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Leg Stiffness: Implications for Injury & Performance

Discussion in 'Biomechanics, Sports and Foot orthoses' started by NewsBot, Mar 3, 2014.

  1. NewsBot

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    Last edited by a moderator: Sep 22, 2016
  2. Admin2

    Admin2 Administrator Staff Member

  3. Nice work fella. I'll pick up a couple of points later.
  4. Griff

    Griff Moderator

    There were a few things I heard myself say on playback that I wasnt delighted with. Suspected they wouldn't get past you...
  5. Here's a starter: if you are going to say that increase cadence = decreased step length, you need a caveat regarding velocity.
  6. And Claire Farley is a she not a he, btw.
  7. Phil Wells

    Phil Wells Active Member

    Hi Ian

    Thanks for this - really enjoyed it (apart from letting everyone know what a 'young whipper snapper' you are - makes feel old before my time!)

    I have a question that I hope you may have thoughts on (and obviously Simon) regarding perceived comfort of surfaces, including shoes and footwear, and stiffness modulation.
    There seems to be some research that shows that perceived comfort is an extremely important factor when 'choosing' footwear etc. Also that some groups, e.g. runners, tend to perceive comfort as softer materials (Shore 3-45 density EVA for example).
    This will obviously result in increased leg stiffness (unless other confounding factors are present) = greater running economy etc.
    So what is the feedback mechanism that tells the body something is comfortable? Our we relying on mechanoreceptors within the foot or some other mechanism?

    I have got a few other trains of thought regarding vibration frequency, natural and impact related, and there effect on stiffness modulation but will not bombard you will question - yet!


  8. Phil, the concept of comfort is complex and probably relates to stimulation of temperature, pressure and pain receptors primarilly. But you can also throw in some visual and psychological factors too.

    http://www.ajur.uni.edu/v10n3/Barkley et al pp 7-14.pdf

    etc etc.

    The question becomes, how does the body regulate leg stiffness in the absence of sensory input, i.e. peripheral neuropathy?
  9. If I am not butting in Phil

    when you say will obviously result in an increase in leg stiffness, not always. Thats one of the keys as far as I am am concerned that we need to be able to workout on a patient to patient basis.

    Some will and therefore keep the CoM travelling in a more similar manor to a harder material when running. This change in leg stiffness may be more efficient, but also cause a breakdown in tissue if the said tissue is pushed out of it's pysiological window.

    inital comfort I would say comes from receptors at the foot surface interface, long term from many different places.

    it all comes back to efficency of motion, the more efficent the body is working , say while running the more comfortable a run is. For some that might be soft surface or other hard.
  10. Phil Wells

    Phil Wells Active Member

    Hi Mike

    I assume you are talking about Nigg's Preferred Movement pathway concept?
    The issue with this is that initial perception of comfort is often static and does not relate to dynamic function e.g the individuals preferred pathway. However the patient will often rely on the initial feeling of comfort from which to judge the shoes, insole etc. and as you say it will vary between individuals on how it effects stiffness and interacts with their pathway.
    From an orthotic designers perspective initial comfort is everything, especially in the retail environment, but understanding stiffness modulation in response to perceived comfort is a big topic as the credibility/effectiveness of the product is critical (for me personally!)

    I am not sure that efficiency can be direct linked to comfort though. For example certain groups will feel that silicone is comfortable. However as the effects of fatigue occur and COM displacement increases, this often changes (Various reasons but personally I feel that the dampening effect of silicone insoles translates in to increased hysteresis within the silicone and the soft tissues). The comfort of the silicone at the end of a run is often different than at the beginning. (Blisters, rubbing etc)
    I am starting to think that vibrations effect on stiffness modulation may play an important part in gait efficiency but has nothing to do with comfort - consequently the conundrum when designing any type of orthotic.
    Will keep thinking at trying to find the 'perfect' material and orthotic design.


  11. Phil Wells

    Phil Wells Active Member

    Hi Simon

    Interesting links - especially the temperature one- socks and shoe weight made subjects feel more comfortable and cooler! You get very similar feedback from RhA patients!

