The AMA Motocross Championship was started in 1972 with two different classes, 500cc and 250cc, then later brought the 125cc class in 1974. All the bikes were two-stroke at the time and and these things were incredibly powerful, especially the 500cc class. Only the most courageous and skilled attempted to take on these monster bikes. The Motocross track can be anywhere from a half mile to two miles long and usually use natural terrain depending on the location of the track. These longer races allowed the bikes to reach higher speeds which meant bigger jumps and also bigger wrecks if things went bad. The AMA Motocross series brought the best riders from all over the world to compete in at least 12 races over the course of the season awarding points depending on what place the rider would finish. Rider with the most points at the end of the season was crowned the Champion. Because motorcycle technology was increasing so rapidly the 500cc bikes soon became too powerful and there wasn’t enough riders whiling to compete on the big bikes so the AMA cancelled the 500cc class after the 1993 season. In 1997 there would be another breakthrough in the Motocross world when four stroke bikes started showing up on the scene. The AMA was forced to make a rule change that allowed the bigger sized four strokes to compete with the 250cc two strokes. In 1997 Doug Henry rode a prototype four stroke bike from Yamaha called the YZ400F and was able to win a couple races. The following year he came back on a newer version of YZ400F and would go on to win the AMA Championship that year becoming the first on a four stroke to do so. Before long almost every ditrbike on the course was a new 450cc and AMA was forced to change the series from the 250 class to the MX class, then in 2009 changed it to the 450 class.