26 SERVO 05.2014
Animals “do the locomotion” every day, whether
it’s walking down the hall to get some coffee or
darting up a tree to avoid a predator. Until now,
scientists believed the inner workings of movement
were pretty much the same: the nerves send a
message to the muscles and there is motion.
In a first-of-its-kind study on wild green anole
lizards, biologists at the University of California,
Riverside have discovered that the link between
muscle function and movement is a lot more
complicated than anyone realized.
“We were trying to understand how animals move in
trees; how muscle, in general, deals with something as
complex as climbing a tree, with its horizontal and vertical
inclines, the tiny little branches, and the upright trunks,” said
Kathleen Foster, a Ph.D. student in Evolution, Ecology, and
Organismal Biology who performed the study. “We were
expecting to find that as the movements were changing, the
muscles would be generating those changes; we’d just show
that and move on. Instead, we saw there isn’t always this tight
relationship between activity in the muscles and the
movement we’re seeing. Now, we have new questions about
“No one has ever looked at this before,” said Timothy
Higham, an assistant professor of biology and Foster’s
graduate adviser. “A lot of people study anoles and a lot of
people remove muscles and study them in a lab, as opposed
to measuring the muscles in the animal as it’s moving. Our
work brings the lab into the forest, and it can help us answer
questions about how these animals are doing what they’re
In their study — “Context-dependent changes in motor
control and kinematics during locomotion: modulation and
decoupling” — Foster surgically inserted electrodes into the
forelimbs and hind limbs of seven male green anole lizards.
She then tracked the lizard’s movements on a flat and 90
degree incline, and a broad and narrow perch using high
speed video to record movements and electromyography to
monitor electrical activity in the muscles.
The researchers found that while the lizard movements
changed considerably when they were running along narrow
perches (compared to broad perches), there were few
significant changes in muscle activity. When the lizards were
running up an incline, they noted more changes in muscle
activity than movement.
Though these two inch long green anoles weigh just five
grams — about the weight of a US nickel — their muscles
work the same way as every other vertebrate.
The study also has implications for people who design
artificial limbs or robots.
“Clearly, locomotion is not as simple as we thought it
was,” Foster said. “This decoupling — big changes in
movement without corresponding changes in muscle activity
— suggests there are other important factors going on and
we need to better understand them if we want to reproduce
these movements in prosthetics or robotics.”
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