Bending stiffness in the 1st metatarsophalangeal joint

They were wearing the shoes. What is the extension of the MPJ's inside the shoe and of the shoe itself? They are calculating motion, but do not give a static position of the motion itself. It is not stated in the study Simon.

Energetics apparently is not either or our specialties! ;-)

Take care!

Bruce

 

Bruce, it doesn't say in the methods section that the markers used for kinematic analysis were attached to the shoe, it references to anatomical landmarks. Yes they were wearing shoes, as the majority of the developed civilisations do. If markers were attached to the shoes it is true we cannot really know what the joint angles were, however, given the reductions observed in the measured variable, I think it's fair to say that it is highly likely that the dorsiflexion angles did decrease. Lets face it, I've seen published papers were the authors measured changes in hip extension from 2d video footage using a goniometer pressed against the monitor screen! So I think this methodology is reasonable. A static reference is irrelevent here since we are comparing between the conditions. Further, static measures have repeatedly been shown not to be good predictors of dynamic function.

 

Hi Simon

As entertaining as it is I don’t have the stomach to join in a tag team wrestling round with you scary bastards over this issue, on second thoughts why not ………here I come . . . . . . ..

My questions are

Firstly the intro states

Reflective markers (1-cm diameter) were
placed on the toe, the head of the fifth metatarsal, the heel,
the lateral malleolus, the lateral epicondyle, the greater
trochanter, and the shoulder for kinematic data collection.

Forgive my ignorance but how do you accurately measure angular velocity of the metatarso-phalangeal joints without marking the joint centre and distal segment (my assumption is by “toe” the end of shoe is meant)?

I presume because the toes are fixed against ground this was calculated by measuring the angular velocity of the metatarsal segment relative to the ground. If this is true then plantarflexion of metatarso-phalangeal joints will not be detected during running because the rapid knee flexion during early swing will maintain metatarsal angle relative to ground. This might be more important in the jump since there was an unexplained increase in performance which may be attributable to unmeasured work output at metatarso-phalangeal joints.

I guess I am missing some fundamental point here . . . . . please help me with this.




Secondly

“Because no energy is generated at
this joint during stance, this energy must be either dissipated
and lost or returned at a time after take-off when it will not
have an influence on performance”.

It seems more likely that most of the energy would be returned outside of the measured joints .

I believe that during propulsive phase there will be eccentric contraction of metatarso-phalangeal joint plantarflexors and passive non contractile energy storage within plantar fascia.

Any disagreements there?

Now as the paper states this energy is lost to the stance phase lower limb but doesn’t speculate what happens to this energy which I think was Simon’s initial quandary?

So what did happen to that stored energy?

My guess is that during running it could have been transfered to contralateral hip effectively adding to acceleration of the late swing phase limb with increased pelvic forward rotation and stride length. No evidence for this pure conjecture.

What do you guys think of this notion?

If this is true then I question that reducing loss of energy at metatarso-phalangeal joint to ipsilateral limb is then actually reducing performance at least during running.

During jumping intuitively it seems to me that the increased performance could be attributed to efficient return of energy from the carbonfibre plate. Although the evidence is contrary to this if my notion of measurement error of angular velocity at metatarso-phalangeal joint is correct then this may explain this. Given the quality of work of these researchers this seems unlikely and you may already have trashed this idea.

Look forward to your response and hoping to learn something (diving out of the ring between the referees legs and peering behind the big guy with a large inverted pendulum in his hand)


Cheers


Martin

 

Martin, we don't need a physical marker on the joint centre as we can calculate the instantaneous centres of rotation from the trajectories of the toe and/ or metatarsal markers. This may be more accurate than sticking a "blob" on the joint itself especially since we know from the work of Shereff that the instantaneous centre of rotation will have varying spatial locations throughout its RoM due to the bones sliding, i.e. it isn't a pure hinge joint (Shereff M.J et al. Kinematics of the first metatarsophalangeal joint. J Bone Joint Surg Am. 1986;68:392-398). Hence, I'm highly confident that the authors here were able to measure angular velocity. The accuracy of this, like all measurements of this kind, is going to be influenced by marker displacement relative to the bones your trying to measure.

Not quite sure I understand what you are trying to say here, you talk about toes being fixed against the ground so hypothetically during stance phase you could take angular measurements relative to the ground. However, this highly unlikely to have been the technique employed given the motion analyses system being used here. Since the ground doesn't have a marker attached to it, it is more likely that the relationships were measured using the toe and metatarsal markers. The second point here suggesting that the authors could not measure plantarflexion is negated by my explanation above. Indeed, if you check figure 3 you'll see that the authors report negative, i.e. plantarflexion, values for the metatarsophalangeal joint. So I don't think you are correct in your assumption here Martin. Moreover, how is plantarflexion of the joint during swing relevant? How does this swing phase plantarflexion improve jump performance?

