The Psoas and the Trapezius have until now, been very mysterious and unknown anatomical creatures. In the literature, much has been done in the form of EMG and cross sectional area (CSA) analysis to determine their true function. Though we have the right amount of data to solve this big mystery, like so many studies and experiments before, the EMG results are misinterpreted. The researchers don't know enough about the surrounding elements of their research to reach an accurate and definitive conclusion. This leads to the results being skewed and unsure and even worse....they swear blind that these results are the one and only definitive answer and then the people who put their conclusions into practice wonder why their clients dysfunctions aren't improving.
Hopefully in this article, I will be able to clear up a lot of this confusion with pure scientific, logical and (unfortunately) not-so-common sense, that ultimately 'rings true' about the obvious similarity between these two muscles and their behaviours.
As a practitioner of movement, I find that myself and others like me have a very different and more experienced outlook on the human body than the researchers and clinicians because WE USE IT! We know what the body is truly capable of and what it takes to get there in terms of mobility, strength, efficiency and general physical intelligence. Our methods are very pragmatic and once we have gone through the tunnel and come out the other side, we know what works and what doesn't. I can't emphasize enough how very little my clients are aware of when it comes to their own body. As Ido Portal said "It's like these people never got the user manual for their bodies", or if they did, they somehow misplaced it when they started puberty.
Enough jibba-jabba, time for the nitty-gritty!
Presenting the Psoas! a muscle that segmentally connects to the lumbar spine and crosses every lumbar segment. It connects the pelvis and crosses the sacro-iliac joint and it connects to the femur, crossing the hip joint...Clearly, it has a massive mechanical role in all of these joints.
Nearly all of Psoas' dysfunction has been based on theory and assumption with very little direct measurement in the research or clinical literature. There are hundreds of papers that do a Thomas test and report a 'short' iliopsoas. The Iliacus and Psoas are two VERY different muscles that do VERY different things (of which I will go into later on). The problem with the Thomas test is that it tests ALL the anterior hip structures! That's the bi-articular muscles such as the Rectus Femoris, Sartorius and Tensor Fascia Lata, and the one-joint hip flexors such as the Iliacus and Pectineus and Psoas (The hip capsule itself should also be adressed for movement restrictions) all at once!...So to get a positive on a Thomas test could mean any one or more of those anterior structures are tight.
However, the Thomas test can be simply modified to eliminate the bi-articular
muscles from the one-joint muscles by simply extending (straightening) the client's leg. If the leg is straight and the client's leg still doesn't rest on the table, then you know for sure it's the one-joint muscles. If the client's leg rests on the table when straight but raises up when flexing (bending) the knee, then you know it's the bi-articular muscles (Which ever group of muscles you test positive in, you can be sure that all of that group will be somewhat affected. In a group of muscles with a relationship like the hip flexors, a muscle getting tight means the others will neurologically get tight (adaptive shortening) due to the limited ROM produced by the initial muscle tightening). This is where the literature has been skewed.
REMEMBER: When we try to get into a position, we mobilize or stretch whatever is tight in that position!..whether it's restoring sliding surfaces like skin, superficial fascia, myo-fascia or the muscle and the capsule itself. It's naive to say you have a tight Piriformis because you lack internal rotation. The Gemellus superior/ inferior, Obturator Internus/Externus, Quadratus Femoris and the superficial gluteals could also be affected...Bottom line? There is simply no way of knowing.
As with the articles before, I try to keep the anatomy basic so that I don't confuse and send the non-anatomically enlightened audience into meltdown.
Now for the interesting stuff!
Here are a few dissected and debunked common myths and misconceptions that all therapists and trainers should now be made aware of! (For references and resources I would highly recommend checking out the work of Mark Comerford and Sarah Mottram).
- Myth 1: The Psoas is a hip flexor.
EMG readings for the Psoas are at their highest in full end range hip flexion. BUT, this doesn't mean it's a hip flexor! The Psoas tendon does not slide over the pelvis as we imagined it did due to what we were taught. It doesn't even have a bursa (A bursa is a fluid filled sack that lies between tendons and bones to allow for smooth sliding of articulating muscles around joints) and is fascially attached (fixed down) to the pelvis as it crosses onto the femur. The reason why the readings are at their highest in full hip flexion is not because the Psoas is flexing the hip but because it's working maximally to stabilise the lumbar spine in relation to where the hip is. With the way the Psoas is attached, it produces a huge axial compression force through the lumbar spine preventing anterior shear and enabling the lumbar to stay intact under directional loads. In other words, if you removed your Psoas and then flexed your hip, your lumbar spine would be very unstable with no structural support in the torso for the hip to relate to. Meaning, that the Psoas is actually a Lumbar stabiliser muscle. Another fact that supports this is that the Psoas can only shorten a maximum of 2.25cm (an inch!)...No where near enough to flex the hip!
"So why does it even need to be attached to the femur then??"
The insertion onto the femur can mean only one thing...It centrates the head of the femur in the acetabulum (hip socket) during ALL hip movements. In other words, it stops it from wobbling around and shredding the labrum in the joint whilst it articulates. The Psoas is a lumbar stabiliser AND a hip stabiliser.
- Myth 2: The Psoas can become chronically short and over-active.
There is NO EVIDENCE of Psoas ever being short!..especially in the presence of pain and pathology. The Psoas is actually inhibited in the presence of pain and is NOT up-regulated during high stress levels. This means that there is no such thing as an over-active Psoas! if anything, it's under-active. The Psoas Posterior fascicals(attachments) are segmentally innovated (powered) from T12 to S1. This means that if injury occurs to anyone of those segments, it will greatly effect the neural recruitment of the other. this means that an injury to a lumbar segment will significantly affect the stability of the other segments. The anterior fascicals are innovated from a single branch arising from the femoral nerve NOT segmentally innovated. Single nerve innovations would imply that the anterior fibres ALL work together to produce a more significant movement. It is also important to note that YOU CANNOT STRETCH THE PSOAS!
- Myth 3: The Psoas Major produces anterior tilt of the pelvis.
The Psoas DOES NOT produce anterior tilt of the pelvis. Remember how I mentioned that the Psoas can only shorten 2.25cm??...well, it turns out that that shortening perfectly matches the range of posterior pelvic tilt from a fully anteriorly tilted position. If you think about it, how can a muscle that is fascially attached to the pelvis and pulls towards the spine produce an anterior tilt of the pelvis??...Answer's simple - It can't!! This posterior tilting action rotates the innominate (total make-up of your ilium, ishium and pubis) to make room for full hip flexion.
- Myth 4: It plays a significant role in movement of the lumbar spine.
Actually it's quite the opposite! It does everything it can to resist it. After reading the above, this part should just be common sense!...the Psoas IS NOT a mobilising muscle, it's a stabilising muscle, so it's job is to keep the lumbar spine compact and secure. Another good key is the fact that the Psoas is also fascially attached to the diaphragm, TrA(Transversus Abdominus) and Internal Oblique. These muscles (of course, when working correctly) stabilize the entire mid-line when under load. The TrA is the human body's natural weight belt and it aids along with the Diaphragm and Multifidus in creating intra-abdominal pressure which enforces stability around the spine and prevents nasty occurrences like disc hernations, slipped discs and other spinal problems.
REMEMBER: When the brain senses a mechanical instability in the spine, it will restrict ROM at the peripheral joints (shoulders and hips) to protect the spine and the central nervous system.
- Myth 5: The Iliopsoas muscle...!?!
There isn't one!.....never was! Iliopsoas was a name given to group the Iliacus and Psoas because people thought they both did the same job...Oh how wrong they were! The Iliacus is a true hip flexor and has the ability to shorten significantly and produce hip flexion. The Iliacus tendon also runs over the top of a bursa to allow smooth working and pain-free movement and is not fascially attached to the pelvis.
Ok!!..so, we are now clued up on the Psoas and why we have one.
Let's move on to the Trapezius.
Beware!!..The anatomy get's a little more in depth in this section due to the nature of the muscle.
The Trapezius has three distinct anatomical divisions. The clavicular fibres (upper trapezius), the acromial fibres (middle Trapezius) and the lower fibres (lower Trapezius).
The upper Trapezius segmentally connects the head (from the Occiput) and the neck (cervical spine) via a thick sheet of fascia called the Ligamentum Nuchae (which isn't a ligament at all, it's fascia...it should've been called fascia nuchae) and inserts onto the lateral 1/3 of the clavicle.
The middle Trapezius comes from T1-T4 and inserts onto the posterior and lateral part of the acromion and the lateral part of the scapula spine.
The lower Trapezius come from T2-T12 and insert onto the deltoid tubicle on the medial end of the scapula spine NOT on the Inferior Spine.
That broad sheet of connective tissue called the Ligamentum Nuchae (fascia) attaches to all the spinous processes of the cervical vertebrae and it's about 3 -5cm thick...'i'll say that again'...it's 3 - 5cm thick around the level of C3. It's also a major attachment site for the Spinalis, Semispinalis, Cervicus and Capitis. The Trapezius also upwardly rotates the scapula during scapulo-humeral rhythm (this is the kinestheological process of laterally raising your arm from your side until your bicep touches your ear) allowing the scapula to stay stable WITHOUT elevation of the scapula and prevent tissues being trapped in the sub-acromial space (impingement).
Time to debunk some more myths and misconceptions!
