Muscle Activation When Performing the Chest Press and Shoulder Press on a Stable Bench vs. a Swiss Ball
James M. Kohler, Sean P. Flanagan and William C. Whiting
Purpose: To evaluate muscle activity of the prime movers and core stabilizers while lifting stable and unstable loads on stable and unstable surfaces during the seated overhead shoulder press exercise.
Conclusions: Little support was found for training with a lighter load using unstable loads or unstable surfaces.
IN PLAIN ENGLISH: To better target a muscle or group of muscles, put the body in a position to maximize the use of that/those muscles (read: become MORE stable) as opposed to a position of instability which will lessen the potential of overload sought.