Today, an athlete visits a surgeon, seeking medical attention for a blown ligament. Tomorrow, an expert "surgeon" will literally circulate through an athlete's bloodstream—affecting repairs whenever and wherever necessary.

In the 1992 book Nanosystems, futurist K. Eric Drexler popularized the concept of nanotechnology: microscopic machines (a nanometer is one billionth of a meter) that will someday perform tasks now relegated to entire factories, laboratories, or hospitals. The ultimate expression of this science will be "nanomedics"—devices that circulate in our bloodstreams, monitoring our health and destroying diseases before they can flourish. "Trends in miniaturization point to remarkable results around 2015," Drexler predicts. "Device sizes will shrink to molecular dimensions; switching energies will diminish to the scale of molecular vibrations."

Nanotechnology may currently be 99.9 percent fantasy, but technicians have already built and operated motors a fraction of the width of a human hair. In 1998, researchers at Cornell engineered a protein capable of using ATP—the body's metabolic "power supply"—to drive a microscopic rotor. In the future, these primitive victories will give way to more sophisticated nanomachines, some fitted out with molecule-size computers.

The athletic application for such devices would be vast. Nanoscavengers could race beneath an impacted patella, clearing away shredded cartilage and building a new layer between track heats. Nanofilaments might circulate to strained muscle groups, forming chains and pulleys of super-strong protein. One Cornell scientist predicts live-in nanopharmacies that will manufacture drugs from chemicals in the body's own cells, feeding them into the bloodstream as needed. "We're no longer restricted to what nature builds," says Ari Requicha, a University of Southern California computer scientist and nanotechnologist. "And that has incredible implications."