Researchers have taken a giant leap to understand locomotion from the leg up by using an avatar-like system that integrates a real muscle and tendon along with a computer-controlled nerve stimulator acting as the avatar's spinal cord. These findings could help create robotic devices that begin to merge human and machine in order to assist human locomotion.
Greg Sawicki, associate professor at North Carolina State University, said, "We tried to build locomotion from the bottom up by starting with a single muscle-tendon unit, the basic power source for locomotion in all things that move."
The research team connected the muscle-tendon unit to a motor inside a custom robotic interface designed to simulate what the muscle-tendon unit 'feels' inside the leg. Sawicki said, "We then electrically stimulated the muscle to get contractions going on the benchtop."
The researchers said, "Resonance tuning is a likely mechanism behind springy leg behavior during locomotion. That is, the electrical system - in this case the body's nervous system - drives the mechanical system - the leg's muscle-tendon unit - at a frequency which provides maximum 'bang for the buck' in terms of efficient power output. In locomotion, resonance comes from tuning the interaction between the nervous system and the leg so they work together."
Sawicki said, "It turns out that if I know the mass, leverage and stiffness of a muscle-tendon unit, I can tell you exactly how often I should stimulate it to get resonance in the form of spring-like, elastic behavior."
The findings could have design implications relevant to designing exoskeletons for able-bodied individuals, as well as exoskeleton or prosthetic systems for people with mobility impairments.
The paper was published in the Proceedings of the National Academy of Sciences.