    Regarding the sensory input issues, I have recently seen a patient with Vestibular impairment who now feels that all her shoes are uncomfortable!
    What is interesting clinically is that if we used initial comfort as a guide to prescribing our orthoses, how many rigid devices would be issued?
  12. I generally do. One of the first questions I ask patients at the dispensation appointment is "how comfortable are the inserts?" Generally, this initial feedback is spot on. I will modify any devices in which the patient's immediate perception of comfort is not subjectively good (upper 25-30% on a VAS). The ones I struggle to make comfortable to at least this level are the ones that usually result in treatment failure. BTW, I prescribe lots of what you might term "rigid" devices and far fewer "compliant" devices.
  13. Phil Wells

    Phil Wells Active Member

    That fits in with some unpublished research done approx 8 years ago that showed that direct milled polypropylene without a top covers had better compliance than those devices!
    However how would you deal with a patient whose comfort perception undermines what you need the insole to do?

  14. Here's an anecdote. I made devices for a pro-rugby player. Long story short I ended up grinding so much of the device away in order to achieve comfort that I was convinced the device would not work. It did. You got to weigh the psychological (placebo) versus the direct mechanical effects.
  15. Phil Wells

    Phil Wells Active Member

    Good point.
    Just out of interest how do you decide the 'stiffness' of the orthotic prior to dispensing?
    I have a general rule of thumb that if the patient is 'fussy' (ticklish feet, had previous insoles that didn't like) then I use a more compliant material. If they are doing lots of standing then firmer materials are preferred.
    Recently I have been looking at how footwear will maintain/control the COP progression and then using different stiffness material to try and get the COP where I think it needs to be - acceleration/deceleration.
  16. Phil,
    One of the major points of foot orthoses function is that they do not have constant load/ deformation characteristics across their interface with the foot. This is one of the methods by which they modify the reaction forces at the interface. The material selection in itself will not determine the load/ deformation characteristics, rather the geometry of the device in conjunction with the material selection will ultimately determine the orthosis stiffness at each point at the foot-orthosis interface, but only the geometry will determine the relative distribution of reaction forces unless you start using multiple density materials in parallel. So, when you ask how I decide on stiffness, we should first need to clarify: where?

    Like you I am thinking in terms of "pulling" the CoP in one direction or another and in terms of preloading tissues via kinematic effects.

    I think we do have reasonable ideas of optimal surface stiffness in runners- we'll talk about this privately I'm sure, Phil. There are clinical methods of estimating leg stiffness too.

    While leg stiffness is interesting, we also need to think about foot stiffness. I think a reasonable starting point for this is to look at the span length of the medial longitudinal arch and the dynamic/ static navicular drop. If we have pressure plate data all to the the good, otherwise we can take a rough estimate of load based on body weight (x 1 static, x1.5ish for walking, x2 ish for running). From this we can calculate foot stiffness (or MLA stiffness). There will probably exist an optimal range of foot stiffness values- ZOOFS if you like. I talked about this some years ago.

    Which reminds me, Ian in his presentation mentioned the relationship between foot type based on arch height and stiffness. He made a throw away comment in the presentation that there is not a lot we can do to change it- I disagree. Think about what foot orthoses do, Griff.

    "Beam theory for dummies", anyone? "It's stiffer cause it's thicker" those that attended the seminar in Zaragoza will remember my discussion of this I hope. :drinks
  17. A further thought on the presentation. Ian talks about minimizing the vertical excursion of the centre of mass. Actually "flat-lining" the centre of mass has been shown to be less metabolically efficient, so some vertical displacement is required. The question becomes "how much?"

  18. Phil Wells

    Phil Wells Active Member

    I think we also need to understand the 'when' of load deformation characteristics in relation to fatigue. If the joint stiffness decreases as fatigue occurs then ankle joint excursion increases = increased flexion moments and velocity.
    We then need to understand which 'when' is moving the tissues out of their ZOOS and some how make the orthotic work - my head now hurts!

