While we're on the subject (Score 3, Informative)

More power is available to the drivetrain by using an elliptical crank, first described in a bicycle magazine in 1890. When the pedals are at the tops and bottoms of their rotation, say 110 to 70 and 290 to 250, very little power is delivered. Basically, the rider is just following the path of the pedals, rather than forcing them. The elliptical crank allows more of the rotation to be spent powering the drive mechanism.