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Effect of Gastrocnemius at the knee joint

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Feb 13, 2010.

  1. Members do not see these Ads. Sign Up.
    Hi I´ve been geeting into lots of shall we say discussions with Musmed aka Paul Conneely over the effect of the Gastrocnemius at the knee and ankle, and what its main roles are in another thread.


    Here is the highlights-lowlights of that discussion from us with a couple from Kevin Kirby.

  2. Ok Paul I´m not sure you needto call me Dumb over the internet but ok lets try and keep this on a professional level.

    I will call you on you knowledge of mechanics of the knee in relation to the Gastroc.

    I will attach some basic pictures for you of the action of a muscle namly the Gastroc. I beleive that you are getting confused on this point.

    Just because a knee joint is going thru a motion of extension it does not mean that the Gastroc is causing that motion, it maybe under a state of work eccentrically contracting to stabilize the knee to stop hyper extension. This would still mean that Gastroc is causing an internal knee joint flexion moment.
  3. Here is one picture for you...

    Attached Files:

  4. and another.....

    Attached Files:

  5. Now the above 2 very basic picture show the action of the muscle when it contracts. I just included the Quads to show a knee extension moment caused by a muscle.
  6. heres some reading for you

    Taken from and old text book- Gait analysis an indroduction Michael Whittle pages 62-63 3rd edition.

  7. Right next...

  8. Paul thats the type of stuff you I beleive should be teaching the groups you instruct on FMT, but it does take some understanding of internal and external moments.

    I think in this way. Gastroc contraction will cause an internal talocural plantarflexion moment......... which will lead to an increase in Ground reaction force which will lead to an increased external talocural dorsiflexion moment.

    So if you have evidence of another action of the Gastroc please provide it
  9. David Wedemeyer

    David Wedemeyer Well-Known Member

    If you look in any text on knee extension it is 10 degrees and the quadriceps perform this function. Paul do you have a citation where Janda claims there is a muscle other than the quads that provides extension of the leg at the knee? The gastroc is a primary knee flexor.

    Contraction of the posterior muscles of the leg and thigh are antagonists to the quads and provide a stabilizing counter-force to the powerful quads, they do not initiate primary knee extension.
  10. Michael and David:

    There is no question that gastrocnemius contractile activity produces an internal knee joint flexion moment. If, however, we consider that the gastrocnemius contractile activity can also cause a shift in the ground reaction force (GRF) vector more anteriorly on the plantar foot so that it now is directed anterior to the horizontal knee joint axis, then indeed it could be said that the gastrocnemius may also create an external knee joint extension moment. However, most of the forward dynamics research I have read seems to suggest that, overall, the gastrocnemius causes a net knee joint flexion moment whereas the soleus causes a net knee joint extension moment.

    All in all, until medical professionals and biomechanics all make it very clear in their discusssions, papers and lectures whether muscle activity is causing either internal moments or external moments or both types of moments about a given joint, then we will continue to be swimming in murky waters regarding the function of muscles of the foot and lower extremity during weightbearing activities.
  11. Peter1234

    Peter1234 Active Member

    i dont think Mr. C is contradicting you M Weber:

    he is simply stating that the gastroc functions better when the knee is extending i.e. when you have already stood up. tension is placed on gastroc and a resultant plantarflexion moment is possible.
  12. Peter Here is a quote from the man himself.

    Sounds like he is saying the Gastroc is a knee extensor infact the strongest......

    Contraction of the Gastroc does not cause an internal extensor moment at the knee but will cause an internal flexion moment at the knee...
  13. David Smith

    David Smith Well-Known Member


    I think I see what Paul may be saying is this: (I might also be completely wrong in my deduction)

    The Gastroc plantarflexes the ankle and so therefore produces a GRF at the forefoot. The force vector projection of the GRF causes an extension moment of the knee and therefore the gastroc is an indirect extensor of the knee.