- Myth 1: Upper Trapezius is the primary muscle for shrugging the shoulders
This is where EMG data gets skewed again. The most common site for surface electrode placement on the upper/middle traps is smack bang over the Levator Scapula. This means you get cross-talk between the muscles and it leads to inaccurate readings. The upper Trapezius certainly plays a part in scapula elevation, but has very little bio-mechanical potential to elevate the shoulders. Now, it's very important to note that the greatest contractile bulk of the Trapezius are the horizontal fibres and they insert between C6 and T1 (see pic above). In other words, the Upper and Middle fibres cannot elevate the scapula above C6 because 90% of it's fibres run horizontally! This means when they contract, the line of pull is medial towards the spine NOT vertical. Upper Trapezius does have vertical fibres between C0 - C4, but these fibres are fascial and NOT contractile tissue. The upper Trapezius is a cervical stabiliser in relation to the position of shoulder girdle AND a scapula rotator. The 'true' elevators that can lift the scapula into full elevation are the Levator Scapula and the Rhomboids. If you look at the way the contractile fibres of the Rhomboids angle up towards the head, this will become clear.
- Myth 2: Upper Trapezius extends, rotates and side bends the neck
Now that we know the upper Trapezius is attached to a sheet of fascia, which is attached to the spinous processes of the cervical vertebrae, this hardly provides an optimal anchor point to rotate, side bend and extend the neck. Combine that with the fact that we have a horizontal line of pull, it's more likely going to pull the neck forward into flexion. BUT, due to the nature of the insertion onto the Clavicle, it's actually going to resist you in full flexion and full extension. Which means it's true function is going to be maintaining a 'neutral' position.
- Myth 3: Upper Trapezius gets excessively overactive, chronically short and needs to be stretched in the presence of neck and shoulder pain
The upper Trapezius fibres are bi-laterally active in ALL functional movements of the neck and the arm. Unfortunately, this has been misinterpreted for being 'over-active' when relating to pain and pathology. It's actually quite the opposite, pain causes inhibition and CSA (cross sectional area) decreases. Some muscles like the Transversus Abdominus are supposed to be continuously active during movement to make sure your mid-line is optimally stabilized. This IS NOT over-activity! it's doing what it was supposed to do. As for the upper Trapezius being short?...there is NO evidence in the literature of it being significantly short! When you see a client with a dropped shoulder or their shoulders hang under the influence of gravity off their neck and the acromion is low and downwardly rotated, it's impossible for the upper Trapezius to be short. It's being posturally stretched! The common mistake for testing this (as seen below) is holding the clients shoulder down and side bending their head the opposite way. Nine times out of ten the client will say "Holy crap! that's really sore and tender!....I can really feel that stretch!" and then the therapist and the client will assume it's short.
REMEMBER: A stretch sensitivity test IS NOT the same as a length test of a short structure. In other words, just because it feels sore and tight, doesn't mean it's short!
Because the Upper Trapezius attaches to the superficial margin of the ligamentum Nuchae, it can generate equal tension throughout the cervical spine. As long as that sheet of fascia has tension, no one spinous process can displace out of line with the others during movement of the head. However, if the fascia does not have tension and the upper trapezius fibres are over-stretched and weak, the muscles won't have a strong and stable base of support to contract from. Meaning the cervical spine will be very unstable.
- Myth 4: Lower Trapezius pulls the inferior angle of the scapula down and in towards the spine
The lower Trapezius inserts on the most medial part of the scapula spine (practically right on the inside!). The fibres of the lower Trapezius run at a 45° angle to the thoracic spine meaning when the fibres contract, the line of pull rotates that scapula laterally! It CANNOT pull the scapula down because it's not attached to the inferior portion of the spine nor does the attachment cover enough area of the spine to do the job efficiently.
"So what muscles do pull the scapula down and in??"
The co-contraction of the Pectoralis Minor and the Rhomboids! The Pectoralis Minor is attached to the Corocoid Process and the ribs bringing the scapula down. If you look at the direction of the contractile fibres, you will see they do not run at the same angle as the Pectoralis Major. The Pectoralis Major fibres run horizontally to the Humerus whilst the Pectoralis Minor runs upward at 45° (funnily enough, the same angle as the lower Trapezius...hmm!). The Rhomboids' fibres also run (roughly) at a 45° angle and one of their primary roles is to retract the scapula.
Is your mind blown yet?? :p
So, after all that info, what's the connection between the Psoas and the Trapezius??
- Both Muscles are spinal stabilizers that have global and local stability roles
- Both Muscles' neuro-physiology is the same! Both get inhibited in the presence of pain and CSA decreases.
- Both muscles constantly and bi-laterally work in the background of functional movement by tensioning a fascial structure to control intersegmental vertebral displacement
- Both muscles have a similar design
- Both muscles do not get short
And there you have it!!..You may now curse your anatomy lecturers and burn your 'out of date' books. Once again, most of the credit has to go to Mark Comerford who is responsible for conducting the meta-analysis for both muscles. If you want to really get down and dirty with the data and details check him out at www.kineticcontrol.com
'Once optimal efficiency has been achieved.....the potential for athletic enhancement of any kind is at it's greatest!!!'
References
Commerford, M. (2012) Psoas Major: Uncovering The Evidence. [Online] Available from: http://www.movementperformancesolutions.com/catalogue.php [accessed 24 October 2014]
Commerford, M. (2013) Trapezius: Clearing Up The Confusion. [Online] Available from: http://www.movementperformancesolutions.com/catalogue.php [accessed 24 October 2014]