This is actually taken from an earlier paper by the same authors. If you go back to that paper they speculate that this could be into the shoe or other structures. Not sure you can say "more" likely though.

I think you need to explain more clearly how this energy is provided to the contra-lateral limb.

Now you've lost me Martin, the authors didn't say there was a reduced performance, so I'm not sure why you are questioning it??

I don't think you are correct in this assumption for reasons already outlined by myself and the authors of the paper.

 

Thanks Simon for your feedback

Simon says

Martin, we don't need a physical marker on the joint centre as we can calculate the instantaneous centres of rotation from the trajectories of the toe and/ or metatarsal markers. This may be more accurate than sticking a "blob" on the joint itself especially since we know from the work of Shereff that the instantaneous centre of rotation will have varying spatial locations throughout its RoM due to the bones sliding, i.e. it isn't a pure hinge joint (Shereff M.J et al. Kinematics of the first metatarsophalangeal joint. J Bone Joint Surg Am. 1986;68:392-398). Hence, I'm highly confident that the authors here were able to measure angular velocity. The accuracy of this, like all measurements of this kind, is going to be influenced by marker displacement relative to the bones your trying to measure.

Martin reply's

I think, because I have exclusively used 2D kinematic and plantar matrix force measurement to interpret gait my mind is not moving properly into the domain of 3D and power analysis. I need to go and study power and joint kinetics in more depth; clearly I am lacking some basic understanding of measurement principles.

Simon says

Not quite sure I understand what you are trying to say here, you talk about toes being fixed against the ground so hypothetically during stance phase you could take angular measurements relative to the ground. However, this highly unlikely to have been the technique employed given the motion analyses system being used here. Since the ground doesn't have a marker attached to it, it is more likely that the relationships were measured using the toe and metatarsal markers. The second point here suggesting that the authors could not measure plantarflexion is negated by my explanation above. Indeed, if you check figure 3 you'll see that the authors report negative, i.e. plantarflexion, values for the metatarsophalangeal joint. So I don't think you are correct in your assumption here Martin. Moreover, how is plantarflexion of the joint during swing relevant? How does this swing phase plantarflexion improve jump performance?

Martin reply's


Again I think confusion here stems from not understanding properly how the measurement system is deriving the data for calculations. My assumption about figure 3 was that the Y axis is measurement of metatarsal angle relative to the ground not relative to the phalanx, my rudimentary knowledge of power measurement is inadequate.

Simon says

I think you need to explain more clearly how this energy is provided to the contra-lateral limb.

Martin reply's


I thought that I would be able to do this. I started drawing out some free body diagrams to illustrate my “sense of how this might work” and got completely bogged down with a lack of really understanding this process beyond a single joint.

Similar issues have recently been discussed on another mailbase and coincidently Kevin Kirby had made the following recommendations which I shall follow up on before trying to contribute to this thread further and may be helpful to others like myself who are currently grappling with this tricky subject.

Is there anyone reading this thread who has been able to make a comfortable transition from creating within your mind an image derived from an instantaneous snapshot representing “kinematics and an appreciation of ground reaction force,joint torque and muscle action” to a fully fledged “notion of power and energy flow” other than the simple excursion of COM representing movement between kinetic and potential energy?

If so how did you approach this?

Here’s Kevin’s quote

In my reading on the subject, I have found the best reference for modelling in foot and lower extremity biomechanics comes from a chapter done by Benno Nigg in one of his latest biomechanics books (Nigg BM: "Modelling", In Biomechanics of the Musculo-skeletal System, 2nd Edition, (B.M. Nigg and W. Herzog, eds), John Wiley and Sons, New York, 1999, pp. 423-532). Nigg describes a model as being "an attempt to represent reality". In this wonderful and rather detailed chapter, Nigg lists an historical account of modelling including Leibnitz's suggestion in 1695 that conservation of mechanical energy for a particle could be modelled as a "live energy" (i.e. kinetic energy) and "dead energy" (i.e. potential energy), to the work of Gibbs in 1881 that developed the mathematics of vector analysis which is used to solve the vector equations that result from free body diagrams, and later on to the work of Elftman in 1938 that estimated internal forces within the lower extremity and energy changes during walking using a mechanical model to make these estimations. The chapter is very detailed and most of the chapter should be understandable to most clinicians, even those who don't have a knowledge of more advanced mathematics.

