There has been on-going controversy about spinal stabilization for the last 9 years or so. Some claim that drawing the belly button towards the spine (drawing-in) is the best and others say that bracing, or tightening up like you are about to be punched is the way. There are fanatics on either side, but as is most things in life, the truth probably lies somewhere right in the middle. Drawing in and activating the TrA (transverse abdominus) and other core stabilizers should precede limb movement, but does probably not provide enough support to the spine against greater forces. On the other hand, bracing alone, which is common with most people who have synergistically dominant movement system (rectus abdominus, external obliques etc.) will not provide inter-segmental stabilization to protect the vertebrae and surrounding structures. In healthy, well conditioned individuals, this should happen automatically. Unfortunately, the chair borne society we are entrenched in weakens our core stabilizers which leaves the movement system to do it’s job and an almost impossible task (because of anatomical arrangement) of providing inter-segmental stability.
Long story short, draw-in to return the feed-forward mechanism, draw in and brace when the load/forces increase and remember posture and corrective flexibility:)
Have a great night!