I Issued A Challenge a few years ago to my fellow researchers: build a robot using muscles of electrically activated polymers that could arm-wrestle a human. I was trying to jump-start research in the field of electroactive polymers, or artificial muscles, and given the state of the art at the time, I didn't really expect to see the challenge fulfilled for a couple of decades.

I was wrong. A little over a year ago, researchers from SRI International, a research institute in Menlo Park, Calif., told me that their technology could be capable of meeting the challenge. Since then, Environmental Robots Inc. and the Swiss Federal Laboratories for Materials Testing and Research informed me that they would be ready to compete less than a year from now! I couldn't be more delighted—even if it means that my obligations as an impresario are a lot closer than I'd envisioned.

The arm-wrestling match, when it does come off, will be a watershed on more than one count. Today's machines—from assembly-line robots to electric toothbrushes—move thanks to rotary power, often cleverly translated by gears, pulleys, hydraulic tubes, and other intervening parts. Yet such watchmaker's cleverness has its limits, and over the centuries, engineers have imagined countless wonderful machines that sadly could not see the light of day. Now, at last, a streamlined solution is at hand: artificial muscles.

Artificial muscles are plastics that change shape and size under electrical stimulation. Because they are plastics—that is, polymers—they are light and can be cheap, pliable, quiet, and shatterproof. Also, they can be designed for particular properties, filled with sensors and other components, shaped for specific actuators, and manufactured on scales both macro and micro. Unlike most active materials, such as semiconductors and shape-memory alloys, however, these electroactive polymers work according to a variety of principles, offering different tradeoffs of power, extensibility, reaction time, and other qualities.