A toad sits at a pond's edge eyeing a cricket on a blade of grass. In the blink of an eye, the toad snares the insect with its tongue. This deceptively simple, remarkably fast feeding action offers a new look at how muscles work.
This fresh perspective could lead to designing more efficient electric motors, better prostheses and new medical treatments for neuromuscular diseases like Parkinson's.
Science has long held that muscles behave largely like motors. Northern Arizona University researcher Kiisa Nishikawa suggests that muscle acts more like a spring.
"Existing theories don't explain how muscles shorten rapidly," Nishikawa said. "Muscles can only shorten to do work; they can't do work by lengthening." A spring also can only do work by shortening.
By example, Nishikawa explains that the jaw muscles in toads and chameleons shorten in the lower jaw, and the opening of the jaws causes the tongue to stretch by its own momentum.
"When a toad or chameleon captures prey with its tongue, it exerts force over a distance. Figuring out how they do it has immense application to any device that actually moves."
A toad's jaw muscles can produce forces greater than 700 times the animal's weight. "The best electric motor achieves about one-third of that force-to-weight ratio," Nishikawa noted.
Muscles also function as self-stabilizing springs.
"They have built-in self-correcting mechanisms. Before the brain can even react, muscles are changing their elasticity adaptively," she said. Think of walking down a flight of steps and missing a step. Leg muscles instantly become less stiff to afford better shock absorption. "It's an intrinsic property of muscle," Nishikawa said.
Tom Sugar and his colleagues Arizona State University have been inspired by biology in designing a robotic tendon. After meeting with Nishikawa about her work, Sugar said, "We were amazed at the speed, energy storage and po
|Contact: Lisa Nelson|
Northern Arizona University