Can Common Measures of Core Stability Distinguish Performance in a Shoulder Pressing Task Under Stable and Unstable Conditions?
Justin W. L. Keough, Sam E. Aickin and Anthony R.H. Oldham
Purpose: To determine whether a range of static core stability measures could distinguish shoulder press performance in unstable vs. stable conditions.
Conclusions: Core stability training may therefore only lead to significant improvements in functional dynamic performance if the postures, mode and velocity of contraction performed training, are similar to the competitive tasks.
IN PLAIN ENGLISH: Specificity of skill execution is evident here. Unstable and stable conditions are specific to the conditions present for each. If you want to make your shoulders stonger, perform shoulder exercises in a stable manner that allow those muscles to be worked as hard as possible.