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Physiological cost of foot orthotics

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Simon Spooner, Jan 25, 2008.

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    Following on from our discussion here: http://www.podiatry-arena.com/podiatry-forum/showpost.php?p=31227&postcount=65

    To make a start in exploring the effects of foot orthosis design parameters, I propose a simple experiment which I hope some of you will complete and let us know the results. It does not require any specialist equipment (a treadmill enables you to easily standardize the walking speed and set distance, but it is not essential you could do this with a stop watch and a tape measure! A heart rate monitor makes life even easier, but if you can take a pulse, your in).

    Take two pairs of pre-form foot orthoses that differ only in stiffness (durometer), for example the Vasyli professional green and the Vasyli professional red, Talar made blue and Talar made black etc..

    The Physiologic Cost Index of walking (PCI) is a measure of the energy cost of walking. It can be used to evaluate "the global physiological cost of walking".

    Background: Reduction in surface stiffness has been shown to reduce metabolic cost in running. "Flat-feet" have been shown to increase metabolic cost in walking.

    Objective: Measure PCI in the same subject wearing the two different pairs of orthoses.


    (1) heart rate at rest in beats per minute

    (2) heart rate when walking in beats per minute

    (3) walking speed in meters per minute

    PCI = ((heart rate when walking: measure this at the same distance for both conditions, i.e., soft and hard orthoses) - (heart rate at rest)) / (walking speed)


    • A low PCI indicates an energy-efficient gait.

    Have fun, let us know the type of orthoses used, some details of the subject- gender, age etc. Obviously standardize the shoes/ clothing. Let the subject rest between trials. Try randomizing which orthoses the subjects wear first with the flip of a coin. Report your findings here. Anyone want to tighten the methodology? Feel free.
    Last edited: Jan 25, 2008
  2. Craig Payne

    Craig Payne Moderator

    Re: Project No.1 physiological cost of foot orthotics

    I have long considered something like this as the outcome measure to determine the efficiency of gait with different orthotic design parameters, based on the assumption that the orthotic is "right" if gait is made more efficient (also assuming that an improvement in efficiency is also related to changes in outcomes).

    The only problem that I have is that the variability and sensitivity of the measure (eg MaxVO2; etc) are not sensitive enough to pick up the changes. It could well be that the PCI is also not sensitive enough (I do not know enough about it).
  3. Admin2

    Admin2 Administrator Staff Member

    Last edited: Jan 26, 2008
  4. Re: Project No.1 physiological cost of foot orthotics

    Simon and Craig:

    Now you are entering my undergraduate field of interest: exercise physiology. Heart rate would not be a very good indicator of level of exertion of a subject since heart rate can be affected by many factors other than the metabolic cost of their activity. For example, heart rate may be affected by level of hydration, level of excitation of CNS, certain drugs and general mood of an individual. Even though heart rate can estimate work load in some cases, you probably won't find any research projects being conducted by exercise physiologists using heart rate as an indicator for metabolic cost of an exercise since it just isn't accurate enough.

    Instead, the best way to measure the metabolic cost of a certain activity, and also the best way to measure how a certain intervention (i.e. a foot orthosis) affects the metabolic cost of an activity is by doing a steady state oxygen uptake study (not VO2 max-which is more a measure of the maximal oxygen uptake ability of the subject for that specific exercise). In a steady-state oxygen uptake study, the subject may be asked to walk on a treadmill at a certain pace while wearing a mouthpiece that measures the expired concentrations of oxygen and carbon dioxide to determine how much oxygen they are extracting and how much carbon dioxide they are exhaling when compared to the inspired atmosphere. These systems will then give a very accurate measurement of the metabolic cost of the exercise, as long as the intensity of exercise being performed is well below the anaerobic threshold of the individual.

    Doing a steady-state oxygen uptake study with and without orthoses would give you a much more realistic representation of whether the orthosis actually makes the subject more metabolically efficient while exercising or not. My guess is that foot orthoses will only increase metabolic efficiency in select subjects where there has been a significant increase in stride efficiency with the foot orthoses.

