After copy & pasting 42 A4 pages from PA including sections of quoted articles, have I got it right,
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If my pt wants to "burn fat" I get her to run on jelly rather than eat it,
but if a runner with stress #'s of the long bones of their leg wants advice I tell him to join the barefooters, preferably on concrete,
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As Simon said we've been talking about this on the phone recently. Here's where I'm currently at with my understanding (courtesy of him):
The CNS will modulate the stiffness of the leg 'spring' (kleg) in tune with the surface stiffness (surface encompassing the ground, footwear and orthoses).
It does this to minimise any significant excursion of the Centre of Mass (CoM)
It is fair to assume that there may be a zone of optimal leg stiffness (Spooners ZOOLS) for a given individual performing a given activity. (Where performance is maximised, and injury risk is minimised - although it should be said that these 2 variables may essentially have differing kleg values)
Several factors can and will change the kleg (e.g. Foot type, running technique, running speed, change of surface stuffness etc)
Generally speaking the injury profile seen with increased stiffness will be bone injury, and with decreased stiffness will be soft tissue injury
As a rule - running on a stiffer surface, such as concrete, (or removing cushioned shoes) will result in the CNS modulating the kleg to become less stiff (more compliant). It seems intuitive therefore that this may be beneficial for those with bone injury (e.g. Tibial stress reactions).
However,
If a runner presents with exercise induced leg pain which turns out to be a stress fracture, our assumption is that there may have been an inability (or failure) of the CNS to effectively modify the leg stiffness, and therefore an approrpiate 'net stiffness' has not been achieved - in essence the leg is too stiff for the environment, and cannot change.
Therefore,
If we introduce cushioned footwear, or advise them to run on softer surfaces, we actually re-tune the net stiffness to be more appropriate. So we soften the surface to bring it in line with the kleg.
I rang Spooner about this as it was bothering me also. The above is what we all do clinically on a daily basis (and we know it works) but taking the leg stiffness concepts to the letter it immediately makes you assume that to lower leg stiffness we need to increase surface stiffness. I think the key here is whether or not the leg stiffness can be modulated by the CNS.
Hope that makes sense and reads ok - apologies if not - I'm typing it on my Blackberry whilst sitting in a conference. -
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Cheers -
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Just a couple of points
Something like that.:drinks
BTW this is really just an extension of Niggs preferred movement pathway paradigm- I'm just saying it's the movement path of the CoM which is key and this is what the locomotor apparatus is trying to maintain in the face of variation in terrain. -
In a lab setting... How about if we could manipuate the CNS / spinal reflexes in some way in order to determine if/where there is some "breakdown" in stiffness regulation? Maybe by using a nerve block? I've also seen 90Hz vibration used successfully to manipulate stretch reflex responses in the gastroc-soleus during running. Could we use techniques like this to manipulate the pathway? -
Are you familiar with the work on Soleus H-reflex stimulation and the phase of gait dependent motor responses which have been obtained? I talked about these studies some years ago on here and on the old Podiatry Mailbase- see if you can find them. If not I'll have a look later. -
Energy is the new stiffness this season. -
Energy storage seems to be important with respect to connective tissue regeneration and repair.
A bit off topic so you might respond with a so?
A book I have been reading about connective tissue regeneration says something along the lines of;
The mechanism in which elastic energy is stored in connective tissue during locomotion brings about fibroblast stimulation in these tissues that directly effects gene expression and the regulation of cellular protein synthesis at the extracellular matrix.(via process called mechnochemical transduction).
A link to the book is below with a nice summary on page 40:
http://books.google.co.uk/books?id=...q=mechanical transduction in a tendon&f=false -
The above quote interests me. If the ROM or stiffness of a given joint is insufficient to allow the CNS to effectively modulate the stiffness of the leg (kleg) then is it possible that the same could be said for the muscle strength being insufficient to regulate C of M. So, conditioning becomes a major factor, especially in cases where someone drastically increases activity over a short period of time
Thanks in advance
Robin -
Ian and Simon thank you, I was completely lost on the previous stiffness threads and your posts really cleared it up for me. Epiphany moment!
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So...
