when I jump up in the air my feet (A) are pushing downward on the ground (B) and the ground is pushing back

when the biker pushes on the pedals, they turn the chain which turn the wheels (A) around which then cause the bike to roll along the ground (B). The reason why the biker has to keep on pedaling is because the ground has friction which causes the bike to slow down

http://commons.wikimedia.org/wiki/Commons:%E6%AF%8F%E5%B9%B4%E5%9C%96%E7%89%87/2006

when the horse is running, the legs (A)push downward on the ground creating an action force, and the ground(B) pushes back creating a reaction force