Your table tennis Mechanics of the arm-swing with a quiet shoulder is the secret of controlling blade angle to eliminate unforced errors.
 
Your upper arm is attached to the shoulder in a round socket, therefore it is impossible to (swing straight) back or forward; when you swing your elbow to shoulder (upper arm) forward your blade angle will automatically open the blade (in proportion to length of the upper arm  travels forward to and through the ball contact. This is the exact opposite of what's best.