 
Integrative
approach to studying penguins, cockroaches and little hairy
noses makes comparative biomechanics group at UC Berkeley the
nation's best
28
Apr 2000
By Robert
Sanders , Media Relations
 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."
###
Links
associated with this story:
Mike
Dickinson Lab, http://socrates.berkeley.edu/~flymanmd/
Steve
Lehman, http://ib.berkeley.edu/faculty/lehmans.html
Rodger
Kram and Claire Farley's Locomotion Lab, http://socrates.berkeley.edu/~hbbiomxl/
Mimi Koehl Lab, http://ib.berkeley.edu/labs/koehl/
Bob
Full's PolyPEDAL lab, http://polypedal.berkeley.edu/
.
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