Welcome to the Podiatry Arena forums

You are currently viewing our podiatry forum as a guest which gives you limited access to view all podiatry discussions and access our other features. By joining our free global community of Podiatrists and other interested foot health care professionals you will have access to post podiatry topics (answer and ask questions), communicate privately with other members, upload content, view attachments, receive a weekly email update of new discussions, access other special features. Registered users do not get displayed the advertisements in posted messages. Registration is fast, simple and absolutely free so please, join our global Podiatry community today!

  1. Everything that you are ever going to want to know about running shoes: Running Shoes Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
  2. Have you considered the Critical Thinking and Skeptical Boot Camp, for taking it to the next level? See here for more.
    Dismiss Notice
  3. Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
    Dismiss Notice
Dismiss Notice
Have you considered the Clinical Biomechanics Boot Camp Online, for taking it to the next level? See here for more.
Dismiss Notice
Have you liked us on Facebook to get our updates? Please do. Click here for our Facebook page.
Dismiss Notice
Do you get the weekly newsletter that Podiatry Arena sends out to update everybody? If not, click here to organise this.

Metabolic Cost of Activities

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Kevin Kirby, Jan 29, 2008.

Tags:

  1. Members do not see these Ads. Sign Up.
    I am splitting off from Dr. Spooner's thread on physiological cost of foot orthoses to make a new thread that more thoroughly examines the ideas of metabolic cost and metabolic efficiency, since I believe these topics are generally poorly understood by podiatrists and many other clinicians.

    The above is a nice summary of what metabolic energy is all about. The animal (e.g. human) body, just like the boiler unit for the steam locomotive trains from years past, needs to burn fuels in order to accomplish work. In the steam boiler, wood is loaded into the burner in order to produce heat energy that will, in turn, heat the water in the boiler to produce the steam that is necessary to drive the wheels of the train. During this wood burning process, oxygen (O2) is consumed by burning of the wood, and water (H2O) and carbon dioxide (CO2) are the combustion byproducts of this process.

    In the bodies of humans, foods are consumed by the individual that are then broken down into their basic components that may then be "burned" or metabolized by the cells of the body in order to perform the activities and functions necessary or desired by the individual. In humans, this metabolism of foodstuffs also involves the consumption of O2 and the production of the metabolic byproducts of CO2 and H2O.

    When the individual is at rest, the energy usage and 02 consumption is minimal and the energy consumed at this state of rest is known as the basal metabolic rate. As the individual requires more energy, for example, when they need to run or work hard, they require more energy to do so, and this increased level of physical activity will also increase the O2 consumption. This is analagous to the locomotive needing minimal wood burning while at rest and needing more wood burning in order to travel at higher velocities.

    The term metabolic efficiency describes the amount of work being done divided by the metabolic energy or O2 being consumed by the individual. For example, if the individual consumes 25% more O2 when running a mile than another person, then we can say that the person than consumes less O2 is more metabolically efficient at running than the other person. Therefore, the individual that exhibits the ability to perform more mechanical work with less O2 consumed that would be said to have good metabolic efficiency. This would be analagous to a comparing the amount of wood burned in a older locomotive with leaky steam valves to a newer locomotive with no leaky valves in order to travel the same distance. The older locomotive would need to burn more wood in order to perform the same mechanical work due to some of its steam heat energy being lost to the atmosphere whereas the newer locomotive would be able to burn less wood to travel the same distance, since it is able to harness more of the energy from wood burning since less of its steam energy is wasted by leaks.

    Now, here are a few questions for those of you who are interested. Metabolic energy in humans is more complicated than the simple description I have described above since humans, like many other animals, can perform work for a time with little O2 consumption. What is this process called? How does it work? What is the metabolic byproduct of this process? What fuel is burned by the body during this process?

    In addition, the rate of O2 consumption is called VO2. The maximal rate of O2 consumption of the individual for a certain activity is called their VO2 max, and is generally accepted as a good indicator of athletic potential in many sports activities such as running, cross-country skiing, bicycliing, etc. What physical activity normally reports the highest V02 rates in humans? Why? Do the athlete's with the highest VO2 rates always win the races? Why or why not?

    Hope this discussion and questions stimulate some interest in this important subject for those of you who have a desire to learn more about how the human body works.
     
  2. Thanks Kevin, nice site here for the interested: http://www.sport-fitness-advisor.com/VO2max.html
     
  3. Mart

    Mart Well-Known Member

    Hi Kevin

    I agree that this a "knowledge gap" for a lot of podiatrists, me included, and glad for your and Simon's guidance on this.

    I feel that my current level of knowledge allows me to understand, at rudimentary level, the equilibrium of anaerobic/aerobic respiration, how that might be effected by cardio-vascular conditioning, disease states of heart, lung, cardiovascular system generally, and MSK fitness, how O2 dept occurs and is resolved, how different muscle fibre types (slow and fast) will influence this equilibrium according to activity type (intensity vs duration of demand).

    At the "highest level” measuring PCI, VO2 and other various indexes of efficiency will give us a “crude” general clue as to gait aberration when comparing a specific subject’s performance to normal established values. This as I mentioned in the initial thread, seems to have a well established clinical role in rehabilitation of extremely compromised gait problems (amputees, CP etc), but less established in the more subtle MSK compromises of localized foot dysfunction which podiatrists typically encounter with chronic MSK foot and lower limb problems).

