Effect of Scapular Retraction on Lower Trapezius, Infraspinatus, and Deltoid Muscle Electromyographic Activity During the Side-Lying Abduction Exercise.
Masaaki Tsuruike, Todd S Ellenbecker
PMID 37425105WHAT IT FOUND
In healthy baseball players, pulling the shoulder blade back during side-lying arm abduction increased lower trapezius activity.
Adding 15° horizontal abduction with a 9.1 kg dumbbell raised it to 55% of the muscle's maximum voluntary contraction.
Key findings
01With the 9.1 kg dumbbell, the lower trapezius reached 55% of maximum voluntary contraction in the retracted, horizontally abducted position, compared with 21% during protraction and 24% during retraction in neutral.
02With the 9.1 kg dumbbell, the upper-to-lower trapezius ratio was 0.50 in retraction with neutral and 0.23 in retraction with horizontal abduction.
03For infraspinatus activity, side-lying external rotation with the elbow flexed to 90° and 40% load produced 44% of maximum voluntary contraction, compared with 17% and 22% during side-lying abduction in retraction in neutral and horizontal abduction.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study included only 20 asymptomatic collegiate baseball players, so it does not show how people with shoulder pain, different ages, or non-dominant sides would respond. The outcomes were muscle electrical activity during brief isometric holds, not pain, function, injury risk, or throwing performance. The dumbbell load was fixed at 9.1 kg, and the lighter load was 40% of each person's measured maximum contraction, so the effect of other loads is unknown. All testing was on the dominant side, and the authors state the findings may not apply to the non-dominant side.
Declared interests
The authors declared no conflicts of interest relevant to the study.
The easy way to misread this
Do not conclude that side-lying retraction exercises reduce shoulder pain or improve throwing performance. The study measured muscle electrical activity in 20 asymptomatic collegiate baseball players on the dominant side only, and it did not report patient outcomes.