David Brockman, a retired CalFire captain and avid outdoorsman, built a deck in the backyard of his home last year, without the use of his dominant right hand, which he lost in an accident. The prosthetic hand he used instead was a crude but functional steel hook-and-harness device.

When researchers at the University of California, Davis, recruited hundreds of fifth-graders and their parents for a health and development study in 2006, they planned to monitor the families for at least three years.