Do the Locomotion
An unconventional Temple researcher learns about human movement by setting lizards and crabs in motion.
Story by Jaime Anne Earnest, CLA ’07
Photography by Joseph V. Labolito
In a lab in the College of Science and Technology, a small, unassuming lizard sits on an ad-hoc plywood runway. Suddenly, a burst of air behind him startles the little creature, and sends him sprinting down the runway at top speed. His gait is wide-rather than having his legs move in front of him, they flare to the side in a kind of propeller motion.
A high-speed camera trained on the runway catches all the action, and records the slightest change in the lizard's movement as he hits a slick spot. But, he keeps right on going, never stumbling, never skipping a beat. How did he do that?
It’s just one of the things that Assistant Professor of Biology Tonia Hsieh and her research team contemplate. She also is interested in how the cute-but-cannibalistic ghost crab can function after sacrificing a limb in battle with another of its species, and how the average cockroach is able to reach its top sprinting speed, hanging completely upside down.
As it turns out, understanding how we get around might depend on understanding how they get around.
Existing research illustrates some of the ways that animals walk and run in their native ecosystems, as well as how we humans navigate the challenges in ours. But many questions about how their movement can improve ours still remain.
By studying the locomotion of these bipedal creatures, Hsieh’s team aims to understand how our bodies instinctively adapt to different surfaces and changing environmental conditions. The results could aid the elderly and enhance our understanding of robotics. “Our world is so complex,” Hsieh says. “As we make our way through our built environment, we have to deal with so many things: broken city sidewalks, grass, potholes. Until now, the biomechanics of movement have been studied in very controlled experimental environments. While that's been essential for understanding locomotion, we need to better understand how animals move in natural environments.”
More than 100 small green anole lizards live in Hsieh’s lab—their slip-recovery methods particularly interest her. She also studies the basilisk lizard and baby frilled dragons, both bipedal runners. The researchers construct most of the surfaces on which their creatures run—like the runway.
“For me, it's one of the most fun parts of the research—getting to build things,” Hsieh says. The runway comprises hard, smooth pieces of plywood and glossy poster board covered with a slick film. Hsieh and her team coax the lizards to sprint down the runway, and study how their movements differ depending upon whether or not they keep their balance on the slick spots.
The lizard can stay upright by rotating its upper body opposite the direction of the perturbed foot. But Hsieh adds that many times, the lizards will fall. That has to do with a number of variables, such as their leg position when they hit the slippery surface, where they are in their stride, and how fast they run. She says that these variables help the researchers understand what causes or prevents a fall, which has implications for physical therapy, and to better prevent injury in groups such as the elderly.
“Slipping and falling are major causes of morbidity and mortality in the elderly,” she explains. “As a result, this is a major public-health concern.”
According to the Centers for Disease Control and Prevention, one in three U.S. adults ages 65 and older experiences a falling accident each year. In addition to broken hips, ankles, pelvises and other debilitating conditions, those falls often contribute to traumatic brain injuries and death. Understanding how elderly bodies adapt to changing surfaces can help create living environments that cater to those most at risk for falls.
The lizards’ neighbor in the lab is Ocypode quadrata, also known as the ghost crab. Named for its nocturnal habits and its pale coloration, it has prominent front claws and shining black beaded eyes that are suspended above its body. Despite its small stature, the ghost crab fiercely battles other crabs when provoked. Hsieh describes their behavior with a discernible hint of glee.
“They’re incredibly cute, but they’re also predatory, cannibalistic and merciless. They systematically rip each other's legs off. They go from being fully intact, to spontaneously not. How are they compensating for limb loss?”
Understanding how the crabs compensate after injury has direct implications for building a better robot, especially for an organization such as the Department of Defense or for the military. “Imagine a robot that can jettison its leg after becoming disabled or stuck, and still be useful,” Hsieh says. Such a robot might be able to better aid soldiers in battle, or continue functioning after damage in conflict.
Traditional robotic design incorporated wheels, but wheels limit a robot’s range of motion, particularly in difficult, uneven terrain. But now, a growing trend among researchers is to use legs, allowing for more mobility. Hsieh says that understanding how those legs work in nature could mean a more adaptable robot.
