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  • Hip flexor function at 90 degrees of flexion

    Hi,

    I just wanted to test the strength of an idea of mine against the fire of this board. As preface, this question has nothing to do with pain only functional anatomy.

    Shirley Sahrmann and other strength coaches/physios inspired by her have argued that at 90 degrees of hip flexion only the Psoas and Iliacus are capable of creating a hip flexor moment. The rationale is that the TFL, Sartorius and Rectus Femoris do not have a moment arm at this angle because their distal insertion is now below their proximal insertion.

    I have never been able to visualize this idea and don't find it biological plausible. It spurred me to write a blog post here:

    http://thebodymechanic.ca/2012/04/23...common-belief/

    Why I think this is significant because the theory spawns a test for the psoas/iliacus that is supposedly effective in finding dysfunction in those muscles (people go on to argue how this leads to pain but lets just avoid that for now). I find that this test and the ideas behind complicate hip function in a way that is not necessary. This again allows some therapists to look like they have some special knowledge and those that do not follow this path may thus be judged uninformed and lacking. I see this occasionally (ok, more than occasionally) and I don't particularly appreciate it.

    Thanks and please let me know if I'm wrong,

    Greg
    Greg Lehman BKin, MSc, DC, MScPT
    No letters allowed learned on weekends.
    Physiotherapist
    Chiropractor

  • #2
    Greg, I tend to view the tests to differentiate hip flexors as less than necessary. Bodies don't move in isolated patterns. If these means I can't test a muscle with precision then so be it.

    Geralyn

    Comment


    • #3
      Okay,

      I may have differing opinions than others at SS....but I do think you gain a lot of information by hypothesizing which tendencies a body has for movement. I do believe there is no single movement, position or posture that is pathological. However, when a pattern of movement is so stereotypical that it excludes other possible movement responses then the body has poverty of choice to solve movement related problems. That is why novel movements are so important because they educate the CNS/movement system that there are other possible choices, combinations and sequences of muscles and joint configurations. Therefore, looking at someones general pattern of movement, detecting a stereotypical response can be an avenue for directing a specific novel movement rather than just any random movement.

      I also know that you cannot isolate muscles. However, positionally you can use proportionally a greater amount of one muscle than another.

      I am of the opinion that if you rotationally bias the hip you can alter this proportional muscular usage. Therefore in a sagital plane hip flexion if you flex the hip with internal rotation you will use the TFL, if you do it with external rotation you will use psoas + adductors, mid-line is probably a combination of both but greater proportion of RF. There are plenty of studies of other body parts showing that a change of rotation will generate differentiate EMG firing patterns of muscles. I am not aware of any of the hip. Partly because the psoas is a terribly invasive muscle to study.

      I watch people move, I see people rotate and flex and extend in sterotypical ways. I use combinations of cueing (tactile and verbal), education and very, very, very specific exercise to give the pt. more solutions to solving movement problems. Often not because one movement pattern was "bad" but they just did not know how to move any other way. I believe rotation is a very powerful selector of proportional use of a muscle for a given pattern of movement.

      The complexity of muscles should never be reduced to simple 2D lines and any biomechanist who does this ignores individual variation. I am not sure you can even pin down an exact attachment site of the TFL as it attaches to the entire fascia, of the leg. Therefore any therapist or clinican whom builds an entire PT theory on some very limited bio mechanical information is therefore going to be greatly limited.


      Eric
      --------------------------------------------------------------
      Body is imbued with mind, and mind is embodied.

      Comment


      • #4
        Eric,

        First thing, I hate you for where you live. I'm ridiculously envious.

        Second, I love you for your first paragraph. I will be stealing and morphing your words for years.