    I understand why Simon would choose to suggest using the mailbase to gather some data for this particularly in looking at variance of values to evaluate how useful this data might be.

    Apart from clarifying what we are measuring when using gait efficiency indices, I am interested to explore (which is probably an exercise in speculation) what might cause these changes (other than cardiovascular and MSK conditioning).


    At the next level down from “what is using the energy” and the “physiologic process involved at cellular and tissue level”, is, as I see it, how the body functionally deals with the mechanical obstacles it is encountering during gait when using its “functional blocks” which we often regard as the rigid body segments, the bread and butter of kinematic and kinetic study .


    At the next level are general demands

    1 Moving COM of body; ideally minimizing this to reduce energy expended with the partial losses occurring with this motion, this being a combination of amplitude reduction (Inman’s determinates of gait) and phase tuning (making the conversion of PE and KE 180 degs out of phase)

    2 Co-coordinating the MSK system so that it is stable, able to move the body forward (mostly) and ideally with co-contraction minimized.

    Implicit in this, when walking, are use of an inverted pendulum model, which has multiple segments which allow adaptation to uneven terrain; That energy transfer between these segments occurs in away which ideally should minimize total energy consumption for given environmental conditions (speed, incline, etc)

    Then a lower level still


    The specific demands, which are very numerous and complex – eg how are the determinates of gait performed (in spite of recent studies suggesting this idea is in itself flawed in several respects)

    Now

    MSK injury, inherited limitation or poor conditioning causing decreased range of motion, loss of strength and flexibility, neurologic dysfunction (or lack of training), or over demand (obesity, sudden change in activity) have the potential to modify either 1 or2.


    If sufficiently sensitive, measuring the efficiency of gait before and after intervention may tell us that we have influenced this significantly.

    My contention is that to achieve this change we need to have some theoretical goal at a lower level than 1 and 2

    Now


    For this to be true, then what I have stated above needs to be logically coherent, which I feel may be stating the obvious but, I am not sure if this is agreed upon.

    I hope this makes sense, please comment. . . .. .. . . . . . .

    OK …. . . this is all obvious …. So what?

    Or

    Whoaa hang on there Jimmy!@!

    If you agree than I will move on to my next bunch of concerns, in the mean time I want to read up Simons suggested papers on studies exploring EMG and gait efficiency.

    Cheers

    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
  4. Good site, Simon. I hope everyone following along reads the valuable information within it. It will definitely help those of you who are trying to improve your understanding of exercise capacity and exercise efficiency.
     
  5. I can see that no one attempted to answer my questions. Therefore, I will answer the questions for you.

    Work that is done with insufficient O2 metabolism at the time of the work is called anaerobic metabolism. Lactic acid is the metabolic byproduct of anaerobic metabolism. Aerobic metabolism means that O2 consumption fully meets the demands of the exercise and uses a different cellular metabolic pathway.

    In general, cross country skiers show the highest VO2s since they work both their legs and arms vigorously, with the next highest VO2s being distance runners. The athlete with the highest VO2 does not always win the races since some athletes can exercise more efficiently than others and also some athletes can push further into O2 debt for longer periods of time without fatiguing, than can other athletes.

    Sorry to see there is so little interest in this subject. I thought more would be interested. My second choice in a career, behind being a podiatrist, was to become a PhD in exercise physiology. Wonder if I chose the right path??
     
  6. Mart

    Mart Well-Known Member

    Geeze Kevin you sound some what disheartened.

    If this is true please do not be so. At the risk of sounding a bit “gushy” I want to make a couple of comments so please allow me to indulge a minute.

    I have spent a fair chunk of my life as a performing musician, have played at festivals to audiences of several thousand enthusiastic vibrant people and Weddings where people don’t even notice there are live musicians. At the “bad “ Weddings there are invariably one or two people though who lurk in the shadows and after the gig will come and tell you “hey you made the party worthwhile where can I get your CD”

    So I am pretty sure that there are more than you might imagine lurking who might say to you “hey you made the party worthwhile where can I get your CD”. BTW I have read both your Intricast “CDs” and they have helped me attempt to bridge the gap from elementary principles missing form my basic podiatry training to making sense of the “real biomechanics” in the literature.

    This past week I have been catching up a bit in knowledge gaps in trying to understand the limitations of measuring COM excursion, interpreting contact phase force time curve shape and using PCI as measures of therapeutic interventions.

    I am sure you understand that when self learning there is a danger of not “getting it” and what I notice is that in the transition from basic understand to deeper knowledge the bridges can be sometime difficult to find.

    One wonderful thing about this forum is the opportunity to have people like yourself to point to bridges, particularly to people like me who are isolated clinicians with no academic community to build maps with. Also delving the huge volume of literature can be very time consuming to navigate even if you are adept with medline searches. You speed this process up a lot.

    It can be very helpful from time to time to see if I am “really getting it”

    Stating “the obvious” might be helpful because it may be wrong, others reading these statements can also benefit from this by noticing errors and correcting them. A bit like being really sure that you have spotted an important typo which contradicts a concept in a text book. I see this as distinct from “suffering fools gladly” when it seems that no attempt has been made to do any work or contribute usefully.

    Nuff said.

