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Foot Strike and Injury Rates in Endurance Runners: a retrospective study

Discussion in 'Biomechanics, Sports and Foot orthoses' started by Griff, Jan 5, 2012.

  1. Griff

    Griff Moderator

    Members do not see these Ads. Sign Up.
    The barefoot running running advocates who have been guilty of misusing research in the past will be all over this once they catch wind of it.

    Its retrospective design won't faze them I'm sure. You can see the headlines already: "Heel striking is twice as likely to injure you"

    Add in the fact that Lieberman is a co-author and you've got yourself a zealot's wet dream.

    Foot Strike and Injury Rates in Endurance Runners: a retrospective study
    Daoud, Adam I.; Geissler, Gary J.; Wang, Frank; Saretsky, Jason; Daoud, Yahya A.; Lieberman, Daniel E.
    Medicine & Science in Sports & Exercise:pOST ACCEPTANCE, 3 January 2012

  2. Craig Payne

    Craig Payne Moderator

    We have to go where the evidence takes us, but:
    - retrospective
    - specific sample (high level college runners)

    The breakdown in type of injury differences interesting:
    MTSS - no differences
    knee pain - no differences
    ITB - no differences
    Achilles tendon (more in forefoot strikers in females, but not males)
    Plantar fasciitis (more in rearfoot strikers in females, but not males)
    Met stress fractures - no differences
    Hip pain (more in rearfoot strker)
    Tibial stress fractures - no differences
    "repetivie joint sprain" - more in rearfoot strikers
    Tib post tendonopathy - no differences

    It is puzzling that there are so many "no differences" in individual injuries, but such a big difference when they all pooled.
    Last edited by a moderator: Jan 13, 2012
  3. It sounds like one of the variables with a difference is really "pulling" the data.

    However, beta error? i.e. the probability that the conclusion of no difference is erroneous is higher in the smaller, un-pooled data sets.

    Not had time to read paper yet.
  4. pod29

    pod29 Active Member

    This one has also just gone online in the same journal by Lieberman's colleagues

    Effects of Footwear and Strike Type on Running Economy

    ABSTRACT Purpose. This study tests if running economy differs in minimal shoes versus standard running shoes with cushioned, elevated heels and arch supports, and in forefoot versus rearfoot strike gaits. Methods. We measured the cost of transport (mlO2/kg/m) in subjects who habitually run in minimal shoes or barefoot while they were running at 3.0 m/s on a treadmill during forefoot and rearfoot striking while wearing minimal and standard shoes, controlling for shoe mass and stride frequency. Force and kinematic data were collected when shod and barefoot to quantify differences in knee flexion, arch strain, plantarflexor force production, and Achilles tendon- triceps surae strain. Results. After controlling for stride frequency and shoe mass, runners were 2.41% more economical in the minimal shoe condition when forefoot striking and 3.32% more economical in the minimal shoe condition when rearfoot striking (p<0.05). In contrast, forefoot and rearfoot striking did not differ significantly in cost for either minimal or standard shoe running. Arch strain was not measured in shoes condition but was significantly greater during forefoot than rearfoot striking when barefoot. Plantarflexor force output was significantly higher in forefoot than rearfoot striking, and in barefoot than shod running. Achilles tendon-triceps surae strain and knee flexion were also lower in barefoot than standard shoe running. Conclusions. Minimally shod runners are modestly but significantly more economical than traditionally shod runners regardless of strike type, after controlling for shoe mass and stride frequency. The likely cause of this difference is more elastic energy storage and release in the lower extremity during minimal shoe running. Key Words: running economy, barefoot running, minimal shoe running, forefoot strike, rearfoot strike.

    I've got the full article if you wold like it
  5. NewsBot

    NewsBot The Admin that posts the news.


    Hashish R, Samarawickrame S, Powers C, Salem G
    CSM 2012 Sports Physical Therapy Section Abstracts: Poster Presentations SPO1100-SPO1125J Orthop Sports Phys Ther 2012;42(1):A114-A124
  6. Craig Payne

    Craig Payne Moderator

    It did not take long:
    Harvard Study Supports Barefoot Running Benefits
    ... but ... duh? .... it wasn't even a study on barefoot!!!
  7. rikmellor

    rikmellor Member

    I don't think it's at all helpful to publish retrospective research in this area. With such specific subjects as Craig says.

