PEC stands for posterior exterior chain. This chain of muscles includes the quadratus lumborum and paravertebrals that are tight and restricted.
In the PEC (more accurately referred to as bi-lateral PEC) this chain of muscles is overactive on both sides. They are also collectively known as the back extensors because they extend (over-arch) our lower back. A PEC is extended on both sides.
Normal human gait (walking) requires one PEC chain to be active while the other is inactive. So when the PEC chain is active on the left, the PEC chain on the right should be inactive.
But a PEC has both sides active at the same time.
As you can see in the image below on the left, having two PEC chains active simultaneously involves a whole lot of muscle.
On the right, you see the hip flexors. They are also generally overactive in the PEC pattern.
All this muscle is located in the front and the back of the body. This makes PEC patterned individuals very “forward and back” type people.
The Frontal Plane is Life
So what’s the big deal?
For starters, walking is primarily a frontal plane endeavor, we simply must have a functioning frontal plane that uses our abductors and adductors. Otherwise we will have to move with compensation.
Planes of Motion
- Moving your arms and legs straight out to the side away from your body is abduction.
- Moving your arms and legs in towards the midline of your body is adduction.
- Side-bending of your torso and neck.
- Heel inversion and eversion.
Similarly, to breathe with our diaphragms, we need to preserve (or restore) our frontal plane.
Basically, normal human movement depends on a functional frontal plane!
While a functioning frontal plane depends on proper alternating rhythm, shifting the center of gravity back-and-forth between the left and right sides of the pelvis, PECs don’t have that going on. Once a pelvis is stuck in an anteriorly rotated resting position, the individual loses all the abduction and adduction movements listed above to one degree or another.
Frontal Plane in the Left AIC/Right BC Pattern
The image above shows frontal plane compensations occurring in the left AIC right BC pattern. The right side is
- internally “oriented” overall
- right leg adducted
- more weight bearing, grounded
- In “stance” phase of gait with compensatory muscle function
The left side is
- externally “oriented” overall.
- Lower back in extension
- left leg abducted
- less weight bearing, ungrounded
- in swing phase of gait with compensatory muscle function
to visualize the PEC all you have to do is imagine that the right and left sides of the body are doing what the left side is doing. Thus a PEC is
- externally oriented on both sides
- lower back extended on both sides
- legs abducted on both sides
- ungrounded (which results in tension)
- in more of a swing phase of gait on both sides with compensatory muscle action occurring everywhere
Gait and Pelvic Mechanics
Both sets of muscles are lengthened and weakened due to the prolonged amount of time that the pelvis is stuck resting in an anterior pelvic tilt on both sides.
On the other hand, the hip flexors and back extensors are overactive for the same exact reason, prolonged amount of time spent in an anterior pelvic tilt on both sides
While there is no problem with an anterior pelvic tilt, after all it is part of the gait (walking cycle), a pelvis should not be resting in a state of anterior pelvic tilt.
Nor should both sides of the pelvis be in an anterior pelvic tilt at the same time.
Under normal gait mechanics, one side of the pelvis should be in an anterior pelvic tilt while the other side of the pelvis is in a posterior pelvic tilt.
To be more precise, the stance leg should have a posteriorly tilted pelvis above it, while the swing leg has an anteriorly tilted pelvis above it.
So if your weight is on your right leg and your left leg is swinging through the air, the anterior tilt will be on the left and the posterior tilt will be on the right. This is what we commonly see in the left AIC pattern.
This is normal stance/swing phase of gait pelvic movement. The right and left sides of the pelvis should be moving in the opposite direction of each other at all times.
Alternating anterior and posterior tilt between sides is the proper gait rhythm.
Transverse Plane Rotation
Heads have to rotate. Necks have to rotate. Spines have to rotate. Arms and legs have to rotate.
When normal pelvic mechanics breakdown, so that both sides of the pelvis are stuck in an anterior pelvic tilt and the spine is extended, normal transverse rotation is limited almost everywhere.
Importantly, an extended spine can not rotate.
This is what makes a PEC a PEC.
The inability to rotate through the thoracic spine.
If someone can’t rotate through their thoracic spine, they’ll be forced to find rotation somewhere else.
And that “somewhere” is the lumbar spine and SI joints.
