US Patent 7018301 Dynamic swing training aid for sports

A rocking footplate alerts an athlete such as a golfer or a baseball player to the occurrence of improper rear foot weight placement. The footplate is placed under the athlete's rear foot and includes upper and lower plates which are joined by a hinge having an axis of rotation which is aligned with the center of the foot. The bottom of the device includes spikes which engage the ground to provide a stable base for the hinged top plate. The top plate is in the anatomical shape of a foot to aid proper foot placement on the device.