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Can foot soles/fat pads be built up?

Discussion in 'Biomechanics, Sports and Foot orthoses' started by collden, Oct 1, 2010.

  1. collden

    collden Member

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    Hello. I am not a podiatrist, but I'm posting this question here to hopefully gain some understanding on the physiology of the foot which I've been unable to find anywhere else on the Internet:

    In the barefoot running community there is a lot of talk of people who claim to gradually build up the toughness of their soles, at least partially by growth of their fat pads.

    On the other hand, reading about various problems related to fat pad atrophy, it is easy to get the idea that the fat pads cushioning your feet cannot be built up or regenerate, they can only degenerate with increasing pressure due to running or standing extensively, and that any degree of wear and tear sustained to these tissues is essentially irreversible.

    So what is the case? Are fat pads (and foot soles in general) dynamic tissues which can respond to increased demands by growing bigger/tougher, or can they only slowly degenerate through decades of accumulated overuse?
  2. collden

    collden Member

    Thank you sir!

    Yes, it seems from the comparison between runners and cyclists that the fat pads do somehow adaptively remodel themselves to accomodate the greater stress. But then, how to explain that overuse/too much pressure over long periods of time, is supposedly one cause of fat pad atrophy? Is the situation similar to muscle response to weight training, where you have to hit a balance between exercise and rest/nourishment to grow muscles, and actually break down muscle mass if you overdo it?

    Is it possible that the soles/fat pads do in fact have an innate capacity to repair, rebuild and strengthen themselves, but that this capacity is lost in certain degenerative metabolic conditions like diabetes, and that this loss of rebuilding capacity is responsible for the degeneration of the foot?
  3. Think of it this way: if I buy a new mattress for my bed and then lay down to sleep upon it, on the first night it will deform by a certain amount under my weight. When I've slept on it hundreds and hundreds of times it will deform more under my same weight due to "wear and tear". At some point we might decide that the mattress is worn out and needs replacing because it compresses so much under my body weight that it fails to "cushion" me. What the research paper on running versus cycling heel fat pad stiffness is saying, is that for a given load the fat pad beneath the heel of the runners feet deforms more than the cyclists for the same given load, i.e. it is less stiff or more compliant in runners. So it behaves more like the worn out mattress than the brand new one among runners. Is this adaptive remodelling or just a wearing out of the fat pad? Take your pick. I know what my money is on...
  4. collden

    collden Member

    Well, maybe I'm comparing apples and oranges here, but I thought that stiffness was actually positively correlated with heel pain problems, ie healthy fat pads are supposed to be more elastic. Diabetics, overweight and the aged all have stiffer heel pads compared to healthy young adults.


    In this light, the runners do appear to have healthier fat pads than the cyclists.
  5. collden

    collden Member

    Well, maybe I'm comparing apples and oranges here, but I thought that stiffness was actually positively correlated with heel pain problems, ie healthy fat pads are supposed to be more elastic. Diabetics, overweight and the aged all have stiffer heel pads compared to healthy young adults. See for instance,

    *Comparison of the mechanical properties of the heel pad between young and elderly adults
    *The relationship between the thickness and elasticity of the heel pad and heel pain
    *Plantar tissue stiffness in patients with diabetes mellitus and peripheral neuropathy

    In this light, the runners do appear to have healthier fat pads than the cyclists.
  6. Elasticity and stiffness are not the same. I haven't read all of the references. From the first reference above: that fat pad is thicker in the elderly, is it stiffer per unit thickness? Or just stiffer because it's thicker? Did they actually measure stiffness, i.e. deformation per unit load and normalise the data for thickness? If I had two identical sheets of material differing only in thickness, the thicker one would be stiffer. The second reference is about elasticity- did they measure stiffness (as defined above)? The third one did seem to measure stiffness (from what I could glean from the abstract, not sure if the fat pads they were comparing were the same thickness or not?), but they didn't say whether this was a good thing or bad thing. I guess there will be an optimal stiffness in the fat pad beneath the heel, too compliant = bad, too stiff = bad. Who's to say the runners heel stiffness wasn't too compliant, while the diabetics weren't too stiff? You've got the references you were looking for, go read and make your own mind up.

    You can't get there from here. In other words, you can't make that conclusion from the research; much as you would obviously like to.
  7. collden

    collden Member

    Sure, it's possible that the runners do in fact have too elastic heel pads as a result of their running, the authors don't seem to comment on this.

    My intent wasn't really to start a debate, but to ask whether there exists some kind of consensus in podiatry about the nature of the foot pads - if they can in fact repair and adaptively remodel and become tougher in response to increased demands, or if they're just completely passive tissues and it's all downhill from the day you take your first steps. Is this just largely unknown? The runner/cyclist comparison aside, it does seem as if there is a dearth of research on how the foot pads respond to long term exercise stress.

