Complete Guide to Plantar Fasciitis

Myths about plantar fasciitis have spread far and wide, thanks to the miracle of the internet.1 Dr. Google mostly supplies either simplistic and brief conventional wisdom from the big medical sites… or an effectively infinite supply of amateurish pet theories and sales pitches for snake oil of every description, from literal oils to stretching contraptions to pseudo-surgical procedures.

There’s nothing “simple” about plantar fasciitis. Most musculoskeletal problems are less “mechanical” and more biological than they seem at first, and plantar fasciitis is actually a good medical puzzle. Most health care professionals don’t know the latest research and can’t offer patients advanced guidance. Many don’t even know the basics of plantar fasciitis rehab, never mind the options for the severe and odd cases — because there’s more to read and know than they could ever have time for.

Would a rub help?

If only! A foot rub is nice, and in fact it can help a little, but massage therapy is actually one of the least effective of the common therapies for plantar fasciitis.

Family doctors are not prepared to treat plantar fasciitis. (Or, frankly, any musculoskeletal condition trickier than a toe stub.2)

Even podiatrists (foot doctors) — especially in North America, where podiatrists are mostly focused on surgical procedures — are not a great choice. They often give poor quality advice about “simple” foot injuries. A few take a special interest in these conditions, but most don’t, and the occasional tough case of plantar fasciitis is just not on their radar — which is understandable but regrettable.

Physical therapists are the best overall bet for good plantar fasciitis care, in my opinion, but many still lack the know-how for coaching people on tough cases. Their profession is also less scientifically rigorous than you’d think, and still peddles a lot of 20^th century “high tech” snake oil.3

Sports and rehab medicine is amazingly primitive considering how much potential funding it has. You’d think anything affecting elite athletes with huge audiences would be getting more attention!4 The situation is improving,5 but only recently and it still has a long way to go.

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Although plantar fasciitis is somewhat tendinitis-y, the plantar fascia is no tendon: it’s actually more like a ligament, although it’s strange even for a ligament. It is a sheet of connective tissue (“fascia”) that stretches from the heel to toes, spanning the arch of the foot, from bones at the back to bones at the front (whereas tendons connect muscles to bones).

The “itis” suffixes in tendinitis and fasciitis mean “inflammation,” but the tissue is rarely inflamed the way we usually understand it (maybe at first, not for long). Instead, the plantar fascia shows signs of collagen degeneration and disorganization. In 2003, Lemont et al. looked at 50 cases and found so little inflammation that they declared that plantar fasciitis “is a degenerative fasciosis without inflammation, not a fasciitis.”11 So it would be better to use a more generic suffix — like opathy (diseased) or osis (condition).

In fact, this is true of all so-called “tendinitis” — chronically inflamed tendons are not so very inflamed. “Recent basic science research suggests little or no inflammation is present in these conditions.”12 And Khan et al. wrote that “numerous investigators worldwide have shown that the pathology underlying these conditions is tendonosis or collagen degeneration.”13

In the plantar fascia, the degeneration is “similar to the chronic necrosis of tendonosis.”14 Necrosis comes from the Greek for “tissue death,” so that’s bad news. In plantar “fasciitis,” the plantar fascia is hurting because it’s dying — eroding like a rotten plank.15 And this isn’t just to make you squeamish: inflammation and “necrosis” are not the same medical situation, and understanding the difference is crucial for effective treatment.

Foot arch-ery

The arch of the foot functions like a bow (as in a bow and arrow), and the plantar fascia is like the string of the bow. The tension in the “bow string” holds the shape of the arch. But every time you step, the “bow string” stretches … and when stretched too hard and too often, it gets irritated, and then it’s like a bow shooting you in the foot!

And why would a plantar fascia degenerate?

Plantar fasciitis is seemingly caused by tissue fatigue in the arch of the foot due to excessive strain, plus probably some vulnerability due to a variety of biological or pathological factors that are usually unknown and probably often unknowable. Genetics are likely part of the mix. Not everyone who asks a lot of their feet gets plantar fasciitis; some lucky jerks can abuse their arches with impunity!

If the arch of your foot is like a bow, think of the plantar fascia as the bow’s string. The plantar fascia, along with several muscles both in the foot and in the leg, supports the arch and makes it springy.16 Too springy, and the foot flattens out, overstretching the plantar fascia. Not springy enough, and the plantar fascia absorbs too much weight too suddenly.

Either way, it starts to burn with the strain.

Other than the fact that it’s on the bottom of your foot and you step on it a lot — that’s the easy part of this equation to understand — why is the plantar fascia vulnerable to strain? Why exactly? What happens?

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Anatomical and biomechanical explanations for plantar fasciitis are as common as plantar fasciitis itself. Many therapists and articles on the internet will insist that you must treat the “root cause” of plantar fasciitis, which is never the most obvious cause, but something more subtle. There are three main usual suspects (which I will cover in more detail over the next three sections):

• bone spurs
• flat feet and/or pronation
• tight calves

None of these really qualifies for “root cause” status. Unfortunately, there are so many possible plantar fasciitis causes — probably several overlapping factors, a “perfect storm” — that it is unwise to make a confident biomechanical diagnosis. It’s just too complicated an equation, and the scientific literature is riddled with contradictions. Let’s start breaking this down with bone spurs …

Surely bony growths in the arch are painful?!