Regards Martin

 

The assumption is that the proximal segment is defined by the heel and fifth met head marker and the distal segment is defined as the fifth met head marker and the toe marker. You have to admit that the segments defined by these markers should at least correlate with 1st MPJ dorsiflexion.

A significant part of the energy could be lost into the muscle. If you think of landing from a jump and knee joint angle. When you are landing from a jump you have a kinetic energy from your downward velocity and mass. (KE = 1/2 mv^2) When you hit the ground your knees flex, with an extension moment. There is a flexion motion with an extension moment so power is lost. When you stop your downward movement your kinetic energy is zero. In a perfect spring all that energy would be stored as elastic energy in the spring. However, in a person most of that or all of that kinetic energy is lost as heat into the muscles. You could choose to land from the jump so that there is no rebound.

I would bet the same is true for the 1st MPJ. A significant amount of energy loss could be lost to heat in the plantar flexion muscles of the 1st MPJ. It does not necessarily get converted to elastic energy in the muscle or plantar fascia.

see above.

Unlikely. For energy to get transmitted to the opposite limb you would have seen a change in power at the other joints, which the article said did not happen. Joint power is the measure of energy transfer.

Any measruement error, from the experimental set up as I understand it, would be in the magnitude of motion or magnitude of velocity and not the direction of the motion. So there may be error in the magnitude of the energy loss, but there was energy loss with hallux dorsiflexion and the plantar flexion still happened after toe off when there is no ground to push against to provide the energy gain.

Entertaining discussion,

Eric

 

Martin:

Hey...Martin....you been "cross-reading" my JISCmail comments where I am trying to get the followers of tensegrity to appreciate the basics of modelling??

 

Yup, that’s the place Kevin, interesting serendipity.

As a generalisation I feel that most podiatric clinicians I know are rather clueless when it comes to a deep understanding lower extremity functional mechanics, I am afraid I have to include myself here.

Always time to remedy this, I hope to make some progress on this before I get too grey and bald


Cheers


Martin

 

Martin:

The problem isn't so much the clinicians who are clueless and know they are clueless, the real problem are those clinicians, teachers and professors within the podiatry colleges teaching biomechanics that are clueless......but think they are experts in biomechanics. Those are the ones I enjoy knocking off their self-erected pedestals the most.

By the way, Martin, from the few postings that I have read of yours so far, I think you are probably in the top 10% of podiatrists in your biomechanics knowledge. I know for myself, there is always much room for improvement in my knowledge.....the problem there is just not enough time in the day for all I want to learn.

 

Conscious incompetent, conscious competent, unconscious incompetent. The last of these being by far the most destructive and dangerous. The question is how does one know where one is upon the spectrum?

500 posts today- wow I feel old.

 

Kevin, thanks for your encouragement, I won’t ask you to substantiate your comment regarding the 10% at risk of denigrating your reputation or my self esteem.

Time is definitely a problem, my wife still makes disparaging remarks regarding my bedside reading pile being a little unbalanced of late (she is not referring to the position of it’s COM) and still doesn’t really feel comfortable with having he lower limb skeleton down the side of the bed, she has given up any expectation of it becoming a sex toy though!

Cheers

Martin

 

Simon said

"Conscious incompetent, conscious competent, unconscious incompetent. The last of these being by far the most destructive and dangerous. The question is how does one know where one is upon the spectrum?"

Martin Replied

Interesting thought.

Trite though it may sound, and said in the context of an less cynical ex Brit and now truly earnest North American, (much to the derision of my longer standing mates who have been seen to be gagging in their beer at any hint of my acquired earnestness), I have more recently tried to live by a notion which I understood from some Zen saying or other which encourages us to look through the eyes of a beginer - or "maintain a beginers mind".

This is not meant to discourage learning but rather, at all times, be open to any possibility (before you then reject it some might add?).

Perhaps that mantra might offer others some protection from ourselves?

ahh . . . . . there I go again


Cheers

Martin

 

I have had the pleasure of meeting many podiatrists from many countries during my 22 years of lecturing on biomechanics and sports medicine topics. Having an ability to speak in biomechancis terms that I understand puts you in the top 50% of podiatrists. Being able to share an intelligent discussion with Eric Fuller and Simon Spooner (both of whom I consider to be one of the most intelligent podiatric biomechanists in their respective countries) puts you in the top 20% of podiatrists. And taking your lower limb skeleton to bed with you definitely puts you in the top 10%.

 

Martin,

If you one day decide to use it in that capacity, make sure the articulations are fastened well. We lost a cuboid......

Name Withheld