If your shoulders are inflexible (90-90 test), your arms will have difficulty rotating and folding. Shoulder issues can cause the left arm to jut away from the body at the elbow during the through-swing and look like a chicken wing. This inflexibility can cause elbow tendinitis and sliced shots.
Holding dumbbells in front of you while in your golf posture, rotate your arms away from each other as far as you can.
Holding dumbbells, bend your trailing arm's wrist into a cupped position and your lead arm's wrist into a bowed position.
Keeping the dumbbell in a bowed position in your weaker arm, simulate a golf swing. Repeat with dominant arm with wrist in cupped position.