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Measuring muscle stiffness

Discussion in 'Biomechanics, Sports and Foot orthoses' started by mike weber, Jan 18, 2011.


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    Over on this thread from post 8 Colin stated that he measured muscle stiffness when it appears that he was discussing muscle tightness.

    In a post I showed some links to measurement of muscle stiffness in the triceps surea muscle group -http://www.ijs.si/~jbabic/files/Article_EJAP04.pdf

    So 1st it´s important to define Muscle Tightness and Muscle Stiffness.

    Ive looked but no ´official ´ definition was found in a quick search, If anyone has any be great if you could post them.

    But muscle stiffness and Muscle tightness are quite different and are related but it is important that these terms are not interchanged.

    Muscle tightness in my mind looks at the ROM of joints are how the length of the muscle effects this.

    Muscle stiffness looks at the Viscoelastic properties of muscles and tendons.

    So the next question becomes is it important to understand Muscle stiffness ? How will it help us in practice ? is it possible to measure muscle stiffness ?etc etc.
  2. Journal of Biomechanics Volume 44, Issue 3 , Pages 424-429, 3 February 2011

    Ultrasound echo is related to stress and strain in tendon

    Sarah Duenwald, Hirohito Kobayashi, Kayt Frisch, Roderic Lakes, Ray Vanderby

  3. Yes. Especially in paediatrics where the range of muscle stiffness is so broad.

    It is another, rather important variable to consider in terms of orthoses prescription. "hypermobility" is a fairly vague term which I've seen applied to both range and stiffness but I think the two must be considered differently.

    For EG, I see a lot of hypertonic patients (CP and such like). When looking at their Triceps surae the range is often quite acceptable... but it takes a ridiculous amount of force to get it there. An assessment of these patients must allude to stiffness as well as range.


    There are rigs which do the job (like the one in the study you referenced.) I have one for adult TS stiffness which is portable enough to use in clinical assessment (though still rather crude). I am also developing another system for doing this, however its not ready yet.

    Measuring aside, a qualatative assessment of stiffness is well within everyones ability and I think is an important part of assessment.
  4. So Robert when you measure muscle stiffness how does the Measurement in kN/m help you make your treatment plans.

    If we are looking at the vaso elastic properties of muscle and you determine Muscle stiffness for the Gastroc is K how does that change things.

    From the paper above
    Again I would like to state Stiffness and having short or long muscles are different things just making sure we are on the same page and we are discussing the spring like properties of muscles and their stiffness.
  5. The measurement value doesn't (yet). I'm not a calibrator. But the stiffness does.

    Let me offer you an example. Two 5 year olds attend your clinic. Both, for the sake of argument, have an AJC range of 90 + 15 degrees. One has Ataxic Cerebral palsy, low tone, and low stiffness. The other has spastic Cerebral palsy, high tone and high stiffness. One takes 10 kn/M to get to 90 + 15 and the other, 100 to get to the same point. One gets a smafo, the other an AFO.

    The range is the same. The feet could not be more different!

    What is this if not using muscle stiffness to alter treatment plans? The Kn/M value is not specifically used, but it would be useful to keep a track of the level of ajc stiffness over time to track the effect of, for example, a stretching, exercise routine. It would also be interesting for tracking a "stiffness curve" through the range.

    Hows that?
  6. I´ve no idea just bouncy around some ideas.- think I´ll go off and read a little - I was thinking about and my reading has been focused on elastic energy return and muscle stiffness.

    Then as the sub-springs individual muscle stiffness are added together it would also effect K(leg) .

    Also are you not measuring Ankle joint stiffness which muscle stiffness will be a component but so will ligament length, joint ROM etc. ??

    So Ill go read some more I think, should pour some casts too.Read Hookes law for the 10 time again.
  7. Yeah, measuring any joint will reveal a composite stiffness of bones, muscles, ligaments, surrounding soft tissue etc.

    Its quite hard, when considering stiffness, to separate it from tone. The properties of the muscle will vary depending on tone and the tone on a hundred other things. Like most things in Biomechanics its easy to observe it at the extremities of the range (like ataxic vs spastic CP) but a minefield when you get up close. I bet diurnal variation would be huge also!

    Fun fun.
  8. During my reading, still have a feeling that we are discussing different things Robert I guess we were, but Ive worked it out . In my reading in the past re Hookes law Ive only considered compression of the spring. ie the bending of the knee in a spring mass model. But in your example you looked at stretch of the spring. If the spring is linear then the formula of Hookes law

    Will still be in play.

    In your rig what are you measuring in reference to :

    Sorry for being slow. Spooner probably shacking his head. saying come on Mike you know this...

    Found these if anyone is interested.


    and this Which if your reading this Simon Spooner I recon if you have not read it will find of interest. They ( David Winter being one person )discuss Leg stiffness and COM and COP in phase.

    Ankle Muscle Stiffness in the Control of Balance During Quiet Standing

    Have a good day folks off to read.
  9. physiocolin

    physiocolin Active Member


    Don't you think that it isn't so necessary to get so bogged down in differentiating between the fact whether a muscle is stiff or tight when the effect is on the receiving joint? In other words if the stiffness or tightness is causing undue compression at the joint we need to see if we can change that.If there is no complex history shouldn't we try to alter the effect using as simple an approach to start with?

    Then??? if it doesn't change things dig a bit deeper.
  10. Colin I´m still reading stuff - but muscle tightness/length is different to muscle stiffness.

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