Form, footwear and footstrike: an e-book on running mechanics review with injury insights

This post is a link to a pdf ebook on the presentation I gave for the MSK-Plus course November 25, 2012.  Below I give a brief intro into the confusion that surrounds these topics.  If you note a huge amount of uncertainty, a whiff of grey and lack of simple answers than your interpretation is correct.


The pdf file is form footwear and footstrike running mechanics ebook nov20 2 2012.

Related posts

1. Barefoot running and footstrike style overview

2. Gait modifications to influence impact loading

3. Barefoot running and running economy

4. Running in the backseat: lack of hip extension and its possible relationship to injury

5. What we know and don't know about running injury prevention


We can change the following variables of running:

1. Kinematics or changing the position of the body (e.g. trying to not let your knees collapse inwards) or the timing of events (e.g number of strides per minute)

2. Footstrike style

3. Footwear: barefoot, "barefoot shoes", minimal shoes, traditional cushioned shoes with an attempt to "correct" something

We also hope that changes in mechanics will occur.  Some variables that may be related to injury:

1. Rate of impact loading

2. Joint forces

3. Muscle loading, timing or activation levels

4. Joint kinematics


We assume that making one change will result in positive changes in other variables. The big assumption is that we know what is bad in running.  It sounds so simple, but in practice it is not. Especially when we deal with something like pain and injury.

What you will see in the attached e book is that nothing is that simple.  Changes in many variables related to running often don't result in the "positive change" in some running variable that we hope for.


Below is a brief introduction to the modifiable variables and their relationship to running mechanics and to a less extent injury.  The attached pdf file goes into a little more detail.


Modifiable variables during running

Run barefoot or run minimal

I wish it were this simple.  We have some data suggesting that some barefoot runners will run with a forefoot strike, reduced stride length and other changes and thus they will have a decreased rate of impact loading.  We have no data suggesting that making this change reduces injury and the link between rate of impact loading and injury is a wee bit murky.  We also have a number of research studies showing that just changing to barefoot is not sufficient to result in decreases in the rate of impact loading.

In Lehman's terms, we may want to be cautious about any blanket statements


Lose the cushioned shoes and run in flats

I do this but I certainly don't think its the answer for everyone. I also run in cushioned shoes because I think variety is important.  As for mechanical changes when going to flats there is not a lot of robust data out there that supports this in terms of biomechanics.  The assumption is that if you lose the heel on your shoes and the cushion you will automatically start to run with a softer gait.  Again, this is not supported in the literature and research exists showing increases in rate of loading and joint loading with racing flat like shoes.  Again, we need to reserve our blanket statements.


Convert from a heel strike to a forefoot or midfoot

The assumption is that heel striking is bad.  Again, not strongly supported in the literature.  Research is mixed with some work showing decreases in the rate of impact loading when going to midfoot or forefoot but we also have conflicting work showing the opposite.  Again, blanket statements are not cool.  The epidemiological research is also in its infancy, is correlational in nature and correlation data sucks for implying causation.

Decreasing stride length and increasing stride rate

This modification may have the most support and may be a common variable in other interventions.  For example, I think that someone might strike the ground with a forefoot strike and have a large rate of impact loading if they have a long stride, while another individual might convert to a forefoot strike and also decrease the length of their stride.  We might initially conclude that the forefoot strike was the variable that resulted in the decrease in the rate of impact loading but really it was just having a shorter stride.  This may also be a factor with barefoot interventions.  Barefooters tend to stride shorter...maybe those barefooters with higher impact loading rates failed to decrease their stride length.  BUT, and there is always a but, we do have a well designed study that showed no changes in impact loading when increasing stride rate (Giandolini 2012).  I am not even sure how that is possible but that was their finding.


Kinematic variables

The ebook does not touch on this but these would be things like increased frontal plane projection angle, hip valgus, hip internal rotation, pelvic obliquity, lack of hip extension, increased anterior pelvic tilt, prolonged pronation, lack of pronation, uneven arm swing, lack of trunk rotation etc.  Surprisingly, we have very mixed data on this.  Even the biggies like increased hip internal rotation and hip valgus.  Sure there is some correlational data that shows that some runners with knee pain have greater amounts of hip valgus when compared with controls but the predictive data is much weaker.  We also have data showing no relationship between assumed gait flaws and any current injury.

