Re: Query re: ankle joint stiffness
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Re: Query re: ankle joint stiffness
Hi Zahra,
Nice to chat with you again. Let me address each question below:
Originally posted by safaee View Post1 At some gait speeds ankle momentangle curve shows no hystersis loop and the enclosed area is nearly zero. Some researchers expalin this as ankle springlike behaviour in whcih no work is done (passive).
As ankle moment is the summation of spring and damping contributions, can we assume the slope of springbehaviour (M teta curve) as an ankle stifness and the moment as spring moment?
Originally posted by safaee View Post2 Can we simply assume the slope of damping momentangular velocity curve as damping coefficent ?
For an excellent introduction into identification analyses in the context on human joints, see the reference listed below. I highly recommend this paper and I believe it will help elucidate some of the differences between the analysis of a dynamic torqueangle curve and system identification.
Kearney, Robert E., and Ian W. Hunter. "System identification of human joint dynamics." Critical reviews in biomedical engineering 18.1 (1990): 55.
I hope this helps and thanks for your interest!
Elliott Rouse, PhD
Biomechatronics Group
MIT Media Lab
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Re: Query re: ankle joint stiffness
Originally posted by erouse19 View PostHi all,
Here is an article we published in IEEE TBME delineating the concepts of stiffness and quasistiffness. Hopefully this helps!
Rouse, E. J.; Gregg, R. D.; Hargrove, L. J.; Sensinger, J. W.; , "The Difference Between Stiffness and QuasiStiffness in the Context of Biomechanical Modeling," IEEE Transactions on Biomedical Engineering, vol.60, no.2, pp.562568, Feb. 2013
doi: 10.1109/TBME.2012.2230261
Cheers,
Elliott Rouse, PhD
Biomechatronics Group
MIT Media Lab
Thank you for the article. When I was reading that, faced 2 questions.
1 At some gait speeds ankle momentangle curve shows no hystersis loop and the enclosed area is nearly zero. Some researchers expalin this as ankle springlike behaviour in whcih no work is done (passive).
As ankle moment is the summation of spring and damping contributions, can we assume the slope of springbehaviour (M teta curve) as an ankle stifness and the moment as spring moment?
2 Can we simply assume the slope of damping momentangular velocity curve as damping coefficent ?
Zahra
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Re: Query re: ankle joint stiffness
Originally posted by erouse19 View PostHi all,
Here is an article we published in IEEE TBME delineating the concepts of stiffness and quasistiffness. Hopefully this helps!
Rouse, E. J.; Gregg, R. D.; Hargrove, L. J.; Sensinger, J. W.; , "The Difference Between Stiffness and QuasiStiffness in the Context of Biomechanical Modeling," IEEE Transactions on Biomedical Engineering, vol.60, no.2, pp.562568, Feb. 2013
doi: 10.1109/TBME.2012.2230261
Cheers,
Elliott Rouse, PhD
Biomechatronics Group
MIT Media Lab
Thanks for your latest contribution!
Leave a comment:

Re: Query re: ankle joint stiffness
Hi all,
Here is an article we published in IEEE TBME delineating the concepts of stiffness and quasistiffness. Hopefully this helps!
Rouse, E. J.; Gregg, R. D.; Hargrove, L. J.; Sensinger, J. W.; , "The Difference Between Stiffness and QuasiStiffness in the Context of Biomechanical Modeling," IEEE Transactions on Biomedical Engineering, vol.60, no.2, pp.562568, Feb. 2013
doi: 10.1109/TBME.2012.2230261
Cheers,
Elliott Rouse, PhD
Biomechatronics Group
MIT Media Lab
Leave a comment:

Re: Query re: ankle joint stiffness
Mark,
Thank you for the references.
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Re: Query re: ankle joint stiffness
Hi,
Here are two of my papers which tried to quantify the real stiffness around the ankle joint using a controlled release method:
de Zee, M & Voigt, M 2002, 'Assessment of functional series elastic stiffness of human dorsi flexors with fast controlled releases' Journal of Applied Physiology, vol 93, pp. 324329.
de Zee, M & Voigt, M 2001, 'Moment dependency of the series elastic stiffness in the human plantar flexors measured in vivo' Journal of Biomechanics, vol 34, pp. 13991406.
Those two papers were inspired by the work of At Hof:
A.L Hof In vivo measurement of the series elasticity release curve of human triceps surae muscle. J. Biomech., 31 (1998), pp. 793–800.
Greetings, Mark
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Re: Query re: ankle joint stiffness
Thank you Elliot, for answer and article.
Regards
Zahra
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Re: Query re: ankle joint stiffness
Hi Zahra,
Originally posted by safaee View Post...to design ankle foot prosthetics, there are some models including both ankle active and passive behavior. However, in these models ankle has been modeled as spring in some phases of gait such as early stance and spring with torque or power generator in late stance (active part)...