    This is more easily visualised in a knee that hyperextends, on a subject with this problem we often see the knee hyperextend as the GRF moves to the forefoot. This would not be possible if the Gastroc soleus complex was not able to plantarflex the ankle.

    I'm not sure tho that it is useful to label the GSC as a knee extensor tho since this concept relies on the GRF vector projection relative to the knee joint. This vector projection can be extremely variable depending on the action of interest.

    Regards Dave
  14. Hi Dave

    While I agree that the FF GRF vector may cause an external extension moment at the knee ( I guess there are a few variable to consider here as well) and that Plantarflexion will add to the force of this Vector along with many other things, I would label this as a secondary action of the muscle and direction action would be an internal plantarflexion moment at the Talocural and internal flexion moment at the knee.

    but Paul language had none of these type of statements, but statments such as this
    which does not read the same to me and when I challenged this statement I got called Dumb in a round about way so thought I had better clear the air so to speak.
  15. efuller

    efuller MVP

    Michael quoted me from another post and added.
    I'd like to clarify the statement that was quoted. Tension in the Achilles tendon will tend to cause an ankle plantar flexion moment and shift the center of pressure under the foot anteriorly. As the center of pressure shifts anteriorly this may change the moment from ground reaction force. With a medially positioned STJ axis this shift in location of ground reaction force will cause an increase in pronation moment from the ground. With a laterally positioned axis the center of pressure will stay close the projection of the STJ axis and there will be little change in the moment from ground reaction force and the tension in the Achilles tendon will cause a direct supination moment and looking at only the interaction of Ground reaction force and Achilles tesnion at the STJ, there would be a net increase in supination moment at the STJ. However, other muscles (peroneals) could change the net moment at the STJ.

    In regards to wedging of the rearfoot and load in the Achilles tendon.

    The Load in the Achilles in gait will probably determined by the activation of the muscles attached to the tendon. The more the activation the greater the load.

    On average, he Achilles has a lever arm of over 2cm at the ankle joint and probably less than 0.5 cm at the STJ. Therefore, for a given amount of force, there will be much greater moments at the ankle joint with tension in the tendon. I've done cadaver work attempting to measure tendon excursion with joint motion to assess lever arm of tendons. The tendon moves a lot more with ankle motion and hardly at all with STJ motion.

    The resistance to the force from the achilles tendon comes from ground reaction force. The further distal the force is on the foot the higher the resistance to ankle joint plantar flexion. So, a rocker bottom shoe that has the center of pressure at the rocker point will decrease the lever arm of ground reaction force about the ankle joint and ankle joint plantar flexion will occur with less tension in the tendon. Again the resistance to moments from the AChilles tendon will have much longer lever arms about ankle joint. Therefore, it is unllikely that shifting the COP with varus or valgus wedges will have very little effect on the load of the Achilles tendon.

    Regarding the shifting of the position of the STJ axis with motion of the STJ. The amount of shift in the location of the axis is proportion to the amount of motion of the joint. Wedging under the heel will rarely cause a change in joint position of more than a couple of degrees. Therefore, I maintain the changes in moments about the STJ axis caused by axis shift will be minimal.


  16. Peter1234

    Peter1234 Active Member

    'I hate to tell you this, but the gastroc is the strrongest knee extensor (just sit for any USA sports medicine exam)
    and there are another 17 beleivers in the UK.'

    Sounds like he was having a bit of fun with you

  17. So your going on record to say that the above statment is wrong ?

    As for having a bit of fun not a chance. It would have been better if he was.
  18. Peter1234

