The AMA Motocross Championship is an American motorcycle racing series. The motocross race series was founded and sanctioned by the American Motorcyclist Association (AMA) in 1972. The series is the major outdoor motocross series in the United States and is managed by MX Sports Pro Racing. The series began in 1972 with the introduction of two classes based on 500 cc and 250 cc engine formulas. A 125 cc class was added in 1974. In 2009, the MX class was renamed the 450 Class and the MX Lites class was renamed the 250 Class, to reflect the fact that all the competing manufacturers had adopted four-stroke machinery.