Your levers are the length of your left arm and golf club. If you swing the club back without cocking your wrists you are using one lever (left arm). Adding the second lever (club) by cocking your wrists substantially increases swing arc length and clubhead speed.
Coach Josh on the Lever System:
More on the lever system:
rory McIlroy using his lever system:
TIGER woods' lever system in perfect Symphony:
a detailed description of the physics & lever system in the golf swing:
