Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Zone of Optimum Leg Stiffness (ZOOLS)

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Griff, Apr 7, 2010.

  1. Griff

    Griff Moderator

    Members do not see these Ads. Sign Up.
    {ADMIN NOTE: This thread has been split off from the thread on Somnio Running shoes, so that thread can stay on topic of the running shoes}

    My only thoughts about this - and they are simply thoughts at this stage - would be the following theoretical situation (Imagining a runner with a large body mass):

    • Runner with large body mass = Somnio midsole with increased stiffness prescribed
    • Increased stiffness of midsole = CNS mediated decrease in leg stiffness

    If our 'heavy' runner was already at the lower end within his zone of optimal leg stiffness (ZOOLS) then an increase in midsole stiffness could theoretically decrease his leg stiffness to a point outside of his given ZOOLS. At best this may cause a reduction in performance, at worst = pathology.

    Lots of ifs and maybes I know - just mulling it over really. Where is Spooner when you need him - that fella shouldn't be allowed holidays...

    Last edited by a moderator: Apr 10, 2010
  2. Re: Somnio Running Trainers

    I would say that said Spooner may tear up a little when reading your post like a proud dad. He may not of course.

    In fact I logged on to post up this paper and say something along the leg stiffness line. So we are both thinking along the same ideas

    Paula I would back up Ian and say read through the leg stiffness thread there is hours of reading It may change your outlook or shoe re control and cushioning.

    Attached Files:

  3. Paulo Silva

    Paulo Silva Active Member

    Re: Somnio Running Trainers

    I see you point, this shoes can be a valuable tool or a dangerous hazard in the least prepared ands, that's why, as I mentioned before we see the midsole stiffness based in the body mass as a "starting point", as far of assessing the ZOOLS we look at the kinematics and how different midsole stiffness influences it.

    I'm not claiming to be the know all (hey I'm a simple shoe fitter). Also with this shoes I discovered some assumptions I ad from the past where not correct.

    I'm not blindly defending this shoes, all I'm saying is "these are better than having one shoe for every one". They certainly have room for improvement, should they be "prescribed" solely by shoe fitters? maybe not, but as far as I know they are working with podiatrists in US.
    Last edited: Apr 7, 2010
  4. Griff

    Griff Moderator

    Re: Somnio Running Trainers

    Paulo, I didn't say these shoes could be a valuable tool or a dangerous hazard. Right now I don't know what they are - I'm just thinking out loud about them really. I don't even know how to clinically assess whether someone is functioning within their ZOOLS (do any of us?) - all this is just fun to talk through with others.
  5. Re: Somnio Running Trainers

    A little off topic but I beleive Not yet unless them patient has a specific pathology that could be linked to increased or decreased leg stiffness. ie Davis et al showed a link between tibial stress fractures and increased leg stiffness.

  6. RobinP

    RobinP Well-Known Member

    Re: Somnio Running Shoes

    I've just read the pdf you posted Mike - thanks. I started reading through the thread on leg stiffness before, but it is such a massive topic, I need to wait until I have a little more free time to really digest it properly.

    So using Ian's example of the "heavy" runner....if he is (conversely)already at the upper end of his ZOOLS e.g. typically supinated foot shape with limited shock attenuation, far from advising something with increased shock absorbing capabilities, we should arguably advise something which has little shock absorption in order to decrease the leg stiffness and bring the patient to the midrange of his ZOOLS? The only potential issue being that reduction in leg stiffness is more likely to create a soft tissue problem distally as opposed to a bony problem proximally(based on what I could grasp from the article)

    This is a bit jumbled but I cannot think of it any more clearly......

    Essentially, in the non pathological runner, there is no way of predicting suitability of a running shoe based on joint kinematics as the mechanical construction of the shoe has little , direct, bearing on the leg stiffness. The change in the interphase stiffness has an inversely proportional effect on limb stiffness......or have I got this totally wrong?


