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In-Shoe force measuring

Discussion in 'Biomechanics, Sports and Foot orthoses' started by reillyshoe, Aug 21, 2011.

  1. reillyshoe

    reillyshoe Member

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    Does anyone here use in shoe force measuring to assess patients? I am specifically interested in the Tekscan F-scan in-shoe system- is this considered to have an accuracy appropriate for research purposes? Limitations of the system? Anyone have the wireless system?

    I have read papers assessing the accuracy of the system, and some of the previous threads on this site. The technology changes, and I am wondering how the perception of the technology has changed in the last couple of years.
    Thanks in advance!
  2. Bruce Williams

    Bruce Williams Well-Known Member

    I consult for Tekscan in the US.
    Email me with questions if you like, docorange1@me.com.
  3. Depends what you want to use it for.

    P.S. I don't consult for Tekscan and as such I have no vested interest in the product.
    P.P.S. lets discuss this in an open forum, rather than via private e-mails!

    As far as I am aware, the hardware is still the same old resistive ink technology which is still influenced by surface stiffness and sensor bending problems.

    Attached Files:

  4. reillyshoe

    reillyshoe Member

    Thank you Simon, your paper is a great help!

    Force plates have some obvious technological advantages, but they also have limitations. I am particularly interested in recording solar pressures during athletic performance, and the footing plays an important role in the forces imparted on the foot. The limitations (pressure/force/conformation of the sensor to the foot) of the Tekscan system not withstanding, it seems there is a place for this technology?
  5. The only way you can measure foot-interface forces is with an in-shoe systems (unless you run barefoot over a force plate), but the in-shoe systems have considerable limitations. If I were going to do this kind of research, I'd use both simultaneously.

    Like I said, it depends what data you are hoping to obtain. If you want to compare shoe X with shoe Y or orthoses A with orthosis B, I'd be very aware of the technological limitations. Also depends on the variable of interest: timing probably isn't so bad as absolute forces.

    This is a nice review too:
  6. efuller

    efuller MVP

    Has the technology changed. Yes, wireless is new, but have the sensors changed? I agree with Simon's point about issues with bending the sensor. A bend can either damage the sensor or change the output, or both. This is a problem with all in shoe devices. Especially if you want to compare shoe only vs. orthotic in the shoe.

    Another issue is proper calibration. One method of calibration is to have the patient stand on the sensor and then put the patient's weight into the system and then the output of the entire sensor is 'calibrated" to the patient's weight. I would trust calibration with a bladder and known pressures more than plugging in the patient's weight method. I would certainly verify for yourself that either method was repeatable before using for research. It's probably good enough for getting a relative pressure difference between treatments.

  7. I have issues with the calibration using the bathroom scales (subject weight) method too. I even have issue with re-calibration between trials using a bladder system. If I was carrying out a piece of research measuring body weight, you wouldn't expect me to use a different set of bathroom scales to measure the weight of each subject without measuring the variation in the weight measured by the different sets of bathroom scales- right? or at least demonstrate the variation between the sets of scales. Rather, you'd expect me to use the same set of scales across the board- right? So why should it be acceptable to re-calibrate the sensors between subjects, i.e. change the bathroom scales for a different set, between subjects in a research study of in-shoe pressure without demonstrating the variation in the calibration sets?

    I disagree with Eric: I don't think it's good enough for getting a relative pressure difference between treatments- this is what we discussed in our paper. Unfortunately, we don't have any other viable options.
  8. reillyshoe

    reillyshoe Member

    I am looking to compare the distribution of plantar pressure on different race track surfaces in the equine hoof. Absolute measurements would be important as part of the standardization on different surfaces (along with speed).

    The calibration worries me a bit, as the standing pressure is very different than the force at the gallop. I do have an Instron available, and it would be possible to calibrate the prepared sensor at at force comparable to what is expected during the trials.
  9. Boots n all

    Boots n all Well-Known Member

    Have you seen nah:D touched the inserts?

    l dont believe they would stand that sort of impact, as for the speed, Bruce will have the answer l am sure
  10. reillyshoe

    reillyshoe Member

    Yes, I have worked with the sensors. I have not tested them for accuracy, and the exchange here has been very useful in understanding the value of the resulting data.

    In this video, the horseshoe is clearly visible. The axial portion of the hoof is also subject to pressure, and it makes sense that the amount of pressure is dependent upon the substrate. Horses race on all types of footing (grass, dirt and synthetic), and quantifying the weight bearing surface might prove useful.

