18/11/2025
The sacroiliac joint (SIJ) can move, but only a little and that tiny movement is essential for upright walking and standing. Because the SIJ sits at the centre of the body, it has to handle huge amounts of force from above and below. Every time we take a step, it manages shear. If it were highly mobile, we’d constantly lose stability through the pelvis.
Instead, humans evolved a relatively stiff but still dynamic SIJ: stable enough to keep us upright, yet mobile enough to absorb force. Compared with joints like the hip, though, its movement is minimal.
People sometimes feel pain around the SIJ, and this often gets labelled as “instability.” But true instability is rare. Pain here is far more likely tied to sensitivity, irritation, or a history of trauma, not bones shifting out of place. Even in hypermobile individuals, attributing symptoms to SIJ “alignment” doesn’t hold up, because the joint simply doesn’t move much.
Assessing SIJ motion or sacral alignment is also extremely unreliable. Pelvic anatomy varies widely, and the bony landmarks we depend on aren’t consistent from person to person. So the idea that we can detect a “misaligned sacrum” with our hands just isn’t supported.
Language matters. Telling people they’re “out of alignment” can create fear and fragility, making them feel unfit to move, exercise, or participate in daily life.
Yes, the SIJ is mobile to a small degree, and that varies between individuals. But it is also one of the most stable joints in the body, reinforced by incredibly strong ligaments. The likelihood of a genuine SIJ “misalignment” in the average Pilates client is extremely low.
Let’s stop fear-mongering and start helping people move with confidence.
Movement is medicine
Tom
