Plantar pressures during gait

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Hi All, could anyone send me in the right direction.

I am looking for the standard %, for the amount of pressure during normal gait???

for example what percentage at heel strike, midstance and toe off.

thanks very much

scott

 

Single stance timing sequence is often quoted as 20% (heelstrike), 60% (mid-stance) and 20% (toe-off).

I've never been able to find a good and reliable reference for these values.
Anyone help on that one?

Regards,
davidh

 

trying to work out percentage of force/load weight on the 1st ray through a single stance.

 

tissue stress

would people agree that the tissue stress acting on a rigid 1st ray would be compression and shearing.

 

Given that there is such a huge subject specific variability, there is no good data that I use on this (eg the % will depend on speed of walking/running) . What are you wanting this information for - maybe can give a better answer.

 

What Craig said.

 

undertaking a case study on tissue stress.
i have limited bio knowhow.

subject- pes cavus foot,concentrating on 1st ray callus formation.

i dont not have access to plantar pressure measurement systems.

i am trying to work out stress levels on the 1st ray-

would i be right in thinking stress= patients weight over the width of the callus area.

how do i measure the strain levels. (how do i measure the stretch in the 1st ray during weight bearing???)

any help would be great, as i am a bit losted at the moment!!

cheers scott

 

Both us:

and Cavanagh's group:

came up with regression equations to predict pressure under the first met head (and other parts of the foot).....suggest you check them out.

 

thank you very much

 

Scott:

If you are speaking of plantar pressure, you need to be a little bit more specific since the medial arch of the plantar foot has no plantar pressure in a high arched foot while the plantar calcaneus has quite a bit of plantar pressure in this same foot. Do you mean plantar pressure or plantar force? These are two very different things.

 

Dear Scott

I think you'll find (without looking up ref's)
(ok ref= Timing of Peak Plantar pressure During the Stance Phase of Walking
A Study of Patients with Diabetes Mellitus andTransmetatarsal Amputation
VALERIE E. KELLY, MS, PT*MICHAEL J. MUELLER, PhD, PT†
DAVID R. SINACORE, PhD, PT‡)
that in the usual gait max f/foot GRF comes at abot 65/70% of gait stance cycle and max f/f pressure comes at 80%. The max force coming at the start of push off as the CoM accelerates and the max pressure is later because the surface area of plantar foot contact reduces relatively faster than the decrease in force.
The GRF value at 80% of stance gait phase is about 85% of b/w and the pressure under a certain area of interest would be the force / area and conversely the force would be the area x the pressure.

Good luck working out stress and strain in the 1st ray thats quite a task
I tried to copy or type a table here from the above ref but it won't format properly when posted but you might get the idea.
Cheers Dave Smith

Table 2. Gait Characteristics

Diabetic Group

Variable TMA Side Contralateral Side Control Group F Ratio P Value
% of stance of peak plantar pressure 79.8 ± 6.6 80.1 ± 4.1 80.8 ± 4.6 0.11 .90
(65.9–86.5) (70.9–87.7) (71.5–88.5)
Peak plantar pressure (kPa) 344.9 ± 224.4 296.9 ± 117.2 334.0 ± 129.3 0.28 .76
(137.7–850.0) (154.3–520.7) (134.7–610.7)
% of stance of peak force 66.2 ± 5.7 66.8 ± 7.2 72.5 ± 6.6 3.44 .04a
(53.1–73.3) (56.4–77.0) (59.5–79.6)
Peak force (N) 834.1 ± 140.3 867.4 ± 162.2 866.2 ± 134.7 0.20 .82
(600.7–1030.0) (599.0–1024.7) (692.0–1130.0)
Area in contact at peak 64.8 ± 18.0 68.1 ± 27.6 63.8 ± 26.7 0.10 .91
plantar pressure cm^2 (39.4–100.0) (15.3–123.7) (22.1–127.0)
Walking speed (m/min) 50.6 ± 18.4 75 ± 9.2 4.08b .001a
(20.8–81.8) (53.6–89.2)

Abbreviation: TMA, transmetatarsal amputation. Note: Plus-minus values are mean ± SD (range).
a Significant difference between groups (P < .05). b Result of Student’s t -test.

 

Hi Kevin, very new to biomechanics, limited experience.

i am looking at plantar force/load of the 1st met.

am i right in thinking-

patient weight devided by the callus width=stress

how do i measure the strain value?????


thanks david i will down load ref

cheers guys

 

Hi david, whats the journal name, don't seem to be able to find it?

thanks again
scott

 

No problem, Scott. I enjoy teaching people when they express a desire to learn.

I don't really know what you are trying to accomplish by trying to predict stress by using body weight and callus width, but you could use the value of plantar pressure under the first metatarsal head (as measured by a pressure mat or a pressure insole) as a guide to compression stress at the plantar skin of the first metatarsal head.

Why do you need to measure strain? The only way I know how to measure strain is to dissect the anatomical part out of the body and load it in tension or compression to see how much it elongates or compresses relative to its original length.

Maybe if you tell me what you really are trying to do then I can help you further.

 

Dear Scott

Journal ref = (J Am Podiatr Med Assoc 90(1): 18-23, 2000)


I’m not sure exactly what values you are trying to find but….
To find strain value in 1st ray you would need to know the youngs modulous and or Poissons ratio of certain tissues of interest EG Bone. Or, as Kevin states, directly measure the strain by attaching extensiometers to the bone = difficult and not user friendly for the subject.
A problem with biological tissue is that even knowing some value of stress V’s strain is not to helpful as, unlike construction materials like steel which have a linear / uniform elasticity up to their limit of linearity/ elastic limit, biological tissue has a non linear value of elasticity. Plus lots of others areas such as visco elastic properties which change output values with loading times and repetition and in vitro V’s in vivo and potential errors like hysterisis, creep and drift.
If you wanted to find moments and compression forces due to GRF on a certain area of interest in the 1st ray then this may be a realistic goal. Finding moments and compression forces using the GRF under the 1st met based of surface area of contact and pressure measurements using say a pressure mat could be fairly accurate if you were to make clear assumptions about forces applied by other tissues for the purposes of your analysis.

If you want to find the strain/stress in the tissues plantar to the met heads you would need to measure the change in tissue thickness in relation to pressure applied.
Good luck with this difficult area you are exploring.

Some more refs which may be helpful

Discrete Plantar Pressure Measurement System - James Solberg

Plantar Pressure and Sole Thickness of the Forefoot Rene´ E. Weijers, et al foot & ankle int.

KINETIC ANALYSIS OF THE LOWER LIMBS DURING WALKING: WHAT INFORMATION CAN BE GAINED FROM A THREE-DIMENSIONAL MODEL?
Janice J. Eng and David A. Winter. Dept of Kinesiology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada


Book- Structural and Stress Analysis By: Megson, T.H.G. © 1996 Elsevier isbn 0-340-63196-1


Graham Payne has reviewed many papers on plantar pressure Biomechanics of the Foot in Diabetes Mellitus Some Theoretical Considerations CRAIG B. PAYNE, Japma 1998
Lots of good refs on plantar pressure pathological and normal there.

Cheers Dave Smith

 

first of all thank you all very much for the help.

i have to present a case study of a pes cavus foot type with a rigid plantar flexed 1st ray.

don't have access to any plantar pressure measurement systems other than impression sheets!

i am focusing on the stress area of the 1st ray!

as i said very new to biomechanics and don't really know what i am doing.

i thought it would be good to present the stress and strain levels of the 1st ray, I thought if i had the stress and strain levels i would be able to report on elastic levels and then the plastic levels of callus formation???

Am I right in thinking the callus is formed in the plastic stage????

don't know if i am making sense( not even to myself never mine you lot!!!!)

cheers scott

 

Scott

Are you getting slighlty mixed up with terminology perhaps.
In engineering terms stress is (force /surface area) within a material (the same units as pressure) So that a large force applied to a steel bar with a small cross sectional area has a high stress value and the same force applied to a steel bar with a large cross sectional area has a relatively low stress value. Strain is the amount of deformation (change in length) caused by that stress. Basically this is the basis of Youngs modulus. Poissons ratio is the relationship between the change in length Vs the change in width (the change in cross sectional area).
Construction materials eg Steel often have a direct relationship between stress and strain which can be characterised by a straight line graph of stress V's strain which is linear both in loading and unloading, this is the elastic range. There is a limit to this linearity when the the strain curve does not return to zero on off loading this is the plastic range ie where the material is permanantly stretched.
All materials have these properties but not always characterised in a linear way and biological tissues have very non linear properties.