  19. One thing you need to remember: Foot orthoses do work. Figuring out how they work was interesting. Maybe we can design better orthoses in this knowledge, maybe not. But they still work, regardless.:drinks
  20. Phil:

    Like Simon mentioned, "shoe comfort" is complex and likely is multifactorial and may or may not be related to only the softness of the shoe. Also, different individuals may use different sensory mechanisms to rate "shoe comfort" and may even rate "shoe comfort" as to whether the shoe relieves or exacerbates preexisting painful foot and lower extremity conditions.

    In addition, I don't think we know enough now to even include "shoe comfort" and "leg stiffness" together as relating to each other or whether they affect each other. These are interesting concepts but I think that "shoe comfort" is even less well understood than "leg stiffness" so much of what we do know is based on so few research studies that I believe we are just now starting to scratch the surface in trying to understand what makes one shoe comfortable and another shoe not comfortable.
  21. To add to Simon's post on orthosis comfort, I ask the same initial question on "how do the orthoses feel?" However, I also closely watch the gait pattern of the patients walking or running and, especially in walking can see evidence of an uncomfortable orthosis as a shortened stance phase with reduced propulsion. It is interesting to me that patient's perceived comfort is also reflected in the kinematics of their gait and I can generally see that an orthosis is more comfortable just in the way they walk.

    It would be a great research study to see the gait changes that occur by making an orthosis uncomfortable on purpose to see if different subjects respond the same kinematically to different "uncomfortable" orthosis modifications.
  22. Good points, Simon. I thought the "stiffer cause it's thicker" was a good one at Zaragoza...much better than the "Cadillac" references....;)

    One of the classic research articles on foot stiffness is the one by Ker et al (Ker RF, Bennett MB, Bibby SR, Kester RC, Alexander RMcN: The spring in the arch of the human foot. Nature, 325: 147-149, 1987) where they measured the stiffness of the longitudinal arch of the foot in simulated running conditions and then showed the changes in stiffness with transection of different tensile load-bearing structures of the longitudinal arch (see attached PowerPoint slide from my lecture on the 10 functions of the plantar fascia). Certainly, foot stiffness does play an important role in returning energy back into the runner and foot orthoses should be able to modify that stiffness to optimize energy return.

    However, like Simon mentioned, "flat lining" the center of mass (CoM) is not ideal in running and too much vertical CoM excursion in running wastes energy also. There must be enough lowering of the CoM during running to "load the foot and leg springs optimally" during the early support phase of running, but not too much CoM loweing or metabolic energy will be wasted. It is up to the central nervous system to determine what optimal leg stiffness is for each different running surface with different surface stiffness. I think we are just starting to understand this and the foot does play a significant role in the stiffness of the whole lower extremity during running.

    Fascinating subject!
  23. CraigT

    CraigT Well-Known Member

    I have a similar protocol when fitting foot orthoses. Additionally I generally have the patient walk for a couple of minutes, then remove the orthoses again- they often report than they are much more aware of what there feet are doing, and immediately feel like they are 'walking better' with the inserts in place...
  24. Getting back to Ian's video, which I thought, Ian, was nicely done, here are a few more thoughts about leg stiffness.

    1. We must remember that the measure of leg stiffness currently is only a measure of the fall and rise of the center of mass relative to the ground reaction force exerted by the foot. Therefore, it is an interesting measure, but may or may not be related to the three dimensional moments and motions that occur within the foot and lower extremity that may cause the majority of running injuries in our patients.

    2. I believe the leg stiffness will be found to correlate more to performance than to injury production since leg stiffness basically measures the stiffness of the "springs" in the runner's legs. I believe, even though I don't know it has been studied yet, that runners with stronger lower extremity muscles will have stiffer legs during running. I'm not convinced measuring leg stiffness will tell us a whole lot about how to treat an injury but will tell us more about how the central nervous system alters the firing patterns of the lower extremity muscles for different shoe/orthosis/surface stiffnesses.

    3. The good news is that leg stiffness is a quantifiable measure, and not a subjective measure, meaning it can be scientifically analyzed much more easily. The bad news is that there is no reliable way to measure leg stiffness during running in a clinical setting without a force plate and a 3D motion analysis system in the clinic. How many of you have that in your offices?

