The Series · Part 1 · Deep Core

The Psoas.

March 15, 2026 · San Francisco
What we explored

The body's central hinge,
worked from the inside.

The psoas is the only muscle that connects the spine to the legs: the deep front line's keystone. Most of what people call a "tight psoas" behaves less like a short muscle and more like a guarding one: a control problem, not a length problem. So this room didn't stretch its way in. It worked on organization first, and let range arrive as a byproduct.

  1. Locating the psoas. Where it actually lives, what it attaches to, and why it guards. Anatomy before sensation.
  2. The quadratus lumborum. The psoas's deep neighbor, and how the two trade work when one stops organizing.
  3. Breath as the way in. The diaphragm and psoas share fascia and rhythm; down-regulating one releases the other.
  4. Side bends under control. Loading the lateral line through range the body owns, left and right compared.
The evidence behind the room

Why we trained it
instead of stretching it.

A meta-analysis of eleven randomized trials found strength training improves range of motion as effectively as stretching (Afonso et al., Healthcare, 2021), which is why this room built control first and let length follow.

And the breath work wasn't a warm-up. A meta-analysis across 223 studies shows slow, diaphragm-led breathing reliably shifts the nervous system toward its down-regulated, parasympathetic state (Laborde et al., Neurosci Biobehav Rev, 2022): the state in which a guarding psoas lets go.

Group-level findings, not personal predictions, and not medical advice.

Where it leads

This room became the method.

Part 1 set the template the Series still runs on: assess first, train what the assessment finds, and compare left to right rather than body to ideal. Part 2, Hip Mobility, took that template and scored it station by station.

Take the Movement Map assessment Apply · 1:1 or cohort Part 2 · Hip Mobility →