    I wanted to support those points regarding injury pooling; I have not read the paper(s) as yet, am keen if anyone is willing to share (rik.mellor@smuc.ac.uk), but I'm very interested to understand what 'hip pain' and 'repetitive joint sprain' are for starters and how accurate the clinical diagnoses can be for repetitive or traumatic injury classification.

    Plus were subjects matched on volume, intensity, surface etc, as well as mileage, do collegiate cross country runners become injured from varied terrain and gradient? With these in mind for me 16 forefoot strike subjects sounds a small percentage.

    You can bet there will be further related research to follow from Harvard.
  8. As long as Vibram is funding these studies, I'm sure that Lieberman's group will cook up some more research studies to support barefoot, minimalist, non-heel strike running. There's money in them thar five-toed shoes!!
  9. Bobba Booey

    Bobba Booey Active Member

    Here's another claiming this study proves barefoot is better.

    It's Official Barefoot is Best

    In an email from Vivobarefoot, they said the following:

  10. Craig Payne

    Craig Payne Moderator

    Someone needs to explain to them how to interpret the results from a retrospective study. ..... but, Ian predicted that this is how they will interpret it!
  11. Griff

    Griff Moderator

    Yep, wasn't a tough call in fairness. They are all at it on twitter. It's confirmation bias crazy over there.

    Another observation regarding the latest "Lieberman study"... When was the last time a 6th author of a piece of work ever had so much attention/exposure for said piece of work?
  12. Craig Payne

    Craig Payne Moderator

    Some of them just don't get it do they?

    See this for how one barefoot blogger interpreted the research (see the attachment; I attached it in case they remove it from the site when they realise how big of a fool they making of themselves)).

    Someone needs to point out that there is nothing "official" about it; that is was only a retrospective study; that it was only on a small group of almost elite runners; that it was not even on barefoot runners; and certainly was NOT comparing a "jogger" to "skilled barefoot" ... and they wonder why they get ridiculed and make fools of themselves with their continued misrepresentation, misunderstanding, misquoting and misusing research?

    Liebermann, after his Nature publication had to take the extraordinary and unprecedented step of publishing a disclaimer on his website to distance himself from the interpretation that so many barefoot bloggers were making from that research. I wonder how long before he has to publish a disclaimer to distance himself from this one!

    Its actually a good piece of research and contributes some good information to our understanding of the topic ... its just the nonsensical interpretations that fools are making of it.

    Attached Files:

  13. Craig Payne

    Craig Payne Moderator

    The diagnoses were probably accurate, but there are potential issues with the retrospective nature of the diagnoses for classification. But that is always an issue with retrospective studies and there is not necessarily an easy way around it. As with any retrospective study design its lower down in the hierarchy of evidence (someone need to explain that to the barefooters making all the wild claims from this study!)
    They were all coached by the same coach; ran the same distances; etc etc, so I comfortable with that.
    I do not necessarily have a problem with that. You have to trust the integrity of the researchers regardless of the funding source. If you going to dismiss any of Liebermanns research as he is funded by a barefoot company, then we have to also dismiss any positive research on running shoes funded by running shoe companies. We can't have it both ways (and neither can the barefoot running bloggers!). Where the biases tend to come in for this sort of case, is not the conduct and analysis of the research, but in the spin that might get put on it in the discussion. The problem is, so many put blind faith in the spin and not the data (classic egs are spin in papers like Craig Richard's systematic review on the evidence for running shoe; the spins the Robbins & Gouw etc put on there really good research - in their case the spin pretty much ruined it).
  14. Craig:

    I would tend to agree that Lieberman and company did a pretty good job with this paper and thought they were pretty fair, but obviously biased toward forefoot strikers. I found it very interesting (as you did in a previous posting) at how few of the injuries showed signficance of forefoot vs rearfoot strikers.

    From their injury table below the only significant (p<0.05) differences in injuries when both male and female injuries were combined were as follows:

    Rearfoot strikers had just barely significant (p = 0.0401) increases in "hip pain" vs forefoot strikers.

    Rearfoot strikers had just barely signficant (p = 0.0417) increases in "repetitive joint sprain" (whatever that is?) vs forefoot strikers.