    Good discussion.
  25. It seems that asymmetry in leg stiffness may be a key factor in injury, which makes sense intuitively. Griff and I were discussing limb length differences and leg stiffness modelling on the phone yesterday, this kind of fits with our discussion- see .PDF attached. So the question becomes, what factors other than limb length descrepency might cause asymmetry within the leg stiffness...

    This study used subject mass, contact time and flight time to determine leg stiffness. These variables should be fairly straight forward to measure with the aid of a video camera and weighing scales: http://scholar.google.co.uk/scholar...r&ei=K7QYU_yEK4aP7AaAvYCACQ&ved=0CCoQgAMoADAA

    Attached Files:

  26. Thinking out loud: if we know the stiffness of a spring and we know it's resting length, then surely we can model and predict how much load/ deformation might induce plastic deformation in a given spring? That is, there has to be a way of predicting the elastic limit of a spring, without actually physically measuring it- right?

    If this is correct and I think it is, then we should be able to predict injury based on leg stiffness. Or, put another way, soft tissue injury occurs when the CNS fails to match the stiffness of the leg to the load being applied such that the deformation in the leg exceeds the limits of proportionality- I like that.
  27. efuller

    efuller MVP

    Which comes first? The injury or the difference in leg stiffness? Limping is an alteration in leg stiffness. Could be in some people there is an asymptomatic difference in stiffness and in other people an injury causes the CNS to change the stiffness, compared to what they were doing before the injury, to accomodate for the injury.

    Does the pain cause the gait or does the gait cause the pain? An age old question.

  28. Of course. The answer, in part, might lie with the researcher that performed the study on the Aussie rules footballers that I attached above. As I recall (I haven't read it in detail for some time) they measured players leg stiffness at monthly intervals across the season, so they should have (even if it's not reported in the paper) data which is prospective in nature, pre and post injury. Might be worth contacting the lead author if it is not reported in the paper.
  29. Phil Wells

    Phil Wells Active Member

    Just to read an article that assessed the viscosity of a muscle post stretch.
    It found that when a stretch was repeatedly applied to the hamstrings for 90 secs, then the viscoelastics stress relaxation of the muscle increased by upto 30% (but did return to normal within 60 minutes) = the muscle was less stiff.
    This could have implications for the CNS/mechanical modulation of stiffness if too vigorous stretching was done prior to activity requiring stiffness modulation.

  30. Simon:

    I'm not so sure that in the human leg, where the "springs" are multiple viscoelastic structures, many of them working in parallel with each other, and all contributing to the spring stiffness of the leg, that it would be possible to determine when plastic deformation would occur in any one or all of those structures simultaneously. In addition, I believe that if you want to predict the elastic limit of a spring then it would be better to know what material that spring is made of rather than just simply looking at the spring's stiffness.
  31. Interesting study: With 88% of the gymnasts becoming injured during the 12 month study period, I wonder if the researchers wouldn't have predicted injuries better if they hadn't measured leg stiffness at all and just hypothesized that all of the athletes would get injured during the year regardless of what was measured.:rolleyes:

    Simon, the study looks a little fishy to me. What do you think of it?

    I do like the idea of measuring leg stiffness in the lab to learn more of how it correlates to lower extremity function but still think this may be difficult to measure in a clinical setting.

    In addition, let's say we measure leg stiffness in a patient to be too high or too low, then what would you do to either decrease or increase leg stiffness to bring it back into more normal values for the athlete?
  32. Petcu Daniel

    Petcu Daniel Well-Known Member

    Taking into account that free moment is a predictor of tibial stress fracture [ http://www.jbiomech.com/article/S0021-9290(05)00436-7/abstract ], do you think it could be used also as a measure of leg stiffness? In a couple of measurement of the free moment in older subjects I’ve obtained a bigger value of the peak value corresponding to the midstance phase than what I’ve seen in the literature which, I think, could be attributed to an increased leg stiffness

  33. I don't know about that one. What do you think, Daniel? I would think that unless the movement pattern is measured above the force plate then stiffness can't be calculated or estimated.
  34. Athol Thomson

    Athol Thomson Active Member

    Hi all,

    Just finished a systematic review on Lower limb MSK stiffness and injury. The abstract is below. I will present the findings at the IOC conference Monaco in April and then hopefully full paper will be published soon.

