A team of researchers at the Royal Veterinary College have discovered that many-legged animals control their movement in a surprisingly different way to bipedal animals, following a study on cockroaches using tiny accelerometers and advanced computer models.

The study, published in the Journal of Experimental Biology (JEB) on 14 May 2010, found that four or more legged creatures do not adjust for hard or soft surfaces in the same manner as humans. 

The RVC says the results were surprising because past work had found that running and trotting animals with four-, six-, or eight legs exert forces on the ground that look remarkably similar to two-legged humans.

The study used cockroaches with tiny accelerometer backpacks as the basis of the research before developing advanced computer models to further the findings.

The accelerometers were developed by Andrew Spence while working in the Poly-PEDAL laboratory of Professor Bob Full at the University of California, Berkeley. Dr. Spence, now following up the research as a Research Council UK (RCUK) research fellow at the RVC, along with his colleague Shai Revzen, attached the device to the cockroaches' back before sending the insects scuttling across a sheet of latex.

The cockroach sank into the soft rubber surface, like humans sink into the mud, but was able to maintain their forward speed, despite the extremely soft going.

Dr. Spence said: "Like humans, four or more legged animals move as if they are bouncing on a virtual pogo stick when running on hard surfaces. However, when humans run over soft surfaces, they effectively "stiffen" their virtual 'pogo stick', so we were keen to discover if this was the same for four or more legged animals."

Following the initial study, a computer-generated model cockroach was developed to help explain how the insect ran on, and sunk into, soft ground, with the 'cyber-roach' confirming earlier findings.

From the 'cyber-roach' the researchers concluded that instead of maintaining the body's centre of mass motion by stiffening the virtual pogo stick leg like human runners, the insect does not change the stiffness of its virtual pogo stick. The reason that the insect is able to run successfully without crashing, despite using the "wrong" leg stiffness, may be due to the change in posture that occurs when a legged animal sinks into a surface, as the legs that are flying through the air hit the ground sooner than they normally would.  

Dr. Spence believes this simplifies the task for the nervous system: "Instead of sending nervous system signals to stiffen muscles, the cockroach may just be able to continue sending the same control signals and take advantage of this change in posture."

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