Motocross is a pretty big sport in the U.S.  There is 5 major bike types.  They are Honda, Yahmaha, Suzuki, Kawasaki, and KTM.  When you race you are required to wear a good bit of equipment.  This includes a helmet, shoulder pads, boots, goggles, pants, gloves, and shin gaurds.  Motocross is a good thing to do so make sure if you have nothing to do get a dirtbike and start riding.