This is a surprisingly in-depth article about a single simple idea: hip weakness, a rising-star of running injury risk factors. In recent years, hip weakness or “dead butt syndrome” has become the most popular new scapegoat for running injuries like iliotibial band syndrome (ITBS) and patellofemoral pain syndrome (PFPS). I don’t think that runners can get excited yet. In fact, I think we shouldn’t: I just don’t think the evidence is compelling enough to “believe” in hip strengthening as a prevention or therapy for any condition.
However, it’s an interesting subject, and the theory is not completely without merit or promise. It’s worth exploring, and keeping tabs on. I will continue to update this article, as a key resource for my many readers interested in running injuries and risk factors. It is already probably the most comprehensive overview of the topic available anywhere — true to the spirit of obsessive musculoskeletal geekery found on this website!
In 2007, a Calgary research group led by Dr. Reed Ferber at University of Calgary, enthusiastically and prematurely tried to blame weak hips for running injuries.
“I think this is a good news study for people who are living with chronic running pain,” says Dr. Ferber. “You can do something about it.”
Then and still, Ferber and his colleagues are among the scientists promoting that concept — and they are “promoting” it.2 Although the idea was already popular, Ferber was the first researcher to strongly make the claim that hip strengthening could be a serious therapy for running injuries. Although his research results may constitute a new piece of the puzzle, both Ferber and the media have made too much of it, and too soon, and the media eats it up.
Reporting on Ferber’s work for the Calgary Herald (reprinted here), Trent Edwards writes that, “While most running injuries happen in the knees and lower legs, it turns out their root cause is almost always weak hip muscles.” This parallels the formal conclusion of the research, that “a hip strength and flexibility rehabilitation program … can effectively resolve pain associated with various musculoskeletal running injuries.”
And beware of running magazines! In the September, 2009, issue of Runner’s World, Ferber’s theory is the basis of a short article, “All in the Hips” (p. 46). This time Ferber comments himself:
Inadequate hip muscle stabilization is a top cause of injury in runners.
No, it isn’t!
These are wild-eyed overstatements. Ferber does not actually have adequate evidence for his opinion. Yet he’s promoting it, without a sign of humility or caution, in the world’s most widely read running magazine, and many others.
Another example: In December 2009, Running Times uncritically reported on Ferber’s opinions, confidently declaring the very precise alleged mechanisms by which hip weakness does its dirty work (every bit of which is debatable, especially the part about pronation3), saying definitely that “this is when misdiagnosis often occurs” (as if this isn’t an entirely unproven diagnosis itself), and concluding that “Ferber drives the point home.”
No, he doesn’t.
This is the kind of language that results in the exasperating and constant churning of “the truth” in science. Patients and media consumers are bombarded with so-called conclusions which are then inevitably replaced next month because there was never really enough data to say anything with confidence in the first place — it is probably the number one reason “Why Most Published Research Findings Are False”. To a certain extent I can understand and expect this kind of error from the media, who merely report the excitement of scientists, but I find it particularly irritating when researchers get ahead of themselves.Both the researcher and the media have made too much of the results, and too soon.
Don’t get me wrong, the data is interesting! I just think Ferber and his team have made (way) too much of it in their conclusions. It’s interesting, exciting stuff. A kinesiology geek like me hops up and down when this stuff is announced, and I’m eagerly analyzing it here for the benefit of my readers, who trust me to stay on top of this stuff and interpret it. I just don’t interpret it the same way the researchers did!
So, let’s look at this new information. What did Ferber et al find? Or what did they think they found?
Ferber’s opinion is based primarily on his own unpublished research.
In 2007, Ferber studied “284 patients who visited his clinic complaining of leg pain” and found that “92 per cent had weak hip muscles.” He then “gave them a program to improve hip strength, along with other recommendations to speed their recovery.” He then claims that the results were “astonishing” — a foolishly emotional word to use in science — with an alleged “89 per cent of the patients reported a significant improvement in pain within four to six weeks.”
So this is the claim: most runners with a variety of overuse injuries in the lower body have weak hips, and strengthening the hips will resolve the problem.
This could be true. But … it probably is not. There are many concerns with this evidence. A few paragraphs back, I referenced Ionnadis’ famous article about how most research is wrong: several of the concerns Ionnadis reported on are highly applicable here.
First of all, although the work was presented to the National Athletic Trainers Association National Meeting (June 2007), and this does involve a peer-review process, this research has not yet (as of early 2012) actually been published in a peer-reviewed medical journal … a process that might well force changes in the wording of their current conclusions. Meanwhile, based only on the media reports of his research, we really cannot get excited about it. Why?