    So, if the researchers weren't so intent on showing that forefoot striking was a better way to run, maybe they would have concluded, from an analysis of the table below from their paper the following:

    I don't think we would ever see Dan Lieberman write an abstract like that, certainly not as long as Vibram is funding his website and all of his running research.:rolleyes:
  15. pod29

    pod29 Active Member

    Craig, hopefully you can help me with this one....

    Why would they have no calculation of effect size or clinical relevance? How do we know the size of the effect even practically relevant? I'm certainly no expert on stats and was hoping you may be able to provide insight. Do you calculate effect size/clinical relevance in a retrospective study? I just find it strange that they have ommitted this, given that this journal makes specific reference to the need to include these calculations when submitting to their journal. Would their be a reason for this? It may or may not make any difference anyway.


  16. AlexDP

    AlexDP Member

    Of course there is money in the big stability shoes as well. Again, this is not a professional attitude. It is right to criticise the funding that goes into these papers. However, one should primarily focus on the results and methods used, because the funding works both ways and cannot possibly be used as an argument.
  17. Yes it can it shows Bias

    That is why a conflict of interest must always be stated in a research paper
  18. Craig Payne

    Craig Payne Moderator

    as I said above:
    I have been involved in and conducted industry sponsored research; my previous employment was right in the middle of a lot of drug industry sponsored clinical trials ... you have to trust the integrity of people when it comes to the conduct of research.

    Where the bias come in are in the spin that often get placed on the interpretation of the results. Here is a classic: Plantar fasciitis symptoms and two different running shoes in which they clearly screwed up the analysis to paint the sponsors shoes in a better light. Try and convince me that they did not do what they did because Nike sponsored it.

    Probably the worst one is the now thoroughly discredited and withdrawn paper in Lancet by Andrew Wakefield that started the whole MMR and autism scare that has now been clearly shown to be false and has led to a huge public health risk. If some of his funding sources were declared at the time, more questions would have been asked prior to publication and his fraud would not have been perpetuated. Despite what I said above about trusting the integrity of researchers, this is one case where the integrity of the researcher has been shown to be extremely misplaced.
    Last edited: Apr 12, 2012
  19. Craig Payne

    Craig Payne Moderator

    I not totally sure how appropriate it is, but I did an effect size (Cohen's D) on Table two of their data; just the first line of mild repetitive injuries (ALL) and the effect size of the difference was 3.4 (assuming my maths was right!) ... that is as good as it gets! ... unfortunately there is not enough data they provided on the overall rate between the two groups to do an overall effect size (can only do it on each row of table two).

    I not sure why the authors did not do the effect size or why the journal's reviewers did not require it. It certainly would be helpful to put the whole interpretation into a better context. Given that there are a number of categories in which there was no difference in the injury rate, the effect size could potentially not be very good at all....would like that data to see!

    The closest I can get is this in paragraph 20:
    so that's 8.66 injuries vs 5.00 injuries for moderate and severe, but we need the SD to do an effect size calculation. As far as I can see, they did not give us the overall numbers for the mild and moderate!If I was a reviewer I would have requested it.

    The more I delve into this paper, the more shortcomings I see in what they are reporting and analyzing.

    Perhaps someone with a better understanding of effect sizes than me can comment.
  20. I'd start by just doing an unstandardised ratio- how many injuries in group one versus how many injuries in group 2.

    For those following and wondering- http://en.wikipedia.org/wiki/Effect_size
  21. Craig Payne

    Craig Payne Moderator

    That's the problem, they don't actually provide that overall number!
  22. Don't have the paper, so can't help any further.
  23. DaVinci

    DaVinci Well-Known Member

    Yet their silence on this one was almost deafening "Impact frequency data suggest unique risks for forefoot strikers" http://www.podiatry-arena.com/podiatry-forum/showthread.php?t=67835
  24. Craig Payne

    Craig Payne Moderator

    this don't figure"

    ...and they wonder why we ridicule and mock them! They only have themselves to blame.
  25. Craig Payne

    Craig Payne Moderator

    I see Ian tweeted them:

    Did you get a response?

    and this tweet:
    I expect that this one would have been over their heads :-(
  26. Griff

    Griff Moderator

  27. Ray Anthony

    Ray Anthony Active Member

    Here's one of my concerns with the study:

    Other researchers who have studied foot strike actually during an event found only 1.4% (Haegawa, et. al., 2007) and 1.8% (Larsen et. al,. 2011) of their running populations to be forefoot strikers. Lieberman concluded that over 31% of his cohort hit the ground forefoot first. 31%! Why so many forefoot strikers in Lieberman's paltry 52 total cohort?