How does foot function have in influence?
Does the stiffness of the foot help modulate total leg stiffness directly?
Or does the stiffness of the foot have an influence on how effectively extrinsic muscles can regulate stiffness?
Interesting stuff. -
After reading this stiffness thread, there seems to be a lot of theorizing going on, with little research evidence to back up the theory. As you all know, I enjoy theorizing also, but I'm not so certain I can agree with all of the statements that have been made so far.
First of all, I'm not so sure that the key for the body is to maintain its CoM in a certain path as Simon says above. Rather I believe that the main driving force is for the body to minimize metabolic energy for running over a given surface stiffness by changing the kinetics and kinematics of the lower extremity, which will, in turn, cause the CoM to move in a certain prescribed path. In other words, is the driving force to change leg stiffness when encountering surfaces of different stiffnesses while running to make the CoM move in a certain path or is the driving force to change leg stiffness when encountering surfaces of different stiffnesses while running to optimize metabolic efficiency of running?
I vote that the central nervous system chooses the most metabolically efficient leg stiffness for each surface of different running stiffness rather than choosing the leg stiffness that will make the CoM move a certain path.
Secondly, in Ian's posting, he alludes to the theory that "Generally speaking the injury profile seen with increased stiffness will be bone injury, and with decreased stiffness will be soft tissue injury". Do we have any evidence for this generalization, or is this pure speculation? It seems, to me, to be a gross over-simplification, just as the barefoot runners like to focus on impact shock as the cause of all running injuries, to only focus on leg stiffness variations causing injury. What happened to such injury mechanisms such as increased magnitudes of subtalar pronation moments, increased tibial bending moments due to eccentric bending loads on the tibia, etc when you are discussing your hypothesis that increased stiffness causes bone injury and decreased stiffness causes soft tissue injury?
Third, how do we measure or evaluate leg stiffness in our practices or whether our patients are properly altering their leg stiffness for the different surfaces they are running on? How do we use this theory that leg stiffness may be important in injury production to better treat our patients or to improve our patient's running performance? And finally, do we have any good research evidence that high leg stiffness in a runner causes any more or different injuries than in a runner that has low leg stiffness?
Just some thoughts that popped out when I read some of the interesting statements made on this thread.:drinks -
related leg stiffness threads
Leg stiffness
leg stiffness, CNS stimulation and Piper rhythm
Bipedal spring mass walking sagittal plane theory
Double support phase and leg stiffness
Some papers you might want to read
Leg stiffness attachment list not complete but a good start Leg stiffness attachment list
Kevin this is a start there is more and I am sure Irene has tons of papers -Attached Files:
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Yes, the foot will be a spring in the series of springs ( muscles) which make up the lower extremity, and if the effectiveness of one spring is reduced that `load`must be taken up by the other springs to maintain kleg , so we have individual muscle stiffness added together to give us net lower extremity stiffness or Kleg. Measuring muscle stiffness
All of the theroy behind this is based around Hookes law - Hooks law
Really good visual explanation Hookes Law Lecture 10: Hooke's Law - Springs - Simple Harmonic Motion - Pendulum - Small Angle ApproximationAttached Files:
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Robbin, precisely. Which is why Janda's muscle imbalance theory may be significant.
I'll come back to Kevin's post a little later when I find time. -
Simon (As the potential I-Phone Guru)
Is there an app for the I-phone that would allow it to be used as a Accelerometer?
If so, could we assess vertical and possibly horizontal displacement over, for example, the duration of a run?
Could we then compare initial in-shoe pressure measurements e.g a force/time curve verses the same measures at the end of the run.
Would an change in CoM correlate to increase foot pressures and consequently an decrease in the body to regulate stiffness?
Just thinking about creating some basic evidence?
Phil -
Attached Files:
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High-Arched_Runners_Exhibit_Increased_Leg_Stiffness_Compared_to_Low-Arched_Runners.pdf
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This is the reason I corrected Ian: it's not about minimising the excursion of the centre of mass (as this will actually increase metabolic cost), it's about maintaining a steady, metabolically optimised, CoM displacement cycle for a given locomotor task. Viz. the preferred movement pathway for the CoM.