We don't know if pain begets gait flaws (e.g hip weakness) or if the biomechanical flaw caused the pain.  What might surprise you is that we can often rehab a patient, get them running injury and painfree and they still present with the initial "biomechanical flaw".  My concern with assuming that some biomechanical variables are faulty is that this views the body as being inherently weak and we forget about its amazing variability and strength.  You will see lots of runners with huge amounts of hip valgus/knee collapse.  You will shudder in horror at this.  But sometimes that is just that person's little idiosyncrasy .  They have always done it and they have adapted.  You will try to fix them under the assumption that they are faulty.  But this a massive assumption.

I am working on a large post on the kinematics of gait and injury.  I will go into a lot of detail on this topic


OK.  So everything is grey.  What do I do?

 Warning: Opinions ahead.

Gait modifications can help with an individual in pain:  We have good data that a slow return to running with modifications to form can help.  I don't necessarily believe that this is always related to biomechanics in the sense that we are changing mechanics to be closer to an ideal.  I think we are changing mechanics and it is the act of change that is important.  Variability and novelty is important to me in all my rehab programs.  Changing your gait loads the body differently and is also different for the brain.  Different gait patterns may avoid certain physical stressors on the body and may not activate our pain neurotags because of the novelty.  Further, most gait re-training is a slow, gradual return to running.  This exploits our innate adaptive abilities.


How should people run if not in pain?

Please note, the suggestions below only relate to running form.  There are a lot of things we can do to reduce the risk of injury.  Below is not comprehensive.

If I have to go out on limb I would suggest four things:

1. Novelty and variety: different shoes, different surfaces, different speeds, different distances.

2. Check your cadence: if you are running a five minute kilometer than  your steps per minute should be greater than 170 per minute.  If  you are "loping" and don't have a quick turnover consider increasing your cadence.  What you are trying to avoid is landing with the foot extremely far in front of the body and this is associated with a close to straight knee at footstrike

3.   With reservation and many exceptions, a midfoot to forefoot strike with the occasional heel strike thrown in:  this one is tough for me to say and I have some hesitancy. If you are novice runner I would probably suggest running with a midfoot strike. I think the bulk of the research suggests that running with a midfoot strike is the way to go.  I know that there is research suggesting heel striking is fine especially if it is not associated with overstriding.  I totally get this.   As  I said, I have some hesitancy - I treat a lot of heelstriking runners and would not consider changing their gait so this suggestion is obviously not a blanket for everyone.  Many heelstrikers have their feet land close to their body and their gait is soft and quick. However,  I also think that thinking about midfoot striking will also help with your cadence.  Last, for slower runners (10 minute miles) I doubt footstrike matters as much.  One caveat, I also think many runners would benefit from using different footstrikes during the same run provided their cadence is not too low.  This is consistent with my views on variety.

4. Gradual increase in running or in changes in form.  This one is obvious.  The body adapts over time we just have to give it some time to adapt.


My bottom line

I would be hesitant to change things about someone's form if they have no injury or past history.  If they have had a series of past injuries or currently have an injury this is where I think we can help the most with changes in form.  What you will see in the e-book is that there are so many exceptions to our commonly held beliefs about certain running related variables.  These exceptions make me quite cautious in just trying to change runner's form when you don't actually know what you are causing when you try to make a change.  I am lucky in that I have access to 3D motion capture equipment.  I can see what happens with different changes in form.  But I don't have force plates and I can make no comment on changes in joint loading or impact loading.  And the "running expert physio" dude with one camera (or who just eyeballs a runner from behind) can't say what changes in force (e.g rate of impact loading are occurring) and is also probably wrong about a runner's kinematics should be a little cautious in just making changes based on one or two cherry picked research papers.  What the research in this e-book shows is that many changes we assume to be good end up resulting in elevated levels of impact loading or joint loading.  Thus, I advise caution.





