Good functional movement has to come from a secure base.  A solid platform creates a stable base from which to propel movement – IN ANY DIRECTION.  We have talked about this in relation to shoulders and also in ankles, so it is that we come to the basic platform for much of the movement of the trunk – THE CORE.  Some may argue that the platform for movement of the trunk comes from the pelvis or the ribcage.   This is true.  But in terms of movement, a strong core is a defining factor in any movement of the body and in particular the limbs.  The core activation helps to stablise both the ribs and the pelvis.