    Hope this helps.
  5. Re: Project No.1 physiological cost of foot orthotics

    I agree with Kevin about using a gas meter- we did this back in about '92 when we investigated cobra pads versus reverse cobra pads. But most people don't have access to a gas meter or Douglas bag etc. I selected PCI because anyone can do it. I suspect you could be right about the sensitivity though. But we could potentially discover that the durometer of the orthoses does influence PCI enough to detect changes. If we find no differences in the PCI between conditions then one of the conclusions we may draw is that PCI is not sensitive enough to pick up the changes or that the durometer of the orthoses doesn't influence PCI signifcantly enough to detect any change. There are number of studies people can do here that would be helpful, not least a simple variability study of the PCI. I think this is worthwhile in it's own right, if it stimulates people to get involved in research.

    Arch Phys Med Rehabil. 2005 Oct;86(10):2041-6. Links
    The reliability and validity of the physiological cost index in healthy subjects while walking on 2 different tracks.

    Graham RC, Smith NM, White CM.
    Physiotherapy Division, King's College London, London, England.
    OBJECTIVE: To investigate the reliability and validity of the Physiological Cost Index (PCI) scores, as a measure of energy expenditure, when healthy subjects walk on 2 different tracks (20-m and 12-m figure eight tracks). DESIGN: Intra- and interrater reliability and construct validity. SETTING: Physiotherapy division of a university in London, UK. PARTICIPANTS: Forty healthy subjects (15 men, 25 women; mean age +/- standard deviation, 34.5+/-12.6 y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Heart rate (in beats/min) and speed (in m/min) were used to calculate the PCI (in beats/m). Rate of oxygen consumption (VO2, in mL x kg(-1) x min(-1)) and oxygen cost (EO2, in mL x kg(-1) x m(-1)) were used as criterion estimates of energy cost EO2. Pearson correlation coefficients between the PCI, components of the PCI, EO2, and VO2 were used to quantify validity. Intrarater reliability was assessed in all participants and interrater reliability was assessed on a subset of 13 subjects using intraclass correlation coefficients and Bland-Altman plots. RESULTS: Intrarater (r=.73, r=.79) and interrater (r=.62, r=.66) reliability were acceptable between PCI scores from 20-m and 12-m tracks, respectively. Correlations between VO2 and EO2 with PCI were weak. PCI scores from the 20-m track were significantly lower than those on the 12-m track (P=.002). Subjects walked significantly faster on the 20-m track (P<.001). Results suggest a large difference in PCI scores would be necessary to indicate a "true" alteration in performance (52% for 20-m track, 43.4% for the 12-m track). CONCLUSIONS: The PCI is reliable but not valid as a measure of the energy cost of walking in healthy subjects, on either track. The 20-m track is recommended for clinical use because it enables subjects to walk at a faster pace.

    Perhaps this is an alternative to PCI?

    Arch Phys Med Rehabil. 2002 Sep;83(9):1266-73.
    A new method of using heart rate to represent energy expenditure: the Total Heart Beat Index.

    Hood VL, Granat MH, Maxwell DJ, Hasler JP.
    Bioengineering Unit, University of Strathclyde, Glasgow, Scotland.
    OBJECTIVES: To develop a new method of representing energy expenditure using heart rate and to determine its reproducibility compared with the criterion standard of oxygen cost. DESIGN: Repeated-measures design. SETTING: University gait analysis laboratory and gymnasium at 2 spinal injury units. PARTICIPANTS: Twenty unimpaired adults and 17 subjects with spinal cord injury (SCI). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Heart rate and oxygen consumption were measured on 20 unimpaired adults walking under controlled steady-state and nonsteady-state conditions. New methods of estimating energy expenditure by using heart rate were compared with oxygen consumption, oxygen cost, and Physiological Cost Index (PCI). Nine subjects with SCI, walking with and without functional electric stimulation, were assessed to determine use of these new measures with this group. Sensitivity to change of the new measurement techniques was investigated in 10 subjects with SCI, comparing wheelchair pushing to walking. RESULTS: The Total Heart Beat Index (THBI) was developed as a new index, calculated by dividing the total heartbeats during activity by distance traveled. High repeatability was found under steady-state and nonsteady-state conditions (intraclass correlation coefficients,.893-.995). Sensitivity to change in activity level was also shown. CONCLUSIONS: The THBI is a simple parameter to calculate from continuous heart rate data and provides a reproducible alternative to gas analysis and the PCI.

    Can you think of any other simple experiments that don't require sophisticated equipment, that would enable the Podiatry Arena community to explore orthoses design parameters in a series of case studies? I thought about vertical jump height, but you would need a video camera. Spatial gait parameters such as step length could be investigated using black paper and talc????
    Last edited: Jan 26, 2008
  6. Craig Payne

    Craig Payne Moderator

    Re: Project No.1 physiological cost of foot orthotics

    Not exactly simple, but my two honours students this year will be recruiting runners with and with a recent history of overuse injury and also with and without foot orthoses (we also going to throw in a couple of running shoe conditions as well). The parameters of interest are the slope of the curve for heel off loading and the timing to the second peak (as % of the gait cycle) from in-shoe pressure measuring.

    The hypothesis is that a more efficient gait (ie maybe the non-injury group and orthotic wearers) will have a steeper 'down' slope to the force time curve under the heel (ie a more rapid shift of weight from the heel to the forefoot) and the second f/t curve peak occurs sooner (ie a more rapid loading of the forefoot).

    Stretching the hypothesis even further is that if the orthotic is "right", it does not matter what foot type it is and does not matter what orthotic design variables are used, if the orthotic is "right", then there will be a more rapid off-loading of the heel and sooner loading fof the forefoot

    I will report back at the end of the year (maybe at PFOLA?)
  7. Re: Project No.1 physiological cost of foot orthotics

    While this is interesting, the majority of folk here don't have access to in-shoe pressure measurement equipment.

    More on PCI:
    Foot Ankle Int. 2003 Jun;24(6):494-9.
    Outcome of orthoses intervention in the rheumatoid foot.

    Kavlak Y, Uygur F, Korkmaz C, Bek N.

    Hacettepe University, School of Physical Therapy and Rehabilitation, Department of Orthotics and Biomechanics, Ankara, Turkey.

    This study was carried out to determine the effect of foot orthoses on pain, gait, and energy expenditure in patients with rheumatoid arthritis. Eighteen patients were evaluated for these parameters. Each patient was given a foot insert or shoe modification suitable for his or her foot deformity. Following 3 months of orthosis use, a significant difference was found in regards to pain (p < .05), step length and stride length (p < .05), and physiological cost index (p < .05). The results suggest that foot orthoses are an important feature in the rehabilitation of the rheumatoid foot.
  8. Craig Payne

    Craig Payne Moderator

    Re: Project No.1 physiological cost of foot orthotics

    BUT, would the PCI be sensitive enough to pick up differences in an orthoses with and without something like a first ray cut out, which is much more subtle than +/- orthoses in a disease state such as RA.
  9. Re: Project No.1 physiological cost of foot orthotics

    Don't know. I selected orthoses durometer as surface stiffness is supposed to effect metabolic cost. Could look into energy expenditure index too. There are a number of such tools which seem to be widely employed. I KNOW about the limitations, but I thought it might be interesting.

    Prosthet Orthot Int. 1988 Aug;12(2):73-6.Links
    Energy cost of walking with flat feet.

    Otman S, Basgöze O, Gökce-Kutsal Y.
    School of Physiotherapy and Rehabilitation, Hacettepe University, Ankara, Turkey.
    A comparative study has been conducted to assess the effects of arch support on oxygen consumption in 20 subjects with flat feet who were generally complaining about fatigue, and also to explore whether their feeling of weariness was objective or not. The resting, walking and final recovery heart rates, blood pressures, and walking oxygen consumption values of the patients with flat feet were measured and calculated and compared to a control group using treadmill and oxygen consumption devices. In stage one the patients did not wear any arch support. Then suitable arch supports were prepared for each patient and in stage two they wore these arch supports. The results did not show any significant difference between the resting heart rates, blood pressure and oxygen consumptions. However, differences in walking heart rate, systolic blood pressure, final recovery heart rate, oxygen consumption, and energy cost values were found to be significant between stage one and two of the test in the patient group. The difference in walking diastolic blood pressure values without and with arch support were found to be insignificant. It may therefore be deduced that oxygen consumption during walking is decreased when a suitable arch support is applied to patients with flat feet.
    Last edited: Jan 26, 2008
  10. Re: Project No.1 physiological cost of foot orthotics

    This may be a sharper instrument:
    The Journal of Strength and Conditioning Research: Vol. 12, No. 1, pp. 33–36.
    Development of a Generalized Model to Estimate the Energy Cost of Walking and Running for Healthy Adults

    Nestor W Sherman
    Department of Health & Kinesiology, Texas A&M University-Kingsville, Kingsville, Texas 78363


    The purpose of this study was to develop a generalized model to estimate the energy cost of steady-state walking and running. The study involved 22 men and 22 women who were mostly in their 20s. Multiple regression was used to develop a model estimating VO2 from walking or running speed. Regression analysis revealed the energy cost model for walking and running had a common slope but different intercept. The derived model, VO2 (ml . kg-1 . min-1) = -1.866 + Speed (m .min-1) × 0.177 + (Run = 4.855 or Walk = 0), was not a function of gender and was highly accurate (R = 0.99, SEE = 1.6 ml kg-1 . min-1). When cross-validated, the model demonstrated similar accuracy. The results show that the energy cost of horizontal walking and running can be estimated from a generalized model.