Perhaps I can delineate these concepts further with an example. Imagine a joint with a simple impedance controller:
T = k*(Theta  Theta_des)
where T is the joint torque, k is the stiffness, Theta is the joint angle, and Theta_des is the controller's desired joint angle. This is an underdetermined system, and for a given T and Theta relationship (i.e. quasistiffness), there are endless combinations of k and Theta_des that can replicate the TTheta relationship. However, the modification of k and Theta_des requires the input (or output) of energy; hence the discussion of powered vs. passive systems.
Originally posted by safaee View Post...what is the best index to calculate and quantify ankle energy storage property?...
Cheers,
Elliott Rouse
Biomedical Engineering
Northwestern University
Center for Bionic Medicine
Rehabilitation Institute of Chicago
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Re: Query re: ankle joint stiffness
Hi Elliott,
As a result of the difference in their definitions, in a powered system the concepts are completely decoupled.
This differs from the concept of quasistiffness, as its definition is completely independent of energy storagequasistiffness can be defined explicitly as the slope of the [ankle's] torqueangle relationship during a task, such as walking.
He and other researchers have been used this socalled "quasistiffness" as spring stiffness to model, design and develop ankle foot prosthetics.
So, if quasistiffness is independent form energy storage, what is the best index to calculate and quantify ankle energy storage property?
Thank for reply since I am doing a research exactly working with this term and this would shed light on what I'm doing next!
Regards
ZahraLast edited by Zahra Safaeepour; July 18th, 2012, 01:55 AM.
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Re: Query re: ankle joint stiffness
Hi Zahra,
Originally posted by safaee View Post...would you please explain more about " quasistiffness"? I could not understand what you explained with Latash work.
There is an area of overlap that may be causing confusion. When the joint is assumed to behave passively, as in sway studies, the slope of the torqueangle curve (quasistiffness) is synonymous with the energy storing nature of stiffness and the two concepts are equivalent. More accurately, in a passive system, the concept of quasistiffness is irrelevant, as the dynamics are completely described by the joint's stiffness. Hence, the application of quasistiffness is best suited for a discussion pertaining to passive dynamics from the analysis of a powered system; for example, the appropriate application in the design of passive prosthetic ankles by Hansen et al. [2004].
Originally posted by dsmith94 View Post...I think maybe we need a term that does not contain the word 'stiffness'.
Cheers,
Elliott Rouse
Biomedical Engineering
Northwestern University
Center for Bionic Medicine
Rehabilitation Institute of Chicago
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Re: Query re: ankle joint stiffness
Originally posted by erouse19 View Post... quasistiffness is not necessarily a stiffness at all. The aforementioned Latash & Zatsiorsky [1993] paper distinguishes between these concepts by the storage of potential energythe quasistiffness does not store energy and cannot therefore be considered a 'stiffness.'
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Re: Query re: ankle joint stiffness
Hi
Thank you for explanation. It means as ankle behaves actively for example by the concentic contraction of muscles , so the term of stiffness would not be correct here but "quasistiffness" is approprate?
So, would you please explain more about " quasistiffness"? I could not understand what you explained with Latash work.
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Re: Query re: ankle joint stiffness
Hi Drew,
Originally posted by dsmith94 View PostI am not sure I understand the whole passive vs active issue, but perhaps it would be clearer (or possibly easier) to use the terms "passive stiffness" and "active stiffness" rather than stiffness and quasistiffness?
Thus, the quasistiffness is not necessarily a stiffness at all. The aforementioned Latash & Zatsiorsky [1993] paper distinguishes between these concepts by the storage of potential energythe quasistiffness does not store energy and cannot therefore be considered a 'stiffness.'
Perhaps an example can help me be clear: Consider an inverted pendulum with a spring at the base with a stiffness greater than the small angle destabilizing torque relationship (i.e. the pendulum will remain inverted, even if disturbed slightly). Now, if the pendulum is perturbed, the torqueangle relationship will always reflect the stiffness of the spring. This is a passive system and this behavior is assumed during sway estimations of stiffness during quiet standing.
Now consider the same pendulum, but with a motor at the base, rather than a spring. Imagine the pendulum angle is being driven by the motor. The only way to determine the "stiffness" of the motor controller would be to interact with, or perturb, the pendulum. Furthermore, the specific torqueangle relationship no longer reflects the stiffness dynamics, unless the torqueangle information is in response to a perturbation. In automation applications, it's common to have a very high stiffness to preserve position fidelitybut these systems still have torqueangle relationships defined by their tasks that do not reflect the stiffness of their control systems, whether the stiffness values are high or low.
I hope this is more clear! Thanks and please let me know your thoughts.
Elliott Rouse
Biomedical Engineering
Northwestern University
Center for Bionic Medicine
Rehabilitation Institute of Chicago
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Re: Query re: ankle joint stiffness
Originally posted by safaee View PostHi
What about ''viscoelastic stiffness" ? Since this quantity differes with speed?
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