Running in the Backseat: A rationale for improving hip extension in runners

Poor hip extension is a favourite of boogeyman for all manner of back and leg injuries. I have reservations about its relevance to pain and injury in terms of how the hip flexors get tight and the relevance of regional interdependence to pain (see here and here). Yet, I do not completely ignore the possibility that hip extension limitations (or not using your available hip extension) can influence function...I just think its over-rated and over used. One area that limited hip extension is proposed to influence function is during gait.  Dr. Howie Dananberg has detailed this in his theoretical ideas about how functional hallux limitus (lack of big toe dorsiflexion) leads to lack of hip extension, which in turn causes a decrease in the stretch of the psoas, leading to the loss of passive muscle recoil (because no psoas stretch) to initiate leg swing during gait and and ultimately increases in stress on the lumbar spine that leads to pain. (see a review here and one from me here).  Another theory regarding running has been championed by Jay Dicharry which is slightly different and puts a strong emphasis on performance as well as the possibility of pain.

Jay Dicharry is a biomechanics researcher and physical therapist with a focus on running injuries.  He runs a gait biomechanics lab at the University of Virginia (blog here) and has published some excellent reviews (here) and original research in the area (here).  He has also a new book out on running injuries (here).  I am a big fan of how Jay explains running biomechanics and he does an excellent job in his book. In the book he proposes a possible mechanism where lack of hip extension may negatively influence runners.  Jay lays out an excellent case for how poor hip extension can compromise efficiency (I can get behind this) and may also increase injury risk (I'm still skeptical when anything comes to pain because of the complexity of the pain experience and the poor track record that biomechanics has in predicting pain but this is no fault of Jay Dicharry).

Theory in a Simplified Nutshell:  Limited Hip Extension causes Overstriding.

Jay describes the swinging leg as pendulum.  It has a front side swing (swinging forward to strike the ground) and a back side swing (backside mechanics that occur before the leg leaves the ground).  What Jay suggests is that if you don't have adequate hip extension the athlete will "sit back" while running and will have increased front side swing (see the picture above from  In other words, the pendulum arc will be shifted to the front side and the runner will land with the foot too far in front of the centre of mass - aka: overstriding.  This problem will be compounded at increasing speeds when the athlete looks to increase their  stride length.

Jay suggests that running in the back seat leads to two things:

  • Increased metabolic cost associated with overstriding
  • Increased impact loading associated with overstriding

Lets look at these two in detail.

1. Increased Metabolic cost associated with overstriding

Two mechanisms may be at a play here:

a. Lack of hip extension loses passive energy return.   The muscle-tendon unit can be viewed as springs.  We use the passive energy that they store rather than merely actively contracting them.  The tendons store energy during impact (e.g. they start to stretch) and then they release that energy during the push off phase.  With limited hip extension it is suggested that the pendulum can not swing backwards past the dashed vertical line and the pendulum must then swing forward excessively.  Without the ability to swing backwards the runner doesn't have the time to release the energy that they stored during impact because they are not able to let their leg swing backwards.  



b.  Overstriding is inefficient and costs more muscular work.  When overstriding the center of mass of the runner increases its up and down motion.  This means we work harder to decelerate the mass during impact and absorption and then we work harder to accelerate the mass during the push off phase of running.  Further, with the ground striking leg being farther away from the body we are at a mechanical disadvantage for absorbing this energy.  Overstriding would then increase the load on the knee and may therefore predispose individuals to knee pain.


2. Increased impact loading associated with overstriding

                                            This one we have heard a lot and is the thrust behind shortening peoples strides, changing foot strike pattern, going barefoot or running in minimal shoes all in an attempt to decrease the rate of impact loading, collision force and joint loading when running.  The closer the foot is to the center of gravity at foot strike the less rate of loading and joint loads we can expect.  Heiderscheit (2011) published a recent paper showing  how manipulating stride length (decreasing it) can decrease ground reaction forces, braking forces and joint loading.  This is also the impetus behind Lieberman's work championing barefoot running - he contends that the combination of a forefoot strike and a foot strike closer to the body (i.e. what occurs with shorter strides which is proposed to  naturally occur when you run barefoot) decreases impact loading (a large review can be seen here).


