This was taken from an article that Charles Poliquin just post on his site about dead lifting. The article was about the dead lift but I cut this out because it was just clear, concise, and to the point….
“I’ll go on record saying it is not a good idea to perform any deadlift variations while standing on an unstable surface, such as a Bosu ball or a rocker board. This may seem like common sense, but in fact these Cirque du Soleil-type exercises have attracted enough attention that a research study was performed on deadlifts performed on a BOSU ball and a rocker board (also called a T-bow, which is a platform that tilts laterally).
That study was published in the October 2010 issue of The Journal of Strength and Conditioning Research with the title “ Deadlift Muscle Force and Activation Under Stable and Unstable Conditions .” The authors of the study concluded that “…the use of instability devices in deadlift training does not increase performance, nor does it provide greater activation of the paraspinal muscles, leading us to question their value in the performance of other types of exercises.” As such, if you are considering performing deadlifts on an unstable surface such as a BOSU ball, first you have to answer the question “Why train your body to be weak?””