Researcher discovers how to predict the movements of animals of all shapes, sizes and speeds

A West Virginia University mechanical engineer has developed a way to predict the neural and muscular patterns controlling the locomotion of animals of any size, moving at any speed.

The discovery by Nicholas Szczecinski, an assistant professor in the WVU Benjamin M. Statler College of Engineering and Mineral Resources, will help roboticists build working models of animals that accurately replicate the limb movements of each species. Not only could robots then replace living animals in some experiments, but tiny animals like fleas or huge ones like elephants could be reproduced in robotic form on a more manageable scale for study.

“I’m an engineer, but it’s biology work that takes into account all the diversity of life,” Szczecinski said. “Each animal does something special. It was very cool to learn that as we try to compare a creature on the order of a millimeter with one on the order of a meter.”

Nexus PNAS published its findings.

The model created by Szczecinski and colleagues works by measuring the distance an animal’s limb moves from its resting position relative to the energy required to move it, parameters that involve size, weight and speed of the member. This measurement predicts how the limb will respond to the four intertwined forces of gravity, inertia, elasticity and viscosity.

“Some animals are so small that their mass doesn’t matter, while others are so slow that their acceleration is too small to have much impact,” Szczecinski explained. “When you do yoga, for example, you generally don’t accelerate much, so the force of inertia doesn’t affect you much. Instead, the way your body moves is mainly an interaction between gravity trying to pulling your limbs down. and the elasticity of your muscles trying to keep everything tight and in place.”

This research has benefited students in their own efforts.

“In my lab, it’s the undergraduate, graduate students and postdoctoral researchers who design the robots, operate them and collect the data,” Szczecinski said. “They are the ones who come up with new solutions for debugging hardware and software.”

Clarus Goldsmith, a mechanical engineering doctoral student from Columbus, Ohio, came to WVU to work in the Szczecinski Neuro-Mechanical Intelligence Lab. Goldsmith applied Szczecinski’s “biologically inspired robotics” to the design of Drosophibot, a robot that is about the size of a cat but moves like a fruit fly. When the fruit fly walks, it experiences forces in the same way as a fruit fly.

“The fruit fly is an important animal model for neuroscientists,” Goldsmith said, “but there are still some experiments that are difficult or impossible to perform on fruit flies because of their small size. Drosophibot allows us to perform biologically informed experiments on fruit flies. the robot and obtain data that can be used to inform hypotheses about the animal.

For Szczecinski’s study, if an animal’s movement matches two main hypotheses, he can predict the neuronal and muscular activity involved and compare it with other animals.

“The first hypothesis is that the movement in question involves a back-and-forth movement,” he explained. “The other hypothesis is that the movement involves phases of ‘loading’ and ‘unloading’, such as when your foot is on the ground and then when it swings freely. Many things besides walking are like this, we We can therefore apply this to a bird or an insect flapping its wings, or even a snail contracting and releasing its feeding muscles.

While existing models have only facilitated comparisons between animals of similar sizes and speeds, Szczecinski thinks his model could be extended to compare animals with different modes of locomotion (the way they move in one direction). place to another) or a different number of legs.

The decision to “see everything as having two legs” was a key simplification that enabled the universality of the model, he said.

“We could make this simplification because when four-legged animals like dogs or horses trot, they put down two legs at a time in fairly close synchronization. Insects, with six legs, have a ‘tripod gait,’ putting three legs at a time.” It’s not the same as walking on two legs, but they work with two pairs of legs at a time. This gave us insight into whether, for example, a fast-running cockroach is similar to a fast-running horse, because there are some really fundamental differences between these animals that previously made it difficult to compare them.

Because mammalian limbs are relatively large and heavy, they work in complex ways against the forces of elasticity, gravity, and inertia. For example, when a human reaches to pick up an object, the muscles move the arm toward the object and prevent it from passing the object. But the movement of insects is completely different.

“A walking bug is like the little kid in ‘A Christmas Story’ when his mother puts all the coats on him and he can’t give up,” Szczecinski said. “This is how an insect skeleton works. If you find a dead insect on the ground, its legs stand up and don’t collapse to the side from gravity. This is a consequence of how “Elasticity changes with size versus the magnitude of mass changes with size is at the heart of this research.”

Szczecinski said he and his collaborators look forward to applying his model to help build robotic versions of animals of interest to researchers.

“Because the mechanisms match, we can use what we see in a robot to tell us about the animal it is based on without needing experiments on living animals. We don’t need to take the animal apart to understand it. We can build a copy that will tell us if we really understand how the movement happens or if there are things we’re missing.”