Abstract: A gear mechanism is provided, having a gear arrangement, and a spindle arrangement to support the gear arrangement, the spindle arrangement having first, second, third and fourth spindles. The gear arrangement, of concentric gears only, that includes a first gear set mounted on the first and fourth spindles and arranged to be driven via a first pedal, a second gear set mounted on the second and fourth spindles and arranged to be driven via a second pedal, and a third gear set mounted on the third and fourth spindles, wherein, for each of the first and second gear sets, the gear set is configured to be alternately driven, via the corresponding pedal being rotated through less than 180°, in a power stroke to drive the third gear set, and, advanced, via the corresponding pedal being rotated through more than 180°, in a return stroke to commence a subsequent power stroke.