Hip weakness could well be an extremely common problem in Canadian society — lots of us could have weak hips, maybe even most of us, whether we have lower body injuries or not. We are flatlanders, living our modern lives on flat, stable surfaces that almost certainly cause our gluteus medius and minimus strength and reflex responsiveness to decline over time, with unknown consequences. In my experience as a massage therapist, I have rarely seen a hip that wasn’t kind of dysfunctional. But this is just a clinical impression: proper research, asking the right questions, is needed to determine whether or not runners with leg injuries in particular have weak hips … or just practically everyone.
Overwhelmingly the most serious problem with this research — a single problem that single-handedly makes it impossible to draw any firm conclusions — is that is “uncontrolled.” That is, the experimental intervention (hip strengthening) was not compared to a neutral group who received no therapy, or a sham therapy. Without doing this kind of comparison, a degree of uncertainty about the results is inflicted upon it that simply cannot be repaired. For instance …
Recovery from “leg pain” is also extremely common — people tend to recover within “four to six weeks” whether they do any kind of therapy or not. Without careful, technical control of research, by intricately comparing different kinds of test groups, there is absolutely no way to tell whether “hip strengthening” was really what did the trick here, or whether it was the “other recommendations,” such as avoiding aggravating activities … or just the passage of time! Practically everyone probably has weak hips, whether they have lower body injuries or not.
However, examination of Ferber’s data does not convince me that the results were even all that good. Only 58% of patients reported “significant” improvement — which does not mean they felt completely better, or that they will never have a relapse, which is a common problem (indeed chronicity is the problem, with these injuries). Although most people tend to get better, many also go on to have intermittent problems for many years (see Karlsson and Blond) — and it is precisely these people that we particularly need to prove that we can help with a given therapy, an issue that this study addresses not at all. In fact, in my clinical experience, virtually all the frustration around runners’ knee injuries concerns cases in which they “felt better at first” after [insert flavour-of-the-week rehab program here] … but then their symptoms came roaring back.
Furthermore, although Edwards’ reports that “89 per cent of the patients reported a significant improvement,” Ferber’s own research actually says that it’s 58% that reported “significant” improvement, while 89% reported only “at least a 50% improvement.” Forgive me for pointing out the obvious, but 50% improvement is actually not all that good at the 6-week mark! To say nothing of the recurrence problem. In fact, I wouldn’t brag about 50%. I wonder if that even beats a sham treatment? Is it possible these people would have done better without the hip strengthening? There is actually a rationale for this perspective (see Strength Training Surprises), and I really think the study should be repeated with a control to find out!
So here we have not only a case of excessive researcher optimism based on numbers that really aren’t all that impressive, but also a media report that is inaccurately skewed in the direction hype — Edwards’ blatantly made an error that makes the results sound way better than they were!
The variety of injuries Ferber studied was also simply too great to determine anything of importance with confidence. Although in some ways studying many injuries was interesting, it also greatly confuses the issue, and makes it much harder to come to any reliable conclusions. It is optimistic indeed to think that a single, easily measured biomechanical factor is going to be equally relevant to several different ways of getting hurt below the waist. Without a bedrock of greater specificity, general conclusions are probably unwise.Edwards’ blatantly made an error that makes the results sound way better than they were!
Ferber claims that “weak hip muscles fail to keep the lower leg aligned with the upper leg after each footfall, putting extra strain on the knees and lower leg muscles.” This is a specific interpretation of a general biomechanical theory of injury that has been studied to death — and a quarter-century of research has done nothing but confuse the issue. For instance, in the case of iliotibial band syndrome, plantar fasciitis, and patellofemoral pain syndrome — three of the most common runner’s injuries — there is a quarter century of contradictory research results which have collectively, resoundingly failed to establish any clear connections between these injuries and any one of hundreds of alleged “biomechanical bogeymen.”4
Countless times, researchers have prematurely announced that they have identified the One True Cause of one of the these injuries — with a brief thrill of media attention — only to be virtually ignored, because newer, better studies soon come along and contradict or simply fail to reproduce the same results. This is known as “Holy Grail disease,” when researchers become overly excited about a single factor in a problem that they should know perfectly well is too complex to ever be explained by a single factor.
Do not get me wrong — it is possible that Ferber’s research is an important piece of the puzzle, and that when it is published we will all get to see how good it is, and we will have some important new data to consider, and other researchers will duplicate his results. Maybe he did control. Maybe he has been specific about injury type.
But until then, in the climate of extreme controversy about all Holy Grail biomechanical explanations for injury, it is way too early — for Ferber, the media, or runners everywhere — to get excited. Researchers are not infallible; there is a long and inglorious history of basic mistakes in science, oversights that seem awfully obvious in hindsight. I think it’s likely that Ferber’s work will prove to be underwhelming. He is not the first to try and fail to prove the hip strength thing, and I doubt that he has the last word.