  7. Re: Somnio Running Shoes

    Here is a request for all of you who are comfortable using the term "Zone Of Optimal Leg Stiffness" or ZOOLS. Please define the term "Zone Of Optimal Leg Stiffness".
  8. Re: Somnio Running Shoes

    Zone of Optimum Leg Stiffness (ZOOLS): The value or range of values for kleg over which the metabolic cost of locomotion is minimised and the stress in the tissues of the lower limb is optimised. Where kleg is the actual leg stiffness describing the mechanical behavior of the leg’s musculoskeletal system during the support phase.
  9. Re: Somnio Running Shoes

    Probably needs a caveat or two in there:

    For a given surface stiffness
    For a given locomotion activity

    Melting by the pool, sipping cocktails. If only I was a lizard, or Judith Charmers.. (think leather back turtle and you're on the money) I'm neither, give me a pint of lager, please!
  10. Re: Somnio Running Shoes


    Good to see you are enjoying your vacation.:drinks

    I am not so sure that the leg stiffness where the metabolic cost of locomotion and the tissue stress are optimised would be the same values. It might be that a stiffer leg makes you a more efficient and faster runner but may also push you away from being a less injured runner, in some circumstances. Therefore, my sense is that performance and injury prevention ZOOLS may need to be separated. Also, does ZOOLS apply for all forms of locomotion? Does it apply for cycling?

    Don't work too hard on your vacation.
  11. Re: Somnio Running Shoes

    Kevin, optimisation of leg stiffness for a given task should result in metabolic efficiency while maintaining the tissues in a healthy state. For any given task there may be a more metabolically efficient leg stiffness range that is injurious to the tissues; this should be classified as being outside of the zone of optimal leg stiffness (ZOOLS).

    The point that the leg stiffness range that is least injurious to the tissues may not be the most metabolically efficient is interesting. This contention may be correct and as such we may need to consider metabolic efficiency and tissue stress as having two different ZOOLS. However, metabolic efficiency and optimised tissue stress both may occur within a similar leg stiffness range. It is interesting to note that McMahon reported an increase in performance that occurred in conjunction with a decrease in injury rate and that metabolic efficiency is also seem to increase within the surface stiffness ranges reported by McMahon.

    I assume there will be a ZOOLS for different activities, which is why I added the caveats above. Can cycling be modelled a mass-spring system?
  12. Re: Somnio Running Shoes


    Exactly my point. Since we know so little at this stage of early research about how leg stiffness affects function, injury-risk and performance, perhaps, when we start discussing the zone of optimal leg stiffness (ZOOLS) for any runner, we should specify if we are discussing the ZOOLS for best running performance or the ZOOLS for the least injury risk. I think this would greatly ease my inherent initial qualms about the use of the term ZOOLS since we were all being more specific about what we are talking about here and not just throwing the term around without having a proper definition of the term. We don't want another term like "first ray hypermobility" now do we?;)

    Another important point is that, depending on when the load vs deformation of the leg is being measured during the support phase of running gait, the leg stiffness values will vary, which will also affect discussing the definition of ZOOLS. In other words, are we talking about leg stiffness from heel strike to peak knee flexion at all times, or are we sometimes talking about another part of the support phase of running? I don't know....what have you found so far in your reading?

    One other thing is that leg stiffness or ZOOLS is probably only important for running and jumping activities. In other words, leg stiffness probably isn't that important for the inverted pendulum kinematics of walking or for the non-eccentric loads of cycling. I don't know this either for sure, but this is an educated guess since neither walking or cycling can be modelled as spring-mass models.

    Just thought a little more clarification of the terms of leg stiffness and ZOOLS would enable everyone to be able to have a better understanding of these important biomechanical concepts when they start discussing them.:drinks
  13. Re: Somnio Running Shoes

    Kevin there is some research which has been made discussing leg stiffness in walking and that the spring mass models may occur in walking ( possibly when the COM is lowering, ie loading the spring) and that the inverted pendulum model may not be the best fit for walking, We discussed this in the leg stiffness thread. Simon did also say that this was the 1st time he had seen walking discussed in a spring mass model, I think we had 2 articles on this approach listed in the thread.

    but as you say still early days
  14. Re: Somnio Running Shoes


    Thanks for the article. However, after reading the article, they weren't too clear on how stiffness is being measured in walking. From heel contact to the middle of midstance?.....When the center of mass of the body is rising in walking?....I am unclear on this and I don't understand....something doesn't seem right in Sweden on this one:rolleyes:.
  15. Re: Somnio Running Shoes

    Me I´m just a guy looking at new stuff, but maybe we can ask the folks from Jena Germany. ;)
  16. admin

    admin Administrator Staff Member

    {ADMIN NOTE: This thread has been split off from the thread on Somnio Running shoes, so that thread can stay on topic of the running shoes}
  17. Craig:

    Thanks for moving our postings to create this new thread.