Other kinematic consequences of limited hip extension

Not all runners with limited hip extension will end up "sitting in the backseat".  Some can increase their backside mechanics (the range of the leg swing backwards) by arching their back.  This is a common explanation we hear for the dangers of limited hip extension in runners and in all athletes or low back pain sufferers in general. In other words, if you don't have hip mobility you steal it from somewhere else (e.g. regional interdependence).  In this instance you get the range from your spine. Many authors have speculated that this increases ones risk for low back pain and for hamstring strains but again the data is not there.  However, if you are  having aches and pain with running this may be one area you could modify to modulate your pain response. Sometimes getting out of pain is just changing a habit, providing something new and different to our body (and brain) and you can feel less pain.

Critique and Comments

What I like about Jay Dicharry's opinions in this areas is that he has access to data and equipment that can support his views.  He is fortunate to have an impressive biomechanics laboratory and he mixes his clinical wisdom with the data is he is able to collect.  Questions/ideas that this theory presents to me are:

- how regularly does a reduction in hip extension lead to overstriding? Is it really the loss of hip extension that causes overstriding or are there other variables.

-if the pendulum arc is shifted forward this implies to me that there should still be enough time for the leg to load and store elastic energy because we haven't shortened the arc just shifted it forward with the overstride.  I could see how there is less time to load and store elastic energy if the actual foot contact time was reduced because of the necessity to take a shorter stride.

-this is still an unpublished hypothesis.  Like all theories of injury or performance it does need to go through rigorous testing.  I look forward to seeing these concepts tested and published.

-the vast majority of people (more than 90%) probably run slower than an 8 minute mile (5 minute kilometer). Strides are typically small and there is a plenty of ground contact time. With plenty of ground contact time the athlete would be able to release that energy.  With less speed there is less impact loading in general and this would provide a buffer for the slight increase in loading with the overstriding. I would question how relevant this is to contributing to injury - the simple biomechanical idea of increases loads being associated with injury is not well supported.  It is not a direct relationship.  In a runner with limited hip extension I would assume they have always had limited hip extension and this would have given them a lifetime to adapt.  Lots of individuals run with greater impact loads and joint loading (even at the same speed) and they may not be more prone to injury - this is even what happens when we age (see a quick review here)


-I don't doubt that people might show up with pain in their knees and also run while sitting in the back seat.  I also don't doubt that changing how they run (or stretching their hips) might be correlated with a decrease in pain.  Seeing these correlations often lead us to thinking that it is the biomechanics that cause the pain when it can be many other factors.  Last, even the act of changing the biomechanics can result in a resolution of pain but not because you changed the biomechanics.  It can merely be the act of change, setting a new contest for running, doing a relatively novel and what is assumed to be a threat free way to run that can result in less pain.

-with respect to Performance I have little say.  This is the most intriguing aspect to me.  I would love to see some research showing improvements in running economy following increases in hip extension.  Jay has laid out an excellent argument for how this style of gait is inefficient.  This is certainly something worth tinkering with in athletes who are pushing their limits.



Barefoot running and running economy

Purpose: summarize three recent papers looking at the running economy of running barefoot Three recent papers have been published looking at barefoot, vibrams, minimal shoes and cushioned running shoes and their associated running economy (i.e. energy cost associated with running at a specific speed).

The research is a bit murky.  Those arguing in favour of barefoot or minimalist running suggest that this method of running is more efficient for two basic reasons:

1. there is less mass and therefore less work required to move the foot (older research here)

2. barefoot running allows the passive structures of the foot and calf to store and release passive energy

So what does the recent research say?

Here are the papers I will briefly review and as a spoiler I have quoted their conclusions directly in case you have somewhere else to be.

Perl et al (2012) - abstract here.

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

Franz JR et al (2012) - abstract here.

