The sacrum is a series of 5 fused vertebrae (S1-S5) that sit at the end of the spine and between the two Iliac bones of the pelvis. It articulates with the lumbar vertebra (L5) above it, the two iliac bones on either side (the Sacroiliac Joints), and the coccyx (or tailbone) below. The front surface is smooth, but the back surface is surprisingly bumpy (though the ligaments that run down the back of it make it seem less so).

The sacrum arcs backwards, sitting at an angle between the two pelvic bones so that it's impossible for it to be flat against the floor in lying. I think of it like one of my daughter's rainbow arches placed upside down on its apex. You can aim one end down or the other, but not both.

Building on the work with the sits bones, the last series of classes focused on the 'sacral clock'. It's a movement that comes out of Feldenkrais technique but which, if combined with the Pilates strengthening exercises, can really change our perception of centre and centering. I'm grateful to Jillian Hessel for reminding me how important this foundational practice is for addressing imbalances from the pelvis.

So often in Pilates classes, the focus shifts directly into stabilising - creating a kind of holding - instead of stability that's a form of dynamic alignment. If the pelvis is constantly held in a torsion, any abdominal work will lead to bracing. It's like layering one holding pattern onto another. What I love about the sacral clock is that it brings the focus down a notch, from the lower back to the pelvis/ sacrum, allowing us to centre by mobilising and then finding stability from a more rounded base of support. Here's a short practice that you can try.

The Sacral Clock - practice

Work with a lightly pumped over-ball under the pelvis, or a cushion.

Imagine you're lying down with a clock placed behind/ under your pelvis.

The top of the sacrum is your 12 o'clock. The tailbone is the 6 o'clock, your left pelvic bone is the 3 o'clock and the right pelvic bone is the 9 o'clock.

Start by rolling an imaginary marble from 12 to 6. Initially I suggest moving without any engagement in the buttocks. Try to control the movement from the lower abdominal region without tucking or pushing into the lower back.

Then roll that marble from 3-9. The knees like to join in and sway side to side when you do this, so try to keep them pointing forwards and allow them to glide a little forwards and backwards like pistons instead. I like to gently encourage a little glut engagement here, pushing off the leg on the side that lifts a little.

Now try to roll the marble around the clock, following as the marble hits each of the numbers on the clock face. Notice if any numbers of the clock were less accessible, stickier, or less clear in your self-image.

Reverse the circles and see if this changes your ability to articulate.

Now find a still point where the marble can rest in the centre of the pelvis. I like to image that I'm trying to access all 12 numbers of the clock face simultaneously here.

From this stable point you can try adding some low level stability work:

• lifting one leg at a time on an out breath

• lifting one arm at a time on an out breath

• lifting opposite arm and leg

• swapping from one to the other (marching)

I like to end the series by opening up the Hip Flexors that can become a little tight in this work - just lengthen one leg underneath you as you draw the other one towards you.

Image Attribution: BodyParts3D is made by DBCLS, CC BY-SA 2.1 JP <https://creativecommons.org/licenses/by-sa/2.1/jp/deed.en>, via Wikimedia Commons