Ideal

• Gaps between elbow/arm and trunk are same on both sides

You See

• Bigger gap on one side between trunk and elbow

Cause

• Arm is abducted (short arm abductors – and/or the arm on OS is more adducted, short arm adductors), check whether spine is straight (SPs on plumb line)
• Scapula is downwardly rotated, short scapular downward rotators (and/or the scapula is upwardly rotated on OS, short scapular upward rotators)
• Spine is laterally flexed
• Pelvis has shifted sideways to OS, hip abductors are short on OS, hip adductors are long on OS (and vice versa for SS)