When I first published this criticism of Ferber’s research, I wrote to him. We had a polite exchange of views which didn’t amount to much except agreeing to disagree. He didn’t particularly concede any of my points or agree with my concerns, and suggested that I review a number of key pieces of research evidence.
Of course, I was familiar with most of that research already. I was proud to be able to reply with the answer, “Yes, I came to this debate already familiar with all of that research.”
In 2005, Niemuth et al claimed to be “the first study to show an association between hip abductor, adductor, and flexor muscle group strength imbalance and lower extremity overuse injuries in runners” (which I suspect Fredericson would object to). However, they also clearly and correctly state that “no cause-and-effect relationship has been established.”
In 2006, Bolgla et al found a “moderate” association between external rotation weakness and increased EMG activity in the gluteus medius, but conspicuously didn’t find a connection between PFPS and hip abduction strength, and they also concluded that they were “unable to determine if hip weakness was a cause or a result from PFPS.”
As these researchers knew, correlation is not causation, there are many possible explanations for the data, the sample sizes were small, the injuries studied diverse ... and so they did not come to any conclusions that we need to be skeptical of. They simply found a few scraps of mildly interesting and not entirely consistent correlations — of which there are countless parallel examples with virtually every measure of biomechanical function you might care to name, most of them contradicting each other!
In 2000, Fredericson also properly drew no conclusions about causation. However, in 2005, they concluded that “studies have also demonstrated that weakness or inhibition of the lateral gluteal muscles is a causative factor in this injury.” Um, what studies? No one has demonstrated any such thing! Yet, bizarrely, Fredericson come out strongly in favour of hip strengthening as therapy, as Ferber et al did in 2007.
Where is the evidence of causation? Fredericson et al. themselves did not produce it. Niemuth et al. openly caution against that conclusion, even while their evidence suggests the need for more research. Bolgla et al. barely even found a correlation, yet alone evidence of causation. And, as of 2009, there were simply no other directly relevant studies!
The other research Dr. Ferber cited in support of his argument is simply too indirect to be of any great interest.5
Yet, with only this research available, in the headlights of the media, Ferber made that sensationalistic statement, “You can do something about it [chronic running pain].” But, in 2007, it wasn’t proven! Not even close!
Fast forward 2 years. Has anything changed?
In April of 2009, Dr. Ferber, Alan Hreljac and Karen Kendall, published a new paper in Sports Health: A Multidisciplinary Approach, once again blaming running injuries on weak hips.6 In April 2009, they did not publish new experimental evidence, and the 2007 experiment was still not published. This new paper had the ambitious goal of reviewing existing scientific evidence concerning risk factors for all overuse running injuries from the knee down. This is an interesting perspective: most papers focus on one injury at a time.
“Few overuse running injuries have an established cause,” they wrote, perhaps understating it a bit. “More than 80% of running-related injuries occur at or below the knee, which suggests that some common mechanisms may be at work. The question then becomes, are there common mechanisms related to overuse running injuries?”
There are a lot of candidate scapegoats. Disappointingly, this paper really only focussed on two of those possible risk factors:
I’m going to start by looking at what Dr. Ferber’s team had to say about pronation, because it’s interesting, related, and provides some interesting context for what they then went on to say about hip weakness.
“Pronation” is the biomechanical bogeyman of runners, the anatomical monster under their beds. There is scarcely a serious runner alive who hasn’t heard the term, and fairly amazing numbers of them have been diagnosed as pronators and bought expensive orthotics and shoes to try to compensate for it. Historically, pronation has been blamed for basically every running injury, and much more besides.
So, what did Ferber et al conclude about pronation? “No definitive answer can be put forth regarding potential running-related injury mechanisms and excessive foot pronation.”
In over 250 studies of long-distance running injuries, there was “no definitive answer” about pronation. Perhaps it’s time to admit that there never will be?
“In many studies … injured runners were more often overpronators when compared to uninjured runners.” But these findings have been (overwhelmingly) simple observations of correlation, the medical equivalent of circumstantial (crappy) evidence. It’s extremely rare for experimenters to go to all the scientific trouble of proving cause. Ferber et al point out this weakness: only one study out of many dozens “partially supported the speculation regarding a cause-and-effect” and “contradictory results were found in a study in which runners who had never sustained an overuse injury exhibited greater pronation.”
And that’s exactly the kind of thing that will happen when you aren’t truly designing your research to sniff out cause-and-effect.