Bone spurs on the heel (aka heel spurs and calcaneal spurs) seem like they must be a smoking gun — a simple, obvious cause of plantar fasciitis. They are certainly common — about 10–20% of the population17 has an extra bit of bone growing on the front of the heel. They often get the blame for plantar fasciitis because it seems so obvious that having a bony outcropping on your heel might well cause heel pain, for much the same reason that you wouldn’t want a rock in your shoe. And they are indeed found more in people with plantar fasciitis than without.

Not as bad as it looks. Having a bone spur is more like stepping on a cracker than a nail. A thin cracker.

Seems straightforward, right?

Unfortunately for common sense, bone spurs aren’t very bone-y, and it’s not like having a rock in your shoe. Spurs are a slight calcification of the plantar fascia, brittle and thin. It’s as much like bone as tinfoil is like sheet metal. They make the back part of the plantar fascia a bit crispy.18 Stepping on them is more like stepping on a cracker than a nail. A thin cracker.

So it isn’t too surprising that lots of people have painless spurs. Even when there is pain, it’s not the spur that hurts but the plantar fascia itself or other soft-tissue structures.1920 And surgically removing a bone spur does not necessarily relieve pain, so was it likely to be causing it in the first place?2122 Spurs also tend to just grow back, because they are probably a by-product by the same chronic inflammation that causes the pain.

So it’s no wonder a 2014 scientific review concluded:23

Though once synonymous with plantar fasciitis, calcaneal spurs have, for several decades, largely been regarded in the orthopaedic literature as incidental findings.

But they probably aren’t completely irrelevant. They also wrote:

However, it may be premature to completely dismiss the significance of plantar calcaneal spurs.

Spurs are probably more painful and problematic when other tissue X factors are present, but those factors can and will also cause plantar fasciitis symptoms with or without a heel spur in the equation — and heel spurs may be completely painless without those factors!

Of all possible “root causes” of plantar fasciitis, bone spurs superficially seem like the simplest and most obvious — and yet it’s neither. You just can’t count on a nice straightforward connection between heel spurs and plantar fasciitis.

Other alleged root causes are even less satisfying…

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I hear this a lot: “My therapist said I’m a pronator.” Even if you are a pronator, it probably doesn’t matter.

Pronating is rolling the foot inward. It is almost synonymous with having flat feet, because the arch tends to collapse as you roll the foot inward. They don’t necessarily go together, but they often do, and they are both routinely claimed as root causes of plantar fasciitis. Personally, I think therapists just like to accuse their patients of “pronating” because it makes us sound like we know what we’re talking about. Sound a little harsh? Some experts believe the idea of pronation is so useless that they’ve called for it to be abolished:24

[Overpronation] contributes nothing to our understanding — it is not definable, not reliable or valid, not diagnostic, its relationship to injury is not fully understood, and it does not dictate what the most appropriate management plan may be. It should not be replaced, it should be removed.

Ian Griffiths, Overpronation: Accurate or Out of Date Terminology?

One professional will blame flat feet, but the next will say it’s high arches … about the same patient. Surprisingly, professionals often seem to have trouble deciding whether a given foot has a flat arch or a high arch!2526 Maybe they contradict each other because both flat and high arches are factors in plantar fasciitis.272829

For years, I incorrectly told plantar fasciitis clients with high arches that they were exceptional, because I knew only the conventional wisdom: plantar fasciitis afflicts the flat-footed. But the plantar fascia can also be irritated by a too-tall arch.30 This is a Goldilocks thing: the arches need to flex and give just the right amount, not too little, and not too much.

Pronation is one side of a Goldilocks equation too. The truth is that excessive supinating — rolling outwards — is probably just as much of a problem31 — but that gets almost completely ignored. You never hear about supinating.

If you walk in a shoe store and their sole basis for choosing a shoe for you is how much you pronate and what your arch looks like, turn around and walk out the door. The science simply does not support this protocol.

runblogger

The desire to stop pronation is so great that there is a popular surgical fusion option just for that purpose!

As much as the body likes things to be just right, it’s also super adaptable. Many flat-footed pronators and high-arched supinators in fact do not have plantar fasciitis. And many people who do have plantar fasciitis have completely normal arches, and neither pronate nor supinate excessively. Arch height and pronation are probably risk factors … but not the most important ones, and not root causes.

Major accidents almost always happen because more than one thing goes wrong. Same with virtually any chronic pain: they are multifactorial. There are all kinds of non-obvious factors that are at least as important, if not much more so, than the “obvious” ones.

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They probably are tight.32 People with plantar fasciitis do have tighter calves — a lot more so than people with happy feet, and also more than people with other foot and ankle conditions. That has only been properly shown quite recently, in 2018,33 but remains debatable. The link was much less certain before then, and tight calves are another classic “common sense” thing to blame.