    But it does seem to me that if there is was a straight link between stress on the feet and degeneration of the foot pads, that the number of foot pad injuries would simply skyrocket when comparing populations that put different amount of stress on their feet. Not only are runners fat pads wearing down much faster than say cyclists, but they are still subjecting their progressively weaker pads to far more stress than the cyclists. The prevalence of foot pad atrophy ought to increase at an astronomically higher rate in the running population with increasing age, compared with the general sedentary population, but is the discrepancy really that great?
  8. You missed my point, perhaps I didn't make it clear the first time: stiffness and elasticity are not the same thing
    This is a forum for academic debate. In order to answer your question you'd need to run a longitudinal study- end of story.
  9. collden

    collden Member

    My bad, but aren't elasticity and stiffness always inversely correlated?
  10. The inverse of stiffness is compliance. Elasticity is the physical property of a material that returns to its original shape after external force that made it deform is taken away. Do you think you can induce plastic set in the heel pad?
  11. DaVinci

    DaVinci Well-Known Member

    They do have a habit of making these unsubstantiated claims.
  12. admin

    admin Administrator Staff Member

    Due to the automated spam features, the above message of collden was sent to moderation and has only just now been added to this thread.
  13. Craig Payne

    Craig Payne Moderator

    There is a difference between correlation and causation. Correlation does not imply causation.

    The positive correlation between heel pad stiffness and heel pain could mean one of three things:
    1. That this was the cause
    2. That the heel pain happened first and the disuse of the fat pad led to the change in stiffness
    3. A third confounding variable is related to both and could explain the correlation
  14. collden

    collden Member

    Anyway, in terms of research it seems these are still open questions. Yet to my understanding there is a widespread belief that fat pads cannot regenerate or become strengthened in response to stress, even in healthy individuals. Why is this so?
  15. Craig Payne

    Craig Payne Moderator

    Tissue properties change in response to stress, I do not think we really know about the plantar fad pad.
  16. wdd

    wdd Well-Known Member

    I think that the consensus is that fat cells can not regenerate. Like brain cells you start with a certain number and it's downhill from there on.

    However I would imagine that fad pad cells are unlikely to be destroyed by running - in a normal healthy person.

    With the gradual reduction in tissue vitality associated with ageing and and the sometimes marked reduction in tissue vitality associated with disease the probability of cell damage and death increases.

    If the fibrofatty padding can adapt to stress, and it would seem reasonable that it can, possibly the collagen envelope around the fat cell and/or the fat within the cell changes quantitively or the qualitatively.

    I have always assumed that the major stresses falling on fat cells are absorbed by the surrounding fibrous envelope?

    Just an idea.

  17. collden

    collden Member

    Thanks for your thoughts wdd. Brain cells are actually a good example of a kind of tissue that was once falsely thought to be incapable of regenerative growth, a belief that has been completely overturned in the past decades, try googling "adult neurogenesis". Likewise, fat cells can also proliferate, at least in certain kinds of adipose tissue. I guess it remains to be shown that it can occur in fat pads, but I don't really see a reason to rule out the possibility.
  18. Collden:

    Here is what I have observed in my years clinical practice and have learned from my reading on this subject:

    1. The thickness of the plantar heel adipose layer tends to thin with age. Young adults have the thickest adipose layer, and plantar fat pad atrophy is quite common over the age of 60 and 70. Other factors thought to thin plantar fat pad tissue are high magnitudes and long durations of compression and shearing forces, a history of plantar heel trauma and repetitive corticosteroid injections. These changes, from my clinical experience and from my reading of the available literature on the subject, are permanent and are, therefore, not reversible.

    2. The plantar adipose tissue of the calcaneus is a highly sophisticated system of fibrous septa which are formed into "pockets" that hold fat cells, very much like the organized fat cell-fibrous septa construction of the human breast. In other words, the fat cells are held in place by these fibrous septa under the plantar calcaneus since, without these fibrous septa holding the fat cells plantar to the calcaneus, these fat cells would simply shift away from the plantar calcaneus to the periphery of the plantar calcaneus during weightbearing activities, leaving the bone and fibrous covering of the calcaneus unprotected and "uncushioned".

    3. The claim that the plantar fat pad tissue can be somehow built up by barefoot running has absolutely no scientific or experimental evidence to back it up. This is just another one of those bits of false propaganda that seem to stream continuously from the barefoot running commuinty. Any changes in the plantar fat pad that occur from running in or out of shoes, or changes that occur from any weightbearing activity, for that matter, will be permanent structural changes in the specialized adipose tissue of the plantar heel. Experiments with silicone injections into the plantar heel have shown that, at best, that this will last only about a year due to eventual migration of the silicone from the plantar calcaneus to the periphery of the plantar calcaneus. This lack of permanence of injectable silicone probably occurs due to the fibrous septa being degenerated in patients with plantar fat pad atrophy.

    4. If any changes occur to the soft tissues of the plantar heel, then it will be the thickening of the epidermis of the plantar heel that will produce the main protective effect for barefoot runners. Thicker epidermis is known to occur with chronic, repetetive forces to skin covering certain body parts. Since the plantar skin of the foot has some of the thickest epidermis in the body, it will also certainly have a large potential, over time, to get thicker and stiffer with long term barefoot walking and running. Unfortunately, it also seems, anecdotally, that developing enough skin thickness to run comfortably barefoot may take longer than days, weeks or even a few months, unless the individual has been habitially barefoot during their standing and running activities also as a child and a youth. My examination of the skin of runners who have grown up barefoot and have trained a good part of their lives barefoot shows that their plantar skin is more like thick, stiff shoe leather than the supple, uncallused skin that many of my patients seem to desire.

    Interesting topic.

    Hope this helps.
  19. wdd

    wdd Well-Known Member

    Excellent Collden.

    I am glad you've found evidence that brain cells and fat cells can regenerate. Now you just have to find out under what circumstances and to what extent and you will not only eliminate the need for running shoes but cure strokes, Alzheimer's, etc, etc.

    In the short term I don't think your on to a winner.

    Best wishes wdd
  20. collden

    collden Member

    Kevin Kirby, thanks for your input.

    Do you think that a prolonged regimen of rehabilitative eccentric heel drops would qualify as "high magnitudes and long durations of compression and shearing forces"? I've suffered from achilles tendinosis for several years (bilateral for the past six months), and have been performing eccentric heel drops daily for that long. My original interest in this question was sparked a week ago when I decided to increase my training volume from 60 to 180 heel drops per day (currently with a 45 lbs backpack and a 10 second eccentric phase). Prior to this I had never had any significant pain on the underside of the foot. After the second day of this I woke up the next morning to find that the ball of one foot had gone partially numb and tingly, and for some days after that I experienced some light burning and tenderness. The sole of the other foot felt normal, though with the increased training volume it hurt more during exercises.

    I persevered with the exercises though, and actually, in the last couple of days they have been getting somewhat easier and less painful on my soles to perform. Perhaps this is just the skin getting tougher, though that supposedly takes longer than a week? It will be interesting to see in the coming weeks if my soles can fully adapt to this new training volume to make it as comfortable as it once was to perform 60 reps per day. Though I suppose if this program carried a significant risk of permanent fat pad atrophy, someone would've noticed by now given how popular it is as a treatment for tendinosis.
  21. wdd

    wdd Well-Known Member

    Hi Collden,

    I think that maybe you can relax a little as far as fat pad atrophy is concerned - at least for the moment.

    'Numb and tingly' usually indicate nerve damage and given the number of reps and the weight of the backpack you are carrying it wouldn't be suprising if the rolling motion, as you lift and lower your heel, had damaged a small nerve. However it sounds as if it's getting better.

    It might be useful if you visited a professional for a hands on examination, diagnosis and management plan. Web diagnosis is a rather inexact science.

    An aside - Do you do these exercises to allow you to take part in some sporting activity or just for normal everyday activity?

  22. collden

    collden Member

    Thanks wdd, yes I was thinking it was more likely some nerve damage, though I wasn't sure if the slow rolling motion itself could produce strong shearing stress on the ball or not. Another thing is that I've also experienced a weird "bubbly" sensation in the tender area of the sole after the exercises when I'm resting the feet. Not painful, but actually quite pleasant, any idea what that could be?

    I'm doing these exercises mostly for normal every day activity as I'm not much of an atlete, I gave up running when I got the injury and likely wont go back to it. My tendons have improved a lot in the past year, but I still have some morning stiffness and can get aches in my achilles if I walk or stand around too much. The ultimate goal would be to get back to normal healthy tendons that could stand sporadic intense activity or long walks without any pain.
  23. collden

    collden Member

    Pardon for going completely off-topic, but I had a meeting with a physiotherapist today about the continued rehab of my chronic achilles tendinosis. He seemed to think that it was absolutely critical I change footwear for my tendons to recover. I wear flat and rather thin soft shoes which I find very comfortable, but he thought I should get much more steady shoes with well-built up heels.

    I was under the impression that using heel inserts or shoes with heel support was good in the acute phase of tendinopathy to relieve pain, but could rather contribute to calf muscle shortening if used in the long term. Is the use of special footwear really that important for recovering from tendinosis?

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