Lit Review: Drop it Like it’s….A Minimalist Shoe?

Does the degree of heel to toe drop on your running shoes influence your risk of injury?

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Last august, a research group out of Luxembourg came out with a randomized controlled trial looking at the effects of heel-to-toe drop on incidence of running injury.  Previous literature has sorta looked at “minimalist” versus “conventional” shoes….but it’s really hard to draw conclusions from those papers because, what even IS a minimalist shoe? Every research group tends to define it differently.  And, okay, even if we did have a consensus definition of  “minimalist”….we still don’t know exactly what it is about these shoes that contributes to injury risk.  Other work has focused on shoe features such as:

-Midsole stiffness (and found that midsole stiffness had no effect on risk of running injuries) (3)

-Motion control systems (and found that among runners with pronated feet, motion control shoes were associated with lower injury incidence,  but in runners with supinated or neutral feet, injury risk did not differ between standard and motion control shoes) (2)

But as yet, no one had really looked at that mythical heel drop.   SO -enter this research group!  They took 500+ recreational runners, randomly allocated them to three groups, and gave each group a pair of shoes to train in. Shoes were IDENTICAL in all other factors except heel to toe drop, of which one group recieved a 10mm drop shoe; the second received a 6mm drop shoe; and the third, a 0mm drop shoe.

Runners were given the shoes and asked to train in them exclusively for a period of six months.  They uploaded data about the intensity, duration, and distance of their runs, as well as any pain or injury (“injury” was defined as any physical pain that prevented them from completing a planned training session for more than one day).  At the end of the six months, statistics were magically calculated (I never said I was good at everything guys…), and the researchers found that…..

OVERALL:  There was NO difference in injury risk between runners who used the 0mm or 6mm drop shoes, as compared to the 10mm drop.

HOWEVER….when data was magically calculated to account for runner’s training level (“occasional runners” – defined by consistent training for less than 6 months out of the previous 1year period – vs “regular runners”, defined by consistant training for greater than 6months out of the previous year),  they found that:

OCCASSIONAL runners seemed to report LESS incidence of pain and injury while wearing the 0mm and 6mm drop shoes, while REGULAR runners seemed to report MORE incidence of injury/pain while wearing these low-drop shoes.

But….but…..minimalist shoes are supposed to be magical injury prevention tools! Aren’t they?? Not so fast.  

1.First, my one problem with this study was that the researchers basically threw these runners a pair of shoes and said “run in these, and only these”.  They also reported than less than 5% of their sample of runners had any experience running in minimal-drop shoes.  So….what happens when we immediately switch from high drop to low drop without any adjustment period or any adjustment to our weekly volume?

OUR TISSUES AREN’T GIVEN TIME TO ADAPT AND WE GET INJURED.

I would love to see if that data would’ve been the same with an introductory/familiarization period.  What if the runners had been given six months to gradually incorporate the lower-drop shoes, and THEN run consistenly in them?  I am willing to bet you’d see less injuries.  WHen you immediately start loading the tissues in a way they’re not used to, well, the too much too fast too soon rule applies.  If you start doing something that’s outside your envelope of function, your tissues are not gonna like it.

2.Second, you have to consider the  LOCATION of the injuries.  I think it’s pretty well understood that minimalist shoes do not inherently prevent injury  – I’ll say it again, MINIMALIST SHOES DO NOT INHERENTLY PREVENT INJURY – they simply change the location of the injury.  minimalist shoes shift the load from the knee and shin to the calf-achilles complex.  The vast majority of injuries in this study were sustained at the knee and distal ( which is typical of running-related injuries) and were progressive/overuse associated injuries rather than traumatic.

HOWEVER – perhaps there was less injury incidence with the occasional runners because they didn’t run enough for the shoes to have any effect?

3.From this study, it seemed that shoe drop didn’t matter quite as much as regularity of running.  The regular runners sustained more injury in the minimalist shoes.  SO….is this a function of the shoes? Or of their regular running?  The more you run, the more at risk you are for injuries (obviously) – so, can we really separate the effects of volume, distance, frequency, and intensity from shoe type here?  I’m having trouble doing it.  Other risk factors for injury were consistent with previous literature.  The factors most predictive of injury were:

-Previous injury

-Training FREQUENCY

Training distance was found to be protective, as is consistent with Tim Gabbett’s model of injury risk (consistent hard training is actually protective against injuries, rather than a causative factor) which we will talk more about at a later date.