PECs are locked up, stiff, compensatory rotators, and often suffer from SI joint, low back, and neck pain.
Compensatory Frontal Plane Movement Through the Quads
The anterior pelvic tilt is causing them to be too stable from front to back (sagittal) but too unstable from side-to-side (frontal).
In fact, their side-to-side movement (frontal plane) is so limited that they have to cheat to do it. After all, just because your frontal plane muscles are dormant doesn’t mean you don’t need to move from side-to-side.
You will still move side to side, but you won’t use your frontal plane muscles, adductors and glutes, to do it.
Instead PECs have to use their quads for side-to-side stabilization and push.
This is why you see such over-developed quads, particularly the vastus lateralis.
The VLs are basically playing ping-pong with your pelvis, trying desperately to not allow you to fall over, while also pushing you back to the other side as best they can.
Of course, the VLs can’t do it very effectively, so frontal plane movement is always very limited in PECs.
You’ll see a bunch of “butt wiggle and jiggle”, but the pelvis never actually shifts.
Furthermore, to add insult to injury, because PECs are so sagittal plane dominant, and their frontal plane is completely compensatory, their brain detects this as a threatening situation and thus “protects” them by keeping them in the PEC pattern, the pattern they so desperately need to get out of!
Heels, Hamstrings, and Internal Obliques
PECs usually do not have good sense of their heels.
What does that mean?
If I ask a PEC to assume a natural stance without shoes on, and sense where they feel their weight, they will quite often say the outside of their feet and towards the forefoot. They generally won’t say their heels.
If they do say their heels, I make sure they aren’t locking their knees. They usually are. “Knees locked” is a compensatory strategy to stabilize their unstable pelvis.
They may also tend to stand with their legs in a wider than normal position to find a more stable base of support.
When a pelvis is forward on both sides, the individual’s spine moves forward, meaning their center of mass moves slightly forward. That is why they feel their weight towards the forefoot.
They feel the weight on the outside of their feet because when a pelvis is forward on both sides, the legs below it may have to compensate by externally rotating.
This externally rotated position tends to put a foot into a position of supination. A supinated foot will have an inverted heel (points in) and higher looking arch. This effectively places their weight on the outside of their feet.
The only thing that will pull the pelvis out of its anteriorly rotated position and into a neutral state is the hamstrings. That’s their primary job. But because someone is stuck in a PEC pattern, the hamstrings have become dormant. They have to wake up!
Hamstring and Internal Oblique Cooperation
PEC = extension = anterior pelvic tilt and elevated ribcage = loss of hamstrings and internal oblique support
Neutrality = posterior pelvic tilt and depressed ribcage through hamstring and internal oblique co-activation
That support must come from the internal obliques.
However, the internal obliques can only do their job correctly if the hamstrings do their job at the same time!
The muscles function as synergists, as partners, in restoring neutrality to the pelvis and ribcage via putting the entire body into flexion. The internal obliques depress/internally rotate the ribs while the hamstrings posteriorly tilt the pelvis.
That’s why any approach that doesn’t restore proper breathing mechanics is bound to fail.
Breathing and Ribcage Expansion
Non-compensatory breathing requires expansion of the ribcage during inhalation.
But a ribcage can only expand if it starts from a neutral resting position. A PEC does not have a neutral resting position of the ribcage just like they don’t have a neutral resting position of the pelvis.
This means they breathe with their neck and back muscles. Upper traps, scalenes, and SCMs are usually involved in compensatory breathing.
Obtaining a neutral resting position of the ribcage depends on elongating exhalations to blow all the air out.
Elongated exhalations will internally rotate the ribcage through recruitment of the internal obliques.
Normal tidal breathing will not engage the internal obliques if someone is in an extended PEC state. Only elongated exhalations will.
A PEC’s entire body is extended and externally rotated. They need flexion and internal rotation of their femurs, pelvis, and ribs to get their system back to neutral. This requires:
- hamstrings that are engaged via a posterior pelvic tilt and inhibition of hip flexors and lower back muscles
- elongated exhalations that engage the internal obliques to internally rotate the ribs.
- expansion of the ribcage during inhalation to eliminate compensatory neck breathing.
The 90-90 Hip Lift is designed to do all these things.