    It is clear from the Haegawa and Larsen studies (with large populations) that both high-quality recreational and elite athletes change their strike patterns from forefoot to rearfoot during the race -- perhaps due to muscle fatigue and reduced speed towards the end of the event -- i.e., forefoot to mid-foot at around 10K, and mid-foot to rearfoot at around 32K (Larsen et. al,. 2011). I have not read Lieberman's study protocol, but my guess is that he assessed the strike patterns of his population from a few high-speed video frames taken from a short period of running, which is probably why his cohort of forefoot strikers is so much higher than reported in previous studies. Therefore, one might be forgiven in assuming that many of Lieberman's forefoot strikers (perhaps 29% of them!) may actually become rearfoot strikers during a race, which means his results should perhaps be treated with some caution.


    1. Hasegawa H, Yamauchi T, Kraemer WJ.: Foot strike patterns of runners at the 15-km point during an elite-level half marathon. J Strength Cond Res. 2007 Aug;21(3):888-93.

    There are various recommendations by many coaches regarding foot landing techniques in distance running that are meant to improve running performance and prevent injuries. Several studies have investigated the kinematic and kinetic differences between rearfoot strike (RFS), midfoot strike (MFS), and forefoot strike (FFS) patterns at foot landing and their effects on running efficiency on a treadmill and over ground conditions. However, little is known about the actual condition of the foot strike pattern during an actual road race at the elite level of competition. The purpose of the present study was to document actual foot strike patterns during a half marathon in which elite international level runners, including Olympians, compete. Four hundred fifteen runners were filmed by 2 120-Hz video cameras in the height of 0.15 m placed at the 15.0-km point and obtained sagittal foot landing and taking off images for 283 runners. Rearfoot strike was observed in 74.9% of all analyzed runners, MFS in 23.7%, and FFS in 1.4%. The percentage of MFS was higher in the faster runners group, when all runners were ranked and divided into 50 runner groups at the 15.0-km point of the competition. In the top 50, which included up to the 69th place runner in actual order who passed the 15-km point at 45 minutes, 53 second (this speed represents 5.45 m x s(-1), or 15 minutes, 17 seconds per 5 km), RFS, MFS, and FFS were 62.0, 36.0, and 2.0%, respectively. Contact time (CT) clearly increased for the slower runners, or the placement order increased (r = 0.71, p < or = 0.05). The CT for RFS + FFS for every 50 runners group significantly increased with increase of the placement order. The CT for RFS was significantly longer than MFS + FFS (200.0 +/- 21.3 vs. 183.0 +/- 16 millisecond). Apparent inversion (INV) of the foot at the foot strike was observed in 42% of all runners. The percentage of INV for MFS was higher than for RFS and FFS (62.5, 32.0, and 50%, respectively). The CT with INV for MFS + FFS was significantly shorter than the CT with and without INV for RFS. Furthermore, the CT with INV was significantly shorter than push-off time without INV for RFS. The findings of this study indicate that foot strike patterns are related to running speed. The percentage of RFS increases with the decreasing of the running speed; conversely, the percentage of MFS increases as the running speed increases. A shorter contact time and a higher frequency of inversion at the foot contact might contribute to higher running economy.

    2. Kaminski J, Decker T, Preble J, Lyons D, McIntyre K, Normile A. Larson P, : Foot strike patterns of recreational and sub-elite runners in a long-distance road race. J Sports Sci. 2011 Dec;29(15):1665-73. Epub 2011 Nov 18.
    Department of Biology , St. Anselm College , Manchester , New Hampshire , USA.