Running barefoot offers no metabolic advantage over running in lightweight, cushioned shoes

Hansen et al (2011) - abstract here.

It was concluded that at 70% of vVO (2)max pace, barefoot running is more economical than running shod, both overground and on a treadmill.

So it looks like barefoot running is significantly more efficient than cushioned shoes in two studies but one study suggest that it isn't. Here is a more detailed look at each study.

Study #1: Perl et al (2012) Barefoot(Vibrams) versus bulky, cushioned shoes

Main Finding: running barefoot/vibrams (even if you add weight to your feet that is the same as shoes) is more efficient than running with shoes.

This is a great and very comprehensive paper of Perl et al (2012). I will only focus on the running efficiency aspect of the paper but the paper explores kinematics and kinetics as well.

The authors investigated four trials of running.  They used Vibrams as a surrogate for barefoot and called these minimal shoes. They investigated four trials of running:

  1. FFS in minimal shoes and ankle weights
  2. FFS in standard shoes (Asics Cumulous 349 grams)
  3. RFS in minimal shoes and ankle weights
  4. RFS in standard shoes.

The authors controlled for a number of variables that might effect economy:

  1. shoe mass
  2. foot strike
  3. running cadence (around 186 steps per minute)

They  measured or calculated:

  1. The oxygen cost associated with running
  2. Joint kinematics and kinetics
  3. Arch strain and Achilles strain (from kinematic and kinetic data)

Each trial lasted a minimum of five minutes, with at least one minute of running after VO2 levels reached steady state. A metronome was used to keep the runner at his/her preferred stride frequency


  1. No difference in running economy when comparing foot strike style regardless of the shoes.  This is huge.  it argues that running technique in terms of landing does not influence how efficient we are.  But remember, this says nothing about INJURY.
  2. Minimal shoes (Vibrams) were more economical no matter what foot strike pattern.  If running with a rearfoot pattern they were 2.41% more economical and if running with a forefoot pattern they were 3.32% more economical
  3. Most subjects were economical when running minimally but a huge range was observed.  One individual was 9.6% more economical but one fellow was 7.32% more costly.
  4. Barefoot runners do not bend their knees more - there is not an energy cost associated associated with cushioning.  This is often suggested but not supported.

Important Things to Remember

  1. These authors added mass to the minimal shoes (Vibrams) so we can expect that without adding mass the minimal shoes would be even more economical
  2. All runners were experienced barefoot runners and comfortable heel or forefoot striking.
  3. Cadence was controlled – very important
  4. We don’t know how other minimal shoes (e.g. racing flats) would compare.  Is there something special about Vibrams that allow one to run as if barefoot or is this something shitty about running in standard cushioned running shoes.  The next studies look at that.  Kind of.

Study #2: Hansen et al  

Main finding: In mostly inexperienced barefoot runners individuals who ran barefoot both on a treadmill and on track had better running economy than while running in shoes.

Study Set Up

- 10 healthy runners (two experienced barefooters)

- ran on a treadmill and on track at a pace comparable to 70% of VO2 max while running completely barefoot and while running in shoes (therefore 4 runs in total)

- track running speed was assessed with the Nike+ accelerometer

- no information on what running shoes were used

- no controls for shoe mass, foot strike pattern or cadence


1. On the treadmill there was no statistically significant difference in oxygen cost when running in shoes or in barefeet

2. When running on the track running barefoot showed a trend  to being more economical (Vo2 was 5.7% greater when shod - a huge difference compared to previous studies)

3. When the two barefoot conditions were combined (treadmill and track) and compared with the two running shoe conditions barefoot running was 3.8% more economical.

4. Rating of perceived exertion was consistently higher in shoes than barefoot

5. Heart rate was higher in shoes than barefoot on the treadmill only.


The thrust of this paper is that running barefoot outside is more economical than running in big, bulky shoes.  This is interesting since this is where races occur.  However, a few limitations of this study when added together may seriously jeopardize this conclusion. Roger Kram and Jason Franz, the authors of the next study wrote an insightful letter to the editor suggesting that a systematic error in how running velocity was calculated would lead the authors to conclude that barefoot running is more economical when it is not.  Thus, the barefoot runners ran slower than the shod runners and therefore consumed less oxygen. Let me lay out their argument:

1. Velocity was measured with the Nike+ accelerometer.  It does this by knowing when the foot first strikes the ground and then leaves the ground (contact time) relative to how fast the foot moves horizontally during that time period.

