The topic of whether it is better to “tuck the tailbone” or to “untuck the tailbone” in our yoga practice is a popular one! Avoid Googling the topic because you’ll end up in a two-day rabbit hole!
Tucking the tailbone is essentially tilting your pelvis in the posterior direction (imagine the pelvis as a bowl of water and you are tipping the water behind you). Untucking the tailbone is the opposite: tilting your pelvis in the anterior direction (and tipping the water in front of you).
Neither of these movements/positions are inherently right or wrong. Whether you choose to tuck or untuck (or to not even bother to think about it) when practicing a certain pose is going to depend on many things including your unique anatomy and what your intention is for practicing that pose on that given day. For example, if you tend to flex your spine in Chair Pose and want to experience having a more neutral spinal position here, you’ll want to try to untuck your tailbone slightly. If your tendency is to deeply backbend when you’re in Chair Pose and, again, you want to experience having a more neutral spinal position, you’ll want to tuck your tailbone slightly. Many of us would probably benefit from regularly moving through the tucking and untucking range in a controlled way. Think of a slow Cat Cow transition and how good that can often feel.
I imagine that one of the reasons why “Tuck the tailbone” has become such a popular cue is the (bizarre) concept of having an “anteriorly tilted pelvis” and how this can cause back pain. No two pelvises are the same shape or size, and no pelvis is symmetrical in any plane. Just take a look at the image below (source: Paul Grilley).
Pelvic anatomical variations
So, what might look or feel like a ‘neutral’ pelvis for one person will look and feel different for the next person. Pelvic tilt is often quantified using the angle between the horizontal and a line connecting the anterior superior iliac spine (ASIS) and the posterior superior iliac spine (PSIS). But how can we go about meaningfully defining an anteriorly tilted pelvis if we each have a completely unique pelvis?
In terms of labelling an anteriorly tilted pelvis as the source of someone’s back pain - if only things were that simple! Herrington (2011) studied 120 adults *without* lower back or pelvis symptoms and found that 85% of males and 75% of females presented with an anterior pelvic tilt, 6% of males and 7% of females with a posterior tilt and 9% of males and 18% of females presented as neutral.
Does tucking the tailbone create more length in the spine? No. It’s not possible to lengthen our spine, i.e., actively move the vertebra further apart from each other to create “space” - there are in fact no muscles that are able to perform this action. We can however diminish the curves of the spine (attempt to straighten it), and this will have the effect of elongating it.
Reference:
Herrington, L. 2011. “Assessment of the degree of pelvic tilt within a normal asymptomatic population.” Manual therapy 16(6): 646–648.
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