    Key Words: intercept, multiple regression, oxygen uptake, slope
    Last edited: Jan 26, 2008
  11. Re: Project No.1 physiological cost of foot orthotics

    Sometimes students may be able to collaborate with other graduate students in other departments that do have access to specialized equipment in order to contribute to a project. Here is how I would do your proposed study.

    Subjects with abnormal gait patterns due to foot pathology would be recruited into the study and one pair of custom foot orthoses are made for them. These subjects would be walked on a treadmill both with and without foot orthoses inside their shoes at two different speeds 2.5 mph and 3.5 mph, while their O2 and CO2 expired gases were being measured. Calculations could then made of their VO2 (oxygen uptake) at each walking speed with and without foot orthoses to see if the foot orthoses altered the metabolic cost of walking on a treadmill at 2 given speeds.

    This study could easily be done in a university setting that already has the V02 equipment and treadmill setup. I was involved as a subect in V02 research such as this (but running instead of walking and not involving orthoses) nearly 30 years ago at the UC Davis Human Performance Lab, so I'm sure the technology has improved considerably since my undergraduate days.
  12. Mart

    Mart Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    Definitely . . . . . .. I could not agree more. :good:

    However, I feel pretty uninformed regarding how to interpret the results of studying the PCI in relation to changes in gait.

    Perhaps I am in danger of raising the obvious but I would be interested to look beneath your suggestion a little.

    I got quite excited when Tekscan introduced a software package which calculated COM excursion via integration of GRF velocity data derived from their pressure measurement system.

    Tagged along with this were analysis of “purity index” which is a measure of how close the COM trajectory comes to a pure sinusoidal waveform, (calculated as the ratio of the second harmonic to the sum of the remaining harmonics).

    I have sat on the fence on this because recently published papers suggest that correlating vertical COM motion with gait efficiency may not only be overly simplistic in terms of having intrinsic therapeutic measurement value but possibly also wrong. (I can cite this stuff if anyone is interested) :deadhorse::deadhorse:

    I understand the notion here is that gait efficiency is at the mercy of the transfer of energy in 2 ways

    1 Segmental Pendulum exchange between the KE and PE during gait
    2 Linear and rotational KE exchange between body segments.

    Respectively these will be most largely influenced by how closely they are to being 180 degrees out of phase and how well neuromuscular coordination is able to minimize antagonist co-contraction.

    When dealing with amputees or people with significant gait inefficiency such as CP this kind of measurement I would estimate could have quite striking implications because, for example, the changes imparted by improving prosthetic design or reducing spasticity via Botox are likely to have a proportionally large effect.

    Also I would think that it is possible to determine, using some simply derived relationships such as in your “sharper instrument” generalization model, if someone is likely to be better off using a wheelchair, a particular prosthetic limb or trying out a rhyzotomy procedure (without being subject to wearing a gas mask) given that established normative data exists for a variety of types of gait .

    Craig has already expressed a skepticism regarding the sensitivity of PCI measurement for detecting the kind of changes we might expect to find from the effects slightly different foot orthoses with the more subtle changes expected.

    I am glad that you posted the citations in response to this, another example where my intuition may have let me down.

    I always liked Chris Kirtly’s quote that. . . .. . .. . . Nothing is more likely to impede investigation than the premature acceptance of an “explanation” . …. …… which is perhaps quite relevant here.

    Anyhow the point I am trying to extract here is where the potential lies in terms of evaluating the effects of foot orthoses using PCI or is this simply a “pure science” idea to simply investigate if there might be some relationship.

    How can you seperate the variables which might be responsible for a signifcant difference in PCI between subject groups unless, as Craig suggests, we examine less generalised parameters such as plantar calcaneal area and forefoot loading velocity?