    Peter1234 Active Member

    happy days :pigs:
  19. HansMassage

    HansMassage Active Member

    OK I learned a lot seeing this from the podiatry view from the ground up. But my view is from the head down. When a client has a forward head posture the weight is on the fore foot and it pushes the knees int hyper extension. The origin of the gastroc is then posterior of the insertion and it fails in flexion potential.
    Therefore I find trigger points in the soleus and planter surface muscles. The gastrocnemius may be diminished due to lack of loading with the knee flexed or it may have trigger points unilaterally from rotational stabilization.
    When I suffered from this as a teen in the 1950's there was a fad of earth shoes which had elevated toes and no heel. This flexed my knees and helped me through the problem.
    The podiatrist that refers to me said I need you because I am only trained op to the knee and many times you have to look much higher for the cause of the problem.
    Hans Albert Quistorff, LMP
    Antalgic Posture Pain Specialist
  20. David Smith

    David Smith Well-Known Member

    I would be interested in reading any papers that show how the GSC is an extensor of the knee. I can't find much, I have attached one that discusses this but is not all that robust in its definitions so its a bit hard to say exactly what they mean. However it seems to be saying that the GSC is an extensor in some cases due to the GRF vector it causes. I believe this is not a useful idea since you could say almost any muscle has any action based on the GRF vector at the time and location of interest. I.E. the gluteus maximus is an extensor of the knee or the deltoids extend the knee when the arms are extended and cause the CoP to move forward on the plantar foot.

    Regards Dave
  21. or that your biceps are a knee extensor..... Drink alot of beer get a huge beer belly, COP moves forward increase in GRF.... external extension moment at the knee.
  22. efuller

    efuller MVP

    Yes, if everything else stays in the same place, and you tilt the head forward the center of mass will move forward. However, the location for ground reaction force may move forward to a location under the forefoot if the patient contracts their gastroc soleus muscles. There are other things a person could do to maintain balance when they tilt their head forward. Someone could just choose to lean back a little bit to put their center of mass over the center of their feet.


  23. HansMassage

    HansMassage Active Member

    Yes this is a frequent adaptation. It usually becomes progressive resulting in inward rotation of the arms and shoulders with a reflex pronation of the feet.
    The term that has been coined for this is bio-implosion.
    Hans Albert Quistorff, LMP
    Antalgic Posture Pain Specialist
  24. Peter1234

    Peter1234 Active Member


    what is 'reflex pronation of the feet?'
  25. HansMassage

    HansMassage Active Member

    Here is the experiment: Chose a subject with good foot reflexes. Have the subject stand bare foot where you can place a finger or two under the longitudinal arch. Have the subject shift the body over one leg. there will generally be a supination of the weight bearing foot and pronation of the other.

    Now to demonstrate the implosion: Have the subject stand with erect posture, hands at sides, thumbs pointing forward. Have the subject rotate the arms so that the thumbs are pointing lateral. There should be a slight supination. Have the subject rotate the arms so that the thumbs point medial and further to posterior. There should be a slight pronation.

    Differences left to right may indicate habitual antalgic posture. Lack of reflex may indicate habitual posture guarding.

    Hans Albert Quistorff, LMP
    Antalgic Posture Pain Specialist
  26. I thought that bio-implosion was what happens in the bathroom (water closet) the morning after eating chips, bean dip and jalapenos and drinking beer the whole night before.:eek:
  27. efuller

    efuller MVP

    You are talking about the supination and pronation of the forearm, right?

  28. Peter1234

    Peter1234 Active Member

    Hi Hans,

    on slightly different note -

    you say on your reflex-posturology website


    with regards to stimulation of lymph: 'The goal is to normalize the signals from the low back and legs to your brain and reduce the chronic tension that stresses the nerves and blocks the movement of lymph that removes wast products from the legs that can set off cramps'

    have you ever tried this therapy on patients with chronic lymphedema, and if so are there any RCT trials to show for, and if not, why not??

  29. HansMassage

    HansMassage Active Member

    It has worked well on localized areas of lymphedema, also reducing there chronic episodes.
    Thank you for searching out and reading my blogs. I am in the process of setting down my findings and communicating with others that I have learned various aspects of the work from. I am trying to organize a trial with local massage students to see if with double blind use of magnetized and non magnetized sphere as a treatment tool there is a difference in time and perception doing trigger point therapy.

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