Stability may be expressed as the ratio of the width of the base to the height of the center of mass above the base. Stability is inversely proportional to the height of the center of mass above the base. As the center of mass is moved higher above the base, stability decreases, and vice versa. Stability is directly proportional to width of the base. As the base is moved narrows, stability decreases and vice versa. When performing a sitting stance, the lower the body, and the wider the stance, the more stable the stance.
Stability may exist in two states: static (not moving) or dynamic (moving). Static stability is important, but Taekwondo involves movement, so dynamic stability is more important to a Taekwondo student. If the body is not stable, then it cannot move quickly to either block or attack, and techniques will lack speed and power. In performing a stance, the body must have static stability. The feet must be far enough apart to form a strong base and the center of mass must remain along and directly over the base. To perform a kick, the body must maintain dynamic stability throughout the kicking motion. This means the center of mass must constantly shift so it is kept directly over the base (which is now the supporting foot).
Any time the center of mass moves away from a location directly over the base or outside the area of the base, the body becomes unstable. As the center of mass is moved higher above the base, stability decreases, so the legs should be bent so the center of mass is kept as low as possible while still permitting quick movement of the body. As the center of mass is moved lower above the base, stability increases until the point is reached where the body may no longer move effectively. Students must develop flexibility and strength so they can make quick shifts of their center of mass to maintain stability and balance. Sometimes, a small twist of the knee or rotation of the foot may maintain stability, while at other times, such as while being grabbed and pulled, great strength may be required to maintain stability. To maintain stability, strength and flexibility are required, not body tension.