers have been puzzled about how elephants move since Edward Muybridge first caught their “ambling” gait on film as part of his major contribution (with Etienne-Jules Marey) to the invention of cinematography. Elephants can move somewhat quickly but never leave the ground with all four feet at once.

Dr. John Hutchinson’s team in the Structure & Motion Laboratory group took up the challenge of understanding how and why elephants do this in the late 1990s and has published a series of 11 papers on elephant anatomy, growth and locomotion since then.

His group’s latest study is a climax of much of that research. Hutchinson’s team, including first author Dr. Lei Ren, former PhD student Dr. Charlotte Miller, and longtime collaborator in Thailand Richard Lair (of the Thai Elephant Conservation Centre and National Elephant Institute), have just published a paper in Proceedings of the National Academy of Sciences (PNAS) entitled “Integration of biomechanical compliance, leverage, and power in elephant limbs.” PNAS is a very prestigious international science journal based in the USA.

The research was funded by the Biotechnology and Biological Sciences Research Council (BBSRC) in the UK. Special thanks are due to Mr. Daniel Seng (Qualisys, Inc.) and Mr. Thanasit Ujjin (United Sports Trading Pvt, Ltd.) for loans of Qualisys ProReflex motion analysis cameras in Thailand.

A summary of the paper follows.

Running with elephants at twilight

In 2006, Dr. Hutchinson's team conducted a series of challenging experiments in Thailand where they installed 16 ‘elephantine’ force platforms in the ground. They then had six Asian elephants traverse the force platforms across a wide range of speeds (from slow walking to about 11 mph, approaching their top speed of 15mph; 24kph). The force platforms measured the forces on elephant limbs while seven high-speed infrared motion capture cameras recorded their movements. This in itself is no simple endeavor but they were lucky enough to be able to share these custom-made forceplates with a research team from Belgium. The team had to work at twilight because their cameras were very sensitive to the strong Thai sunlight.

Dr. Hutchinson's team used these analyses, in addition to anatomical dissections of elephants that had died in captivity from unrelated causes, to address three related questions about how elephants move. Here is what they found:

Are elephant limbs like pillars?

Elephant limbs are compliant (showing elastic or bouncy aspects) even in walking, against classical dogma that they are stiff and columnar. Elephant limbs are often described as the epitome of a pillar-like limb structure for supporting their weight. Dr. Hutchinson's team found that elephant limbs actually bend and rebound small amounts during each step, acting less like pillars than previously thought and more like bouncy struts. This compliance seems to help keep the forces on elephant limbs low, acting like a shock absorber, which is important for such large animals.

Do elephant limbs have the best leverage of any land animal?

Previous theory held that animals tend to adopt straighter limb postures as they get larger during evolution, which helps to improve their leverage and provide them with more efficient support of their weight. Dr. Hutchinson's team used this theory to predict how good the leverage of elephant limbs should be, and found that it was only one third to one half as good as predicted. Indeed, elephant limb leverage is worse than that of horses' and almost precisely the same as humans'. Also like humans, and unlike horses and other quadrupeds, elephant limb leverage gets worse as they speed up from a walk to a run. This means that when running, elephant muscles must work even harder to prevent the limbs from collapsing than they otherwise might. Their compliance (bounciness) may help alleviate this problem. However, the study showed that the metabolic costs of running in elephants might get so high that endurance would become a major problem, which may be why elephants seem not to run often or for very long. This link between leverage and metabolic cost had not been shown before in elephants, and could only be determined with these measurements.

Do elephants use their limbs to propel and brake their mass in the same way as smaller animals?

Four-legged animals divide the labour between their fore and hind limbs during walking and running. The forelimbs mainly brake the animal and the hindlimbs mainly propel it; together they help the whole animal maintain a steady speed. So when Dr. Hutchinson's team measured these braking and propulsive forces in elephants, they were surprised to find that this division of labour was absent. Elephant fore and hind limbs did similar things; they all contributed to braking and propulsion, not predominantly one or the other. Thus elephants use their limbs like the wheels of 4x4 vehicles, which should help them to maintain a steady speed at low cost, with a smooth ride. As far as we know, this way of moving is unique to elephants.