    Just in transit at the moment so I will tune in again later tonight and try and contribute to some of the previous posts.

    In the review I looked at MTU stiffness, Leg stiffness, Vertical stiffness and joint stiffness and the possible relationship to lower limb injury in athletes.

    More soon,


    Br J Sports Med 2014;48:665 doi:10.1136/bjsports-2014-093494.280

    Abstracts from the IOC World Conference on Prevention of Injury & Illness in Sport, Monaco 2014



    A Thomson,1
    + Author Affiliations

    1ASPETAR, Doha, Qatar
    2Ulster Sports Academy, University of Ulster, Northern Ireland.

    Background Lower limb injuries are prevalent in sports involving running, hopping and jumping. Musculoskeletal lower limb stiffness is a modifiable mechanical property that may be related to injury risk in athletes.

    Design Systematic Review.

    Objective Examine the relationship between musculoskeletal stiffness and lower limb injury in athletes.

    Methods Literature searching was undertaken on 3 electronic databases (MEDLINE/SPORTDiscus/google scholar) up to September 2013. All prospective and case-control studies evaluating lower limb MSK stiffness and injury in athletes were included. Two researchers independently extracted outcome data and assessed the quality of included studies using a modified Downs and Black index. Effect sizes were calculated using RevMan software (version 5.2).

    Results 11 studies (6 prospective and 5 case controlled) were identified, comprising a total of 474 participants (378 M, 96 F) with a mean age range of 13–39 years. The majority of studies (9 out of 11) were undertaken on international or elite athletes. Quality index scores ranged from 13 to 16 (max 19). Athletes with a history of unilateral lower limb injury displayed less stiffness when compared to their un-injured contralateral sides. Pooled data from three case control studies also found tendon stiffness was significantly lower in athletes with tendinopathy compared to un-injured matched controls (SMD 0.70, 95% CI 0.07–1.48). Data from prospective studies could not be pooled due to clinical heterogeneity. There was a clear trend that athletes with bilateral differences in leg stiffness or higher mean leg stiffness were more likely to develop a non-contact lower limb injury.

    Conclusions Case controlled studies show a clear relationship between musculoskeletal stiffness and athletic injury. Prospective research provides further evidence that musculoskeletal stiffness may have an important causal role; however this may be implicated by previous injury.
  35. Petcu Daniel

    Petcu Daniel Well-Known Member

    I’m thinking at a method of evaluation at a level of clinical setting. A stiffer leg, with a lower transverse mobility, will transmit more quickly the movement to supporting surface [greater friction with the ground ?] which means a greater value for free moment in opposition with a less stiffer leg which, I suppose, will produce smaller values of the free moment because of greater transverse mobility in the joints
    A relation between movement pattern and free moment pattern could be seen in : Willwacher, Steffen et all. “Free Moment Patterns in Distance Running.” Footwear Science 5, no. sup1 (2013): S10–S11.
    [ http://www.tandfonline.com/doi/abs/10.1080/19424280.2013.798686 ]

    Another reference article is : Holden, John P., and Peter R. Cavanagh. “The Free Moment of Ground Reaction in Distance Running and Its Changes with Pronation.” Journal of Biomechanics 24, no. 10 (1991): 887–897.
    [ http://www.sciencedirect.com/science/article/pii/002192909190167L ]

  36. Athol Thomson

    Athol Thomson Active Member

    There are many different types of stiffness measures that can be calculated for the lower limb. The more "Global" measures such as leg stiffness or vertical stiffness give an idea of how all the muscles, tendons ligaments, joints and bones of the lower limb interact with the ground. These terms are often confused even by the authors of good prospective studies looking at leg stiffness and injury. They are not the same and require different methodology to calculate them.

