Part 1 looked at the foot, Part 2 at the lower leg and the pelvis. The point of view has been rising one level at a time.
Part 3 goes higher still, because the muscle that carries the leg forward comes from above the pelvis.
Walking is also falling
Before that, the act of walking itself is worth a look.
When you walk, the body’s center of mass moves like an inverted pendulum. The center of mass is the single point where the weight of the whole body gathers, and it sits roughly in the middle of the pelvis.
An ordinary pendulum hangs from a point above and swings its weight below. Walking is the reverse. The pivot is the foot on the floor, and the body — the weight — passes over it in an arc. With every step the body travels along the top of a curve.
A pendulum gives energy back when what rose comes down. Walking works the same way: at the top of the arc, the center of mass falls forward. That fall becomes the drive for the next step.
Walking, then, is a matter of falling forward continuously and putting a foot out before the fall completes.
Running works differently. There is a moment when both feet leave the ground at once, and the Achilles tendon lengthens, stores energy, and springs the body forward. The Achilles tendon is the thick tendon where the calf muscles meet the heel bone. Running is spring mechanics.
Walking is not slow running. It is a different event altogether.
And since the drive comes from falling, you cannot walk unless the center of the body can travel forward. Moving the feet is not yet walking.
Where does the leg begin?
When you walk, where do you feel your legs begin?
Most people take the leg to be everything below the hip joint — everything below the belt of the trousers.
But the muscle that carries the leg forward does not begin there. It begins on the front of the lumbar spine, which is to say just below the ribs. The lumbar spine is the set of five bones at the low back, and its front is the side facing the belly — the opposite side from the bumps you can feel through the back.
That muscle is the iliopsoas.
The only muscle joining the upper body to the lower
Iliopsoas is the collective name for psoas major, iliacus, and psoas minor.
Psoas major begins on the front and sides of the lumbar vertebrae — the front of the spine. From there it passes diagonally through the pelvis and attaches to the lesser trochanter of the femur, a small prominence at the inner base of the thigh bone.
Iliacus begins on the inner surface of the pelvis and joins the same attachment. The inside of the pelvis is a shallow bowl-like curve; the muscle spreads across it and merges below into a single body with psoas major.
Beginning at the spine and attaching to the leg — almost nothing else in the body does this. That is why it is called the only muscle that connects the upper body to the lower directly.
The two halves are joined in bone at the sacrum and the pelvis. But the route by which the work of carrying the leg forward is received directly from the spine is this one muscle.
Its run is unusual, too. It descends vertically from the spine, then crosses the pelvis on a diagonal toward the femur. Vertical and diagonal in combination.
As I have written elsewhere, that shape resembles the arch of a building. Weight from above and support from below are handed across through a diagonal member. Part 1 looked at the arches of the foot; the same structure exists at the center of the body.
When walking changes, so does the sense of it
As the iliopsoas becomes available, walking changes.
So does the sense of where the legs begin.
From walking with the sense that the leg starts at the belt, to the sense of two legs hanging from beneath the ribs. The place you move from, when you walk, shifts upward.
When that happens, the spine lengthens as well. Swinging the leg from the hip requires fixing the pelvis: the reaction to the swing pushes the pelvis backward, and without something holding it, the body gets carried along. Fixing it is work for the muscles around the low back. But once the leg can be carried from the iliopsoas, the pelvis is free to move rather than held. The low back has less to do, and there is room for the spine to lengthen.
Low back pain and stiff shoulders often move in the direction of relief as a result.
Sitting shortens the walk
There are several reasons the iliopsoas stops working well.
The largest is how long we sit.
Sitting in a chair is a posture in which the hip stays fixed in flexion. The iliopsoas is held in a shortened position. Spend most of the day in that shape, and that length becomes the body’s default setting.
A shortened iliopsoas limits extension at the hip. Extension at the hip means the thigh traveling behind the body. In walking, this is the movement with which the trailing leg pushes off the floor. Limit it, and the push-off goes shallow.
What cannot be gained behind gets sought in front. Reaching the front foot further out to make a longer stride puts the landing away from the body, and the force there works to stop you. The foot put out to travel forward ends up braking instead.
And the pelvis rotates less easily. The stride shortens. With less drive available, the knees and low back take over the shortfall.
There is also a relationship with the abdominals.
Core training is widely recommended, and plenty of people work rectus abdominis for the look of it. Rectus abdominis is the muscle running vertically from below the ribs to the pubic bone — the one whose divisions show as a six-pack. But strengthening it can make psoas major harder to use.
The belly is layered from the outside in: rectus abdominis, then the organs, then psoas major. When the outermost layer tightens, the organs behind it lose the space they need to move. As the organs lose their movement, psoas major, deeper still, comes under pressure. And the body becomes one in which psoas major cannot easily work.
A weak psoas major shows up in walking and running. The thigh lifts less easily, and tripping and falling become more likely.
The pelvis turns four or five degrees
When the iliopsoas works, the pelvis becomes free to move.
During walking, the pelvis rotates four to five degrees to each side with every step. Rotation here is the same movement Part 2 described at the ankle and lower leg; what turns is the pelvis, around the body’s vertical axis. The number looks small, but it is what produces the stride.
A small angle becomes a distance further out. When a door opens a little, the area near the hinge barely moves while the far edge travels a long way. Pelvic rotation is the same: out at the foot, far from the center of the turn, the angle turns into stride length.
The mechanism runs like this. As the right foot goes forward, the right side of the pelvis turns forward with it. However far the pelvis has turned, that is how much further the foot reaches. The leg has not changed length, and yet the stride is longer.
If the pelvis is locked, you can only walk the length of your legs. The stride shortens, and the same distance takes more steps.
And the rotation of the pelvis travels upward too.