        Last, I agree with your final synopsis. But when you write

        I am of the opinion that if you rotationally bias the hip you can alter this proportional muscular usage. Therefore in a sagital plane hip flexion if you flex the hip with internal rotation you will use the TFL, if you do it with external rotation you will use psoas + adductors, mid-line is probably a combination of both but greater proportion of RF. There are plenty of studies of other body parts showing that a change of rotation will generate differentiate EMG firing patterns of muscles. I am not aware of any of the hip. Partly because the psoas is a terribly invasive muscle to study.
        I pretty much disagree with this but don't want to make a big deal about it because I want to focus on the 90 degree of hip flexion theory. However, to substantiate my massive blast (but kind) against your idea I would stress that we can't put a lot of weight into changes in EMG amplitude. I spent a decade using this as a primary outcome measure for my research and know how limited it is. For example, if you flex the hip with IR your TFL will shorten and you will get a greater amount of EMG. This does not mean that it is contributing a greater amount of force just that we have recorded greater amounts of EMG. So many factors influence how much EMG you measure under two electrodes. Small movements, changes in fat distribution that occur with movement, skin folding with movement etc, all influence muscle EMG amplitude and it is not a good surrogate for force. So, while changing the hip IR might change the line of pull of the TFL it might also change all the other factors that influence EMG amplitude. Its tough to tease out the differences. Hence,the rationale for the post.

        I am in agreement with the TFL having a broad insertion but I think that this would strengthen my argument that its moment arm is still in existence with flexion greater than 90 degrees.

        Anyways, thanks for the input. There is a lot to discuss biomechanically but probably none of it helps a patient get better as your post illustrated perfectly.

        BTW, I went to your website from my comment section and it did not appear to be working. Under construction?

        Greg
        Greg Lehman BKin, MSc, DC, MScPT
        No letters allowed learned on weekends.
        Physiotherapist
        Chiropractor

        Comment


        • #5
          "Shirley Sahrmann and other strength coaches/physios inspired by her have argued that at 90 degrees of hip flexion only the Psoas and Iliacus are capable of creating a hip flexor moment."

          I know you don't want to hear this but, who cares?

          Their argument may be grounded by the rectus femoris attachment at the AIIS. From a purely flexion argument and line of force, it no longer has a distance from the fulcrum rendering it obsolete.

          From a physics standpoint, any muscular attachment that has a distance from the fulcrum will create a moment of force, even if it is minimal. In the end it's splitting hairs, not clinically relevant, has not improved outcomes and allows for physical therapists to sound smarter they need be while making money on the weekends. I wish Shirley would grasp hold of her PhD in neurobiology and back off the biomechanics. I think the profession would benefit much more.
          I may not be as smart as most people, but I'm sure as hell not as dumb....
          "The views expressed here are my own and do not reflect the views of my employer."

          Comment


          • #6
            Matthew,

            You are making a point for me about why it is important.

            If i am right i want people to forget about this type of thinking. I want athletes to train hip flexor strength not because some invalid tests says it is weak but because that is a movement they should do. For people in pain, i want them to move and not to think about their oh so terribly dysfunctional psoas.

            I know this can seem academic but i think it is the start of the wedge. Questioning the buomechanical model with biomechanics can lead to an openess to other ideas of explaining phenomenon (e.g. A neurofriendly approach).

            Anyways, any data suggesting that i am wrong. As far as i know the aiis is still superior to the axis of rotation.

            Greg
            Greg Lehman BKin, MSc, DC, MScPT
            No letters allowed learned on weekends.
            Physiotherapist
            Chiropractor

            Comment


            • #7
              However, to substantiate my massive blast (but kind) against your idea I would stress that we can't put a lot of weight into changes in EMG amplitude. I spent a decade using this as a primary outcome measure for my research and know how limited it is. For example, if you flex the hip with IR your TFL will shorten and you will get a greater amount of EMG. This does not mean that it is contributing a greater amount of force just that we have recorded greater amounts of EMG. So many factors influence how much EMG you measure under two electrodes. Small movements, changes in fat distribution that occur with movement, skin folding with movement etc, all influence muscle EMG amplitude and it is not a good surrogate for force. So, while changing the hip IR might change the line of pull of the TFL it might also change all the other factors that influence EMG amplitude. Its tough to tease out the differences. Hence,the rationale for the post.
              I agree 100% EMG and force are not well correlated. However, my point was more theoretical. If you change the rotational aspect of a joint and have the distal segment of the bone move through the same straight in this case the hip. You will use, and fire a different combination of muscle patterns and thus proportionally this will be different than before.


