For 25 years, inventor Keahi Seymour has dreamed of running with the speed and loping gait of an animal. His inspiration struck at age 12, while he was watching a program about kangaroos. "The announcer said it moves at such an efficient gait by using its Achilles tendons as springs," Seymour says. "I thought, 'Why not replicate that in a device that could propel a human?' " He began sketching footwear using ostriches, which, he discovered, run more like humans, as his model.

By the age of 17, he had built his first prototype using old Rollerblade boots, steel tubing, and bungee cords. Then, he built some 200 more. Today, Seymour's Bionic Boot can propel him forward at 25 miles per hour. "You really feel superhuman," he says. Eventually, Seymour hopes to boost the speed to 40 miles per hour, perhaps by enhancing the boots' springy heels with electrical actuators. That, he expects, will take a few more prototypes.