The arms do not swing for balance
As the right foot goes forward, the left arm goes forward.
This is sometimes explained as a movement for balance. That is not wrong, but the role is more active than that.
When the pelvis turns to the right, the rotation travels up through the spine. If the upper body simply turned with it, the whole person would end up facing right. So the shoulder girdle turns the other way. The shoulder girdle is the ring formed by the two collarbones and shoulder blades; it rests on the trunk rather than being fastened to the ribs by bone. Shaped like a collar laid over the shoulders, it can change direction independently of the trunk. That counter-rotation is what appears as the swing of the arms.
And if pelvis and shoulder girdle turn in opposite directions, the trunk between them is being wound. Wound tissue wants to return.
It is the same as a model airplane driven by a wound rubber band. Winding stores force; release it and the force turns the propeller. As you walk, the trunk is wound and released with every step.
That return is the drive for the next step.
The swing of the arms is not shedding surplus energy. It is storing energy for the next step and handing it on.
Which is why walking without swinging the arms is tiring. With no winding, force has to be produced afresh for every step.
Differences across the diagonals are traces of use
If walking is built on diagonals, then a difference between the diagonal lines will show up in walking directly.
The diagonal lines are the connections from right foot to left hand and from left foot to right hand. As you walk, the two take the lead in turn.
Watching the coordination of the limbs with someone lying face up, you find things like this: the line from the left foot to the right hand engages readily and tends toward tension, while the line from the right foot to the left hand engages less. It is not that one side is weaker. The quality differs by diagonal.
That difference is not treated as a distortion. It is evidence of use.
The dominant hand, a movement repeated at work, a practice kept up for years. Each of these gives the body a direction.
In my own case, close to ten years of Ashtanga vinyasa yoga left the pattern of using the right hand strongly and the left weakly. Yoga asana are arranged to be done evenly on both sides. The asymmetry remains all the same, because an evenly arranged practice is received by a body that is not symmetrical.
The difference is visible when watching someone walk. The arms swing differently. One shoulder turns first. One stride is shorter.
Removing the difference is not the goal. As long as the diagonal connection runs through, the whole can coordinate with the difference still there.
Where does the shock go?
Part 1 said that the arches receive the shock of landing. But the arches do not handle it alone.
The shock produced each time the foot meets the floor is dispersed in order: the instep, the knee, the hip, the spine.
And the S-curve of the spine is the last of the shock absorbers. The front-and-back curves formed by the cervical spine, the thoracic spine, the lumbar spine, and the sacrum pass the shock along as a wave. The cervical spine is the neck; the thoracic spine is the part of the back the ribs attach to; the lumbar spine is the low back; the sacrum is the inverted triangle of bone at the back of the pelvis. The four of them arch alternately forward and back.
In a straight rod, shock arriving from below would reach the head unchanged. The curves make it diminish along the way. A bow bends and lets force pass through it; here too, being curved is the work.
Part 1 said that the arches of the foot are made by the same process as the secondary curves of the spine. The secondary curves are the forward curves drawn out after birth, as the head is lifted, the body comes upright, and walking begins. In walking, the arches of the foot and the curves of the spine are doing the same job: receiving shock underfoot, passing it along through the spine.
When the head is carried forward, this dispersal works less well. The head is not sitting on top of the curves, so it falls outside the route the shock travels. The neck ends up supporting the head by itself, and the load concentrates there.
The place called the tanden
The iliopsoas lies close to the body’s center of mass.
That is the region of the tanden in East Asian understandings of the body — the bandha of yoga, which names the practice of engaging the inside of the body to make a path for force. The line running from the front of the lumbar spine, through the pelvis, toward the femur passes right through the center of the body.
For the iliopsoas to be available is also for the center of the body to be felt. Conversely, when a person tries to find that center and cannot get hold of it, the iliopsoas may not be working.
Brought back to walking, it comes out like this. Without a felt center of mass, falling cannot become drive. The sensation of falling forward is frightening, so the foot goes out first to make a support. The stride shortens and the upper body is left behind.
With the center available, falling forward is safe to do. You fall, and the next foot arrives.
Where this meets the fifth Rolfing session
The fifth session of the Ten Series works with the iliopsoas.
It cannot be touched directly, being deep in the body. The surrounding muscle and fascia are softened to make room for the iliopsoas to move. Fascia is the membrane that wraps muscles and organs individually, separating neighbors while joining them. That alone is enough: given the room, the iliopsoas begins to move on its own.
What is being watched in the session is not whether the iliopsoas has softened. It is whether the support rising from the pelvic floor passes through it and out along the front of the spine. The pelvic floor is the layer of muscle closing the lower opening of the pelvis, slung front to back and side to side like a hammock.
The fifth session is also where breath and gait meet at a deep layer. The diaphragm, moving with every breath, and the iliopsoas, working with every step: both attach to the front of the spine, and the two are continuous with each other. While you are walking, the breath and the legs share the same address.
Where this goes next
Part 3 has climbed from the foot through the lower leg and the pelvis to the iliopsoas.
That walking is a whole-body event should be visible by now. The foot presses the floor, the pelvis turns, the trunk winds, the arms swing.
One thing has not been taken up: gravity.
If walking is falling, then what decides where the fall is headed is gravity. And what makes it possible to fall and stay upright is a system for supporting the body within gravity.
Part 4 reads gait through gravity. The triangle of eye, foot, and inner ear, promised in Part 1, is taken up there as well.
The series
- Part 1: The Foot Changes Shape With Every Step — How the Arches Are Made
- Part 2: The Problem in the Foot Is Not in the Foot — From the Lower Leg to the Pelvis
- Part 3: The Leg Begins Below the Ribs — The Psoas and the Diagonal (this article)
- Part 4: Reading Gait Through Gravity — Tonic Function and Palintonicity