Here’s a juicy detail: it’s mainly the medial gastrocnemius muscle that gets tight, and not the lateral.34 This information will come in handy later.

The big calf muscles (gastrocnemius, soleus muscles) can put extra tension on the plantar fascia.35 This situation might be a predictable effect of wearing high-heeled shoes for many years,36 or even just thanks to a tendency not to use our full ankle range of motion — a cultural tendency, no doubt more pronounced in some folks than others.

Just for interesting contrast (quirky tangents are my jam) the Twa people of Africa grow up climbing trees, which earns them amazingly limber calves that allow their ankles to bend halfway (45˚) to the shin37 — two to four times greater than the average urban person! (A good video of this flexibility has unfortunately disappeared from YouTube.)

But hang on to your muscle tone, because it turns out that it’s tricky to even define “tight calves,” let alone make a villain out of them. They might be plantar fasciitis culprits, but good luck proving it. Why? The answer lies beyond the paywall…

Testimonials on health care websites reek of quackery, so publishing them has always made me a bit queasy. But my testimonials are mostly about the quality of the information I’m selling, and I hope that makes all the difference. So here are some highlights from the kind words I’ve received over the years … plus some of the common criticisms I receive, at the end. These are all genuine testimonials, mostly received by email. In many cases I withold or change names and identifying details.

I'm sure you hear this all the time, but your plantar fasciitis book is the best material on the subject and all it's complications that I have come across. I am a sufferer who has received inconsistent messages from practitioners, good ones, and your thorough analyses in multiple areas is invaluable. Your writing style is great, accessible and not too dumbed down. Keep up the good work. Your book is well worth the price. I have told my top notch PT about it, too.

Janet

Great book on plantar fasciitis! It really opened up my understanding of the issue. I had it for 8 months. The toe stretch exercise really helped, but doing behind-the-knee deadlifts is what really cleared it up. Amazing how my feet feel now, but your book is what opened up my eyes to try a different approach. Thanks again for your help!

Jerome Rodrigues

Thank you for your website, it is really a great resource. I have purchased 2 tutorials (trigger points and PF). I also love the concept that you permanently update them and that we have permanent access. I have never seen this concept anywhere else but I find it is really worth the money and better than a book, in the long run.

Bryn Gonzalez

Your website is FANTASTIC! I bought the tutorial on plantar fasciitis, but have also been reading lots of other articles. Well written, amusing, and very well referenced.

Connagh Gilliam

What a read, so interesting! I have been suffering with plantar fasciitis for three months. Your tutorial makes so much common sense. I have spent my working life in the acute sector of the NHS in the UK (Bristol) as a qualified nurse, now retired, and I would love to have handed out your tutorials to some of my patients!

Jan Mahoney, Jan Mahoney, retired nurse (Frenchay Hospital and Bristol Royal Infirmary)

Really interesting reading. I quickly found information I haven’t seen anywhere else, and it was referenced. No one has ever even suggested that lower leg muscles might be involved. I’ve often wondered about that.

Steven Coombs, plantar fasciitis sufferer

I’ve been practicing in podiatry for 16 years and I have successfully treated thousands of cases of plantar fasciitis. The condition is often misunderstood, and there are a myriad of theories out there, but this tutorial is one of the best things I’ve read on the subject; it provides an excellent overview of the latest treatment and self-treatment options, and makes sure that patients know when to see a medical professional. The crucial point Paul makes that I would like to back up is that plantar fasciitis can be successfully treated, but often requires multiple therapies and persistence.

Mark Heard, Podiatrist D.App.Sci, M.A.Pod.A., Australia

Thank you! There is more and better information here than anywhere else I found. What a relief to have a truly comprehensive resource. I was so sick of reading all the same old basic advice.

Jan A., triathlete, Oregon

I have been waking up to pain for almost ten years, and I’d been through every popular remedy, and there are a lot of them. Not once in all that time did I know science. Not once did any doctor or therapist inform me what the latest research says about this condition. Thanks for finally correcting that! (And, yes, I’m finally feeling better, probably because of the night splints, which I actually hadn’t tried before.)

Andrew Hall, IT guy, Ithaca, NY

It was (almost literally) killing me that I couldn’t walk. I’d gained weight, morale was very low. Thanks a million for this article, it’s so much more informative than anything else I could find it’s just crazy. Why isn’t this information more available?

Janice Campbell, mother of five, enthusiastic recreational walker, Oregon

One more noteworthy endorsement, with regards to this whole website and all of my books, submitted by a London physician specializing in chronic pain, medical education, and patient-advocacy (that’s a link to his excellent blog):

I’m writing to congratulate and thank you for your impressive ongoing review of musculoskeletal research. I teach a course, Medicine in Society, at St. Leonards Hospital in Hoxton. I originally stumbled across your website whilst looking for information about pain for my medical students, and have recommended your tutorials to them. Your work deserves special mention for its transparency, evidence base, clear presentation, educational content, regular documented updates, and lack of any commercial promotional material.

