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Integrative approach to studying penguins, cockroaches and little hairy noses makes comparative biomechanics group at UC Berkeley the nation's best

University of California - Berkeley

At San Diego's Sea World, Rodger Kram videotapes penguins waddling across a force-measuring platform to rate the energy efficiency of their distinctive gait. Meanwhile, at the University of California, Berkeley, Claire Farley tapes bright dots to the legs of students and videotapes them running across a similar platform to determine the relationship between muscle stiffness and springy legs.

Across campus, Robert Full tests cockroaches, crabs and centipedes to discover how springy legs provide stability, while down the hall, Steven Lehman stretches rabbit muscle fibers to find out how they work as brakes and springs as well as motors.

Michael Dickinson tracks blowflies in a test chamber to determine how feedback from their eyes affects the flight muscles and ultimately allows spectacular maneuverability. And Mimi Koehl builds foot-long models of lobster antennules to learn how these crustacean noses pluck odor molecules from the water swirling around them.

These half-dozen UC Berkeley professors in the Department of Integrative Biology comprise the largest and most diverse group in the country studying how animals -- including humans -- move.

What has emerged from the comparative biomechanics group at UC Berkeley and from their associates around the world are a set of principles that apply to animal locomotion of all kinds, whether it's running, swimming, flying or wriggling. As Koehl has found, these principles even apply to movement not associated with locomotion - with sampling the environment, capturing food or just trying to stay put in the face of wind or water currents.

Earlier this month, the UC Berkeley team summarized key findings from more than a decade of research at UC Berkeley and elsewhere in a review article titled "How animals move: an integrative approach," published in the journal Science (4/7/00).

Such principles are not merely academic. Full, Koehl and Dickinson, for example, regularly share information with engineers eager to learn the secrets of animals' amazing speed, control and mechanical stability so that they can adapt the principles to the design of robots. Lehman has found that his work on muscle fatigue is of interest to ergonomics specialists trying to deal with an epidemic of repetitive stress problems. Kram, an assistant professor, recently even hosted computer animators from Pixar Animation Studios to give them tips on creating more realistic animal movement for their next blockbuster movie. Full consulted with Pixar on an earlier film, "A Bug's Life."

"In classic locomotion research, everyone focused on the force pushing an animal forward. Power and efficiency became central," said Dickinson. "That emphasis has really shifted, because the way animals execute motion is very, very complex and dynamic. Animals throw force out in all directions, seemingly out of control and not optimized for moving in one direction. We've found that these forces help produce stability and maneuverability."

One of the key recent findings in the field of biomechanics, Full added, is "that it's not how much power animals can produce, but how they stabilize and control themselves."

Full has demonstrated this with numerous creatures. He has shown that these animals run by bouncing along like pogo sticks with the same patterns seen in humans. The difference lies in the squat stance, where splayed, springy legs are superb in providing passive stability. This frees the brain to deal with navigation rather than tedious, instant-by-instant corrections at all the joints.

"The control is built into the structure, their sprawling stance," he said. "It's a self-stabilizing system that can simplify immensely how we think about animal motion, and help in the design of robots no one has seen before."

Similarly, Dickinson has dissected the flight muscles of the fly and the nerves that control them to find out how flies are able to wheel around in midair and even turn upside down and land on the ceiling. In the process he has shown how a pair of vestigial wings, the halteres, act as the fly's gyroscope, relaying signals to the wing muscles to alter their stroke or angle of attack.

He built a pair of 10-inch Plexiglas robotic wings, dubbed "Robofly," to reproduce in mineral oil the wing motions he saw in high-speed video, and discovered three distinct wing motions that allow insects like flies and bees to execute amazing acrobatic maneuvers.

"We look at the whole gestalt of motion," he said, "not only how muscles act as motors, but how they serve as brakes, struts, springs and even a transmission."

Farley has shown, too, that power output from muscles is not necessarily the main factor determining the top speed at which an animal can run. Her experiments show this is true of lizards, and suggest it may also be true of humans.

Lehman noted that the historical emphasis on muscles producing power has led scientists to ignore what is involved in stopping motion. To understand how muscles do this, he measures the forces generated by lengthening, rather than contracting, muscle.

This involves studying individual muscle fibers from rabbits and relating that to the back and forth hand motions of human volunteers. He has even teamed up with Full to look at cockroach muscle fibers, hoping that their single motor unit will be easier to study than human muscle, with its hundreds or thousands of motor units.

This illustrates a major strength of the group -- collaboration. This often emerges from weekly meetings where faculty, students and postdocs assemble to hear about new work and, as the seminar winds down, throw out silly ideas that often lead to great insight.

Kram noted how one student mentored by Koehl and Full used his findings on how humans move in reduced gravity -- he had suspended human volunteers from a harness while running -- to predict how crabs move underwater. When the student videotaped real crabs, she found the predictions to be amazingly accurate. These data led to the design of Ariel, the first legged amphibious robot.

Since water and air are both fluids, crab locomotion fits well with Koehl's interests in aerodynamics and evolution. Ten years ago she won a MacArthur "genius" award for her work applying principles of engineering to understanding basic biological processes, ranging from how kelp withstand wave action to the evolutionary origins of novel modes of locomotion, such as gliding. She and her students are still studying the aerodynamics of gliding, taking high-speed video of Costa Rican "flying frogs" and related tree frogs gliding in a wind tunnel in search of clues to the origin of this behavior.

"The enormous hands and feet that we see on all the 'flying frogs,' but not on their non-flying relatives, enhance the ability of the flyers to maneuver. For these frogs, being able to steer while gliding through a complex forest is probably more important than how far they can travel horizontally, which is how glider performance is usually evaluated," Koehl said. "We create epoxy models of frogs and measure the aerodynamic forces on them in a wind tunnel when we vary their postures or the size of their feet. That way we can find out which factors contribute to the aerodynamics of their maneuvers."

She also has focused on understanding the function of a common feature of many water creatures, rows of little tiny hairs. Tiny copepods -- abundant zooplankton that form a critical link in marine food webs -- use appendages bearing rows of small hairs to move about and capture food. Crabs and lobsters, on the other hand, flick antennules bearing tiny chemosensory hairs to sniff the water.

"All of us in the biomechanics group are at the interface between biology and engineering," she said. "While engineers need to design structures to perform specific functions, we are studying organisms that already have a structure, and our job is to figure out how they function."

Kram concentrates on much larger animals. Recently he and his students measured the forces exerted by a lumbering, 1,000-pound baby elephant. They're curious whether elephants ever truly run, lifting all feet off the ground simultaneously. The larger question is: What are the ultimate limits on speed? Is it muscle power, or the strength of the bones and tendons? Kram hopes to learn principles that will tell him how large, extinct animals moved, including mammoths, mastodons and dinosaurs.

Many of the principles discovered are now being co-opted by engineers to design robots. Dickinson is working with UC Berkeley engineer Ron Fearing to design a robotic fly, while Full is collaborating with various robotics labs to create robots that use principles employed by cockroaches, crabs and even geckos. "With the invention of artificial muscles and novel techniques to manufacture flexible body parts," said Full, "we are on the verge of a revolution in biologically inspired robotics.

"Nature can now be a good teacher of engineers. But you don't want to copy, you want to extract principles. Nature has all kinds of screw-ups. Evolution is based on the principle of just good enough, it's not perfect at all. I think we can build robots today better than any one organism. We can do that now."

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