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The hammer handle should reach well past parallel with the floor.
The rear lever is used to train ulnar deviation of the wrist. Stand with the feet parallel to one another. Place a sledge hammer to one side, with the hammer head on the ground parallel to the feet, and handle pointing straight up. Holding the arm straight, against the side of the body, grasp the end of the hammer handle. Moving only the wrist (be sure to keep the arm straight), bring the head of the hammer up behind the body until the handle is past parallel to the ground. Slowly lower it. Rear levering a 32" long, 8lb sledge is a worthy starting goal.