AF/IR describes the movement of the AF joint, which is the intersection of the acetabulum and the femur. “Acetabulum on Femur” Internal Rotation. A quick review of anatomy: you have a pelvis. The pelvis is a ring consisting of four bones: the left innominate, the pubic bone in front, the right innominate, and the sacrum in the back. Each innominate consists of an upper part and a lower part. The top part is called the illium and the bottom part is called the ischium. Keep in mind they are the same bone.

Your femur (upper leg bone) connects to the ischium at a particular location called the acetabulum, usually known as the hip socket. In the picture below, you are looking at a right acetabulum and a right femur.

This point of intersection, commonly referred to as the hip joint, in PRI speak, is often given two names: AF- Acetabular/Femoral Joint. FA- Femoral/Acetabular Joint. Remember, the AF joint and the FA joint are the same joint. There are two different names given so as to separate the movements that occur at this important joint articulation.
The fact that a femur moves inside the acetabulum is well established. As you walk, run, kick, jump, and squat, your femurs will move on/inside the acetabulum. What is rarely considered, but what is one of the main cornerstones of PRI, is that the acetabulum also moves on top of the femur. It’s not a one directional system. Both bones move on each other all the time. And in PRI thinking, the movement of an Acetabulum on a Femur (A on F or simply AF) plays a more critical role in explaining movement dysfunction than how the femur moves inside the acetabulum (F on A, or FA)
The Left AIC Pattern

The Left AIC pattern is identified by the Postural Restoration Institute as a neuromuscular pattern that is inherent in all humans due to the structural and functional asymmetries built into the human body that biases us to favor the right side of our body. This pattern of neuromuscular activation puts us in a particular position that leads to us losing full tri-planar motion in our pelvis.
For example, in a pure Left AIC position, you will not be able to fully adduct or extend your left leg due to the position of the pelvis. In a left AIC pattern, your left pelvis will be in AF/ER.
Restoring true tri-planar movement will necessitate regaining AF/IR. In this post I hope to explain what AF/ER really is. In the typical Left AIC pattern, the left ilium moves forward on the femur.
This positions the left hip into a state of flexion. That is what you are seeing above, the left ilium is forward compared to the right ilium.
This also has the effect of orienting our entire pelvis, and our lower spine, to the right.
Not only that, since all pelvic movement occurs in three planes of motion, the illium (upper part of the innominate) also moves away (abduction in the frontal plane) and rotates away from the midline of our body (external rotation).
So the resting state of our left ilium becomes one of “ER”: flexion, abduction, external rotation.
Since the pelvis is a ring, when something occurs on one side, the opposite movement has to occur on the other side. In this case, as the left ilium moves forward, the right ilium moves backwards into extension, moves closer to the body (adduction) and rotates towards the midline of the body (transverse).
The right ilium is doing the exact opposite movements. The resting state of our right ilium becomes one of “IR”: extension, adduction, internal rotation
And What's the Problem?
The problem occurs when this particular pelvic position, a left ilium forward and in “ER” and a right ilium back and in “IR” becomes our default pattern.
This position should only occur when standing on your right foot. It should not be our pelvic pattern when our weight shifts to the left leg.
The pelvic position should switch so that our right ilium moves forward and into Right AF/ER” and our left ilium moves back and into Left AF/IR when we stand on our left foot.
But in the Left AIC pattern it doesn’t. It says as is.
Removing all the biomechanical lingo, let me express the idea in another way.
Let’s say you have two possible pelvic positions: Position #1 and Position #2. Alternating between these two positions enable you to walk properly.
When your weight is on your left foot, your pelvis should be in Position #1.
When your weight is on your right foot, your pelvis should be in Position #2.
However, in the Left AIC pattern, your pelvis is in Position #2 even when you are on your left foot.
Remember, on your left foot you should be in Position #1.
To move and walk like a human being should, you must shift into Position #1 when your weight is on your left foot. But that’s not happening.
Now, obviously your pelvis does move (otherwise you couldn’t walk), but it doesn’t completely move into the opposite pattern, so you are essentially stuck in one pelvic position since you can’t be in two different patterns at the same time.
You are either in Position #1 or Position #2.
Even while you are transitioning from Position #1 to Position #2 or from Position #2 to Position #1, you are still in one position until the point that the positions change.
Even when standing on two feet with our weight seemingly evenly distributed, it’s likely that our pelvis is still in the position of a left illium forward and the right ilium back at least to a minimal degree, even if we have gone through PRI programs. What we want, what is desirable, is for our pelvis to alternate positions like this
Position #1- Left Stance

Postion #1- Left Stance

Position #2- Right Stance

Postion #2- Right Stance

This alternating sequence of pelvic motion is called “walking”. In the Left AIC pattern, our pelvis is not alternating its movements like in the pictures above and instead our walking sequence becomes this:




As you can see, I gave you the same picture four times. That’s because in the Left AIC, your pelvic position isn’t changing, it’s not alternating between Position #1 and Position #2. It’s stuck in Position #2.
When your pelvis stops alternating its position as you walk, you are no longer walking like a human should walk.
Don’t get me wrong, you will walk, but you will have to walk by using compensation patterns.
And that is where the trouble begins.
When you compensate, you substitute incorrect movement patterns in other parts of your body e.g, your feet, legs, spine, ribs, shoulders, neck, and even cranium, to gain movements that are limited due to the fact that your pelvis is no longer alternating its patterns.
Quite simply, you can’t limit movement in one area of the body and not have it affect other areas.
Here is a list of pain that I experienced in my adult life prior to PRI, likely due to compensational movement patterns that occured in response to my pelvis losing the ability to move fully in three planes of motion.
- Plantar Fasciitis in both feet
- Shin Splints
- Hip Impingement
- SI joint pain on both sides
- Generalized lower back pain
- “between the ribs pain”
- Upper back and neck spasms that originated between the shoulder blades
- Upper trap/neck tension and discomfort
This is why everything PRI does first starts at the left pelvis to restore its ability to get into Left AF/IR.
Your left ilium has to move out of its flexed and ERd position and into an extended and IRd position.
The iliums must alternate between “IR” and “ER” to eliminate deleterious compensational movement patterns that can build up and cause pain, instability, and muscle weaknesses.
For more information about Left AF/IR and how to strengthen it, check this post out.
So glad I found you, your videos and your information. I am a certified trainer extremely interested in PRI for about 2 years now. I have been studying all i can get my hands on. I also had been to the Bodmechanic, Andreas Saltas for a few sessions in NY, who practices PRI. I want to take PRI courses but it seems I do not possess minimum requirements. Thanks.
Hi Michael, thanks for commenting. I’m trying to be a resource for people new to PRI and trying to figure it all out. When I started four years ago I could find bits and pieces of PRI related material on different blogs, which was helpful, but that’s all it was, bits and pieces. If you have any questions, I’ll do my best to answer them.
In regards to the minimum requirements, you could always try e-mailing PRI and asking for some sort of waiver. You never know.
Neal
Hi Sir,
I am a huge fan of your blog and will purchase the home study of PRI.
I just have a few things confusing me. If you can, please answer my questions:)
Biomecahnically, anterior pelvic tilt goes with internal rotation of femur and external rotation of tibia. Because of that, the passive component, patella, seems to be tracking laterally, causing knee pain. To prevent the knee pain, do we have to strengthen hamstrings and glutes first to solve this biomechanic problem (fixing the ant innominate and femoral internal rotation)?
What I am confused about is, L) AIC pattern shows anterior rotated innominate but compensatory femoral external rotation and abduction. Does this mean people with L) AIC pattern are not likely to have patellofemoral pain syndrome? (Due to the position of the L) external femoral rotation).
My third question is that can people develop R) AIC pattern or bilateral AIC pattern?
I would appreciate it if you could help me with them. so I can move onto next vids.
Warm regards,
Bobby
Hi Bobby, thanks for the questions.
1. On the left side, we want to first reposition the left pelvis with the left hamstring and then train internal rotation of the left femur which will target the left adductor (the lower portion in particular), the left medial hamstrings, and the left anterior glute medius. All these muscles support the left leg in “left stance” phase of gait, and all PRI exercises do this.
2. The tibia can compensate for the position of the femur by staying in internal rotation or by externally rotating. This will then influence whether someone’s left foot is in a more pronated state (more common on the left) or supinated state (less common on the left but more common the right).
3. If the femur and tibia are rotating in opposite directions, for example if the femur stays internally rotated and the tibia externally rotates as a compensation, knee pain can certainly be the result. I experienced this myself.
4. People will not develop a right AIC pattern by itself. Patterns aren’t a bad thing, we use them to move. However, in a left AIC pattern we are in “right stance/left swing” phase of gait, so our weight is on our right leg while our left leg is swinging through the air. This left AIC pattern is what we want when we are on our right foot. The problem occurs when we attempt to put our weight on the left foot and the left AIC pattern doesn’t turn off. When our weight is on the left foot, we should be in the right AIC pattern (left stance/right swing). Someone who is “stuck” in the left AIC pattern is using the same pattern for both right stance (which is good) and left stance (which is not good). It is the alternation of left AIC and right AIC patterns that allows us to walk forward as humans. So we need both patterns, not just the left AIC pattern. PRI exercises attempt to give us the right AIC pattern (which is left stance/right swing).
5. Yes, people can develop a bi-lateral pattern which means that both sides of the pelvis anteriorly rotate. We call that a bi-lateral PEC pattern. Due to the bi-lateral anterior rotation of the pelvis, the PEC’s back is over-active and neither side of the their pelvis is moving correctly.
Hope that helps.
Neal
Neal,
What kind of a doctor should I seek for this?
You definitely do not seek a doctor. Check the PRI website for a provider in your state/area.
Hi Neal i! I have a rotated pelvis to The right as you say. The problem is that on me my QL on my left side is thigr and dragning my torso to The left, so i have flared ribs on The right. Dose it mean i have to do The exercise diffrently? And why is left QL staying on not The right? Do you have any experience of this position OR tips to share? Best regards Erik
It could mean that you are a PEC or patho PEC. I made videos about those situations on my YouTube page. I’d try the All Fours Left ZOA exercise on my “beginner program” page.