The body should track the object throughout all of the AF points after you have locked it on the central focus point.  Check your manual and read the small print on AI Servo :)

Also - you may be a bit far away with 200mm for the "object" to register well enough to track...

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography