Leg Stiffness

No worries Simon.

The bit in red has been a if not the biggest stumbling block for me.

Say we take plantar fasciitis in a decreased leg stiffness pt. I beleive to have the greatest change in kinematics a harder device will have more effect, but the hardness of the device may lead to a further decrease in leg stiffness.

 

Kinematics at which joints? While the greater stiffness of the device may lead to a further decrease in leg stiffness, the shape of the device may lead to an increase in leg stiffness- understand?

 

I think so.

It come down to internal-external moments.

The hardness of the device may lead to a CNS reponse which will cause muscle function change - an internal moment

By the shape of the device will have a direct mechanical effect on the joint - an external moment.

if the external moment is stronger that the internal we will have a change in joint kinematics.

So if looking at the knee.

hard device CNS response. increase knee flexion-internal rotation of tibia-stj pronation

hard device (medial skive) increase in external moment supination moment-external tibia rotation-external extension moment at knee.


Thats what I´m thinking-

 

Sounds good to me.

 

I came this paper this morning in my travels. I don´t remember it being posted up before.

 

@ Mike: I have been trying to do more reading on stiffness over the weekend and thought you may like a copy of these articles I've attached (if you don't have them already).

@ Simon: I can't seem to find much in the way of literature on foot orthoses stiffness - got a starter for 10 for me?

 

Not really, Ian. You could look for studies where they have compared hard and soft materials, but beware that the orthosis geometry should be the same. When I was doing the finite element work on foot orthoses a couple of years ago- I found very little. Which is why I did the FEA stuff! We've talked about it before, but we need a standardised approach to measuring orthoses stiffness. Kevin suggested a protocol for this somewhere on here.

 

Ian and others heres a couple more for your collection.

 

Here you go fellas - all this talk of the leg being like a spring of variable stiffness and some dude just goes and bangs a spring in a shoe: http://www.zcoil.com/index.php

Discuss...

 

Nothing new. As McMahon knew the key is matching the spring stiffness with the leg stiffness- read McMahon's patent.

 

..What are your thoughts on it Ian ?

Heres what I came up with.

The spring may help with energy return in propulsion the shoe may take away from the use of the triceps sure in the spring/catapult effect, which maybe good, maybe bad.

It should also mean a change in the leg stiffness, same in shoes. The softer the shoe the stiffer the leg in relation to leg stiffness.

There maybe some stability issues which may effect leg stiffness as well, with changes in the tibia position in relation to the knee which maybe effect the bodies ability to regulate leg stiffness.

 

In "Foot orthotics affect lower extremity kinematics and kinetics during running" , Anne Mundermann and collab. it was used a compliant device [control insert -EVA-shore C: 50-55 ] and a stiff device posted and molded [Polypropylene shell]. There was no indication related to the leg stiffness : 21 volunteers - range of motion of the joints and strength and flexibility of the muscles of the lower extremities measured manually were required to lie within normal values.In conclusion: posting and molding of foot orthotics did affect lower extremity kinematics and kinetics

Could we deduce [suppose] from fig. 2, 3 and 4 [the kinematics results for every subject] which of the subject has a greater leg stiffness and which one a lower leg stiffness ? [ex : why subject no 18. has an increase of maximum tibia rotation ? -fig.3]
It is the leg stiffness the cause of "extremely different" results [ex. subjects no 18 and no 9] ?


Respectfully,

Daniel

 

Mike,

My initial thoughts were similar to yours regarding these shoes changing the leg stiffness - but give me 10 mins to eat my sandwich and read the McMahon patent Simon just uploaded...

 

From what I can gather after scanning the patent, McMahon proposed a shoe which was individually "tuned" to its specific wearer - given the discussion so far on this thread it makes sense how this could be a very good thing.

However on the Z-coil website it says they can make 'adjustments' but it does not sound as if they are talking the same language as McMahon. They also say that studies have shown the footwear provides 50% more cushioning than conventional shoes. This increase in surface compliance would theoretically lead to a CNS controlled increase in leg stiffness - and for some could move them outside of the ZOOLS and actually cause pathology perhaps?

Correct me if I am on the wrong train of thought here...

 

It could be if the ground remains constant, Like that paper where they adjusted the running track stiffness. But if the person wears the shoes on different ground surfaces- grass and concert it would need to be tuned for each surface.


Edit: Ian being a idot sorry . If the shoe can be tuned to make the leg function in the middle of the it´s ZOOLS on a middle stiffness ground , then when the ground changes to harder or softer the bodies CNS should have a greater ability to regulate it´s leg stiffness. Sorry...

I think thats the correct train

 

From the gender differences paper Ian posted up- "therefore, the females continued to demonstrate less leg stiffness"

A couple of things "spring" to mind (couldn't help that one), the leg stiffness of females may well vary with their menstrual cycle given Simon Bartolds research. Running shoes for females should probably be stiffer than those for males; I'm sure I've seen marketing which suggests the opposite.

Question: are stress fractures of the lower limb more common in males or females?

Answer:
"In particular, estimates of stress fracture rates of 5-12% have been reported among women undergoing various entry-level military training programs, rates that are about twice as high as those reported for men undergoing the same training.4,16"
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA452677&Location=U2&doc=GetTRDoc.pdf

The stiffer legs of males observed in the hopping study should make them more susceptible to stress fractures if the theory of stiffer leg = bone injury, but this is not held out here. = Doh. I suppose we could argue that the shoes are too soft for the women, therefore the CNS mediates an increase in their leg stiffness, gets it wrong makes 'em too stiff = stress fracture. That's it, it's all down to the shoes ;-)

 

I assume that Calcium levels play a role it this as well. Army high training levels, etc. maybe the Calc levels are lower in Army females compaired to the normal population ?

 

Seems to pertain to cortical thickness... http://www.ais.up.ac.za/med/sport/militaryrecruits.pdf

 

Maybe the mean leg stiffness for women and men should not be compaired.

Say out 100 men the mean leg stiffness is X

100 women the mean leg stiffness is X-Y and we say that women have decreased leg stiffness, but maybe we should compair males-males and females-females .

So maybe the stress fracture in the females in the army occured in the group of increased leg stiffness when compaired to other females.

Seems a thin arguement now I´ve written it down but will post see what othes think.

 

Mike, we are of course extrapolating between different studies. Do females really have stiffer legs? Does having stiffer legs really = bony injury? Do females really have greater incidence of stress fractures of the lower limb than males?

 

A wafer thin arguement....The meaning of life- the autumn years

 

Females also generally have greater muscle fatigue resistance than males http://escholarship.umassmed.edu/cgi/viewcontent.cgi?article=1076&context=lib_articles

We need some general population stats on stress fractures incidence, but my gut feeling after a couple of decades of seeing patients is that I've seen more in women than in men.

 

Only did a quick glance through the recent literature (before Flash Forward starts on TV) but seems your gut was on the money - women certainly seem to be generally considered much higher risk. Not found and hardcore incidence stats yet

 

That´s not so good, the mud was clearing, it was all starting to make sense. Something to consider tomorrow when I should be doing something at work.

 

Somebody, somewhere is wrong, but not us gentlemen. We are just reading the research and trying to make sense of it.

Either, bone injury is not more frequently associated with stiffer legs- Irene Davis?

Or, women don't generally have stiffer legs than males?

Or, we missing something?

 

Here another paper women win the stress fracture more common award.

this is taken from the sex section:

So maybe the led is less stiff in women but fact the women get amenorrha which maybe more likely to occur due to training loads indicates that the stats in higher trained populations have an x factor or big blue elephant in the room ?

So women maybe have a decreased leg stiffness when compaired to men, just not reduced enough if the training loads disrupt the menstrual cycle.

 

This one says that if you normalise data for body mass women don't have less stiff legs than males
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1624931/

This one shows gender differences disappear in maximal speed hoping.
http://www.jssm.org/vol8/n2/15/v8n2-15abst.php

See also:
http://www.ncbi.nlm.nih.gov/pubmed/...roller.PPMCArticlePage.PPMCPubmedRA&linkpos=1

 

Ok I did what I do best in these situations I ask questions. Not really sure if it´s the done thing but got a very nice response from Irene Davis. She now also knows we are having the discussion so maybe she might pop over, we will see.

I wrote this..

and Irene responded with this and said it was ok to post it here.

Irenes reply

 

Heres the abstract Irene mentions in her response anyone got access ?

 

Thanks for that Mike - I've attached it for us

 

In my clinical experience, as far as stress fractures are concerned, females seem to be more likely to develop these injuries in the tibia and metatarsals. My guess is that due to the lower bone density and more narrow bones, females' bones bend more under eccentric load than do males' tibias and metatarsals. The bending moments that result from these eccentric loading forces increases the magnitude of bone bending and probably increase rate of fatigue fracture in females compared to males.

 

Simon:

Not quite sure I understand your question. Do you mean sagittal plane stiffness or frontal plane stiffness of lower extremity, or do you mean isolated stiffness of tibia or metatarsal? For those of us reading yours and Michael's lengthy discussion, I think that if you first defined the plane of stiffness of the foot and lower extremity you are talking about, and which lower extremity components you are talking about, then it would be more educational for those struggling to follow your discussion.:drinks

 

Touche, Kevin. In this discussion we have predominantly focused upon stiffness of the lower limb as a whole.The literature reports this as leg stiffness, although when I went to school the term "leg" was reserved to describe the segment of the limb below the knee. Regardless, we have been using the currently accepted terminology employed within the published biomechanics literature, that of leg stiffness to refer to the sagittal plane stiffness of the entire lower limb. Good point, well made, thanks Kevin.:drinks

So, in relation to my question to you: sagittal plane stiffness, entire lower limb, just as described in all of the papers we've posted up within this thread- like you didn't know that already :butcher:

If you are struggling to follow the discussion, please feel free to ask questions and if we can, we'll try to answer them and to clarify any points of confusion :drinks Although, in speaking only for myself, I have to say much of what we are discussing is new to me too.

Inman suggested that during walking the frontal plane displacement of the COM was either a "U" or a "lazy figure 8 on it's side", how does the centre of mass displace in the frontal plane during running? I love you and hate you sometimes at the same time Kirby. Help me out here...