    I have done some reading on leg stiffness this weekend and wanted to make a few observations on the subject.

    1. Leg stiffness is measured many different ways, from measuring the center of mass (CoM) displacement versus the ground reaction force (GRF) from a force plate to measuring the knee joint moments versus knee joint rotation. Therefore, when researchers speak of "leg stiffness" they are not defining it the same way which, I believe, is currently very confusing . My guess is that as time goes on, better definitions of each type of "leg stiffness" will be proposed which will improve the clarity of the subject. In other words, don't assume you can compare the "leg stiffness" from one study to another, because you can't, unless they are measured the same way.

    2. Leg stiffness is used to describe the mechanical characteristics of the spring-mass model of running, jumping and hopping where the CoM displaces downward as the GRF increases. The one paper that said it measured "leg stiffness" in walking seems to me to be questionable and I think would not stand the pressure of peer review in a journal since, in walking, the CoM is displacing upward as GRF is increasing.

    3. Leg stiffness adjustments are nearly instantaneous with the first step of encountering a surface of different stiffness and leg stiffness is controlled by the central nervous system.

    4. The optimum leg stiffness for performance and for injury prevention may not be the same values.

    Time to go. Maybe the rest of you can add to this list so that we can develop a primer on leg stiffness for those that are learning more on this fascinating subject.
  18. For anyone reading this you may want to read some of the papers on the subject and see the thread where Simon Spooner 1st introduced the discussion of Zones Of Optimal Leg Stiffness (ZOOLS) and where leg stiffness is discussed go to here "Leg Stiffness thread".

    There is alot of reading and many papers for you to get some information on the subject of leg stiffness. Unless you have seen the thread of course.
  19. Agreed.
    While the inverted pendulum model of human walking provides a reasonable prediction of energy fluctuations it does not predict the ground reaction forces observed in-vivo. This appears to be due to the "compression" of the leg that occurs during walking as oppose to the rigid legs employed in the inverted pendulum model. The peer reviewed paper published by The Royal Society (attached) provides a better overview of the bipedal mass-spring model for human walking than the overview previously attached by Michael. The authors of this paper write: "Moreover, closer than the inverted pendulum, the bipedal spring–mass model describes the out-of-phase changes in the forward kinetic and the gravitational potential energies that occur in walking".

    I have other pdf files (some from peer reviewed journals) which discuss compliant limb behaviour during human walking. If anyone would like me to attach them to this thread I shall. Alternatively google "mass spring walking" "compliant walking" etc.

    The key researchers here appear to Hartmut Geyer (his PhD thesis is the basis of the attached paper) and Andre Seyfarth.
    Geyer, in his PhD thesis notes the importance of the double limb support periods of human walking! I've attached this too.


    Attached Files:

  20. Hope you had a nice break !

    Yes please to the papers if you have not posted them in the leg stiffness thread.
  21. Attached Files:

  22. Thank you Sir. I read thru the Compliant paper Geyer et al ( I opened the PHD but the 133 pages scared me a bit although much seems to be in German) Seemed like a well put together piece which made some good sense to me, but maybe thats what I want it too;)
  23. Scroll down the PhD, it's in English and mathematics!
  24. Is that ment to help you have read more of my posts than anyone :D :D

    Just joking (sort of) I´ll look into it.
  25. Simon:

    I wonder if Geyer's paper would past the muster of a biomechanics journal review. Maybe it is time to pose a question to Biomech-L again on the validity of the spring-mass model approach to human bipedal walking.
  26. Kevin, neither you, nor I, know who reviewed the Geyer article prior to its publication by The Royal Society; could have been R.M. Alexander for all we know. Nor do we know who examined Geyer for his PhD, but I'm sure they were academically credible. The Whittington paper I linked to above was published in the Journal of Biomechanical Engineering, does that cut the muster? I should be interested in reading any comments made on this model by anyone who cares to read it and discuss it. Perhaps it is time to write to Dr Geyer personally? So that I may focus my questions to him, exactly which parts of his paper is it that you disagree with/ question, Kevin?

    BTW, the inverted pendulum model is really just an extreme example of the bipedal spring-mass model in which the springs (legs) stiffness are very, very high.
  27. Ok I´ve read most (not the PHD yet).

