CAREER: The Musculoskeletal Biomechanics and Control of Limbless Locomotion

This project uses locomotion by lateral undulation in snakes as a model system for investigating how animals meet and prioritize mechanical and control demands, especially when these demands are constrained or conflicting. Terrestrial limbless locomotion, despite being used by almost 20% of terrestrial vertebrates, remains understudied. In lateral undulation, the most widespread and common mode of limbless locomotion, waves of bending pass down the body, pressing against structures in the environment (e.g. plants, rocks) to propel the snake forward.

Lateral undulation poses several simultaneous challenges, including meeting mechanical power demands, overcoming the force of friction, and controlling forces at multiple, constantly shifting contact points. These demands may conflict; for example, the body posture that generates the most effective propulsive force from a contact point might reduce muscular force or power output.

This project addresses how snakes handle this conflict and investigates whether mechanisms exist to mitigate or avoid potential tradeoffs, by testing animals in environments that impose different mechanical and control demands. This research will provide general insights into how animals manage competing demands during locomotion, particularly the need to simultaneously meet mechanical and control demands.

Understanding limbless locomotion can also benefit snake-inspired robots, a target of bio-inspired robotics due to the exceptional ability of snakes to move through complex, cluttered, and confined spaces. In partnership with the University of Akron field station, the project also provides a unique outreach opportunity in bio-inspired robotics to nearby high schools serving economically disadvantaged youth, by leveraging a new type of feedback-based robotic programming based on stop-motion animation to eliminate the need for students to learn how to write code.

A central challenge of biomechanics is understanding how the physiological properties of muscle influence the movements of animals, often examined in specialized systems adapted to maximize a particular metric (e.g., power or cycle frequency). However, most animals must meet numerous independent mechanical and control demands simultaneously and can modulate their movements in a wide variety of ways to accomplish this.

This project uses terrestrial lateral undulation in snakes as a model system to understand how animals meet these demands, particularly when the demands conflict. The friction-dominated mechanics of terrestrial limbless locomotion impose straightforward demands on mechanical force and power output, which will be directly measured from instrumented test arenas.

The highly variable patterns of midline bending in snake locomotion suggest correspondingly variable muscle strain trajectories, which will be measured via fluoromicrometry. The multiple propulsive reaction forces depend upon local posture at each contact location. If both muscle mechanical output and control are determined by body kinematics, there is potential for conflict between these goals: control of reaction force orientation may compromise muscle mechanical outputs, and vice versa.

This project involves a novel outreach program using a combination of live-animal demonstrations and robotics to provide students with a bio-inspired robotics design experience in which they observe a snake’s movements, hypothesize mechanisms, and test those mechanisms using snake-inspired robots. Two post-doctoral fellows and a graduate student will contribute to the research, thereby benefitting from interdisciplinary training and mentoring.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.