    I went back and read Kirtly’s brief comments regarding using PCI, he mentions a couple of methodology issues which might be worth adding ;

    reducing the effect of heart rate stimulants at by avoidance least 4 hrs prior to trials (caffeine other stimulants)

    allow subjects to rest before starting test,

    As usual I am enjoying your posts and look forward to learning some stuff on this thread as it develops



    The St. James Foot Clinic
    1749 Portage Ave.
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    Last edited: Jan 27, 2008
  13. CraigT

    CraigT Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    This is a project along the lines of one we have been looking at tackling... so great to see the interest!
    Myself and my new sidekick- Luke- have access to a full physiology lab as well as pedar which gives a bit of an advantage with this stuff.
    The problem with the walking test is that it can be quite variable day to day and may not be sensitive enough to detect change (this includes if you use oxygen consumption as a measure)- this comes from the physiologists that we work with.
    Our plan would be to test the following conditions- no orthosis, EVA milled orthosis, shell device (same prescription) and perhaps also low Dye taping- We manufacture our own orthoses on site using an AMFIT system which has some limitations, but has one useful feature in that we can mill an EVA device, and then manufacture the same device in a shell by milling a positive model and vacuum forming.
    You would have to standardize the footwear, as well as the weight of the footwear with orthoses. Having the subject hooked up to the pedar at the same time would not be a problem.
    It would probably be best to have a biomechanical profile of each subject- maybe when testing subjects with the 'worst feet' mechanically you could detect a change. Foot posture index would be one possible method, but maybe someone could suggest another way that they think indicates poor foot posture (remember it needs to be a reliable measure).
    It would be great to get the input from Podiatry Arena members for this type of project.:drinks
  14. Mart

    Mart Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    Hi Craig

    I rambled on a bit in my last post attempting to clarify why gait efficiency might be relevent in examining the relatively subtle gait effects foot orthoses we typically use as podiatrists have compared to more extreme rehabilitation requirements of a typical prosthetic department.

    Perhaps I am putting the cart before the horse but am curious to extend my request for speculation/examination of underpinning of notion(s) for what exploring PCI might amount to.

    Simon has suggested that FO durameter may effect gait efficiency presumably by altering the amount of energy removed or returned during each contact phase.

    Craig P suggested similarly that timing and slope of vertical GFC may effect efficiency and it would be interesting if this is true to speculate how this might work.

    Any thoughts about how FO could effect gait efficiency? What might you look for with your Pedar system?



    The St. James Foot Clinic
    1749 Portage Ave.
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
  15. Re: Project No.1 physiological cost of foot orthotics

    There is some evidence that orthoses positively influence the efficiency of gait. I listed references previously within this thread that demonstrate this. I wouldn't attempt to measure gait efficiency using a pressure plate. Played with CoMnalysis when it first came out. Spooner's half time verdict- rubbish, told me I was more "efficient" when I did my quasimodo impression.
  16. Re: Project No.1 physiological cost of foot orthotics

    I think a video of that could be a big hit on YouTube!!:pigs:;):pigs:
  17. CraigT

    CraigT Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    Without having any reference at hand (perhaps Simon does), my personal belief is that part of the effect of a well designed orthosis is to assist the subject to stabilize the foot into propulsion- perhaps this is the windlass mechanism being allowed to function? Toe off with a stable foot vs an unstable foot may preserve energy/ increase 'drive''. I know I have many patients reporting that they feel 'lighter on their feet' with orthoses and feel a similar benefit from low Dye taping. Maybe this can be demonstrated?
    The Pedar may show what changes have occurred if we do see any change in efficiency. Perhaps there would be less 1st IPJ loading suggestive of inproved windlass function...
    Pure speculation, but adding this to experiment would be quite simple here.
  18. Re: Project No.1 physiological cost of foot orthotics

    Ultimately gait efficiency comes down to "fuel used" for distance travelled. The things burning the fuel are the muscles, so orthoses will potentially alter efficiency through their effects on muscles activation levels.

    G. Murley, A. Bird: The effect of three levels of foot orthotic wedging on the surface electromyographic activity of selected lower limb muscles during gait. Clinical Biomechanics, Volume 21, Issue 10, Pages 1074-1080.

    Mundermann A, Nigg BM, Humble RN, Stefanyshyn DJ. Orthotic comfort is related to kinematics, kinetics, and EMG in recreational runners. Med Sci Sports Exercise 2003;35:1710-1719. 46.