Fascinatingly, Ferber et al go on to explain that a normal range of foot pronation has not really been established, and much of the research about pronation is basically based on assumptions about what “normal” is. Kind of puts an interesting perspective on all those times you’ve been told that you’re a pronator, doesn’t it? Compared to what? Chimps? Maybe a wide range of pronation is just how human beings work.
The take home message here is simple: with no clear research “signal” in decades, it’s extremely unlikely that there is a strong link between pronation and injury. Perhaps a link, but almost certainly not a strong link.
How fascinating that Ferber et al were unimpressed with years of experimental evidence that sorta, kinda, maybe makes a connection with pronation … but then went on to, once again, make quite a bit of even less evidence about hip weakness.
My main reason for criticizing Ferber et al’s 2007 research is not just that didn’t show anything compellingly sinister about weak hips, no one else had either up to that time. The scientific evidence available up to 2007 was extremely scanty.
But then, two years later, Ferber et al were back at it, still claiming — like so many researchers before — that they had found the One True Risk Factor for running injuries. To support this, they cited a modest amount of evidence — most of which a substantial portion of which is their own unpublished research, or the same scanty evidence I’ve already dismissed. There has been some interesting new evidence, but certainly nothing conclusive.
Yet they have published the rather confident conclusion that “a large and growing body of literature” backs up the idea that weak hips cause running injuries.
Really? “Large?” Not even a dozen weak experiments, none of which clearly show cause and effect, is “large”? And the word “growing” is just a careless, informal exposure of bias: the only relevant thing to say is how much evidence actually exists now.
So, once again, Dr. Ferber and his colleagues put their names to conclusions that simply aren’t yet justified by the evidence, and once again I’m criticizing him for it. It’s particularly ironic that he points out how correlations alone are not compelling with regards to pronation, but then fails to make the same reasonable observation that all the weak-hips research suffers from the same problem. The whole thing just reeks of “pet theory” syndrome. I feel quite safe predicting that future generations of scientific reviews will fail to find any clear sign of the weak hips connection … just like Ferber et al failed to find a pronation connection! It really seems like researchers hunting for biomechanical bogeymen only seem to find the ones they like the sound of.
The idea that weak hips are important has spread far and wide now, with “experts” routinely asserting that strengthening in general and hip strengthening in particular is critical for runners, just exactly as though someone had actually proven this — and yet I am unaware of any evidence other than what I’ve discussed. For example, late in 2010, the New York Times published a piece that was crammed with vague hand-waving about “dead butt syndrome” — all presented as though it’s a scientific fait accompli, the cutting and confirmed edge of running injury prevention.
And yet to my ears it all sounds just as vague and confused as running injury science from 20 years ago.
When Darwin and Wallace jointly presented the theory of evolution to their colleagues for the first time, there was virtually no response from the audience. One scientist quipped: “What was correct was old, and what was new was wrong.”
I think that phrase describes this new paper pretty well. It asked an ambitious and interesting question, but its conclusions do not satisfy: it’s old news that we can’t pin running injuries on pronation … and blaming hip weakness is premature and probably just as wrong as all the other biomechanical theories of overuse injury that have already failed to stand the test of time.
If more and better evidence emerges, I certainly won’t hesitate to endorse the hip weakness theory. But it’s not ready for prime time in my opinion.
Original publication date 7/16/07. Started logging changes 4/12/10.
Wednesday, December 29, 2010 — Added some content about “dead butt syndrome,” which seems to the be the “hip” (ha ha) new way to refer to hip weakness in runners.
Monday, April 12, 2010 — Just a little editorial cleaning up: fixed some errors, clarified some language, started logging updates.
This intensely intellectual paper — it’s completely, hopelessly nerdy — became one of the most downloaded articles in the history of the Public Library of Science and was described by the Boston Globe as an instant cult classic. Despite the title, the paper does not, in fact, say that “science is wrong,” but something much less sinister: that it should take rather a lot of good quality and convergent scientific evidence before we can be reasonably sure of something, and he presents good evidence that a lot of so-called conclusions are premature, not as “ready for prime time” as we would hope. This is not the least bit surprising to good scientists, who never claimed in the first place that their results are infallible or that their conclusions are “true.”BACK TO TEXT
In 2006, Hreljac’s review (co-authored by Dr. Ferber!) does not seem like any kind of real support: “Isokinetic research of hip muscle function is helping to link our understanding of lower extremity kinematics, but requires more research to be proven as a causative factor.” Yep. That’s pretty much exactly what I keep saying, not what Dr. Ferber believes! And they say little else in that paper, glossing over vast quantities of inconclusive and contentious debate about other biomechanical factors.
And Boling do not have data anywhere near specific enough to draw conclusions about hip strength and causation.
And Powers’ opinion piece does not help us in the slightest way in terms of actual evidence. Etc.BACK TO TEXT