What effect does running around a track have on momentum?

During Track and Field meet, momentum can be observed almost everywhere. Especially in the field events (jumping events and throwing events) where maximizing momentum is the key to performing well. In throwing events such as javelin, shot put, hammer and discus, competitors get to apply force to the object for a brief moment of time. After that, forces acting on the objects are all against the forward motion (i.e. gravitational force, air friction…). At this point momentum is all that is left to keep it going forward.