The core: it's the buzzword in rehab and fitness circles. Everyone talks about how important it is for treating low back pain and for athletic performance. But what is it really and what are the most effective ways to strengthen it?
It is important to know that the core is not just your abs. To date, there is no definitive definition of what truly is the core. A May 2010 study by Escamilla et al. described the core as "the lumbopelvic-hip complex, which involves deeper muscles, such as the internal oblique, transversus abdominis, transversospinalis (multifidus, rotatores, semispinalis), quadratus lumborum, and psoas major and minor, and superficial muscles, such as the rectus abdominis, external oblique, erector spinae (iliocostalis, spinalis, longissimus), latissimus dorsi, glute maximus and medius, hamstrings, and rectus femoris."
As you can see, that covers a lot of muscles including ones that directly affect the upper and lower extremities as well as the lumbar spine and pelvis. These muscles are important for both movement and stabilization of the pelvis and spine.
Which muscles are most important to strengthen and which exercises are most effective? There is still great debate on all of this. Research is starting to show that it is important to strengthen the core as a stabilizer versus a mover. This means exercises where the trunk is stable and static (ie. planks vs. sit ups). A 2002 article by Cholewicki and VanVliet in the journal Clinical Biomechanics reported that "no single core muscle can be identified as most important for lumbar spine stability" and "no one muscle contributes more than 30 percent to overall spine stability."
How do we contract/activate the core? There are numerous techniques used to facilitate activation of the deep core musculature: abdominal hollowing, abdominal bracing, draw-in maneuver, and posterior pelvic tilt just to name a few. None of these has been shown to be the most effective at core activation, even with EMG studies. The key is to contract the deep abdominals, including the pelvic floor. You should feel your abdominals tighten above and below your belly button as well as in your love handle region (obliques). The Kegel exercise, which is used to contract the pelvic floor, is another good way to activate your core musculature. However you achieve this core activation, you have to maintain it throughout the repetition/exercise duration. If you're holding your plank for 2 minutes, you probably lost your core control at about 30 seconds.
So, let's put it all together.
The following link is a beginner core program that I use with many of my athletes. If it makes you feel better, some of these world-class athletes have trouble even with this basic program.