Bracing, or bearing down through the trunk, comes naturally to people in aligned bodies. For the rest of us, this will help to locate and isolate this action:
* blow out through your mouth as if blowing out a candle, or cough a few times.
* notice the pushing-down sensation through the core of your torso. This is active engagement of the transversus abdominis muscle.
* See if you can engage this muscle when you are neither blowing out nor coughing. It has a definite bearing-down like quality, like having a bowel movement or pushing out a baby.
Once you have figured out how to isolate this action in the muscle, you are able to protect yourself when lifting or pushing something heavy by maximizing this core strength with the natural strength of your arms and legs.
—from Ageless Spine Lasting Health by Kathleen Porter, Synergy Books (2006).