The ankle joint is one of the four areas of your body (ankle, hip, spine and shoulder) that is designed for multiplanar movement. Although we have always believed that golf requires good rotation for success, recent research suggests that rotational movement is the key for efficiency in a golf swing. The ankle joint is often overlooked as a rotational joint in the body. There are approximately 20 degrees of rotation available in a biomechanically normal subtalar joint. However, it is uncommon to find a foot that is positioned to use all of the available range in the ankle because many feet are found to have a flattened arch (pronated) and therefore are not in a neutral subtalar position. When this occurs, the body is predisposed to an increased demand for rotation from other rotational segments. In its search for additional rotation, stability of the lower body is often compromised. Consequently, a foot placed in a subtalar neutral position at address will be more likely to transfer rotational energy up through the body and out to the club head without sacrificing stability.
A common misunderstanding of many amateurs and professionals is that the weight needs to be on the inside of the trailing foot at address. This is often suggested by a well meaning teaching professional in an attempt to stabilize the trailing knee in the backswing. A commonly used drill that follows this suggestion involves placing a golf ball underneath the outside the trail foot to pitch the inside of the foot into the ground. Doing this drill limits the rotation potential of the ankle and begins a sequential search for rotation up the kinetic chain. If excessive rotation (greater than 45 deg) isn't available at the next rotational segment, the hip, the body will seek lateral or vertical movement to accomplish a "stable" foundation from which to begin the downswing. The result is a swing fault or compensation known as a sway or reverse weight transfer.
To avoid compensation when seeking a stable lower body, it is critical that the ankle joint is placed in a neutral position at the address position and has the ability to pronate (or flatten the arch ) at the top of the backswing. By doing this the lower body will be stabilized and the weight will remain on the inside of the trailing foot during the backswing.
If you are unsure if your ankle joint has the ability to start in a neutrally rotated position, or flatten during the backswing, you may need to perform the following exercise to help form or flatten your arch. Sitting with feet on the ground, place fists between knees, without allowing knee to separate from each other, lift arches so that inside of foot raises off ground. Return to foot flat position and repeat 20 repetitions 3x/wk.