    Although the biomechanical properties of the various types of running foot strike (rearfoot, midfoot, and forefoot) have been studied extensively in the laboratory, only a few studies have attempted to quantify the frequency of running foot strike variants among runners in competitive road races. We classified the left and right foot strike patterns of 936 distance runners, most of whom would be considered of recreational or sub-elite ability, at the 10 km point of a half-marathon/marathon road race. We classified 88.9% of runners at the 10 km point as rearfoot strikers, 3.4% as midfoot strikers, 1.8% as forefoot strikers, and 5.9% of runners exhibited discrete foot strike asymmetry. Rearfoot striking was more common among our sample of mostly recreational distance runners than has been previously reported for samples of faster runners. We also compared foot strike patterns of 286 individual marathon runners between the 10 km and 32 km race locations and observed increased frequency of rearfoot striking at 32 km. A large percentage of runners switched from midfoot and forefoot foot strikes at 10 km to rearfoot strikes at 32 km. The frequency of discrete foot strike asymmetry declined from the 10 km to the 32 km location. Among marathon runners, we found no significant relationship between foot strike patterns and race times.
  28. :good:Agreed. I am slowly working my way through the paper and had already annotated my copy with a similar question. Strike characterisation was done for some subjects on a treadmill and some on a track. Might this account for the high percentage of forefoot strikers in the subject population?
  29. Craig Payne

    Craig Payne Moderator

    You two party poopers! We cant let even more trivial facts get in the way of letting this study prove barefoot running is better :boohoo:
  30. BEN-HUR

    BEN-HUR Well-Known Member

    Not sure if the following has been discussed/found as yet...

    [Frankly, I'm a bit fed up with the whole barefoot running issue (& I would be considered one of the more considerate towards this position/movement based on my personal involvement with barefoot/minimalist running)].

    Hence I haven't bothered keeping track of recent discussions on this topic. Yet, I felt the following was best posted on this thread due to the recent advert submitted by shoe company Vivobarefoot regarding foot strike. Submitted on their website here (link) on the 12th Jan. 2012... "Proven. It's official - barefoot is best"...


    Is it any wonder why Podiatrists get annoyed :craig:... yet the wilful (narrow minded) perception of this annoyance is seen to be directly related/targeted to the concept (barefoot/minimalist running) & not the interpretation & subsequent conveying of the information to the lay public. Isolating one issue (i.e. foot strike) targeted to the masses without the consideration of multiple biomechanical factors is nonsensical (&/or irresponsible/negligent) in the above advertised context. Like I've said before, based on one's position - it would seem fame, fortune & what can be perceived as idiosyncrasy, reigns precedence over science, logic, reason, honesty & common sense for many in this deemed 'barefoot' movement/industry.

    For those cardinal exponents in the barefoot brigade... using tactics such as smoke & mirrors to fulfil an agenda has not & will not cut it in the future... hence the viewpoint of many on this forum.

    When all is said & done... one's own physical condition will let one know what is appropriate at a given time or future endeavour. Pain is an effective mediator on this topic... no matter what your inclination on foot attire. Our (i.e. Podiatrist's) role is to treat pain... better still - prevent it from occurring! The above Vivobarefoot submission can lead to consequences to the contrary.
  31. BEN-HUR

    BEN-HUR Well-Known Member

    Whoops... sorry, just noticed the above issue was covered in post #'s 9 & 12.

    Note to self - best read the whole thread before submission. Anyway, my opinion has been stated - for what it's worth :eek:.
  32. Craig Payne

    Craig Payne Moderator

    It probably bears repeating as Vivobarefoot should be hanging there head in shame over their interpretation of this! They open themselves to mockery and ridicule because of this ... not to mention the legal action like what is happening with the toning shoes (Lawsuit filed against Skechers & Reebok faces lawsuit over toning shoe from unsatisfied customer).

    Remember all the headlines about running shoes causing knee osteoarthritis based on a study that was not even on osteoarthritis! (The Effect of Running Shoes on Lower Extremity Joint Torques)?

    Remember all the headlines from Lieberman's study in Nature that Lieberman had to take the unprecedented step of publishing a disclaimer on his website to distance himself from the way the study was being interpreted?

    ....it don't figure
  33. It figures to me just fine.