However, things like pain avoidance may also trigger a change in the CoM pathway. But again, a steady state cycle would seem desirable.
But then of course you also have this: http://w4.ub.uni-konstanz.de/cpa/article/viewFile/3337/3137
Hopefully you will now find this thread a little more evidence based, Kevin.Attached Files:
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However, I am not so convinced by the paper provided that we can be so certain that lower stiffness lower extremities will always tend to develop soft tissue injuries and higher stiffness lower extremities will always tend to develop bony injuries. Again, I think those that truly believe this are placing way too much emphasis on lower extremity stiffness during running as the key factor in running injury production.
For example, what if I have a high school female distance runner who is just beginning to run longer distances, has relatively low leg stiffness and then develops a tibial or metatarsal stress fracture more due to their low bone density and narrow diameter bones (i.e. decreased moment area of inertia) than due to whether their legs were more or less stiff.
http://www.orthometrix.net/downloads/human12.pdf
I have seen countless stress fractures in the metatarsals and tibias in young female runners much more so than in their male counterparts. And, typically, the male runners have much more stiff legs than do their female counterparts, but have far fewer stress fractures (stiffness being determined by how little time the runners feet spend on the ground for a given running speed).
Certainly, lower extremity stiffness is one factor to consider and it is fun to talk about and theorize about. However, I am not convinced that it is the most important or even in one of the most important factors that tend to produce injuries in runners from what I have seen in the 27 years I have been treating injuries in runners. -
Lets take your example with two identical female athletes with the same cortical thickness in their tibias. They follow the same training plan. One runs with high leg stiffness, the other with more compliant leg stiffness. Which one is more likely to develop tibial stress fracture and why?
More on gender differences in musculoskeletal stiffness and risk of injury here: http://www.jelectromyographykinesiology.com/article/S1050-6411(02)00002-0/abstract and here:
http://www.jelectromyographykinesiology.com/article/S1050-6411(02)00003-2/abstract
and here:
http://www.jssm.org/vol8/n2/15/v8n2-15pdf.pdf
etc. etc.
Now, I'm not saying that leg stiffness is the be all and end all, it's far more complex than that. However, leg stiffness does seem to be being linked with injury and performance in a relatively large and ever growing number of peer reviewed publications in highly respected journals. This one I linked to earlier, being published just this month is the latest: http://www.ncbi.nlm.nih.gov/pubmed/22117105 Whether we like it or not, this kind of evidence trumps that of "expert opinion" in the hierarchy of evidence. As of today there is far better evidence in the peer reviewed literature suggesting a link between leg stiffness and injury/ performance, than there is to suggest a link between subtalar joint axial position and injury/ performance. So while the significance of subtalar joint axial position in injury "is fun to talk about and theorize about" there is little evidence to support it. Can you resist that contention, Kevin? :drinks To quote Craig: "you got to go where the evidence takes you". Only playing.
In my "expert opinion" and with my 21 years of post-graduate experience treating running related injuries, leg stiffness is worthy of further serious study. Judging by the number of publications in this field it seems I'm not alone in this view. But each to their own. -
Forces generated by muscle are stored as elastic strain energy during tendon deformation, then transferred to bone to allow for joint movement.
Some of this energy goes into moving the joint and some of the energy is transduced into cellular changes via a process called Mechanochemical transduction.
This dictates how cellular activity will respond to the forces and ultimately lead to changes in the mechanical properties and composition of the connective tissue.
Stored energy drives mechanochemical transduction during locomotion so I was thinking that leg stiffness/surface stiffness will have a part to play. Especially when the practitioner is attempting to accelerate connective tissue repair after injury. Maybe as the patient returns to straight line running.
More later,
Athol -
Do you actually think, Simon, that athletes with stiffer legs during running suffer more bone injuries and athletes with less stiff legs during running suffer more soft tissue injuries? What does the science so far tell us about this? Does bone density, and cortical diameter of long bones have less to do with the possibility of the runner developing stress fractures than does their leg stiffness?
