There are a couple of things you could do with a med ball to work your back/biceps plyometrically... Vertical toss - throw the ball/object as high as you can Overhead toss - throw the ball backwards over your head as far as you can Slams - Throw the ball downwards as hard as possible onto the floor
With the Med ball is it better to use a heavier one? Most I see are around 12lbs, but I have seen one that was 20lbs.