    These things only happen when there is a financial interest behind the research that causes the researcher to overstep their bounds of them just being objective scientists. It can also happen when their is a financial interest behind a product that causes the manufacturer of that product to overstep the bounds of truthful advertising. That is why journals and seminars now make these researchers claim any conflict of interest....it is simple human nature to be biased about people or products that people have a financial or personal interest in. Biased papers and biased lectures that "improve the research findings" will always be present as long as the desire for more money and more fame influences the good judgement of people. That is why, as long as Dan Lieberman is being funded by Vibram, that I will take his Vibram-funded research with a grain of salt.
  34. JohnD

    JohnD Member

    You have to keep in mind that the general running population is of a very different makeup than the highly competitive college running population. I haven't read the study yet—it doesn't look like I have access right now, and it might be a few weeks until I can get access (unless a kindly podiatrist would lend a hand...). But last year, I used high-speed video to categorize 18 runners on my own college running team; these were my results:

    rear-foot: 14 (77%)
    mid-foot: 3 (16%)
    fore-foot : 1 (1%)

    While this is NOWHERE near enough data to make any "real" conclusions :dizzy: , we certainly did NOT have 30% forefoot strikers. Even among competitive runners, I'd wager the proportion of midfoot AND forefoot strikers at normal training paces is probably ~20%. In my own investigation, footstrike patterns were fairly stable from 8:00/mi down to about 5:30...once it gets faster, all bets are off. I think Steve Magness cites some unpublished studies (not sure if they ever ended up getting published) on footstrike patterns in 1500m and 800m races and found that, predictably, a much higher proportion of runners forefoot strike.


    What I'm really curious about is why this was a retrospective study. If you are going to look at college runners, it would seem relatively easy to look at the runners' footstrike styles BEFORE the season, not after it.

    Finally (again, I have NOT read the full study!) but the table full of p-values for each injury bugs me from a statistics perspective. If you only START with 54 runners, and only 3/4 get injured in a year, the number of runners who have any given injury is going to be quite small. So to compare, for example, the number of runners in each group who get plantar fasciitis, is a bit silly. Anyone read the full study and want to comment on this?

  35. Craig Payne

    Craig Payne Moderator

    I have no problem with a retrospective study. Like any retrospective study, it is usually done because of the availability of data to answer the research question. In the hierarchy of evidence a retrospective study is lower dower down than a prospective study … which makes the vivobarefoot interpretation of this study even more bizarre – I wonder if they even know the difference between a prospective and retrospective studies?
    Yes there are issues with pooling data this way, but I not sure of the importance of this.
  36. If your agenda was to "prove that forefoot striking is better than rearfoot striking" for the sponsor of all your running research and your website (a sponsor that makes lots of money selling shoes that promote forefoot striking) don't you think it would be easier, at the end of the season when you already know what injuries had already occurred in those runners, to "properly classify" some marginal "forefoot strikers" who got injured that season more as "rearfoot strikers" and some marginal "rearfoot strikers" who didn't get injured that season as "forefoot strikers"? I can see very clearly why this was done as retrospective research rather than the more "risky" but much better prospective research.
  37. Peter

    Peter Well-Known Member

    Not necessarily. Publication bias. If the reseacrh showed no difference, the financial backers would have omitted to publish it, probably.
  38. JohnD

    JohnD Member

    I've finally got full access to the article and read through it. As you can see in the table posted earlier, it's an epub ahead-of-print. For all the huffing and puffing on here, it really is quite tame for most of the paper. It's just the media that's blowing this way out of proportion....

    Anyways, getting back to the paper itself: The introduction actually does quite a nice job of introducing the current state of affairs when it comes to running and injury: a few fairly obvious factors (age, bmi, running experience) are known to correlate with injury rates, but efforts to reduce injury rates have not been particularly successful. I imagine several posters here will be irked at Daoud et al. for being too dismissive of the success of orthotics in reducing injury (e.g. this study), but outside of that I did not see too many issues with the introduction. Daoud et al. bring up the issue of impact forces and rely heavily on Irene Davis' work, but they also point out that Benno Nigg has not found impact loading rates to be related to injury risk (they omitted the fact that Nigg found that loading rates to be inversely correlated with injury risk...). In a few places, the paper simply says "impact" when it really ought to say "impact loading rates," since it's only these loading rates, not the magnitude of the impact itself, that have been associated with injury risk (mostly by Irene Davis' group). They also briefly bring up the issue of joint torques and possible differences between forefoot and rearfoot striking.