SO….why the lack of GLOBAL effect?  Well, most “minimalist” shoes also boast a lack of cushioning.  The authors report that the shoes utilized for this study were of standard cushioning, therefore they speculate that perhaps the cushioning allowed for maintenance of whatever biomechanics the runner had previously trained with.  We also know that minimalist shoes, while they may encourage a change in biomechanics, do not alter footstrike as much as barefoot vs shod running does.  So….maybe shoe drop doesn’t matter that much?

There were also several limitations in this study.  namely, we can’t assume that their definition of “regular” vs “occasional” runners are actually representative of those running populations.  There’s also a TON of variety there – you could get everyone from the beginner who runs once a week to the local elite who clocks 100 miles in that same time frame.  Too broad.  Too much variability in training volume, frequency, and intensity, and also no look at how different workouts affected reports of pain/injury with different shoes – for example, LSD runs vs track workouts. Also – everything was self-report. And we all know how that can skew the reliability.

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But overall, the message is clear:

-Wear whatever you want.  If it aint broke, don’t fix it. Stick with what feels good! If you’re healthy and running consistently, why change things?

-If you want to switch shoe types, break yourself in SLOWLY and progressively rather than all at once.

-Be mindful of WHERE the load is shifted based on what type of shoe you’re wearing. Calf and achilles problems? low-drop shoes are not for you.  Shin and knee problems? low drop shoes might be a good solution! THink about your own injury history.

-If you’re a regular runner…you might do better with a higher drop shoe. But then again, we need more than one study!

-Above all: stick with what FEELS GOOD TO YOU! Currently running in a minimal shoe and feeling good? Keep on keeping on.

-Maybe monitor your symptoms as you increase the mileage and/or intensity of your running

Happy Running!

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REFERENCES: 

Malisoux L, Chambon N, Urhausen A, Theisen D. Influence of the Heel-to-Toe Drop of Standard Cushioned Running Shoes on Injury Risk in Leisure-Time Runners: A Randomized Controlled Trial with 6-Month Follow-up. Am J Sports Med. 2016 Nov;44(11):2933-2940.

Malisoux, Laurent, et al. “Injury risk in runners using standard or motion control shoes: a randomised controlled trial with participant and assessor blinding.” British journal of sports medicine (2016): bjsports-2015.

Theisen, Daniel, et al. “Influence of midsole hardness of standard cushioned shoes on running-related injury risk.” British journal of sports medicine (2013): bjsports-2013.

 

 

 

 

2 Comments Add yours

  1. Vincent Hui says:

    Love this post! I’m a 1st year SPT and just wrote a paper on this topic. Great point on how shoes don’t actually prevent injury, but rathter change the location. I believe you should also point out that metatarsal fractures are very commonly seen with minimalist transitioners along with increased Achilles/calf injury. You make great points of slow transitions in your take-home points. Fuller JT et all (Body mass and weekly training distance influence the pain and injuries experienced by runners using minimalist shoes) found in their research that transitional increases from shod to minimalist shoes should not exceed 5% of weekly mileage, with higher mileage runners with even smaller increases, to decrease risk of injury. Also, you point out that minimalist shoes do not affect foot strike. However, wouldn’t minimalist shoes mimic barefoot running with forefoot/midfoot strike rather than a rearfoot strike due to increased GRF from decreased cushioning? Also note that some minimalist shoes (0mm drop) are basically barefoot with protection. With that in mind, could you argue that footstrike might be more important than shoe type and that running biomechanics plays a larger role in running injury? Murphy K et all (Barefoor running: does it prevent injuries) compared FFS vs RFS and found that there was flip-flop in injuries.

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    1. fitnerdaimee says:

      Thanks for the comment Vincent!
      Minimalist shoes do not necessarily mimic barefoot running. Just because you put someone in a minimalist shoe does not mean they’ll automatically begin running with a forefoot/midfoot strike. For example, I actually run in minimalist shoes from time to time and I still rearfoot strike. Now if I were to run completely barefoot I would forefoot/midfoot strike but running in minimalist shoes and running barefoot are not always equivalent. Here’s an article about it if you’re interested: https://www.ncbi.nlm.nih.gov/pubmed/23314887. If I had to choose between the shoe and the footstrike I would tend to agree that footstrike may play more of a role, but the best indicator of running-related injury is not biomechanics, it’s training error. I’ll be posting an article next week on this!

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