The Core Muscle Group has recently been redefined to include all of the muscles from the pelvic floor to the neck with some of these core muscles extending into the extremeties. This is a major departure from the previous definition of "Core" being a group of 8 muscles surrounding the abdominal region.
One part of Dr. Wright's research in the biomechanics lab was on an exercise that balances the Core. An article on the exercise correction of an imbalanced Core was published in an international journal out of England in 2008. the following video provides instructions for that exercise.
Your core muscle group is your center of gravity. Tightness on one side of the core creates imbalance. This exercise will balance your core. Research shows that only 2 % of the population has a balanced core. An imbalanced core creates a left or right hip rotation due to muscle tension on one side of the core. This exercise will balance your core for approximately 4 to 8 hours. If you do this exercise, you will eliminate a major balance variable when you address the ball.
Stance width changes from a balanced to imbalanced stance width also impacts the core muscle group. When you stand out of balance, your core muscles tighten on one side causing a rotation of your hips either left or right.