    Whereas the more specific measures such as MTU stiffness, joint stiffness are more location specific and in the case of MTU stiffness, require the use of ultrasound of a tendon to measure the change in length of the tendon or aponeurosis for a given force .

    There are two excellent reviews of the types of stiffness and the mathematical models used to calculate stiffness for each method below.


    Happy to email PDF of these if you PM me.

    Reliability of these measurements is an issue. A friend called Corey Joseph has studied the reliability of each method and his findings are attached.

    On the point about measuring stiffness in the clinic. It can be done with a contact type-mat (pressure mat) with one of the models covered in the reviews above.

    However, The most reliable method seems to be hopping on a "proper" force plate. You don't need kinematic data for vertical stiffness as you can do a double integration to work out the COM displacement using the kinetic data only. (again see reviews if interested). I think this is not far away for pre-season screening in elite sport and with Australian rules football already trying this in two prospective studies.

    There are studies that have shown how certain types of training alter lower-limb stiffness such as plyometric, power, strength, endurance, eccentric or heavy slow-resistance training. Each type of training has a certain effect on lower limb stiffness or MTU stiffness.

    So if we can measure the stiffness as podiatrists/biomechanics specialists we might then be consulting with physiotherapy and strength & conditioning colleagues to tailor a treatment plan that we can then objectively measure again after a given amount of training or time.

    All the best,

    Attached Files:

  37. Athol:

    :good: Great posting.

    By the way, for those following along MTU means "muscle-tendon unit".

    Let's say I want to measure leg stiffness of a patient in my clinic and don't have a force plate in my office. How do I measure leg stiffness in my patients without this rather expensive piece of equipment? How reliable would this measure be? In addition, how does body weight affect stiffness? Is there any correlation?

    Thanks for the information!
  38. Athol Thomson

    Athol Thomson Active Member

    Hi Kevin,

    You could use a contact/pressure mat to calculate vertical or even leg stiffness in clinic. Some studies have used in-shoe pressure (e.g pedar-x) and even an optojump system to work out flight times and contact times. These values are then put into a large equation or some software with the function set-up already to calculate stiffness measure you require. I emailed you the Brughelli et al. review which outlines all the methods used in previous literature very well.

    I think it is still a stretch to calculate stiffness in a clinical setting with time constraints. There are some clinical tests that seem to correlate well with leg stiffness such as a 3-single leg hop test for distance. These are the tests that will give an inference to what the actual leg or vertical stiffness is while being clinically useful.

    I'll try and find the study that used the hoping test for distance and post a link.

    When using the force plate methods for calculation you can "normalise" for body mass so the stiffness is not dependent on just the mass.

    I imagine that this can be done with all the methods.

  39. BEN-HUR

    BEN-HUR Well-Known Member

    As far as I know I haven't seen the following article cited on this forum... doesn't seem to be on this thread (which is probably the more appropriate thread out of the "Leg Stiffness" threads)...

    Warm-up with a weighted vest improves running performance via leg stiffness and running economy (link):

    Journal of Science and Medicine in Sport:
    K.R. Barnes, W.G. Hopkins, M.R. McGuigan, A.E. Kilding.
    - Received 24 June 2013; received in revised form 5 December 2013; accepted 13 December 2013. published online 27 January 2014.

    I have posted on weighted running vests in the past on this forum... but can't recall the thread/topic. Anyway, I sometimes train with one... & I can relate to the above findings (by feel/perception only... haven't done measured testing myself). Hence, I do think they are a valid training tool (related to this topic i.e. injury & performance)... albeit not an aid/tool that many athletes (especially distance runners) tend to use (I've seen sprinters use similar).

    In fact, now that I think about it... there was a distance runner from the U.S - Hobie Call (marathon PR of 2:16.39 as of 2012) who believes he could be the first to break 2:00hr in the marathon; article here: http://www.runnersworld.com/elite-runners/hobie-call-would-be-sub-200-marathoner...

    Many appear to question Hobie's views/reasoning... but I find them interesting nonetheless.

    I use the following...

    MiR Weighted Vests.


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