Can common measures of core stability distinguish performance in a shoulder pressing task under stable and unstable conditions?

Keogh, JWL, Aickin, SE, and Oldham, ARH, Can common measures of core stability distinguish performance in a shoulder pressing task under stable and unstable conditions? J Strength Cond Res 24(2): 422-429, 2010-The primary purpose of this study was to determine whether a range of static core stability (CS) measures could distinguish shoulder press performance in unstable vs. stable conditions. Thirty resistance-trained men gave informed consent to participate in this study. One-repetition maximum strength (from <6 repetitions) was predicted in the seated shoulder dumbbell press performed in unstable (Swiss ball[SB]) and stable (back-support bench) environments. Three CS muscle endurance tests were performed, with 4 CS ratios also calculated. The degree of strength decrement, referred to as the instability strength level (ISL), was calculated by dividing the predicted 1RM Unstable score by the 1RM Stable score. All subjects were categorized as high (ISL > 0.90), moderate (0.85