    The experimental design is more problematic. To their credit, the researchers collected much more data than I had expected: all runners logged every workout on an online training log, so they were able to track total number of miles run through the duration of the study. As the study says:

    For reasons that are not clear, some of the subjects had their footstrike categorized on a treadmill and others had it done on a track. While it does not seem like there would be any major differences, it's just not that hard to film a runner on a track, so I don't understand why they weren't ALL filmed doing overground running. In any case, in the duration of the study there were 16 forefoot strikers, 36 rearfoot strikers, and zero midfoot strikers. This alone should cause us to think twice about the sample size in this study, since from the two largest studies on footstrike patterns, we know that midfoot striking is three to seventeen times more common than forefoot striking, at least among elite, sub-elite, and recreational road runners (Hasegawa et al., Larson et al.—as an aside, maybe I should publish my results from filming my college team...I don't think Pete Larson is any more qualified to do this than I am!). Even in my puny sample of 18 DIII runners, we had three midfoot strikers...

    Daoud et al. also note that some runners switched striking styles based on their running speed (the three speeds they were evaluated at were "easy," "intermediate," and 5km race pace). Later in the analysis they use some statistical tricks to show that removing them from the study does not alter its conclusions. They also constructed a pretty complicated statistical model to evaluate injuries based on their severity and to control for distance covered in training, and formulate a list of "predicted" FFS and RFS injuries. This is also a flaw in my eyes—forming hypotheses are great, but you can't pick out what injuries you think rearfoot strikers will get BEFOREHAND and then go looking for them. It is completely arbitrary and artificial, and likely exploits artifacts in the data by narrowing the effective pool of subjects even further. Daoud et al. make a big deal in the conclusion about rearfoot striking being a significant factor associated with "predicted" rearfoot striking injuries, but make no mention of statistically significant or near-significant factors that seem spurious (like duration in the study, my next point).

    My third major grievance with this study is that it does not give equal weight to all of its subjects. For example, some runners were in the study all four years of college, while others graduated before the study ended. Daoud et al. claim this is not a bias since their generalized linear model showed that not associated with the overall rate of injury (P = 0.565). However, when broken down into the FFS and RFS injury categories, it jumps to P = 0.0333 and 0.0377! There is obviously some sort of double standard here—why are significant differences in "predicted RFS injuries" important to talk about, but study design flaws that show up when that same category is used are not?

    All injury rates are reported in injuries per 10,000 miles of running. I'm undecided on what I think of this: on one hand, it seems to control for the obvious fact that mileage is associated with injury rick; on the other, it seems like it's the same problem of unequal subject treatment again. Every college team probably has one "indestructible" high mileage guy who runs 100+ miles a week year-round and rarely or never gets injured. What if he happened to be a forefoot striker? Especially with only 16 forefoot strikers in the study, that would totally throw off the data analysis. Thoughts?

    Daoud et al. also use some advanced statistics to do some more data analysis showing that (as we would predict) women get more injuries than men and that higher mileage is associated with more injuries, but also that the occurrence of "predicted RFS injuries" is indeed more common in rearfoot strikers, but there was no greater occurrence of "predicted FFS injuries" in forefoot strikers. My best guess as to why they did this is because they did not have enough data to categorize specific injuries, even though they saw non-significant trends among clusters of injuries. As I mentioned earlier, I think this is a misleading procedure, since they have virtually no reason to suspect that some of the injuries they classify as RFS-associated are in fact more common in rearfoot strikers. As some earlier posters pointed out, the only statistically significant differences AMONG SPECIFIC INJURIES were the following:

    *Achilles tendinopathy was more common among FFS females
    *Plantar fasciitis was more common among RFS females
    *Hip pain was more common among pooled (male and female) rearfoot strikers
    *Traumatic joint sprain was more common among FFS females
    *"Repetitive joint sprain" (what is that exactly?) was more common among male and overall RFS
    *Sacral stress fracture was more common among RFS males.

    I think Lieberman's lab is losing sight of the statistical forest on account of the trees. I suspect many of these 'statistically significant' injury rate differences are statistical artifacts due to extremely small sample sizes and they KNEW it—otherwise they'd have to account for why forefoot striking causes more joint sprains. How many males have you seen in your practice who have ever had a sacral stress fracture? Very few, I'd guess. It's an extremely rare injury, particularly in men, and I suspect there was only one or perhaps two in the entire study. Despite that, we're supposed to accept that this is a "statistically significant" difference because the p-values say so?