    Since, unless very sick or gait compromised , we operate well below VO2 max I guess my interest in VO2 is not so much with VO2 max and the aerobic/anaerobic equilibrium, but more using simplified measures of gait which look at metabolic cost such as Simon suggested with PCI measurement.

    I had not done my homework properly when thinking about providing a synopsis of optimizing gait efficiency and I now notice that Stephen Tucker has already done this quite nicely.

    http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=4695


    My simplified understanding so far is:

    That pendulum gait is most efficient because it allows forward motion with reasonable “recycling” of stored PE which occurs after max COM excursion, pushing body forward as COM drops and returning as KE. This occurs with minimum stabilization from quads so long as knees remain almost fully extended during midstance using little energy to achieve this. During Groucho gait a large amount of energy is used stabilizing the flexed knee with the quads and since COM excursion is minimized this energy is lost as heat, not recycled in PE to KE conversion. So if you really want to get good cardiovascular workout and bugger up your knees go walk like Groucho.

    Would it be theoretically reasonable then to regard measurement of COM motion using Tekscan COM module as indicator of gait efficiency provided that simultaneous measurement of knee flexion during midstance was normal for walking. Are there other significant energy consuming factors which need taking into account?

    There is a limit to maximum speed we can walk, this is derived using simple models examining acceleration applied to body COM by gravitational forces and limb length. To exceed this we start to run and the “running gait” then becomes the most efficient at higher speeds because there is increasingly a period of flight which requires no stabilization energy, and energy conservation then switches from PE to KE return of pendulum gait , to “spring” return between” landing” and “taking off” provided by tendons (and ligaments?).

    Please could you comment if this is a good grasp of the basic principles of gait efficiency.

    I wanted to move to an area which I don’t think has been discussed on the forum and that is how we can usefully integrate and interpret what we see clinically using the simple measures in our tool box, namely force time curve shape, simple kinematic observation and possibly PCI. I have a bit more reading to do yet but I’d be grateful for your comments on this post


    Cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
    Last edited: Feb 2, 2008
  7. Asher

    Asher Well-Known Member

    Well said Martin. Forever in your debt Kevin (and others like you who have the knowledge and are so generous with their time). :drinks

    Rebecca
     
  8. Mart

    Mart Well-Known Member

    I just went to the gym read a couple more papers, realized I should have done more reading before making any further comment and driving home thought

    “that last post I made was bull****, I mostly hated playing weddings, what I was doing was justifying asking someone to be my internet based teacher . . . . for free.”

    No disrespect Rebbecca but Sorry Kevin

    Perhaps I am a bit strange, and misinterpret mailbase behaviours of others, but I notice that when I get immersed in ideas banded around on the mailbase, there is an initial inertia and excitement which seems to demand response and when this is not forthcoming it dies, either from lack of interest in the idea, or it comes to its natural end or spawns other ideas.

    It is tedious for better read members when there is a large disparity in knowledge between posters on a given subject, I guess the response is then to simply not respond to those posts which are not that enlightened.

    But I want to get in there and keep the momentum going at times and then get a little paranoid that I am out of step with the general intent of this forum.

    My point here I guess it to fathom a reasonable approach to allow members to self organize into motivational subgroups which can maintain the excitement and momentum assuming that others might feel the same way or that this isn’t actually what is already happening.

    I just read the attached paper and feel that it is important to the issues discussed on gait efficiency, running vs walking, COM measurement etc but find it pretty difficult to understand in some places and to really get the most out of it have to go and spent some time to understand what is meant by things like

    “shape factor, a ratio of Fourier coefficients that describe the course of the force exerted on the ground”.


    Anyone interested in trying this. . . . . CraigT, Rebbecca anyone else ?

    To improve learning efficiency, a group of us could read the paper a couple of times, make notes of concepts which are not immediately clear, post them to create pool on knowledge gaps, and each take on the task of researching and explaining one to the others.

    I guess this is simply called a study group.

    Any takers?

    Cheers


    Martin



    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
  9. Mart

    Mart Well-Known Member

    I couldnt post the paper, it was too large to attatch if you cant get a copy email me and I'll email it directly

    Abstract:

    A simple model predicts the energy cost of bipedal locomotion for given speed, stride length, duty factor and shape factor. (The duty factor is the fraction of stride duration, for which a foot is on the ground, and the shape factor describes the pattern of force exerted on the ground). The parameters are varied to find that the gait that minimizes metabolic energy cost, for each speed. A previous model by Alexander calculated the work that the muscles have to do, but the metabolic cost (calculated in this paper) is more likely to be the principal criterion for gait selection.

    The model gives good predictions of human stride lengths, and of the speed at which we break into a run. It predicts lower duty factors and higher shape factors than are normally used, but the relationships between these gait parameters and speed parallel the empirical relationships.



    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  10. An inverted pendulum type of gait is most efficient for walking due to the peculiar bipedal arrangement of the human skeleton. You are correct that the energy expended in maintaining a knee flexed position during the stance phase of walking is significant and would also tend to increase patellar-femoral contact pressures.

    The only way I would try to accomplish this task of measuring CoM motion for research purposes would be to do video analysis of subjects with markers on their pelvis and other lower extremity segments. Using ground reaction force for determining CoM motions may be possible, but I'm not sure how accurate it is.

    You have a fairly good grasp of the basic principles of gait efficiency. You may want to read some of the papers by Rick Neptune who has a special interest in the walk-run gait transition speed and what determines it. This would probably be very helpful for you.

    In general, as one starts to walk faster, and tries to move the legs faster to do so, it becomes more efficient to bend the knee more during swing to decrease the moment of inertia of the leg and decrease the hip flexion moment to swing the leg faster forward during swing. This is only one factor but certainly, in my mind, this seems to be an important factor in determining the walk-run transition speed.
     
  11. Martin:

    E-mail me the paper and I'll post it to the list for you.:drinks
     
  12. Asher

    Asher Well-Known Member

    I know what you mean Martin. Part of me thinks that its wrong to rely on colleagues who I don't even know and who certainly owe me nothing, to give me their valuable advice. There is nothing I could do in payment or action that could ever repay these people. Then the other part of me thinks that this forum is here, these podiatrists keep offering their valuable insights and advice and I marvel at the freedom of exchange, as one-sided as it is, and it gives me a warm fuzzy feeling about the profession that I am a part of. I don't know, its a strange mix of good and guilty feelings. The last thing I would want to do is take advantage of anyone who contributes to my posts and to other threads that I learn from. It would be interesting to hear from those top posters who give their expertise and time so selflessly.

    Maybe one day I could be a valuable giver of insight and advice, on Podiatry Arena or in other ways on a more local level and to a small degree, I do this and it does give me quite some satisfaction. This must have something to do with what our big posters get out of it?

    I'm not sure how this will work Martin but I'd give it a go. I certainly am bouyed by the 'Thanks' I received from the walking vs running thread - what you're suggesting is we do something similar to that - yes?

    Rebecca
     
  13. Rebecca and Martin:

    I enjoy teaching subjects that I am interested in. Since I am a full time clinician in my own practice, teaching is a part time job for me. I only get to teach when I lecture at the podiatry school (CSPM) in Oakland (about 5 times a year), when I lecture at national seminars (about 3 times a year), when I lecture at international seminars (about 1-2 times a year), and when I have the 3rd year surgery residents from Kaiser Sacramento rotate through my office on Thursday afternoons. I also have been writing (and still do write) a Precision Intricast newsletter every month for the past 21.5 years and am involved in writing papers for assorted research projects and journal/publication articles. Otherwise, Podiatry Arena, is where I do most of my teaching.

    Podiatry Arena is an interesting diversion for me during my busy day and it is personally satisfying for me to be able to offer information that may be helpful to one of my national or international colleagues and/or their patients. In addition, I enjoy having intellectual discussions with my colleagues who I often lecture with and get to see at seminars here and abroad. It is my strong belief that I should share the knowledge that has been passed on to me by my professors and that I have gained during my many years of studying the mechanics of the human body so that I can contribute, in my small way, to the knowledge base of foot-health care professionals around the world. I also strongly believe that if I didn't make the effort to pass on this valuable knowledge, then all that I have learned would be wasted when I am no longer living. I don't know if I will always be able to spend so much time contributing on Podiatry Arena, but, for now, I am enjoying my time here.
     
    Last edited: Feb 3, 2008
  14. Mart

    Mart Well-Known Member

    Kevin and Rebecca I am glad you responded so positively, I guess I felt somewhat insecure and wanted to probe my assumptions about how others regard using the mailbase rather than carry on regardless.

    When that warm fuzzy feeling that Rebecca mentioned comes from intellectual resonance with others (as opposed to egotistic self satisfaction) I think we recognize the most valuable human potential.

    Kevin I’ll email the paper, to you thanks for disseminating this, and thanks for the other papers too.

    On the paper itself:

    It falls into the category of optimization modeling and I was glad of Simons reference to “Modelling approaches in biomechanics” also by Alexander, to understand better how these ideas of modeling work and if unfamiliar with modeling methods it is a must read first.

    What I had in mind is to pull out the bits which need to be made intelligible and “divi” up the work of helping each other deepen our understanding.

    BTW Rebecca, the questions and approach you have made since you started posting are right on the mark as far as I am concerned . . . . Consider your ego well massaged but more importantly your intellect “resonated” at least with me

    Because of my limited mathematical knowledge I quickly get lost in some of the language and hence conceptual depth of how the model arrives at its conclusions.

    Recently I looked at my daughters High school Math approach at understanding the relationship between algebra, geometry and experimental data (it is 35 years since I last looked at this) using a plotting calculator and it blew me away how much better math teaching is today and how quickly I could really grasp the language of linear and quadratic equations, understand the relevance of graph plots and shapes etc which are so basic to experimental design and thinking in biomechanics. This was very encouraging.

    The next step is to do the same for calculus. Time being precious and there being too much to learn I am not sure if to go this route yet and am still vacillating over the value of spending this time on calculus. I mention this because it seems that once we get to a certain point in trying to understand what we might encounter clinically, which tools and ideas have the most merit, and how to sensibly move forward, knowledge gaps increasing need filling and I would guess that for podiatrists math I a big one. It would be fun to go back to school and do a math degree but that “aint gonna happen”. So I am curious to hear from the “well educated in math” podiatrists out there how much value they place on their math knowledge and how they approached this issue.

    I have a hunch (which may be misguided) that we may be able to fine tune a narrow core math curriculum for ourselves but will need some guidance.

    Look forward to seeing where this might lead


    Cheers



    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  15. Asher

    Asher Well-Known Member

    Hi Martin

    Which paper are you referring to Martin? What about instead of each doing different aspects, we (you, me, others) read the whole paper, each discuss what we made of it, think a bit more about the hard bits and then get some advice from above to make sure we really do get it?

    Ditto!

    I have a maths teacher in the family and if I knew which bits I needed, I would have a go at it. Trigonometry, calculus?? What is going to help me in understanding this mathematical modelling such as that in Alexanders 'Energy-saving mechanisms in walking and running'?

    Rebecca
     
  16. Phil Wells

    Phil Wells Active Member

    Kevin

    I would like to pick your brains (A south Yorkshire term and not an invite for canibilism) about metabolic usage and its impact on fatigue.
    In my clinic, I often have my patients fatigued prior to assessment as I get a far more accurate picture of causative mechanisms. This is particularly important with athletic subjects.

    My questions are - what is the direct cause of this - are we talking muscle or nerve?
    Can we design treatments that can address the impact of fatigue - insoles, shoes, excercise etc?

    Do you have any other salient points re fatigue that I need to be aware of in my patients?

    Thanks in advance


    Phil
     
  17. Mart

    Mart Well-Known Member

    I tried to post the paper as an attatchement but it was too large, Kevin has offered to sort htis out. I'll emeil it to him when I get in to the clinic today, I dont have electronic copy at home.

    Your math contact sounds like they may be very helpful.

    The conclusions of the paper are not difficul to understand but arriving at that point for me requires simply accepting this as true. Nothing particularly wrong with that, however I feel that I am miising some important concepts which I would like to try and find.

    the 2 main ones are

    1 really grasping this idea of frequency analysis, ie the fourier transformation.

    2 there is a very clever and for me complex evaluation of gait which involved defining the force time curve as a function, and the proportion of the time spent in support on one foot of the whoke gaot cycle and then plotting these functions against each other for different velocities.

    Looking at the geometry of mathmatical functions is relatively intuitive for msot minds but this one really boggles mine in terms of really conceiving what I am looking at here.

    More later, there is a lot to pick on and chew over here if you dont simple goe tho the conclusion and accept the finding - which may of course in the end be most sensible thing to do!

    please let me know what you think


    cheers


    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
    3rd February 2008 09:37 AM
     
  18. Alexander RMcN, Jayes AS. Fourier analysis of forces exerted in walking and running. J Biomech 1980;13:383-90
     

  19. Phil:

    "Pick your brain" is a common term here in the States also.

    During my undergraduate studies at UC Davis in exercise physiology 30 years ago, there was a lot of debate regarding what actually caused "fatigue". The thoughts at that time were that it was at least partially due to metabolic byproducts (e.g. lactic acid) building up inside muscle along with some sort of change in the neurological firing patterns that caused the known decrease in physical performance as the athlete exercised longer and harder. Certainly, well designed foot orthoses can affect fatigue of muscles, especially the fatigue of the plantar instinsic muscles. They may also be able to affect the fatigue of the posterior tibial and peroneals if the orthosis is designed properly to address any increased contractile activity from these muscles due to subtalar joint axis deviation. You may want to do a websearch using the keywords, fatigue, exercise, and foot to see what types of hits you come up with. If you could post them back to the list, then that would certainly be helpful for all of us.
     
  20. Mart

    Mart Well-Known Member

    I was unable to get copy of this from my library, if anyone has a pdf they could email me I'd be very grateful

    thanks

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  21. Mart

    Mart Well-Known Member

    Rebecca[/QUOTE]

    I think this is good question, I not entirely clear that I have clarified this properly in my own mind and exploring this paper in depth is part of the reason I think trying this worth a bit of effort because it will help answer the question.

    Here’s a quick rambling of why I think this.

    Investigating things scientifically generally requires trying to isolate variables and testing effects of one variable on another for probability these effects which are not simply random.

    These effects sometimes quite obvious because they are linear , change one thing (y) by x amount and the other will change by x amount or x amount +- some other constant. Plot these variables on a graph it will approximate to a straight line. Weight something on a scale – you are measuring F=mass*acceleration( from gravity ) nice simple linear relationship, we do it every day. Bingo something interesting to work with.

    The relationships may be a bit less obvious – logarithmic linear for example or may be a quadratic relationship (the square of one variable) +- constants, these create parabolas rather than straight lines, intersect the axes a certain points which allow solving of 2 equations because of this, complex relationships written in algebraic form usually become more intuitively identifiable when graphed.

    High school math . . . .. . that’s as far as I get.

    Because gait is such a complex interaction of mechanics, anatomy, neurology, material science and even psychology to mention the obvious it is tricky to isolate and study most of what happens.

    Modeling is helpful because it creates artificial scenarios to analyze specific facets. Models can be just thought about , physically created and tested, run as virtual computations and then the results compared to what is seen in reality.

    The paper I want to explore creates a simplified computational model of lower limb and looks for relationships which for a biomechanist are probably pretty basic but I have a “knowledge block” in understanding.

    As a podiatric clinician I examine people’s motion in very simplified way, occasionally I take high speed video, synchonising frontal and saggital views (to identify parallax problems and get better views).



    I do this to attempt to better understand why they have a therapeutically non responsive problem or to create ideas about what might be problem or how to approach it. Observational gait analysis has been shown to have poor reliability, taking video allows me to ponder and revise ideas, slow things down so that I can concentrate at one variable at a time blahh blahh.

    I also similarly take some kinetic data from a pressure sensor matrix mat or inshoe sensors.

    I create templates to regionalize anatomic landmarks, compare PPs and FTIs with normal values, create F/T curves to explore forefoot to plantar calcaneal area loading patterns blah blahh


    Sometimes my interpretation of this data seems quite revealing and I use this as a guide in my overall impression. Other times I scratch my head and lose some hair. Because of the limitations, systemic or knowledge wise I try to look for consistency in what I interpret, the more things seem consistently supporting my “clinical ” hypothesis the more weighting I put on it and visa versa.

    What I struggle with is interpretation. There are clearly identified limits in the techniques, and my knowledge.


    I think math or at least an understanding of more sophisticated analysis might be a major problem for me to get behond my basic stage.

    I am thinking of investing in emerging 3D systems to get a better "view" of things but need a more comforable handle on what this might have to offer.

    There are some ideas being banded around regarding how to use technology to enhance clinical decision making. Some are driven by researched findings and slowly evolving ideas eg. Craig Paynes comments regarding looking at shapes of FT curves of plantar calcaneal area and FF loading in terms of functional efficiency of gait (saggital plane function?).

    Some are I suspect driven by commercial interests of selling systems. The danger here is taking a compelling idea and using it without really understanding what it amounts to.

    It bothers me looking at the case studies disseminated by system manufactures claiming success of foot orthoses because it does XXXXXX . .. the ones I have looked at are horrible and are also being done with the apparent blessing of podiatrists.

    Now these compelling but untested ideas and may be right.

    It may be possible to reject compelling ideas by deeper understanding of what they amount to, or to use them effectively by applying conditions to their use according to identified limitations

    So what to do?

    Learn as much as I reasonable can but as usual the more you learn the more you find you don’t know, and there is too much to learn in single life time, I love Craig Payne’s signature rational for his immortality.

    BUT

    Find out soon than later what is worth learning

    As usual your question is right on the mark!

    Hope the ramble makes sense

    Cheers


    Martin

    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
  22. Asher

    Asher Well-Known Member

    Hi Martin,

    I enjoyed your ramble, I like the way you can explain where you're at. Hopefully some guidance is forthcoming.

    Rebecca

    BTW, I don't have any force-measurement equipment in my clinic. Is there any literature that you know of that is reputable discussing the pros and cons of the sorts of data you get from this gear and how podiatrists can use it - at least, what has proved the most informative for you / others?
     
  23. Mart

    Mart Well-Known Member


    My experince is this.

    I sat on the fence for many years, I did not buy anything but kept in touch with some of the literature. I am a natural skeptic and was apalled by the cavalier and frankly fraudulent justifications I got as part of a sales pitch from a visiting plantar pressurement system rep. Top that off with seeing colleagues buying into this approach and promoting their clinics with what amounts to witchcraft mascarading as science.

    However I became disatisfied with the limits of my understanding and ability to investigate patients I was seeing with chronic musculo-skeletal problems which I suspected being of mechanical origin.

    There is no text book which really addresses an encompassed practical approach to using technology for investigating lower limb MSK function, that exisits (as far as I am aware) is superfical basic stuff in an isolated chapter.

    I think the issue is that it is too early in the technology to be able to do this with reasonable conviction.

    I figured I would have to judge the merits of this use myself - spent a bunch of money based on what seemd to represent best value and gradually have incorporated using it, trying to fathom it's value as I go.

    Main concern is cost to patient and poor interpretation, I employ a podiatry assistant for data collection and preparation to keeps cost very low and regard my interpretaion with caution.

    I would love to discuss what this amounts to in more depth but have time restraints to add this to my list right now and also feel I need to get better grounded in my knowledge before discussing this too much

    definately a topic for the future though

    cheers

    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     

  24. Here is the paper that Martin wanted to post to Podiatry Arena. Looks like a good one. (Minetti AE, Alexander RM: A theory of metabolic costs for bipedal gaits. J Theor Biol, 186:467-476, 1997.)
     
  25. Phil Wells

    Phil Wells Active Member

    Kevin et al

    I have found out a couple of bits that I think are interesting for our clinical practice.
    The 1st one - http://ajs.sagepub.com/cgi/content/abstract/24/5/615 - shows that anterior tibial translation is increased in fatigued patients - fits with my observations of knee injuries patterns.
    The 2nd ref - http://www.ingentaconnect.com/content/tandf/rjsp/1997/00000015/00000003/art00010 - talks about interval training helping with fatigue resistance - again something I found in my own training routines.

    I would hope that most people take into account the effect of fatgue on there patients and assess them appropriately but I would be very interested in counter arguments against this.

    Cheers

    Phil
     
  26. David Smith

    David Smith Well-Known Member

    Hi All

    As Phil guides as back on track to the original topic that Kevin posted I wondered what it is in the physiology of efficient movement that we as podiatrists can affect.