The stress under the 1st met that you are refering to is possibly better called pressure, friction and shear forces and is the plastic deformation you are refering to possibly the physiological change in properties of keratinised cells that have undergone extended pressure and friction making them plastic in nature and tend to stick to underlying keratinased cells, instead of sloughing off, leading to hyperkeratosis and hyperkeratotic lesions ( callus and corns).
I don't know of any refs for the relationship of time pressure etc and callus formation.
I see feet with plantarflexed 1st met and stiff 1st ray that have no callus there or 5th met head as might be expected so there may be no fixed or linear relationship of force to hyperkeratosis. I would have thought tho that there would be some co relation between gait stance phase pressure/force time curves and callus formation Maybe you will be able to find and review some research in this area.


Cheers Dave Smith

 

hi david, i think thats the problem, i am confused by terminology!
pressure/stress?

i think i need to forget about callus formation and focus on stress levels.

cheers scott

 

To expand a little on David's posting, all biological tissues are viscoelastic in that they do not behave like inert materials such as a steel bar, a polypropylene rope or a sheet of glass. What this means is that, due to their fluid component, the stress-strain curve http://darkwing.uoregon.edu/~struct/courseware/461/461_lectures/461_lecture24/461_lecture24.html
of biological tissues will change depending on the strain rate (i.e. is the bone, ligament, tendon, muscle or cartilage being compressed or elongated at a fast rate or slow rate). With increasing strain rate, an increased slope of the stress-strain curve will result and, thus, increase the stiffness of the material. Slower strain rates will decrease the slope of the stress-strain curve and will decrease the stiffness of the material.

Viscoelastic tissues also exhibit a mechanical characteristic in which they will lose energy to heat during deformation so that when they are compressed or elongated, they will not return the same amount of energy as the energy put into them in order to deform them. This is in contrast to a purely elastic material (ideal) that will load and unload along the same straight line on the stress-strain curve. The term hysteresis refers to the energy loss that happens to a viscoelastic tissue (or other material) when it is loaded and deformed and then unloaded and released back to its original length/shape.

Viscoelastic tissues also exhibit two time-dependent phenomena called creep response and stress-relaxation response. In creep response, a tissue subjected to a loading force will tend to deform more rapidly to a certain contant force level but will then tend to deform more slowly as the force is continued over a period of time. This is the probable physiological reason for the therapeutic efficacy of plantar fasciitis night-splints in relieving the post-static dyskinesia of plantar fasciitis.

The stress-relaxation response occurs when a tissue is subjected to a deformation and then held at that deformation level (i.e. held at a certain length). The material will tend to have a decrease in stress over time, or a "relaxation", as the material is held at a certain length.

Engineers design the structural sizes and types of materials used within a building or bridge so that they will operate within their elastic range on the stress-strain curve. In this way, engiineers can be assured that the material is not subjected to such large magnitudes of stress that could cause disastrous plastic deformation and/or failure under the loading forces that the structural material is likely to be subjected to.

In the same way, the structural components of the body such as bone, ligament, tendon, muscle and cartilage, are meant to function within their elastic range on the stress-strain curve. In this way, injury of that tissue is less likely to occur. When too much stress occurs in one of these structural components of the body (such as in the increased tensile stress within the posterior tibial tendon with posterior tibial dysfunction), then plastic deformation, partial or complete failure of that tissue may occur. So, when we make orthoses and recommend shoes or recommend stretching or strengthening exercises for our patients, we are basically trying to bring the tissues of the body back to operating within their elastic range on their stress-strain curve to prevent plastic deformation or tearing/fracture of the biological tissue and to ensure decreased pain and more rapid healing to the painful musculoskeletal pathology that is present within the patient.

 

thanks for the advice

cheers scott