A body in balance is a dynamic system where the center of gravity is oriented over the base of support. For example if you lean backward and orient your center of gravity behind your base of support you will have to respond by taking a step back in order to remain balanced.
If the center of gravity by nature is unstable and weak, the challenge to the base of support increases in the same fashion as ‘spinning plates’.
The lower extremities must respond with increasing rate of adaptation often leading to loss of balance. Balance is an involved topic consisting of many potential problems, but oftentimes increasing the stability of the torso can help reduce erratic movements of the center of gravity thus reducing the adaptation demands of the lower extremities.