    Maybe it's because I haven't taken a formal statistics class since the tenth grade, but I don't buy this statistical glitz and glamor. I don't care WHAT the p-values say, at the end of the day, this study still only has sixteen forefoot strikers in it. There are going to be statistical artifacts when you start parsing that already-too-small group into smaller pieces; that's self-evident. While the results of this study ARE interesting and DO merit further study, I'm seriously troubled by the methodological flaws. I don't think we should throw it out as worthless, though. See the end of my post for some thoughts on an improved investigation.

    Getting back to the paper itself, the discussion is, like the introduction, really quite good until the end. Daoud et al. are careful to caution readers not to read too far into the data, and warn that there are a lot of unanswered questions. But unfortunately it seems their thinking-caps fell off while composing the last few paragraphs, as the paper takes quite an alarming, unsubstantiated turn in the final page or two. Read for yourself:


    Hold on, stop, back up.
    1) This study had nothing to do with impact forces—does forefoot striking really make a runner "more aware" of them?
    2) This study offers ZERO proof that CHANGES to running form—or indeed even being more "conscious" of it—has ANY effect on injuries. All of these runners were presumably natural forefoot strikers, not heelstrikers who became forefoot strikers. Even IF we accept that forefoot strikers have a lower incidence of injury, it is by NO means a foregone conclusion that heelstrikers who SWITCH to forefoot striking will have a lower injury risk.
    3) The naturalistic fallacy returns, having briefly poked its head up in the introduction but thankfully quickly being forgotten about. Would you ever read a phrase like "Because hominins have been living with cancer for millions of years (5), often to very long lifespans, it is reasonable to conclude that late stage cancer used to be more common [and is thus desirable]" in The Lancet? I would certainly hope not.
    4) Footstrike is a very small part of running form as a whole. To suddenly jump to running form as the new "big thing" for minimalist runners is a stretch. I imagine the leg stiffness guys will have a few words about "more compliant limbs" as well.

    Why do Daoud et al. suddenly jump to running form being more important than shoes? This study had NOTHING to do with shoes. Wasn't Lieberman's last study all about how modern running shoes are at fault for wrecking our running form? Perhaps he has some unpublished data that runners in minimalist shoes (I wonder what brand? :D) do not get injured less than runners in "normal" running shoes.

    Or perhaps Lieberman is going to get into the running form business. I can see it now....
    In all seriousness, though, this does merit some future work. I've been trying to think of ways to remedy the flaws in this study; let me know what you think of my proposed reworking.

    If I was doing this study, I'd do it with high school runners rather than college runners, simply because it's a whole lot easier to find a few thousand of them. I would forget about trying to control for mileage, BMI, training pace, etc., and let large sample sizes take care of that. Either that or build a control group that is matched for those factors. If the true prevalence of natural forefoot strikers (among runner who wear "normal" shoes) is 1-2%, you'd need somewhere in the neighborhood of 5,000 to 10,000 runners. This is daunting, but the upside of it is that actually collecting footstrike data does not take all that long. With a car, a high-speed camera, and photogates, you could collect data from a few dozen high school teams in a major metropolitan area for a few years and you'd easily get a big enough sample size. You'd have to find an efficient way to document injuries, and it would not be as extensive of a system as Daoud et al. came up with, but the bigger sample size would easily counteract any issues associated with this.

    Opinions? Anyone else worked through the full version?
  39. Hi John still going through your post - nice work by the way
    there is a difference I will look for the paper and come back to you

    but here is a few abstracts http://scholar.google.com/scholar?hl=en&as_sdt=0,5&q=treadmill+running+versus+overground

    nothing that I can see re FF striking increasing etc

    but stride length is more frequent and shorter , so assume more FF striking as longer strides would require heel striking generally

    make of that what you will .......
  40. CraigT

    CraigT Well-Known Member

    JohnD- nice work!

    Agree- very strange that they had NO midfoot strikers.
    I wonder how many of the heelstrikers were 'proprioceptive heel strikers';)

    Yep- I think this is the biggest issue.

    It would be interesting to have an injury data base developed in collegiate runners the same way they have in Australian Rules Football or in the UEFA in Europe... then you may be able to start drawing more conclusions. Having said that- and this is another issue- Collegiate runners are quite a different type of athlete to regular recreation runners... so the conclusions would be limited also.

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