Over the past number of years, core stability has really jumped in popularity as a way to protect the back or improve overall function. While this is all good, there seems to be some trouble with making this happen properly because I am meeting more yoga teachers who have pain, and/or who are limited in their movement, despite practicing what they think is "core work".
Tucking the tail bone, or lengthening the tailbone creates an action of posterior tilting of the pelvis (a little or a lot depending on who is practicing). The rectus abdominus contracts and the lumbar spine flattens (a little or a lot depending on who is practicing). From a "feeling perspective", many teachers tell me that they feel this in their lower abdomen - and this feeling makes them believe that they are "doing it right". All fine and good to "feel contraction in the lower abdomen" but that doesn't mean the core is "on".
The inner core stabilizing muscles are the transversus abdominus, the pelvic floor, and the multifidus. The largest of the 3, the transversus abdominus is made up of horizontal fibers. When the muscle contracts it squeezes like a girdle. The multifidi attach vertebra to vertebra and "check" the vertebral movement helping to stabilize segmental movement. The pelvic floor produces a squeezing inward action like when you wrap your left hand around your right finger and gently squeeze.
You'll notice in these descriptions that none of these muscles have the fiber arrangement nor the attachments to cause a posterior pelvic tilt.
So what is happening with a posterior tilt or "tucking the tailbone" or "lengthening the tailbone"? The superficial abdominal muscle - the rectus abdominus - is contracting, as are the hamstrings. These aren't core stabilizing muscles.
Okay, well, what about people who have an anteriorly tilted pelvis - wouldn't they still benefit from tucking? In my experience - no. The mistake that is often made when wanting to improve movement is people assume that the "pelvis woke up one day and decided to be anteriorly tilted". That just doesn't happen. Instead - the body responds to stimuli. In the case of the anteriorly tilted pelvis, it is in that place because of other forces at play - like issues in the shoulder girdle, issues in connection between the pelvis and feet etc. If we want to improve an anteriorly tilted pelvis, we need to clean up those issues (and these issues are different for everyone). When those are cleaned up, the pelvis finds its place and lightness emerges.
So now what? One of the key things you can do as a teacher teaching core work is to show your students how to do the following:
1. Move in a pain-free range of motion, or if your student is already in pain, in a range where the pain levels don't increase. If you are in pain, your core is not as functional as it could be.
2. Breathe easy. When you force your breath, you will be bracing and not using your core muscles. You may even be doing "breath holding".
3. Move in a range of motion that is optimal and "pure" for you. This is the single biggest thing people can do to improve their core stability and overall function.