  11. Bruce Williams

    Bruce Williams Well-Known Member

    Tekscan does walkway with horses and I think "In-hoof" as well.
    Check with their sales person to find out for sure.
    Their sensors can gather at 750hz as well with the wireless data logger system.
    I'm sure the sensors would not last long due to weight and forces of the horse gait.
    That said I suppose geometry of the flat hoof not such a big deal in this case! ;-)
    Good luck!
  12. Boots n all

    Boots n all Well-Known Member

  13. F-Scan system has changed and evolved. Hardware (electronics), software and sensor have gone modifications. Other that has been addressed is equilibration and calibration procedures and goodness, in addition to trial goodness. Protocols to determine and ensure sensor goodness, calibration goodness and trial goodness are also avialble to verify accuracy and repeatability of the data.

    Those desiring more information on the above, contact the Tekscan Territorial Representative. Inform me if you do not know the Tekscan Terrirorial Representative for your area or country, and I will reference him/her to you.

  14. reillyshoe

    reillyshoe Member

    As a general question to those with the system- do you use it for clinical purposes or as a research tool?
  15. Bruce Williams

    Bruce Williams Well-Known Member

    I use it primarily for clinical purposes. I am working with my local university to do in-shoe running shoe studies with material studies as well for potential cross validation.

    It can be used very well for both areas.

    Is your focus primarily equine research and treatment?

    Bruce Williams
  16. Hi Norm, I trust you are well. I also trust you more than I trust any area representative. Are you able to provide more details on how the software and hardware has been updated to negate some of the problems with the use of in-shoe pressure systems in foot orthoses research that have been discussed in our paper and the work of several others?
  17. docbourke

    docbourke Active Member

    I have owned and operated a Pedar wireless pedobarograph in my rooms for the last 10 years. I also have a Zebris pressure sensitive treadmill. These are great toys and good for research but apart from detecting areas of high pressure in diabetics there are very few validated clinical uses for them. I have no expreience with horses but think the hooves would mush up any pressure sensitive insole pretty quickly.
    I preferred the Pedar over the Tekscan because of durability and reliabilityof the insoles. The Pedar insoles last for years and only need recalibration (with pressssure bladder) once per year or so. Tekscan insoles are once only use or at the most a few repeat uses depending on the number of steps and the footwear. They also demonstrate loss of accuracy and wear at an unpredictable rate. The ink can break much more easily than the more robust and flexible Pedar insoles. They do have the advantage of being able to be cut to size and in the case where the test is going to destroy the insoles such as you may have are probably more economical. Also look at the software package as the amount of data when measuring dynamic gait with pressure insoles is huge and can be overwhelming and unmanagable.

    I am endeavouring to find clinical uses for the insoles and will keep you posted.

    Gerard Bourke
  18. Boots n all

    Boots n all Well-Known Member

    We only use our in-shoe Fscan for Diabetics also, to assess both pressure and trajectory path
  19. Hi Simon,

    Doing fine and traveling in Asia.
    I get back from travels 1st week September.
    Will then provide you details on software, hardware and sensor up-dates.

  20. Qas

    Qas Member

    Hi there, I thought I’d throw our hat into the mix :), I work for Tomorrow Options, who have an in-shoe plantar pressure system.

    Our system, WalkinSense, was designed specifically for clinical use and so is extremely lightweight and easy to use. The device weighs around 67grams and is strapped around the front of leg above the ankle. Not only does it measure in-shoe plantar pressure but it also simultaneously collects lower limb activity data, such as walking speed, cadence, step amplitude, stride length and distance walked. As you guys must be aware, walking speed plays a huge effect on plantar pressure, and so considering this for any plantar pressure analysis this is important. Most other devices will have to have patients walk on treadmills etc to keep this constant, whereas because ours measure this (correct me if i’m wrong but I think ours is the only device that measures this simultaneously), you can let the patients walk normally and then choose the appointments with the same/similar walking speeds to get a true reflection of any off-loading intervention etc.

    Our device has two modes of working, real-time and offline. Real-time utilises Bluetooth technology to allow users to see each individual step data on their laptop whilst the patient is within Bluetooth range, hence allowing to see effects of intervention’s quickly and easily. The offline mode, utilises our long lasting battery (between 5-7 days) for longer studies, e.g letting the patient walk for an hour or at home etc. Offline data is captured in segments and displayed as an ‘average step’ of the data.

