US Patent 7537550 Exercise weight stack methods and apparatus

Weights are arranged in a vertical stack and movably mounted on a frame. On some embodiments, variable length members are provided to exert upward force against a weight supporting member associated with the stack when the weight supporting member is proximate its rest position relative to the frame. On other embodiments, the weights are rotated relative to the frame to selectively engage and disengage the weights for purposes of providing resistance to exercise motion.