Dr. Jonathon Tomlinson, MBBS, DRCOG, MRCGP, MA, The Lawson Practice, London

What about criticism and complaints?

Oh, I get those too! I do not host public comments on PainScience.com for many reasons, but emailed constructive criticism, factual corrections, requests, and suggestions are all very welcome. I have made many important changes to this tutorial inspired directly by critical, informed reader feedback.

But you can’t make everyone happy! Some people demand their money back (and get it). I have about a 1% refund rate (far better than average in retail/e-commerce). The complaints of my most dissatisfied customers have strong themes:

• Too negative in general. Some people just can’t stomach all the debunking. Such customers often think that I dismiss “everything” … which I disagree with.
• Too negative specifically. Some are offended by my criticisms of a treatment option that they personally use and like. Or sell!
• Too advanced. Although I work hard to “dumb” the material down, quite a few people still just find it too dense and dorky.
• Too simple. Some people think they already know everything about the topic. Maybe they do, and maybe they don’t. I always wish I could give these readers a pop quiz. 😉 In my experience, all truly knowledegable people get that way by embracing every new persective and source of information.

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Thanks to every reader, client, and book customer for your curiosity, your faith, and your feedback and suggestions, and your stories most of all — without you, all of this would be impossible and pointless.

Writers go on and on about how grateful they are for the support they had while writing one measly book, but this website is actually a much bigger project than a book. PainScience.com was originally created in my so-called “spare time” with a lot of assistance from family and friends (see the origin story). Thanks to my wife for countless indulgences large and small; to my parents for (possibly blind) faith in me, and much copyediting; and to friends and technical mentors Mike, Dirk, Aaron, and Erin for endless useful chats, repeatedly saving my ass, plus actually building many of the nifty features of this website.

Special thanks to some professionals and experts who have been particularly inspiring and/or directly supportive: Dr. Rob Tarzwell, Dr. Steven Novella, Dr. David Gorski, Sam Homola, DC, Dr. Mark Crislip, Scott Gavura, Dr. Harriet Hall, Dr. Stephen Barrett, Dr. Greg Lehman, Dr. Jason Silvernail, Todd Hargrove, Nick Ng, Alice Sanvito, Dr. Chris Moyer, Lars Avemarie, PT, Dr. Brian James, Bodhi Haraldsson, Diane Jacobs, Adam Meakins, Sol Orwell, Laura Allen, James Fell, Dr. Ravensara Travillian, Dr. Neil O’Connell, Dr. Tony Ingram, Dr. Jim Eubanks, Kira Stoops, Dr. Bronnie Thompson, Dr. James Coyne, Alex Hutchinson, Dr. David Colquhoun, Bas Asselbergs … and almost certainly a dozen more I am embarrassed to have neglected.

I work “alone,” but not really, thanks to all these people.

I have some relationship with everyone named above, but there are also many experts who have influenced me that I am not privileged to know personally. Some of the most notable are: Drs. Lorimer Moseley, David Butler, Gordon Waddell, Robert Sapolsky, Brad Schoenfeld, Edzard Ernst, Jan Dommerholt, Simon Singh, Ben Goldacre, Atul Gawande, and Nikolai Boguduk.

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Regular updates are a key feature of PainScience.com tutorials. As new science and information becomes available, I upgrade them, and the most recent version is always automatically available to customers. Unlike regular books, and even e-books (which can be obsolete by the time they are published, and can go years between editions) this document is updated at least once every three months and often much more. I also log updates, making it easy for readers to see what’s changed. This tutorial has gotten 126 major and minor updates since I started logging carefully in late 2009 (plus countless minor tweaks and touch-ups).

Dec 10, 2024 — Science update: A small but important update: new good quality negative evidence. Sigh. [Updated section: Fancy ultrasound: Extracorporeal Shockwave Therapy (ESWT).]

January — Minor improvements: Integrated and updated barefoot running advice, and other minor changes. [Updated section: Now what?: An action-oriented round-up of my recommendations.]

January — New content: Added specific information about the effect of barefoot running on plantar fasciitis, and related minor editing. This chapter now fits in better with the new one about barefoot walking. [Updated section: Should you run naked? On faddish running styles and running shoes (or the lack thereof).]

January — New chapter: No notes. Just a new chapter. [Updated section: What about barefoot walking? On a treadmill? Okay, that might be worthwhile.]

2023 — Rewritten: Expanded the scope of the section to include dry needling generally, and not just Sconfienza's peculiar version of it. Added some citations. Confirmed that the “Sconfienza protocol” trial remains unpublished (fifteen years later). [Updated section: “Dry needling” (sort of) and steroids… together at last?]

2023 — Refinements: Several minor improvements and additions, mostly about foot straps, taping, and heel lifts (as opposed to support), adding up to a solid chapter upgrade. [Updated section: Orthotics and other arch support, heel cups and lifts, arch bands, and metatarsal pads.]

2022 — Addition: Added “toe spreaders” to the hall of shame. [Updated section: Hall of treatment shame: the most bogus plantar fasciitis treatments.]