              There is probably no way to measure in vivo forces accurately, esp to compare the relative contribution of the psoas versus the illiacus and therefore biomechanics inevitably relies on computer modeling which is relatively quite limited. Total force output will always be a contribution of many muscles and the greater total force required you will get overflow recruitment of opposing muscle groups to stabilize vectors of force away from the main vector of force generation.

              I agree this is a very complicated issue.

              I disagree with Matthew on its importance. Lets just not go building an entire treatment rationale on it.

              Thanks for the kind words regarding my previous statement. I appreciate the crispness of your thought in your blog. There is a place for biomechanics we just have to understand its limits. I think this the prob with many pseudo theories that claim biomechanical rationale. Is that people whom come up with them don't actually know or appreciate the limits of biomechanics.

              Eric
              --------------------------------------------------------------
              Body is imbued with mind, and mind is embodied.

              Comment


              • #8
                Since we do a lot of deep hip flexion in yoga I've has a lot of personal experience with this.

                Long before I knew anything about Sahrmann I'd come to a similar conclusion from observing carefully how I got into a very deep forward bend and what was going on with my students.

                At the end range of movement the RF and TFL do need to relax to get one deeply tucked in against the legs. I've also seen many students with ASIS pains and they would often have some issue with the coordinating the movement to deep hip flexion and were trying to use RF and TF from start to finish. This lessened their ROM and eventually could lead to a pain situation.

                To say TFL and RF stop contributing at 90 degrees might be a bit much, but there is certainly, from my experience a good deal of coordination that one can produce throughout the entire hip girdle to create deep hip flexion.

                Comment


                • #9
                  Eric,

                  Did you know your website is in Latin? And they said they don't practice witchcraft here. What other reason could it be?

                  Comment


                  • #10
                    Off at a tangent perhaps Greg but given your focus on running athletes is hip flexor strength really that important?


                    regards
                    ANdy
                    "Here is Edward Bear coming downstairs now, bump, bump, bump, on the back of his head behind Christopher Robin. It is, as far as he knows, the only way of coming downstairs, but sometimes he feels that there is another way, if only he could stop bumping for a moment and think of it." A.A. Milne

                    Comment


                    • #11
                      What you don't read latin. Yeah I am still in development with my website. I am prob 2 mo from completion of the basic architecture of it. Some things get bogged down when you do it yourself.

                      Cdano, I think you have a great observation there. Is what your talking about with yoga a position where your pushing the body into the hip using the ground as a lever point aka pigeon pose. Or something else like it without the extreme end of ER?

                      I think a concentric pattern versus an actively relaxed one with passive movement would have drastically different firing patterns as you observed and even agonist contraction of a muscle may limit motion via the compression and translation it may produce @ the joints.

                      Eric
                      --------------------------------------------------------------
                      Body is imbued with mind, and mind is embodied.

                      Comment


                      • #12
                        Hi ANdy,

                        You asked
                        Off at a tangent perhaps Greg but given your focus on running athletes is hip flexor strength really that important?
                        Absolutely, I say. Probably the most important. There being a few reasons:

                        1. Running is more pulling than pushing. Halfway through the gait cycle the extensors of the stance limb shut off...this is called the extensor paradox.

                        2. Recovery of the stance leg (the start of the swing phase) is preceded by strong hip flexor contractions. it is this hip flexor contraction and subsequent contraction that causes the knee to flex. Thus we don't even have to flex our knees actively they happen passively.

                        3. Comparing elites from even very good runners we say greater hip flexion during the swing phase and often less extension.