Can't wait to discuss this in Belgium over some good Belgian beer...yum.... -
Knowing your capacity for alcohol... knowing how strong Belgium beer is... It'll be a walk over.:drinks
P.S. the parcel might be coming from an "Angel"- he assures me it is posted this week!!!
P.P.S. Statements like this: "I acknowledge that I am guessing, which I, again, am pretty good at doing" make me smile, remind my why I love you and where I get it from. Will I ever be that confident? -
Re beer in Belgium
make sure you 2 have a beer or 10 with Toni Arndt -
But that doesn't make you right.;) -
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so you can all talk behind my back :D -
Lets not loose this as it is potentially an important exercise to the understanding of leg stiffness and performance.
Kevin wrote: ... "typically, the male runners have much more stiff legs than do their female counterparts (stiffness being determined by how little time the runners feet spend on the ground for a given running speed)."
I replied:
"If you were just looking at contact times did you normalise the data for body mass? http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1624931/ There is an obvious comeback to this... Anyone? Think about y'all."
What is the "obvious comeback" given that Kevin suggested increased leg stiffness in males compared to females observed via contact times (not necessarily true, but lets run with that for this exercise)? You'll need to understand simple harmonic oscillators, the influence of spring (leg) stiffness and mass on resonant frequency and how this relates to contact time and how contact time relates to performance to answer this.
If you're interested in leg stiffness, tell me why normalising for body mass becomes irrelevant if Prof. Kirby's contention is correct, men being generally heavier than women (it's not, but lets just help his ego here by pretending he's right; like he needs his ego massaging- "I acknowledge that I am guessing, which I, again, am pretty good at doing"- extraordinary :rolleyes:) -
For two runners, running at the same velocity, one with a support time of 200 msecs and the other one with a support time of 400 msec, why wouldn't the runner with the shorter ground contact time also have a stiffer leg? Wouldn't this be a good qualitative way of measuring relative leg stiffness between one runner and another, having them run at the same speed and measuring the duration of their support phase of running?
In addition, one of the training effects I have noted in runners as they become more fit is that their support time decreases over time, which I assumed was related to them increasing their leg stiffness with increased conditioning. Do you know of any study that has measured leg stiffness in runners during a longitudinal conditioning study? -
I believe that any good clinician will have the ability to be "pretty good at guessing", since, in all reality, how many absolute truths do we know about the physiology and biomechanics of the human body? Therefore, the decisions we all make for our patients are based many times on educated guesses. -
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Simon:
Let me ask the question again, but this time, more precisely:
For two runners of the same body mass, running at the same velocity, one with a support time of 200 msecs and the other one with a support time of 400 msec, why wouldn't the runner with the shorter ground contact time also have a stiffer leg? -
I think you know that I know the answer to your question, Kevin. But differences in foot length might be significant in altering contact times in the presence of identical leg stiffness and identical mass and velocity.
Let me ask the same question again, third time lucky: "Lets take your example with two identical female athletes with the same cortical thickness in their tibias. They follow the same training plan. One runs with high leg stiffness, the other with more compliant leg stiffness. Which one is more likely to develop tibial stress fracture and why?"
I really do need to go to bed now though. -
However, if the point of application of GRF, the 3D location of the GRF vector relative to the long axis of the tibia, the bone density in the tibia, the moment area of inertia along the tibia, the muscle strength in the lower leg muscles, the training habits, and racing frequency are all the same in these two hypothetical runners, then I guess that the runner with the stiffer leg would be more likely to develop a tibial stress fracture due to the greater vertical loading force occurring across the tibia over a shorter period of time.:drinks -
I sure do see lots of short duration stance phases in the elite runners....wonder how many of these elite runners get bone vs soft tissue injuries...isn't the Achilles tendon a soft tissue? My guess, is that elite middle distance and long distance runners get just as many soft tissue injuries as bone injuries even though their leg stiffness is probably on the high side compared to the population of runners as a whole.
Great discussion, Simon. Thanks for forcing me to learn more about this subject. Certainly seems that gaining a better understanding of leg stiffness has the potential to help clarify some of the mysteries of running biomechanics. Looking forward to speaking further in person with you on this subject over some Belgian waffles, Belgian beer and Belgian chocolate.:drinks
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