    The thread has covered the cycle of efficiency of gait in terms of O2 metabolism.
    Here is a summary:

    -----------Efficiency of Respiration-----------------
    -----------------------V---------------------------------
    ----------O2 Availability to person-- PPO2 in air
    ----------Collection--- Breathing -- lung capacity
    Vo2 >--- Delivery-- ---uptake thru lung -- uptake by Haemoglobin- Blood saturation
    ---------Assimilation-- Cell respiration
    ---------Disposal -------waste products -H2O CO2 Lactic Acid

    ---------------------------------------------------------------------------------------------------------

    And in terms of the relationship of metabolic energy to metabolic work V's physical work:

    O2 availabilty to muscle cells

    Efficiency of cellular respiration

    Efficiency of Energy conversion

    Muscle Type

    Muscular activity -- Aerobic - Anaerobic

    Muscular contraction - isometric/isotonic - concentric - eccentric

    Anatomic variation.

    What can we change?

    Efficiency of Motion
    Efficiency of Muscular action
    Anatomic variation

    How?

    By directly altering the external forces (orthoses) and so indirectly altering internal forces

    By directly altering internal forces (surgery) and so indirectly altering external forces

    By altering neuromuscular action

    By influencing behaviour
    -------------------------------------------------------------------------------------------
    Therefore Improve VO2 to physical work ratio


    Would you say this is a reasonable summary?

    Cheers Dave
     
  27. Mart

    Mart Well-Known Member

    Since, as usual, I am a bit prone to taking the "scenic route" I have split of a new thread whcih looks at (Minetti AE, Alexander RM: A theory of metabolic costs for bipedal gaits. J Theor Biol, 186:467-476, 1997.) from a viewpoint of potential use force/time curves and the math involved in doing this


    any one interested go to

    http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=8000

    and I'll leave you in peace with the VO2 max :dizzy:

    cheers


    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  28. Dave:

    I would agree with most of what you say above. However, here are a few points to consider.

    In people of normal fitness, for normal speed walking activities (that are well below the VO2 of the anaerobic threshold), lung capacity has little to do with efficiency since the respiratory frequency can always be increased. In addition, lactic acid is probably not produced in significant amounts during normal speed walking since it should be a completely aerobic activity.

    During running, however, the VO2 increases significantly which puts all individuals at their anaerobic threshold at one running speed or another. During running, maximal VO2 will be very much dependent on oxygen carrying capacity of blood (hematocrit, Hbg), capillary density of muscle, cellular concentration of mitochondria, muscle mass, and cardiac efficiency, to name a few factors. Lung capacity is also not much of a factor in VO2 max, since the lungs are not the limiting factors in O2 exchange in most individuals, whereas, having a higher density of O2 carrying hemoglobin in the blood is a major limiting factor. Because of this fact of exercise physiology, artificially enhancing the O2 carrying capacity in an athlete's blood has been often used method of cheating in endurance sports for the past three decades (e.g. blood doping and EPO ).

    Can we as podiatrists alter metabolic efficiency of walking in most people? Probably not. However, in those individuals with significant gait pathology where the gait efficiency can be significantly altered with stretching exercises, changes in shoegear and/or well-designed custom foot orthoses, I do believe that podiatrists can significantly alter the metabolic efficiency of walking. In fact, this research needs to still be done and would be one of the most significant pieces of scientific research to support the potential benefits of foot orthoses and podiatric biomechanics treatment for certain individuals.

    The next question, is: can we, as podiatrists, alter the metabolic efficiency of running? This seems to also be unlikely except in a few cases where we can change the running style to a more efficient running gait type (e.g. make runners stop overstriding) or make a lightweight orthosis that allows the runner to utilize more elastic energy within their lower extremities during the support phase of running. The problem with orthoses and metabolic efficiency during running has always been the added mass of the shoe from the orthosis increasing the moment of inertia of the lower extremity and thus the work required to swing the leg forward rapidly during the forward recovery phase of the running gait cycle. This is why I often make plastazote #3 orthoses for many runners (rather than polypropylene) so that they can be "lighter on their feet".

    Finally, surgery alters internal structure which directly alters both internal and external forces.

    Good discussion.:drinks
     
  29. ely

    ely Member

    This is why I need to go back over physiology. I can't remember ever coming across VO2max in my own studies; the people who did human movement subjects did I think.

    I'm trying to sort through in my head the implications of this for my own practice... maybe giving a more scientific rationale to different treatments/explanations of problems than just "it's what the guidelines say". I'm thinking potentially about the effects of non-enzymatic glycosylation in connective tissues in increasing hysteresis in tendons and requiring more energy input... and how ischaemic skeletal muscles interact with metabolic efficiency, i.e. whether improving lower limb perfusion (and by extension skeletal muscle perfusion) is involved.. Wondering if distal motor neuropathy requiring more work from proximal musculature is related to metabolic efficiency. Wondering if the lower limb could have any independent effect on cardiovascular mortality and morbidity, rather than being purely confounded by the fact that they are all vascular beds. E.g. if by improving utilisation of O2 overall, decreasing metabolic demand, could decrease stress on the more central parts of the cardiovascular system... Also wondering how decreased insulin sensitivity (-> decreased uptake of glucose -> decreased "fuel" for ATP production/energy supply) fits into the picture.

    I think I'm totally off track here... again, I need to revise my physiology. Thanks for bringing the topic up though.
    Thanks,
    Regards,
    Ely.
     