    We use a net of 8 discrete sensors, which allow the clinicians to evaluate plantar pressure at 8 user defined points. All our sensors are pre-calibrated (no need to calibrate for each person), however a simple calibration tool allows for recalibration within minutes.

    A brief demonstrative video can be found on Youtube here:

    Or on our website: www.tomorrow-options.com
    Our devices are being used by a couple of PCT Podiatry departments, a University research department along with private podiatrists throughout the UK. In sports, if any of you follow football, l it is being used by FC Porto (last year’s UEFA Europa league winners as part of a domestic treble). It was recently used to screen the entire first team of a top four football club, and to highlight its speed and ease of use, 14 players were assessed in just under 2 ½ hours!!!

    This is just a brief snapshot of our device, if you do have any further questions, do PM or reply to this thread. I just thought that some of the guys here may have heard of our system but might not know any further info :)


  21. docbourke

    docbourke Active Member

    Sounds a very practical tool. The only disadvantage may be if you require data in more than 8 sections, ie over the whole surface of the sole with 1 X 1 cm sensors. If that is not the case sounds great.

  22. Qas

    Qas Member

    Thanks docbourke, our aim was to make it a practical and affordable tool so that most clinics with an interest in biomechanics can have a system ;)

    The WalkinSense was designed with a net of 8 discrete to allow flexibility for the clinicians to choose regions of interest. I do see the limitation of only having 8 sensors if you do want to measure at more than 8 regions, however studies have shown that 8 sensors are sufficient to measure the plantar pressure distribution.

    For anyone interested:

    Henning EM, Milani TL., In shoe pressure distribution for running in various types of footwear. Journal of Applied Biomechanics, 1995; 11: 299-310.


  23. Qas:

    Let's say we have a diabetic patient with peripheral neuropathy and we want to determine which areas of the plantar foot have the highest plantar pressure during walking gait so we can help prevent plantar ulceration. How does a pressure insole system with only 8 sensors help us find where the area of maximum pressure is on the plantar foot to help prevent ulceration? Do you have any studies that show "that 8 sensors are sufficient to measure the plantar pressure distribution" in the pre-ulcerative diabetic patient?

    I would think that using a plantar pressure insole system such as the F-scan, E-med or RS-scan, which all have many more sensors under the foot, would be much better systems to help determine the areas of maximum plantar pressure. Don't you think their pressure insole systems would be better than your WalkInSense system for this clinical application?
  24. I agree with your sentiments here, Kevin. Actually the interesting part of this system is not the pressure measurement part of it at all (after all, it's basically an electrodynogram- which is hardly cutting edge). Rather it is the accelerometer which has far greater potential. At the moment this company are not exploiting this correctly (in my opinion) measuring gait speed is interesting, much better to add 3 axis accelerometry and the ability to measure and moreover, display tibial acceleration. I did chat to the owner of this company and a representative regarding this a while ago. I'm not sure if they took on board my comments or not. Linking tibial accelerometry with in-shoe pressure measurement at a reasonable price point in a user-friendly package would go some way to make up for the lack of sensor resolution- don't you think?
  25. Qas

    Qas Member

    Hi Kevin

    Apologies in advance for the long reply ;)

    Looking at the diabetic foot ulceration problem from a clinical point of view, I believe our device to be a strong candidate based on the following points:

    1. Measuring plantar pressure in diabetic foot patients is important when neuropathy has also occurred. If there was no neuropathy then patients usually protect themselves (e.g. they feel pain in these areas and do something to alleviate this).
    2. We never aimed for the WalkinSense to be used as a diagnostic tool to identify areas at risk of ulceration, but instead be used as a complimentary tool to existing practises within diabetic foot clinics. Therefore it should be used in conjunction with existing practises which highlight risk areas such as neuropathy tests (e.g. monofilaments), visual inspection or even force plates.
    3. You mention that other systems (that use an insole full of sensors) may be better to help determine the areas of maximum plantar pressure. I have to say I agree with this. Purely because they have more sensors, you get more quantitative information. However, diabetic foot ulcers are caused by a combination of neuropathy and elevated plantar pressure, and thus the neuropathy tests must also be used with these systems. Therefore after identifying areas of high risk, our device can be used in the same way, but only providing information in these areas of interest.
    4. Our device (please correct me if I’m wrong) is the only device in the world that measures plantar pressure and walking speed simultaneously (along with other lower limb variables). Therefore from a clinical point of view, you don’t need to purchase another device (e.g. treadmill) to take this into consideration, allowing the patients to walk ‘naturally’ (as opposed to on a treadmill where they may alter the way the walk to fit the way they think they should walk). This is great for testing the effectiveness of off-loading devices. For example after prescribing a pair of orthotics, you can test to the plantar pressure at these regions to determine if they are having the desired effect, but more importantly you can eliminate the effects of walking speed etc to get a true effect of these orthotics.