2022 — Addition: Added a discussion of a possible link between plantar fasciitis and hallux limitus. [Updated section: Differential diagnosis: several conditions that might get confused with plantar fasciitis.]

2022 — New chapter: No notes. Just a new chapter. [Updated section: Muscle strain in plantar fasciitis.]

2021 — Added information: Added extra detail about the implications of what little data we have, in particular about the unsolved riddle of whether low versus high estrogen is the risk factor. [Updated section: Women and plantar fasciitis: the possible role of estrogen and menopause.]

2020 — Major expansion: Added an introduction about regenerative medicine in general, a more bullish assessment of PRP, and some new basic notes about stem cell therapy. [Updated section: Regenerative medicine? Platelet-rich plasma injections and stem cell therapy.]

2020 — Science update: Substantially improved referencing, with some small but genuinely useful and interesting implications. Best kind of science update! [Updated section: Probably my calves are too tight!]

2020 — Science update: Minor but interesting extra detail about exactly how common plantar fasciitis is (spoiler alert: very common). Upgraded referencing on the topic of plantar fascia thickness. [Updated section: Nature of the Beast: What is plantar fasciitis? The advanced basics.]

2020 — Science update: Discussed some interesting new data on the clinical relevance of plantar fasciitis thickness. Do thicker soles mean you’re in worse trouble? Probably not. [Updated section: Ultrasound and plantar fascia thickness.]

2020 — Added info: Added basic information and a brief cautionary tale about metatarsal pads. [Updated section: Orthotics and other arch support, heel cups and lifts, arch bands, and metatarsal pads.]

2020 — Science update: Cited a more recent review and added a little bit of extra analysis. [Updated section: Fancy ultrasound: Extracorporeal Shockwave Therapy (ESWT).]

2020 — More content: Added magnesium supplementation. [Updated section: Hall of treatment shame: the most bogus plantar fasciitis treatments.]

2020 — More detail: Added a general intro to therapeutic strength training and some commentary on intrinsic foot muscle strengthening and “corrective” exercise. [Updated section: Strengthening is a strong option.]

2020 — New chapter: No notes. Just a new chapter. [Updated section: Prolotherapy (irritant injection).]

2019 — Science update: Upgraded the rationale and referencing for icing in the absence of acute inflammation. [Updated section: Icing: more is better?]

Archived updates — All updates, including 94 older updates, are listed on another page. ❐

2007 — Publication.

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1. In 2012, the The Journal of Foot & Ankle Surgery ranked 136 websites about common foot and ankle diagnoses. Expert reviewers gave each a quality score on a scale of 100. The average score? Just below fifty. Fifty! See Smith et al.

   Or see Starman et al. for a review of other kinds of health care information (with nearly identical grades).

   P.S. These references are aging now… but nothing’s really changed!

2. Most doctors lack the skills and knowledge needed to care for common aches, pains, and injury problems, especially the chronic cases, which they tend to underestimate the complexity of. This has been shown by many studies, like Stockard et al., who found that 82% of medical graduates “failed to demonstrate basic competency in musculoskeletal medicine.” It’s just not their thing, and people with puzzling or stubborn pain should take their family doctor’s advice with a large grain of salt, and even lower their expectations of specialists (who tend to be too specialized). See The Medical Blind Spot for Aches, Pains & Injuries: Most physicians are unqualified to care for many common pain and injury problems, especially the more stubborn and tricky ones.

   Comic by Loren Fishman, HumoresqueCartoons.com

3. The popular physical therapy treatments of the last few decades are almost all nonsense — things like ultrasound, transcutaneous electrical nerve stimulation (TENS), laser therapy — and yet to this day many of them still seem mainstream, scientific, and technological, and consumers do not suspect just how obsolete they are. See Pseudo-Quackery in Physical Therapy.
4. Ingraham. A Historical Perspective On Aches ‘n’ Pains: Why is healthcare for chronic pain and injury so bad? PainScience.com. 4042 words. We can put a man on the moon, but we can’t fix most chronic pain. The science and treatment of pain was neglected for decades while medicine had bigger fish to fry, and it remains a backwater to this day. The seemingly simpler “mechanical” problems of musculoskeletal health care have proven to be surprisingly weird and messy. The field is dominated by obsolete conventional wisdom and the speculations of desperate patients and opportunistic cure purveyors. Ignorance is widespread thanks to professional pride and tribalism, ideological momentum, screwed up incentives, and poor critical thinking skills. But the worst single offender? The pernicious oversimplification of treating the body too much like it’s a complex mechanical device that breaks down: (“structuralism”).
5. Grant HM, Tjoumakaris FP, Maltenfort MG, Freedman KB. Levels of Evidence in the Clinical Sports Medicine Literature: Are We Getting Better Over Time? Am J Sports Med. 2014 Apr;42(7):1738–1742. PubMed 24758781 ❐

   Things may be getting better: “The emphasis on increasing levels of evidence to guide treatment decisions for sports medicine patients may be taking effect.” Fantastic news, if true! On the other hand, maybe I should be careful what I wish for, since my entire career is based on making some sense out of the hopeless mess that is sports and musculoskeletal medicine …

6. Mohseni-Bandpei MA, Nakhaee M, Mousavi ME, et al. Application of ultrasound in the assessment of plantar fascia in patients with plantar fasciitis: a systematic review. Ultrasound in Medicine & Biology. 2014 Aug;40(8):1737–54. PubMed 24798393 ❐

   Mohseni-Bandpei et al. did a systematic review of 34 studies of ultrasound used to diagnose plantar fasciitis and monitor the effects of treatment, and concluded that plantar fasciitis patients do indeed have thicker plantar fascia than can be detected with ultrasound.

