IAP stands for intra-abdominal pressure and is the single most important component in core stability. You can do all the situps, leg lifts, planks you want but if you maintain your IAP doing these things you WILL hurt yourself at some point!
So how do I achieve this? Easy, can you control the diaphragm and transverse abdominis (TA) ? EXACTLY what I thought, "I don't know!" Here's a couple things you can look for that might indicate your ability to do so: 1: Do you have a sexy six-pack ? If so, that's a NO! 2. Does your "love handle" area have an " hour glass" look? If so, NEGATIVE! 3. When looking in the mirror can you see those creases going into the groin from the stomach at the waistline? You know, the ones that are right inside the hip bones that everyone wishes they had! If so, NEGATORY! 4. Do you have chronic low back pain? If so, thats a big fat NOPE! 5. When you take a breath do your shoulders elevate? If so, DEFINITELY NOT!
All of the above are signs that you are either unstable or you are focusing on the wrong muscles when you work out the "Core". In an ideal situation, the abdominal area should look like a rounded cylindrical shape and the breath should be taken into the belly not the shoulders. If you are properly activating the Diaphragm and TA the belly should expand with every inhale. When you tighten the abs there should be just as much tension in the sides and back of your belly as in the front. And don't forget the lower abs, usually the hardest area to activate. It's important to understand tension on inhale is the easiest part. The long-term goal is to maintain similar pressure on the exhale as well. This is more difficult due to the elevation of the diaphragm which is like the piston of a motor. As it descends the chamber pressure increases easily. When it ascends, exhale, the sides of the chamber must contract in order to maintain pressure.
Not all of you have a problem with your core activation but for those of you that can't seem to shake the "injury bug" I'd suggest this is an area worth investigating. Once you've accomplished this ability to maintain the core contraction its now time to dial it back. Most people when learning proper activation of core stabilization give it a full 100% effort. This isn't proper, it's unrealistic to think you should be walking around with full contraction at all times to stabilize your core. You don't give a full biceps contraction when lifting a pillow, do you? It's important to learn how to apply appropriate contraction based on the activity. When lifting heavy weights you'll activate near 100% but when just walking around town you should be closer to 20-30% contraction.
You want an idea of what this looks like, look up pictures of an Olympic weightlifter. That's not fat in the belly, maybe some of them but for most of them its the Transverse abdominis at its finest! Another good example, Roger Federer! You don't become the oldest number one ranked in tennis with constant injury. The guy is a freak of nature when it comes to stability, in all aspects and not just the core!