    If we consider the Triceps surea in discussions with Leg stiffness and energy return. It seems to me, to make more and more sense that a spring mass model fits well with walking and running.

    Ie the greater the compression in spring the greater the energy return. The energy return in the achilles tendon also increases in running when opposed to walking.
    Which may be an indication of different requirements in leg stiffness for the different activities ?

    Just thinking out load.
  28. Very nice reads especially the 1st- Intersting that the knee tendons don´t seem to return energy as well as the ankle- but the amount of flex of the knee will play a role in how much energy the Achilles is able to store and then return for required gait motion. All things being equal.

    Body is a pretty amazing machine.
  29. Simon:

    Or maybe the bipedal spring-mass model for walking is really just an extreme example of trying to fit the concept of leg stiffness into the more standardly accepted inverted pendulum model of walking?:drinks
  30. From my reading what does seem standardly accepted is that the inverted pendulum model does not provide accurate modelling of ground reaction forces and viz. centre of mass displacement observed in-vivo, whereas the bipedal spring mass model does :drinks
  31. For me, the energy exchange aspect (kinetic to potential energy and potential to kinetic energy) of the motions of the center of mass of the body makes the more standardly-accepted inverted pendulum seem a better model than does a spring mass model for walking. However, I can definitely see how adding stiff leg springs into the inverted pendulum model would make the model predict ground reaction forces better for walking.

    As you know, Simon, I've been writing about springs in the foot for at least the last decade so there is no problem on my part in accepting and assigning spring functions to the foot and lower extremity. However, these concepts must be used appropriately in order to not muddle the understanding of the biomechanics of the foot and lower extremity for those seeking to gain further clarity on the subject.:drinks
  32. Kevin while I can understand some of your words of caution is discussing new topics such as ZOOLS. Is it not worth looking at the Geyer paper and others on spring mass model in walking to see if the standardly-accepted model really does hold true.

    While it might "muddle" maybe this model may be the more accepted model in the future maybe not.

    If we just accepted the standard model then maybe we would be still only discussing the model of Root et al. So I would have though that looking into this in detail is a good thing ?

    I always find expressions hard in writing so just so your aware I´m asking this in a non aggressive manor, I´m just after an option.
  33. The key for me Kevin is that according to Geyer, the spring mass model provides a better prediction of both the energetics and the kinetics of walking than does the inverted pendulum model. This being true, it is a better model of human walking than the inverted pendulum model- can you resist this argument?

    I have written to Prof. Geyer on another related matter, if I get a reply, I shall ask him to comment on the energetics issue.

    I do not walk with rigid legs. To walk in the way suggested by the inverted pendulum model I would need to have bi-lateral above knee amputations replaced with "pirate" wooden peg legs. Hence, I question the validity of the inverted pendulum model.

    P.S. if we add
    we have a bipedal spring mass model for human walking which, as you say,
    Yeah, that's right. So, we are agreed then?
  34. Lets go back a step and see if we can work this through:

    How is the kinetic versus potential energy calculated for a human walking?

    How is the position of the the centre of mass (CoM) calculated for a human walking?

    How is the position of the CoM related to the kinetic and potential energy of the human walking?
  35. Simon:

    Here is the best review paper that I have seen comparing energetics of walking versus running (Novacheck, Tom F.: The biomechanics of running. Gait and Posture, 7:77-95, 1998). Also, R. McNeil Alexander has written books on these subjects. I have also attached one of his papers from 13 years ago which describes his inverted pendulum model with leg springs which makes total sense to me).

    The energy transfer of running and walking are 180 degrees out of phase with each other, so, to me, to use the same spring mass model to describe the energy transfer of both walking and running seems to ignore the fact that during the early stance phase of walking the center of mass (CoM) is rising and during the early support phase (i.e. stance phase) or running the CoM is lowering. Maybe we are talking about two different things here Simon?? I do have limited time now (preparing for my lectures in Italy) so if you or someone else could do a synopsis for me explaining this conundrum for me, then I would greatly appreciate it.

    Attached Files:

  36. What is the difference between "inverted pendulum model with leg springs" and the bipedal spring mass model? As I said earlier, the inverted pendulum model is the equivalent of the spring mass model with very high spring stiffness.
    It's not the same spring mass model, the walking model applies two springs in parallel and has periods of double support.
  37. Agreed. I think I am back on track now.:drinks

Share This Page