Setting up with slack in your arms causes you to extend towards the ball when you swing and hit the ball with the heel of the club
Our main concept in golf fitness is to understand how your body works with your golf swing, looking at the dysfunctional areas of your body and how they effect your swing
When an instructor refers to open and closed first you must determine if it is the body or the clubface he is talking about, an open clubface has the face aimed to the right while an open stance has your body aimed to the left