2. The Nike+ assumes that you run with the same foot contact time when you are running to calculate your speed.

3.  If the device was calibrated when wearing shoes we might have a case where the foot contact time is different in shoes than during barefoot (this was seen in a study by Squadronne).

4. Kram suggests that barefoot running has a shorter foot contact time  therefore there is a bias in how the Nike+ reported the speed to the runner that was running.

5. With a shorter contact time during barefoot running the Nike+ would give an overestimated speed during running.  Therefore, barefoot runners would have run slower than their counterparts thus the changes in VO2 seen in barefoot running versus shod are due to running slower not because of the shoes.

Study #3: Franz et al (2012)  barefoot versus minimal shoes (Nike Mayflys)

This study has been blogged about previously here and here.

Main Finding: Barefoot running is not more economical than running with a light weight trainer even though there is less mass with barefoot running.

This great study looked at the oxygen cost while running barefoot (not with Vibrams but while wearing a thin sock) and in a minimal cushioned running shoe (the Nike Mayfly 150 grams).  The authors also controlled for a number of variables:

1. Barefoot running experience (all were experienced)

2. Foot strike pattern (all used a midfoot strike)

3. Mass (lead strips were added to the barefoot condition and to the running shoe condition

4. Cadence was not controlled

Study Set up

Subjects ran barefoot and at multiples of the weight of their shoe (1x, 2x and 3x the weight).  They also ran in the shoe with multiples of the weight added to their shoe.  While running at a constant speed of 3.35 meters/second (about a 5 minute kilometre or 8 minute mile) the subject's VO2 was calculated.


Directly from the study:

Without added mass, the mean and gross metabolic power were both 2.1% lower when running in shoes compared to barefoot (BF0M vs. SH1M), but these differences were not statistically significant (p=0.092 and 0.118, respectively).

For eight of the twelve participants, running in the lightweight, cushioned shoes was less metabolically demanding than running barefoot, despite the greater mass.

Subjects selected 3.3% longer stride lengths during shod running. Importantly, the longer strides adopted when running in shoes reflected an effect of footwear and not of added mass; stride length did not significantly differ between BF0M and BF1M (p=0.342).

Main Points

1. Adding 100 grams of mass increases energy costs 1%

2. Barefoot running (with socks) is not more efficient versus light weight trainers despite the weight of the shoes.

3. Runners decreased their cadence and increased their stride length 3.3% in shoes

4. When running barefoot with added mass equal to the mass of the shoes the runners used 3-4% more oxygen when compared to running in shoes.

5. The authors suggest that running barefoot "costs" more oxygen because of the need to provide cushioning (e.g. more knee or hip flexion).  However, the authors did not measure this and the kinematic data from the Perl study above suggests the exact opposite of this.  In that study, running barefoot (in Vibrams) lead to less knee flexion (e.g. cushioning) when running.

Why do we have different results across studies?

Shitballs, I really don't know for sure.  But lets look at some ideas and differences between the studies.

First, the Hanson paper may be limited due to the means of measuring velocity in overground running and it does not provide much more insight than any of the previous studies in the past decade have so will limit the discussion to the Perl study and the Franz study.

The two great studies by Perl et al (2011) and Franz et al (2012) make two seemingly opposite conclusions.  Both of these studies also controlled for many of the same variables with the exception of the Franz study which did not control for running cadence.  However, there were differences between the two studies and a number of uncertainties.  Those being:

1. The Perl study compared Vibrams versus a large cushioned shoe that weighs 349 grams.  They concluded that even adding weight to the Vibrams to equal 349 grams the Vibrams were still more efficient (3% more O2 cost in the big shoes)

2. The Franz study compared barefoot (socks) running to running in minimalist shoes (shoes that had a sole but a limited upper).  These authors found that even when the weight of the shoes equaled the barefoot condition with weight added shoes were always more economical (3-4% more O2 cost in barefoot).