   (See more detailed commentary on this paper.)

7. That’s from a fascinating talk about the athletic toughness of human beings, Brains Plus Brawn, by Dr. Dan Lieberman, evolutionary biologist of “Born to Run” fame.
8. Chandler TJ, Kibler WB. A biomechanical approach to the prevention, treatment and rehabilitation of plantar fasciitis. Sports Med. 1993;15. PubMed 8100639 ❐

   Chandler and Kibler reported a 10% occurrence rate of plantar fasciitis in runners way back in 1993.

9. Scher DL, Belmont Jr, Bear R, et al. The incidence of plantar fasciitis in the United States military. J Bone Joint Surg Am. 2009 Dec;91(12):2867–72. PubMed 19952249 ❐

   How common is plantar fasciitis exactly? It’s surprisingly hard to find data on this topic, and this is probably still the best study available as of 2020. Skipping to the punchline, it’s about 1% of the population per year, which is roughly 4x the rate for strokes.

   More technically now: it’s about 10.5 per “1000 person-years.” Which means that if you followed a thousand people for a year, 10.5 of them would get plantar fasciitis. That adds up to about 3.5 million Americans every year, or about 82 million people globally (give or take quite a bit, because the incidence probably varies a lot around the world).

   This was also a study of risk factors — how common plantar fasciitis for certain types of people — and it flagged women as particularly at risk (roughly double). Aging is a risk factor too, of course: you’re more than three times likelier to develop plantar fasciitis if your over forty than if you’re in your twenties.

10. Riel H, Cotchett M, Delahunt E, et al. Is 'plantar heel pain' a more appropriate term than 'plantar fasciitis'? Time to move on. Br J Sports Med. 2017 Nov;51(22):1576–1577. PubMed 28219944 ❐

    “We propose the term ‘plantar heel pain’ to describe the condition of pain under the heel when no differential diagnoses are indicated and until further research is undertaken to arrive at a clear understanding of the appropriate terminology and associated diagnostic criteria.”

    The authors quite correctly point out that there are several possible causes of the condition that have nothing to do with the plantar fascia, and none of them correlate cleanly with symptoms. So an imprecise label is really the only honest one.

    See also: one-minute video summary of this paper (which is a bit of a novelty).

11. Lemont H, Ammirati KM, Usen N. Plantar fasciitis: a degenerative process (fasciosis) without inflammation. J Am Podiatr Med Assoc. 2003;93(3):234–7. PubMed 12756315 ❐
12. Andres BM, Murrell GAC. Treatment of tendinopathy: what works, what does not, and what is on the horizon. Clin Orthop Relat Res. 2008;466(7):1539–1554.
13. Khan KM, Cook JL, Taunton JE, Bonar F. Overuse tendinosis, not tendinitis, part 1: a new paradigm for a difficult clinical problem (part 1). Phys Sportsmed. 2000;28(5):38–48. PubMed 20086639 ❐
14. Young CS, Rutherford DS, Niedfeldt MW. Treatment of Plantar Fasciitis. Am Fam Physician. 2001 Feb 1;63:467–74. PainSci Bibliography 56910 ❐ Such degeneration is “similar to the chronic necrosis of tendonosis, which features loss of collagen continuity, increases in ground substance (matrix of connective tissue) and vascularity, and the presence of fibroblasts rather than the inflamatory cells usually seen with the acute inflammation of tendinitis.”
15. The necrosis “features loss of collagen continuity, increases in ground substance (matrix of connective tissue) and vascularity, and the presence of fibroblasts rather than the inflammatory cells usually seen with the acute inflammation of tendinitis.”
16. The arch muscles do less work than you might think: Basmajian et al. showed in 1963 that muscles in the arch of the foot only kick into gear under heavy loads: about 180 kilograms. Although that sounds like a lot, loading may spike that high in an average person with every step, so the strength and responsiveness of the arch muscles may still be routinely important. We don’t have muscles there for nothing, of course. Nevertheless, this study pretty clearly shows that “the first line of defense” against arch collapse is the shape of the bones, the elasticity of ligaments, and probably the “stirrup” tendons from leg muscles — but not so much the strength of the arch muscles.
17. In 1995, Barrett et al. found that 21% of 200 randomly selected American corpses had heel bone spurs, and in 2014 Moroney et al. found 12% in about 1100 foot x-rays (though they qualify that: “This is a lower rate than that cited in many published series.”)
18. Some bones spurs are undoubtedly thicker and harder than others, just like some people have much larger calluses than other people. (I have a callus on one foot that is always far thicker and sturdier than I seem to need.) But regardless, the spur tends to disintegrate the further it gets from the heel.
19. Osborne HR, Breidahl WH, Allison GT. Critical differences in lateral X-rays with and without a diagnosis of plantar fasciitis. J Sci Med Sport. 2006 Jun;9(3):231–7. PubMed 16697701 ❐

    From the abstract: “ ... the key radiological features that differentiate the groups were not spurs but rather changes in the soft tissues.”

20. Tountas AA, Fornasier VL. Operative treatment of subcalcaneal pain. Clin Orthop Relat Res. 1996 Nov:170–8. PubMed 2663678 ❐

    This paper reports on a study of twenty patients in the years after surgical removal of bone spurs. Although most of the patients had “excellent” or “good” results three years later, their spurs had reformed in many cases, and analysis of the soft tissues showed that “changes within the fascia, rather than the spur, are primarily responsible for the pathogenesis of the syndrome.”

21. Onwuanyi ON. Calcaneal spurs and plantar heel pad pain. Foot. 2000;10.

    From the abstract: “Calcaneal spurs cause plantar heel pad pain, but the roles of other co-morbid factors are significant. The excision of these spurs does not necessarily abolish pain.”

22. Fishco WD, Goecker RM, Schwartz RI. The instep plantar fasciotomy for chronic plantar fasciitis. A retrospective review. J Am Podiatr Med Assoc. 2000 Feb;90(2):66–9. PubMed 10697969 ❐ In this study, surgical outcomes were similar — and generally good — with or without heel spur removal.
23. Moroney PJ, O’Neill BJ, Khan-Bhambro K, et al. The Conundrum of Calcaneal Spurs: Do They Matter? Foot Ankle Spec. 2014 Apr;7(2):95–101. PubMed 24379452 ❐
24. Kinetic-revolution.com [Internet]. Griffiths I. Overpronation: Accurate or Out of Date Terminology?; 2012 Sep 28 [cited 13 Dec 11]. PainSci Bibliography 54396 ❐
25. Sensiba PR, Coffey MJ, Williams NE, Mariscalco M, Laughlin RT. Inter- and intraobserver reliability in the radiographic evaluation of adult flatfoot deformity. Foot Ankle Int. 2010 Feb;31(2):141–5. PubMed 20132751 ❐ Although the reliability isn’t terrible, even x-rays of the same foot get judged differently (just fine with some measures, merely okay for others). However, that’s when radiologists evaluate x-rays, and they are probably better at it than anyone else. The problem is with some kinds of clinicians (see next note).
26. This is a bit of a cheat: I don’t have a proper reliability study to back this up, just a professional story: when I worked as a massage therapist, it was common for people to come into my office with so-called “flat” feet, convinced by a previous massage therapist (or chiropractor) that they “have no arch left” (or some other motivating hyperbole) … when in fact I could still easily get my finger under their arch up to the first knuckle. That’s something that you simply can’t do on someone who really has flat feet. Similarly, though not so common, I have often seen people accused by another professional of having high arches, when in fact they look nothing like it to me. So take such diagnoses with a grain of salt.
27. Huang YC, Wang LY, Wang HC, Chang KL, Leong CP. The relationship between the flexible flatfoot and plantar fasciitis: ultrasonographic evaluation. Chang Gung J Med. 2004 Jun;27(6):443–8. PubMed 15455545 ❐

    From the abstract: “There was a higher incidence of plantar fasciitis in the flexible flatfoot group than the normal arch control group in this study.”

28. Kwong PK, Kay D, Voner RT, White MW. Plantar fasciitis: Mechanics and pathomechanics of treatment. Clin Sports Med. 1988;7(1):119–26. PubMed 3044618 ❐

    This is an expert opinion paper — not original research — which simply states that excessive pronation in the foot (part and parcel of having flat feet) is “the most common mechanical cause of structural strain resulting in plantar fasciitis.” This is debatable. The relevance of the reference is simply to demonstrate the diversity of opinion on the subject. It may well be that pronation and/or flat feet is the most common cause of plantar fasciitis, but it is certainly not the only mechanical factor that does so.

29. Bolgla LA, Malone TR. Plantar fasciitis and the windlass mechanism: a biomechanical link to clinical practice. J Athl Train. 2004 Jan-Mar;39(1). PubMed 16558682 ❐ PainSci Bibliography 56983 ❐

    From the article: “A review of the literature reveals that a person displaying either a lower- or higher-arched foot can experience plantar fasciitis. Patients with lower arches have conditions resulting from too much motion, whereas patients with higher arches have conditions resulting from too little motion.”

30. If the arch is high, it means the arch-support system may be too rigid and not springy enough, so it absorbs too much force too quickly.
31. Hertling D, Kessler R. Management of common musculoskeletal disorders. 3rd ed. Lippincott; 1996. p434. “Functionally abnormal supination is a failure of the foot to pronate, resulting in a foot unable to compensate normally. There is prolonged supination during the stance phase and a delayed pronation during the gait cycle. Stress fractures, metatarsalgia, plantar fasciitis, and Achilles tendinitis are common in this type of foot.”
32. “Tight” is an informal term with several possible meanings. In this context, it probably means that the muscle tone is high enough to resist elongation. In severe cases in older people, it might refer to minor contracture — that is, “freezing” in a shortened position, the muscle tissue actually changed.
33. Nakale NT, Strydom A, Saragas NP, Ferrao PNF. Association Between Plantar Fasciitis and Isolated Gastrocnemius Tightness. Foot Ankle Int. 2018 03;39(3):271–277. PubMed 29198141 ❐

    As of 2018, a hypothetical link between plantar fasciitis and calf tightness remained poorly studied. This study sought to put the question to rest with the right design to detect a correlation, and enough people. They measured gastrocnemius extensibility in three groups of people: 45 with plantar fasciitis, 117 with other foot and ankle problems, and 61 healthy people.

    80% of the plantar fasciitis patients had calf tightness, compared to 45% of the people with other foot problems, and only 20% of the healthy people.

    Calf tightness is generally prevalent in the population. 20% of healthy calves is a lot of calves, and “almost half” of calves in people with miscellaneous foot problems other than plantar fasciitis is also a great many calves. But 80%? That’s even more!

    The comparison of calf tightness in plantar fasciitis versus other kinds of foot trouble is important, because it clearly suggests that there’s something about plantar fasciitis in particular — not just any pain in the area — that involves calf tightness.

    Calf tightness could be a cause of lower limb trouble, but this study does not show that: it just shows that they go together, correlation only. Calf tightness could also easily be a symptom of lower limb trouble. But whichever way the arrow of causality points, calf tightness is linked quite a bit more strongly to plantar fasciitis specifically than other conditions. And while correlation is not causation, “it sure is a hint” (Tufte).

    Note that the Silfverskiöld test used in this study may have poor reliability (Molund 2018, see Is Diagnosis for Pain Problems Reliable?), which would cast doubt on the results. However, it’s likely that the inaccuracy of the test leans towards underestimating calf shortening (Goss 2020). Also, other more recent and objectively obtained data has backed these findings up (Zhou 2020).

34. Zhou JP, Yu JF, Feng YN, et al. Modulation in the elastic properties of gastrocnemius muscle heads in individuals with plantar fasciitis and its relationship with pain. Sci Rep. 2020 02;10(1):2770. PubMed 32066869 ❐ PainSci Bibliography 51889 ❐ The gastrocnemius is divided into two prominent heads, both clearly visible in any lean leg. Zhou et al. used a cool technology, sheer wave elastrography, which can convert differences in soft tissue stiffness into a picture. They confirmed that plantar fasciitis patients have tight calves, but specifically medial calves: it’s the medial gastroc that gets stiff, not the lateral. That’s useful data. Read more about this study. ❐
35. Cheung JT, Zhang M, An KN. Effect of Achilles tendon loading on plantar fascia tension in the standing foot. Clin Biomech (Bristol, Avon). 2006 Feb;21(2):194–203. PubMed 16288943 ❐

    This is a tricky thing to measure directly, so this was a modelling study, a “thought experiment” extrapolating from biomechanical properties of the leg, ankle, and foot. The methodology does cast some doubt on the reliability of the results, but it’s certainly a lot better than an educated guess. Specifically, they modelled the response of plantar fascia tightness to Achilles tendon tension. The authors reported that “increasing tension on the Achilles tendon is coupled with an increasing strain on the plantar fascia.”

36. Csapo R, Maganaris CN, Seynnes OR, Narici MV. On muscle, tendon and high heels. J Exp Biol. 2010 Aug;213(Pt 15):2582–8. PubMed 20639419 ❐ PainSci Bibliography 55265 ❐

    High heels are often vilified, but this carefully done 2010 study showed that the body adapts effectively and minimally, producing quite similar functional results. The most interesting implication of their results is simply that “muscle structure may adapt to a chronic change in functional demand” — which might seem obvious, but that little bit of science has been hard to nail down over the years, and this is a good piece of the puzzle.

    Chronic high-heel wearers do have shortened calf muscles, stiffer Achilles tendons, and a smaller ankle range of motion, but these changes “seem to counteract each other since no significant differences in static or dynamic torques were observed.” In other words, high heel wearers are not progressively disabled: their ankles work fine, just differently. This doesn’t mean there’s no conceivable harm (for instance, Kerrigan found evidence of harm to the knees), but it does tend to downgrade concern on the topic.

37. Venkataraman VV, Kraft TS, Dominy NJ. Tree climbing and human evolution. Proceedings of the National Academy of Sciences of the United States of America. 2012 Dec. PubMed 23277565 ❐ PainSci Bibliography 54672 ❐

There are 202 more footnotes in the full version of the book. I really like footnotes, and I try to have fun with them.

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