    Nawoczenski DA, Ludewig PM. Electromyographic effects of foot orthotics on selected lower extremity muscles during running. Arch Phys Med Rehab 1999;80:540-544.

    Tomaro J, Burdett RG. The effects of foot orthotics on the EMG activity of selected leg muscles during gait. J Ortho Sp Phys Ther 1993;18:532-536.


    How do you measure "efficiency" from this?
    Last edited: Jan 28, 2008
  19. CraigT

    CraigT Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    More efficient passive stability (?windlass).... perhaps less active propulsion effort required (?muscle work).

    I was not suggesting that you would measure efficiency with the Pedar.
    What I was thinking is that if we measured, say, 30 subjects and examined the results, we may find that some had a measureable change in efficiency, but others didn't. Perhaps these subjects that didn't have a change, also did not show significant plantar pressure changes. Perhaps the subjects that did show a change in efficiency will show a change in plantar pressure that may suggest the effect the orthosis had.
    This is why I think it would also be good to have a reliable biomechanical profile of each subject- maybe there is a clinical indicator which may help us pick which patients will show an improvement (if, of course, we can actually measure this:rolleyes:).
    This then begs the question as to what measures would we put in this profile?
    A lot of speculation at this stage...
    All input appreciated!
  20. efuller

    efuller MVP

    Re: Project No.1 physiological cost of foot orthotics

    With the question being, how could an orthosis improve gait efficiency, I'd like to add a comment. Foot stabilty is one of those non defined parameters that was used to explain how orthoses work. I agree with Simon's point of how would you measure stability.

    My theory on gait efficiency is related to joint power and pain avoidance. In gait you need energy to make the trailing leg become the leading leg. You can use ankle push or hip pull to do this. The hip muscles have a much shorter lever arm on the leg at the hip than the horizontal ground reaction force generated by ankle push. So this theory is similar to the comment about stability in propulsion. They are similar in that they both look a propulsion from the foot. However, I believe that people choose a less propulsive gait to avoid stress (and pain) on the foot. An orthosis ccould be working by maiking the foot more able to handle the stress. This is not exactly making the foot more stable, but stronger. Anyway, joint power is something that is measurable.

    On Windlass functioning and IPJ loading. First we have to define what windlass functioning is. I'm worried that people will start saying that orthoses will work because it will make the windlass function better without really understanding what that means. The term "windlass functions better" is as poorly defined as saying the foot is more stable.


  21. Re: Project No.1 physiological cost of foot orthotics

  22. Mart

    Mart Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    Eric, you are delving into the area which I am most curous about in trying to interpret theoretical explainations for changes in gait efficiency other than cardiovascular fitness. I need some time to mull over your idea now. You probably noticed that Kevin K has started a parallel thread on this subject


  23. Mart

    Mart Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    This simple exercise in thinking about PCI has helped me clarify a few thoughts which have bugged me for a while.

    What follows may be a little banal or obvious to the wiser owls out there but thought it worth a couple of minutes for the sake of the more pigeon like amongst us.

    I realized that walking like Groucho Marks (Simon I assume you meant this not Quasimodo) would likely reduce COM amplitude during walking and therefore using COM as an index of gait improvement without deeper interpretation is questionable. Likewise I never bothered with the COM analysis module but it has been in the back of mind to consider this further. Too busy, lazy un- knowledgeable . .. . . whatever to explain this.

    So I spent this lunch time doing a little data collection.

    Before doing the walk I considered some explanations why we all don’t walk like Groucho

    1 Because we are to shy to look so stupid, well if there was evolutionary advatange to this we would all be doing the same and nobody would find this interesting on U tube. Unlikely

    2 Because it would make us obvious to predators and we would not have escaped the clutches of the Sabre Tooth and passed required adaptations on with our genes. Mildy plausible.

    3 Something takes precedence over COM efficiency in our gait patterning algorithm. Most attractive.

    4 It would cause premature joint degeneration. Possible but doesn’t seem to hurt Kangaoos to bouncy around.

    Using an FMat I collected some steps of my normal walking and (after considerable practice ) some Groucho steps.

    I was able to flatten out the force/time curve consistently using the Goucho walk and made the assumption from this that this was reducing COM excursion given that contact phase was of similar duration (650ms).

    My plan was then to do a PCI measurement with normal walking gait and then Groucho Gait and see what happened.

