How heavy of a medicine ball should be used?
The cfts gives a section with the amount of weight used for medicine balls. Angella was using 6-9 pnds.It depends on the exercise. In general upper to core work would be done with 4-6 pnds. The ball would be smaller in size to get better grip on it. The lower body exercises would be heavier with a bigger sized ball. Depends on the athlete.
Of course, it is a drag (pun intended!) to carry around a selection of med balls. I tend to stick with a 4kg one which seems to be a fairly good compromise for upper body work, core work and explosive throws. My heavy explosive workouts are done either on the track at full speed or in the weight room with significant weights.