While in his teens, growing up in a family running a candy factory in Guatemala, Luis von Ahn said he often fantasized about creating a gym anyone could join for free.
Now 34, von Ahn, an IT entrepreneur and associate professor of computer science at Carnegie Mellon University in Pennsylvania, said he thought a gym could be made free for anyone to use if all the kinetic energy of the people using the exercise equipment was converted to electricity and sold to the power grid.
Unfortunately, von Ahn soon learned that human effort is an inefficient way to generate electricity.