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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.
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Elastic behaviour can be described by the relationship
between the deformation of an elastic structure and the
force applied to it. For an ideal linear spring, deformation x is a linear function of the force F
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.
Ultrasound echo is related to stress and strain in tendon
Sarah Duenwald, Hirohito Kobayashi, Kayt Frisch, Roderic Lakes, Ray Vanderby
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The mechanical behavior of tendons has been well studied in vitro. A noninvasive method to acquire mechanical data would be highly beneficial. Elastography has been a promising method of gathering in vivo tissue mechanical behavior, but it has inherent limitations. This study presents acoustoelasticity as an alternative ultrasound-based method of measuring tendon stress and strain by reporting a relationship between ultrasonic echo intensity (B-mode ultrasound image brightness) and mechanical behavior of tendon in vitro. Porcine digital flexor tendons were cyclically loaded in a mechanical testing system while an ultrasonic echo response was recorded. We report that echo intensity closely follows the applied cyclic strain pattern in time with higher strain protocols resulting in larger echo intensity changes. We also report that echo intensity is related nonlinearly to stress and nearly linearly to strain. This indicates that ultrasonic echo intensity is related to the mechanical behavior in a loaded tissue by an acoustoelastic response, as previously described in homogeneous, nearly incompressible materials.
Acoustoelasticity is therefore able to relate strain-dependent stiffness and stress to the reflected echo, even in the processed B-mode signals reflected from viscoelastic and inhomogeneous material such as tendon, and is a promising metric to acquire in vivo mechanical data noninvasively.
So the next question becomes
is it important to understand Muscle stiffness ?
Yes. Especially in paediatrics where the range of muscle stiffness is so broad.
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How will it help us in practice?
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.
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is it possible to measure muscle stiffness ?etc etc.
Sometimes.
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.
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
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Muscle stiffness is generally a linear function of tension and is independent of muscle length, stimulus rate and fatigue (Morgan1977; Hunter & Kearney1983)
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.
So Robert when you measure muscle stiffness how does the Measurement in kN/m help you make your treatment plans.
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.
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?
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.
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!
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
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The formula for Hooke’s Law is F=kx where “F” is the force applied, “k” is the force constant of the spring, and “x” is the amount of deformation in meters.
Will still be in play.
In your rig what are you measuring in reference to :
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x is the displacement vector - the distance and direction in which the spring is deformed
F is the resulting force vector - the magnitude and direction of the restoring force the spring exerts
k is the spring constant or force constant of the spring.
Sorry for being slow. Spooner probably shacking his head. saying come on Mike you know this...
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.
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?
Colin
Then??? if it doesn't change things dig a bit deeper.
Muscle stiffness is generally a linear function of tension and is independent of muscle length, stimulus rate and fatigue (Morgan1977; Hunter & Kearney1983)
Colin I´m still reading stuff - but muscle tightness/length is different to muscle stiffness.
Measuring muscle stiffness
Linear Mode
