Abstract: A variable length, pedal driven, crank mechanism, suitable for use on human powered vehicles; with gear driven transmission assemblies mounted on each end of an axle which is supported by and rotates on bearings. These arms have an inner and outer housing that bolt together forming rigid sealed assemblies, each containing a train of gears that engage the fixed, non rotating, pinion gears, transferring rotation to the proximal drive gears. The proximal gears have splined shafts that extend outside the primary housings on which secondary outer crank arms are attached. The outer crank arms are internally threaded on the side of their proximal ends for the attachment of pedals. This assembly causes the outer arms to extend on the down stroke and increases the amount of leverage available to the operator.