  30. Ely and Colleagues:

    I thought it would be useful to include a thread on this important subject here because so few podiatrists have studied exercise physiology. This information is especially valuable for the podiatrist that treats athletes. Here is a nice review of O2 consumption and VO2 max for your reading pleasure.
     
  31. Mart

    Mart Well-Known Member


    In A theory of Met Cost for BPG page 475 it says

    The differences between the theoretical lines and
    the empirical points in Fig 5 suggest that the gaits we
    use may be a little different from those that would
    minimize energy expenditure.

    Some other evidence suggests the same, according to the estimates of Ker
    et al. 1987 only half the kinetic and potential energy
    lost at each footfall in running is stored as elastic
    strain energy and returned.

    If the duty factor were
    reduced\ the peak force on the foot would be greater\
    more strain energy would be stored and the cost of
    transport might be less.

    It seems possible that the
    limited strength of muscles\ or the risk of injury by
    very large forces\ may make optimum duty factors for
    running higher than the duty factors that would
    minimize energy cost.

    SO

    I am thinking . . . . .. .. if this is true in the real world

    Then increasing surface area of contact using could arguably reduce peak pressures, which may be more important than peak force in terms of surface tissue viability.


    AND


    Also the effects of the peak forces on the tensile structures might be moderated by the velocity attenuating effects of strategically placed ground reaction force from foot orthoses (eg rearfoot posting medial to sub-talar joint axis moderating ankle/STJ pronatory attenuation at HC)

    SO

    foot orthoses may allow better tolerance of reduced duty factor


    BUT

    Simon S has bought up the issue before that foot orthoses may have ADVERSE effect by reducing return of stored energy by destressing tensile structures and not allowing return of stored PE (if I understand him correctly).

    HOWEVER



    at the same time we may improve efficiency because higher
    duty factors reduce time for the leg to be
    swung forward making the force and work
    requirements of the swing higher.


    Clearly this seems to indicate an equilibrium which the body normally seems to have some mechanisms to optimize, hower it seems that there MAY actually be a theoretic possiblilty of shifting the equilbrium point in favour of increased efficiency based on this model using by the right kind of foot orthoses.


    Just food for thought.

    Any contra thoughts?

    Also I am surprised that you feel that, what I would regard as fairly inconsequential difference in mass between plastazoate and PP foot orthoses, would have noticeable effect of gait. Have you ever seen calculated relative change in what this might amount to in terms of change in moment of inertia of distal segment?

    Cheers


    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    Phone [204] 837 FOOT (3668)
    Fax [204] 774 9918
    www.winnipegfootclinic.com
     
    Last edited: Feb 7, 2008
  32. Mart

    Mart Well-Known Member

    Hi Kevin

    Not exactly a foot orthoses but this made headline news in Canada last night.

    Toyota prius hybrid eat your heart out . .. . . . hamstrings rule :dizzy:


    Biomechanical Energy Harvesting: Generating Electricity During Walking with Minimal User Effort

    J. M. Donelan,1* Q. Li,1 V. Naing,1 J. A. Hoffer,1 D. J. Weber,2 A. D. Kuo3

    We have developed a biomechanical energy harvester that generates electricity during human walking with little extra effort. Unlike conventional human-powered generators that use positive muscle work, our technology assists muscles in performing negative work, analogous to regenerative braking in hybrid cars, where energy normally dissipated during braking drives a generator instead. The energy harvester mounts at the knee and selectively engages power generation at the end of the swing phase, thus assisting deceleration of the joint. Test subjects walking with one device on each leg produced an average of 5 watts of electricity, which is about 10 times that of shoe-mounted devices. The cost of harvesting—the additional metabolic power required to produce 1 watt of electricity—is less than one-eighth of that for conventional human power generation. Producing substantial electricity with little extra effort makes this method well-suited for charging powered prosthetic limbs and other portable medical devices.

    1 School of Kinesiology, Simon Fraser University (SFU), Burnaby, BC V5A 1S6, Canada.
    2 Department of Physical Medicine and Rehabilitation, University of Pittsburgh, Pittsburgh, PA 15213, USA.
    3 Departments of Mechanical Engineering and Biomedical Engineering, University of Michigan, Ann Arbor, MI 48109, USA.

    cheers


    Martin


    The St. James Foot Clinic
    1749 Portage Ave.
    Winnipeg
    Manitoba
    R3J 0E6
    phone [204] 837 FOOT (3668)
    fax [204] 774 9918
    www.winnipegfootclinic.com
     
  33. David Smith

    David Smith Well-Known Member

    Hi All

    Here's an iteresting and relevant newish paper that deals with the reason for muscle fatique. The lactic acid build up = muscle fatique model has been discredited and this new theory attempts to explain why muscles become fatiqued. Apparently it is to do with leaky calcium channels and "when muscles grow tired, the investigators report, tiny channels in them start leaking calcium, and that weakens contractions. At the same time, the leaked calcium stimulates an enzyme that eats into muscle fibers, contributing to the muscle exhaustion."
    Apparently experiments with mice using new drugs to control calcium leakage dramatically mproves muscle stamina.

    Ref:http://www.pnas.org/cgi/content/full/105/6/2198

    Cheers Dave
     
Loading...

Share This Page