  

(this will be updated as we receive pertinent questions)

What is this research useful for?

It is basic science that is about how elephant limbs function, at a fundamental level, and this is interesting and important in itself, for many reasons (probably some of which no one can predict).

But the data we have collected are precisely the kind of data routinely used in human (and other animal) clinical/orthopaedic gait studies to compare normal and abnormal individuals, e.g. with arthritis or foot problems. Because elephants experience similar health problems, our data form a useful (and to date the only) baseline for beginning to understand how, why and when elephants develop musculoskeletal health problems that have an underlying biomechanical basis.

We also reveal some factors influencing metabolic costs in elephants, which ultimately could help understand their migrations and even aid in conservation. This is a long way off, but would depend on analyses like ours.

How does this research relate to our and others’ previous research?

We have published 11 papers on elephant anatomy and biomechanics since 2003, and this paper is a climax of much of that work. We always hoped to measure how elephant limbs actually worked with forceplates but this was our first opportunity to do so, and has shown us aspects of limb compliance, leverage and power in elephants that we did not initially suspect. It has shown that some of our prior assumptions about elephant limbs, especially that they divide braking and propulsion between the fore and hind limbs, were incorrect.

Our findings that elephant limbs have somewhat mediocre leverage are surprising in one sense, but also fit into emerging theory that very large land animals face uniquely stringent constraints imposed by gravity, that cause them to be limited in their speed and gait in ways that smaller animals are not. However, elephants are still capable of remarkable athletic performance despite this, which is fascinating. An example of parallel research is Dr. Hutchinson and others’ work on Tyrannosaurus was not a fast runner.

What research are you doing now, or next?

We are using computer models to “peer inside” elephant limbs and estimate how their muscles, tendons and bones generate the dynamics we have observed experimentally. We are also studying fossil elephants to understand how their bizarre anatomy and gait have evolved, including in fantastic island dwarf (“hobbit elephant”) forms. We are also doing more experiments focused on the feet of elephants and other “hoofed” mammals, with an aim to use biomechanics to better inform the health care of those animals, as often ~50% of mortality (including in elephants) in captivity can be traced back to foot health as a major cause. And finally we are investigating how elephant limbs grow and how that growth influences the mechanics of their tissues (especially bones), because elephants experience drastic changes in size and presumably loading as they mature.

Why do elephants use this unusual mode of moving?

This is a hard question. Elephant anatomy certainly is very different from that of other large mammals’. A good contrast is with rhinoceroses, which have a more “standard” body shape for their size. Elephant limbs, as most mammals go, are unusually long relative to their size; rhino limbs are not. This is an important distinction. The slender limbs of elephants are weak when not loaded in their standard standing/slow-walking “pillar-like” fashion. They also are so slender that the muscles themselves have poor leverage around the joints- you cannot see really big bumps and crests and other muscle attachment sites on elephant limbs, compared with the outrageously robust limbs of rhinoceroses.

The rhino-like evolutionary design seems to be good for remaining athletic at a large size, without forfeiting too much performance from smaller ancestors, but one could speculate it comes at a cost of expensive maintenance (big muscles and bones aren’t cheap) and poorer long-distance walking capacity.

The elephant-like evolutionary design seems to be good for walking, maybe even long distances (which elephants do sometimes), but bad for athletic performance (they can’t gallop, jump, etc., even as babies). So this unusual way of moving in elephants may simply have been something early elephants settled into doing and stuck with it for ~50 million years. Being as huge as they are means that athleticism may not be so critical e.g. for escaping predators, especially in the large social groups that elephants often form (unlike rhinoceroses).

But there is a lot left we could learn about this question, and much of it should relate to the unique behaviour, ecology and evolutionary history of elephants.

  

  

  

  

  

  

Elephant Run:

Motion capture video:


motion capture still image
motion capture still image

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