This week’s BEACON Researchers at Work blog post is by University of Idaho postdoc Anne Gutmann.
In the classic Monty Python skit “Ministry of Silly Walks”, the comedian John Cleese demonstrates a series of hilariously weird and wacky walks while maintaining the prim and proper demeanor of a British government official. One reason Cleese’s “silly walks” seem so strange and comical is that although humans (and other animals) are capable of a wide variety of movements, they mostly use just a few typical gaits such as walking and running to move from place to place. But why do animals generally choose to use only certain common gaits and not a multitude of other uncommon, “silly” gaits?
As a scientist in the field of locomotion biomechanics my research addresses this question on two main levels: 1) the evolutionary level and 2) the muscular level. On the evolutionary level, I am interested in understanding how natural selection shapes animals’ bodies and gaits, and on the muscular level I am interested in understanding how the mechanical properties of muscles and tendons determine which gaits are possible and preferable for a given animal. For example, I might hypothesize that natural selection should favor animals that use energy-efficient gaits because animals that cannot obtain enough food to meet their energy needs risk starvation. However, to understand why certain gaits are more energy efficient than others, I must also examine how muscles and tendons function during locomotion. The most energy-efficient gaits might provide energy saving opportunities by allowing the tendons to store and return energy like springs or by allowing the muscles to function at the most efficient contraction velocities.
Currently, I am studying the evolution of bipedal hopping as a postdoc in Craig McGowan’s lab at the University of Idaho. My work is part of a collaborative project between the McGowan and McKinley labs (University of Idaho and Michigan State University respectively) which is funded by a BEACON seed grant. Our goal is to understand why animals as diverse as kangaroos, wallabies, kangaroo rats, and jerboas all hop. These animals span a surprisingly wide range of body sizes and habitats, but all have the same basic leg design and hop on two legs to move from place to place. One hypothesis is that hopping evolved as a means of producing the high accelerations needed to escape predators. However, differences in muscle-tendon architecture suggest that some hopping animals have evolved for energy efficiency rather than high acceleration. We will use an interdisciplinary approach that integrates biomechanics, computation, and physics-based simulation to understand how selective pressures shape the evolution of leg design and gait in these animals. Graduate students in the McKinley lab will use a physics-based simulator and evolutionary algorithms to determine which selective pressures produce bipedal hopping. I will develop a detailed musculoskeletal model of a kangaroo rat to determine the effects of muscle-tendon architecture on hopping dynamics. This process will include using micro CT scans to create a 3-D model of a kangaroo rat skeleton and doing careful dissections of kangaroo rats to determine the points at which the muscles attach to the skeleton. I will also collect mechanics data from real kangaroo rats to allow me to develop realistic simulations of hopping. Once I have a detailed musculoskeletal model of a normal kangaroo rat up and running, I will adjust the leg design of this model to match the designs that emerge in the physics-based simulator. I can then use these modified models to compare the effect of different limb designs on muscle-tendon dynamics. This integrated approach will provide novel insight into why and how the musculoskeletal system of certain animals evolved for hopping.
Results from our study can be applied design biologically-inspired robots and prosthetic devices. Currently, most legged robots must move slowly and carefully to avoid falling over and have high energy requirements. Similarly, amputees often are forced to move more slowly than non-amputees because they must use more energy to walk and run. This can deter amputees from engaging in physical activity and reduce their overall quality of life. Developing a better understanding of how kangaroos, wallabies, kangaroo rats, and jerboas hop will allow us to design agile legged robots that can navigate rough terrain quickly and efficiently and less-tiring prosthetic devices that will allow the wearer to walk and run at high speeds with ease.
For more information about Anne’s work, you can contact her at agutmann at uidaho dot edu.