In order to effectively study her small, speedy subjects, Hsieh employs movie magic: 10 high-speed, super-high-definition video cameras, each capable of shooting up to 16,000 frames per second. A standard video camera shoots only 30 frames per second. One six-camera system is even the same type that was used to prototype Avatar. Using infrared light, the team films at 500 frames per second, gathering information from reflective markers placed on the lizards’ bodies. The data is fed through software that recreates the markers in three-dimensional space, allowing Hsieh and her team to track the creatures’ movements more precisely.
In another part of the lab, Hsieh uses a fluidizable trackway: essentially, a 1-foot-by- 3-foot tank filled with tiny glass beads between 2 and 300 microns in diameter. For comparison, a strand of human hair is about 50 microns in diameter.
Hsieh uses a wet vac to force air between the beads, which have the consistency of sand, and can assume the properties of a solid (think hard, compacted sand) or liquid (think of sand being poured out of a pail). When the volume changes from solid to liquid, the surface ripples like water. This particular setup provides the perfect controllable platform on which to simulate more of the variation of surfaces seen in nature.
The fluidizable trackway is used to study how changing surfaces affect the crabs’ ability to run. Surprisingly, Hsieh notes that crabs use pointy feet on the softer, granular surfaces, though humans would use snowshoes to adapt to a similar surface, like snow.
Much of Hsieh’s work crosses boundaries both within biology and across other disciplines, including engineering, physics, genetics and even architecture. It also challenges the notions of long-held theories in biomechanics.
One of the basic assumptions of the prevailing model, known as the Spring Mass model, states that all running animals will bounce like a pogo stick. The model assumes the constants are a hard, high-traction surface, and that gravity always points downward, toward the feet. Studying the water-running behavior in the plumed basilisk lizard—known as the “Jesus lizard” for its ability to run across the surface of the water—Hsieh found that this model did not apply to the mechanisms of the lizards running on water. And some animals, including the cockroach, run upside down.
“Cockroaches are remarkably stable and simple,” Hsieh says. “They make a great model for understanding how animals move, because they have a very simple neurological system and run with incredible stability. What is most amazing is that research both in my lab and by others shows that cockroaches are so stable, they use the same mechanisms for running in very different environments.”
INTO THE WILD
To interact with subjects in their natural habitats, Hsieh and her team have travelled throughout the Caribbean, Panama and Guam. Through her travels, she added yet another animal to her menagerie: Alticus arnoldorum, or the Pacific leaping blenny, which she first observed during a trip to Guam in 2002. Hsieh says these little fish demonstrate extraordinary feats of locomotion, and can even climb glass.
“These fish are incredibly dynamic and acrobatic,” Hsieh says. “They can twist their tails and direct most of the force for jumping into the ground.”
In 2010, Hsieh published her findings about the blenny, citing its ability to curl its body into a “C” shape, then twist the tail axially, using it to push its body off of the ground--whereas other types of fish can only move their tails side to side. She credited the blenny's unique tail-twisting abilities as a contributing factor to its being able to set up shop on land.
Hsieh says her love of animals began in childhood: “I wanted to be a veterinarian.” That is, until a research trip to New Zealand as an undergrad at University of California, Berkeley. “I was sitting atop Stephens Island, taking a break from fieldwork and staring into Cook Strait, when I suddenly realized I wanted to be a researcher, asking interesting questions and striving to find answers.”
Since then, Hsieh (who claims to have “science A.D.D.”) sometimes mirrors her tiny research partners when it comes to her work, running at high speeds from one project to the next, always conducting more than one study at a time. She has published nine papers relating to animal movement; her first was a study on how geckos are able to stick to surfaces, which earned her an article in the coveted journal Nature while at Berkeley. She is currently writing a paper about how tail loss in lizards affects their running stability.
It is clear that Hsieh loves what she does; in the lab, she lets the lizards crawl all over her, and as she watches them run, she smiles. As one nearly launches itself off the runway, she and her colleagues hoot with delight.
“I get to play with things that I've been chasing since I was a kid—this is my job,” she says with a laugh. “It’s really fantastic.”
Jaime Anne Earnest, CLA ’07, studies interdisciplinary science and is the Lord Kelvin/Adam Smith doctoral scholar at the University of Glasgow in Scotland.