There is a connection between activating the body’s deep core muscles and activating another very important muscle that forms part of the swing called the Serratus Anterior. Let me explain: The Serratus Anterior muscle activates when performing protraction of the Scapula. The Serratus also activates the stabilizers of the position of arms and shoulders. In protraction, upper and lower Trapezius muscles acts to prevent downward rotation, and the lower Trapezius muscles act to prevent elevation, and downward rotation. Protraction helps in finding natural limitations in Scapular rotations by a significant degree. This seems relevant to me, because if you look at all the pros when they set up, and when they make contact, they all have this in common. They protract the scapula, by activating the serratus anterior muscle.