    You ask specifically if I think clinically the WalkinSense is not as good as the alternatives. For me the answer would be that the WalkinSense is the best tool around for the clinical setting. Not everyone can afford (both financially or time wise) the alternative systems (which are more expensive and time intensive to set up). Our device is affordable, easy and quick to use (using our device takes minutes) and several tests can be carried out in single appointments. Using a net of sensors allows either foot to be measured, and feet of all sizes. What are the running costs of insole based systems (e.g. for different sizes and replacement of insoles etc)? Don’t the insoles only last for a number of steps? Our nets can survive miles of steps! Also the insole systems don’t take into consideration if a foot is too big for the insole? If this is the case, then don’t you have missing data?

    I may also be out of line for saying this, but I’ve come across several clinicians in the UK, who have invested in the other systems, but do not use them frequently (if at all!). This is purely because they find these devices either too time consuming or complicated to use. I’m not saying this is a justification for not using these devices, as mentioned they are very good devices, but this is where I believe the WalkinSense to be superior as it is very quick to set up and interpret the data. Surely it would be better to have a device that is simple to use and use it on many patients than have a device that is complicated and provides a lot of information, but then gathers dust on a shelf as its not being used?

    As mentioned, our device was designed to complement existing practises within the diabetic foot clinics. Therefore used in conjunction with monofilaments etc, I believe the WalkinSense to be the best package available to clinicians due to its size, affordability, ease of use and ease of interpretation of data.

    I have a paper which highlights the arguments for and against insole based and discrete based systems, I'll have to dig it out for you and post it later if interested ;)



  26. next...
  27. Boots n all

    Boots n all Well-Known Member

    Strangely true, that some have purchased this and other technologies & do not use them often enough, its like anything, put the time aside charge the client appropriately and use it, the more often you do the easier it will seem.

    But the big question, how can your system be any easier/quicker?
    You still need to attach to the client and from what l understand there would be more information gathered(?) and needed to be read through with your system.

    QAS said "We never aimed for the WalkinSense to be used as a diagnostic tool to identify areas at risk of ulceration..."

    This is something l feel the Fscan does very well.

    So yours is more focused on sports people than rather than the DB client type
  28. Qas

    Qas Member

    Hi Simon,

    Your suggestions were taken on board, however at that time, and still to be fair, we are currently working on several other projects (e.g WalkinSense for sports etc). We do appreciate your suggestions, its just at the moment we have had to prioritise other projects, however if in the future we get round to something like this then we will be in touch ;)


  29. Qas

    Qas Member

    The way our system can be quicker is that no time is ‘lost’ in setting up the device by calibrating the device. Our sensor nets are pre-calibrated, and only need calibrating every several months or so (and even then just to test). And as its such a lightweight device that straps around the top of the ankle, once the sensors have been placed on regions of interest, then its simply strapping the device and installing an appointment (a couple of minutes max).

    Even though we provide extra information, no don’t get reams and reams of data and so have to sieve through for the relevant data. Instead, it is displayed clearly and graphically, so you don’t need to have a biomechanics degree to understand. I’ve posted a screenshot below to show how all the information is provided in one simple screen, allowing the clinician to take all the variable into consideration.


    For anyone, who would like to see how simple our device is to operate, I can organise a skype demo at a convenient time ;)

    TBH, I would have to disagree with this point. Within in the diabetic foot clinics that I have visited, plantar pressure is measured in patients after an ulcer (to prevent reulceration) and high risk areas have already been identified based on visual inspection, knowledge of previous ulceration and barefoot pressure measurement. This way they determine the offloading characteristics of the therapeutic shoes/orthotics prescribed to reduce pressure at these exact locations. To determine whether the shoes offload pressure at these specific high risk areas, the WalkinSense works perfectly, and allows these tests to be carried out quickly for clinicians.

    We are currently in the process of releasing the WalkinSense for Sports, which will be more orientated for sports podiatrists etc. This will incorporate video synchronisation, but more specifically, ANY video synchronisation. So you will be able to synch with something complicated like ultra slow-mo cameras to simply your mobile phone camera!

    But thats another story ;)



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