                        4. The quads act as brakes rather than "pusher offers". Calf flexors are still important though when it comes to increasing speed.

                        5. Faster sprinters have larger hip flexors than less fast sprinters

                        Here are a few links from my site to waste 15 minutes on:

                        http://thebodymechanic.ca/2010/12/20...nsight-part-2/

                        http://thebodymechanic.ca/2010/12/20...soas-part-one/

                        http://thebodymechanic.ca/2011/02/02...he-hamstrings/
                        Greg Lehman BKin, MSc, DC, MScPT
                        No letters allowed learned on weekends.
                        Physiotherapist
                        Chiropractor

                        Comment


                        • #13
                          Originally posted by Greg Lehman View Post
                          If i am right i want people to forget about this type of thinking. I want athletes to train hip flexor strength not because some invalid tests says it is weak but because that is a movement they should do. For people in pain, i want them to move and not to think about their oh so terribly dysfunctional psoas.

                          Greg
                          Greg,

                          I agree with the last sentence. Can you expound on the sentence I've bolded?

                          Nick Nordtvedt
                          Nick Nordtvedt, PT, DPT, Cert MDT

                          You will never succeed if you are not prepared to fail.

                          Comment


                          • #14
                            I know this can seem academic but i think it is the start of the wedge. Questioning the buomechanical model with biomechanics can lead to an openess to other ideas of explaining phenomenon (e.g. A neurofriendly approach).
                            This is precisely what Jason Silvernail, Supreme Rule of the Universe (or something like that), did in his recently published research study on knee joint mobilization.

                            It's a very smart approach, but certainly not the only way to traverse the chasm.
                            John Ware, PT
                            Fellow of the American Academy of Orthopedic Manual Physical Therapists
                            "Nothing can bring a man peace but the triumph of principles." -R.W. Emerson
                            “If names be not correct, language is not in accordance with the truth of things. If language be not in accordance with the truth of things, affairs cannot
                            be carried on to success.” -The Analects of Confucius, Book 13, Verse 3

                            Comment


                            • #15
                              Hi Nick,

                              You wanted me to expound upon this:

                              I want athletes to train hip flexor strength not because some invalid tests says it is weak but because that is a movement they should do.
                              For runners I want them to train everything regardless of what an assessment says. Say, you believe in movement pattern tests (e.g. Janda's stuff) and the athlete performs beautifully. I would still advocate doing all of the exercises/movements that you might choose if the test was considered "poor". The "corrective exercises" are still good in building capacity, tolerance or performance and are I believe are beneficial regardless of what an assessment tells. So what if the assessment says you are already good...you can be better or your train the movement because the assessment does not tell us enough about the reason for doing the exercises. The assessment does not tell the entirety of the movement experience. Just some snippet of function that someone thinks is important.

                              Specifically, in respect to hip flexors, Hip flexors and all associated muscles and nervous system commands are used in running and I therefore advocate that they build the capacity of these muscles, movements and neuromuscular engine. Not in anyone position but in all positions. Lets train the whole potential of your joints and nervous system.

                              All movement is good (I really believe that, have felt it for decades but have struggled against conventional beliefs on "form", injury and performance). I have a bias to believing that strength training improves running performance. Whether it prevents injury is another topic but I tend to believe that it may help some individuals as well, regardless,I think increasing hip flexor movement is good in and of itself for a happy body

                              I've linked to a few blog posts in a previous post about what I see as the importance of hip flexion for runners and athletes.

                              Does this help? Or where you looking for me to address something else? Thanks for the opportunity to think about this...it helps me understand my thought process and rationale as well.

                              Greg

                              Greg
                              Last edited by Greg Lehman; 04-05-2012, 06:40 PM. Reason: typo
                              Greg Lehman BKin, MSc, DC, MScPT
                              No letters allowed learned on weekends.
                              Physiotherapist
                              Chiropractor

                              Comment

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