    Thing was that I was actually becoming breathless just refining the groucho walk, no need to even take my pulse, this was a hugely inefficient way to move.


    it seems reasonable to test out the idea further that in gait patterning improving gait efficiency has higher importance than reducing COM amplitude


    Inman’s predetermines of gait implicitly consider that our gait patterning is primarily a function of reducing COM excursion because this improves gait efficiency, and that deviations from this are generally indications of dysfunction.

    This rule generally seems to hold true which is what makes measuring COM excursion with a simple software tool quite compelling.

    I am pretty sure that I understand why Groucho’s gait contradicts this principle though I have never seen it spelt out (perhaps it is too obvious!).

    I thought it might make a good exercise AKA Kevin K’s moment calculation exercises.

    As a suggestion; I’ll post my explanation tomorrow and have the vultures swoop, suggest that the wise old (and young ) owls (they know who they are) butt out for a while and decent on the debris left by the pigeons later.

    Pigeons explanations are requested.



    The St. James Foot Clinic
    1749 Portage Ave.
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
  24. Re: Project No.1 physiological cost of foot orthotics

    My thoughts: the human organism is incredibly lazy, or incredibly good at minimizing energy cost. Basically, the purpose of locomotion is to get us from a to b using the minimal energy cost, without (minimizing) pain or excessive stress on the tissues, so that when we get there we can feed, reproduce etc. (Selfish gene theory- Dawkins) "Natural" walking, i.e. the way you walk naturally without thinking about it, is the most efficient way to do this, given the biomechanics that you have for a given environment. If you try to change your biomechanical function, i.e. the way you walk, in this environment- efficiency is reduced (ref to this if required- brain needs time to drag it up- maybe some study to do with step length changes, possibly Inman???). SO in order to improve gait efficiency we need to change the environment, i.e., the surface that we walk upon, then the biomechanics will be optimized for this environment. Clever little organism.

    P.S. this is simply explained using quantitative genetics models
    Last edited: Jan 31, 2008
  25. Re: Project No.1 physiological cost of foot orthotics

    Humans, like other animals, will tend to perform necessary work tasks or physical activities in such a fashion so that metabolic energy expenditure is kept to a minimum. This is a huge driving force in how we, as animals, choose the specific motion patterns that consitute the activities of walking, running, swimming, bicycling, playing sports or performing work activities. Of course, why would an animal want to expend more fuel, especially if the fuel (i.e. food) is scarce, if they could perform the same activity with the same net results more efficiently?

    Also, humans, like other animals, will tend to modify the kinematics of their activities to avoid painful motions since pain avoidance, or avoidance of noxious stimuli, is seen in all animal species. Finally, since the central nervous system (CNS) drives these activities, then depression or stimulation of the CNS will also cause a change in the kinematics of activities.

    Therefore, when a certain kinematic pattern of an activity is observed, there are many factors that go into producing that activity. The clinician needs to be very aware of all of these factors.
  26. Mart

    Mart Well-Known Member

    Re: Project No.1 physiological cost of foot orthotics

    Having started to think a bit more critically about this,I got a little excited about what this might amount to and commented;

    " am pretty sure that I understand why Groucho’s gait contradicts this principle though I have never seen it spelt out (perhaps it is too obvious!)"

    Well it turns out that Groucho has been very very thoroughly examined, thought about and published in much more depth than I had any knowledge of. Rather than regurjuate my very basic obersations and ieas as I had intended,becasue there seems to have been a lots of "hits on this subject, I'll digest the papers I have found and attempt a synopsis of the less mathmatical aspects of these when I get a chance, I'll post it on Kevins parallel thread on gait efficiency which is probably the best fit



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  27. NewsBot

    NewsBot The Admin that posts the news.

    The physiological cost of restricted weight bearing.
    Westerman RW, Hull P, Hendry RG, Cooper J.
    Injury. 2008 Mar 7 [Epub ahead of print]
  28. pretschko

    pretschko Member

    Re: Project No.1 physiological cost of foot orthotics

    Dear craig,
    My thesis compared drastic changes in transtibial prosthetic alignment (treadmill walking) vs. knee, hip and contralateral ankle kinematics and oxygen consumption. (You'll find it archived and covered in plenty of LaTrobe dust). Dr.. Tim Bach might have a copy.
    The amputees were able to compensate for huge changes in alignment (and knee flexion and extension moments) without any effect on oxygen consumption.
    I have doubts whether changing insole density will change gait efficiency parameters with such subtle changes in variables.
    Paul R

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