3. The Franz study did not control for cadence and runners in shoes increased their stride length on average 3.3%.

4. We can't conclude that barefoot runners in the Franz study bent their knees and hips more (e.g. the cost of cushioning).  The authors did not measure this and the Perl study suggests that this does not happen.

5. We don't know how minimal shoes (e.g racing flats or the shoes used in the Franz study) compare with big, bulky cushioned shoes (e.g the ones used in the Perl study).  We also don't know how running in Vibrams compares with running in socks although a previous study (Squadrone link here, although they made this conclusion in the discussion but there was no data in the results about this) suggests that Vibrams may be more efficient than barefoot alone.

Some thoughts...

It may be possible that running in Vibrams confers greater energy efficiency than running in barefeet alone  and that this could be similar to the greater efficiency achieved in the lightweight trainers (e.g. the Nike Mayflys studied by Franz) versus running in socks.  These conflicting results may not be conflicting at all since they did not measure exactly the same thing. It would interesting to know two things:

1. What is the difference between running in the Mayflys (lightweight trainers) and big, bulky shoes (i.e. the shoes used in the Perl study that compared Vibrams with shoes)

2. What is the difference between running in Vibrams and running in the socks that the Franz studied compared the Mayflys with.

The implication for these questions is whether it is plausible that running lightweight running shoes (the Mayflys at 149 grams) is similar to running in Vibrams (149 grams).  If these two footwear choices are comparable then we don't have any discrepancy between the studies.  It suggests that light weight footwear (Nike Mayfly or Vibrams) is more efficient than barefoot/socks even when the weight of the shoes are controlled for (i.e. the conclusion of the Franz study) and that Lightweight footwear is more efficient than big, bulky shoes even with the weight of the shoes are controlled for (i.e. the conclusion of the Perl study).


1.  The Franz study certainly argues in favour of running in light weight trainers.  It suggests that you get many of the benefits of barefoot running without the drawbacks of the added weight associated with the large cushioned shoe.

2.  The Franz study also suggests that we don't always have to shorten our stride to get efficiency.  This is sometimes advocated but the study suggests that a longer stride is associated with improved efficiency when wearing shoes.  This is not new and was the conclusions of Cavagna's research for years (sample abstract here) when he looked at preferred stride frequency.  He basically suggested that the body finds the stride frequency that is most efficient for it.  Sounds simple.  The body seems to have some inherent wisdom.

3. We have no idea what happens after running for 90 minutes.  This is what I am interested in.  I think the arguments for barefoot running and performance can really break down when it comes to running at extremes of fatigue.  We see this anecdotally with barefoot runners starting to heel strike at the end of races.  The cushioning cost has to come from somewhere and I would rather this have been something passive (like my shoe) than something that can fail and fatigue (e.g. arch strain, achilles tendon etc).

Case Study: Unexplained dead leg when running. Altered nerve tension?

Purpose: Demonstrate a case of an altered nerve tension in a runner that may be exacerbated by their running technique. Case Details

Female, late twenties, competitive runner (sub 20 minute 5km, 1:30 half marathon, 3:15 full marathon)


- 2 year history of left lateral lower leg pain that comes on with running

- begins around 20-30 minutes into a run and often feels like she can't control her leg with a sense of numbness (like she might fall)

- but no obvious swelling, shininess or pain in the anterior compartment during these bouts

Select Physical Exam Findings

- neuro screen, strength, ROM, single leg squatting, usual "functional tests" are all normal

- no significant pain on palpation of entire lower leg

- positive Slump test with a bias toward the superficial peroneal nerve.  This also occurs during a straight leg raise test with a superficial peroneal nerve bias.  The sensation felt is the same as that felt during running.  The video below is essentially the test movement (except change the ankle dorsiflexion for plantar flexion/inversion)

Running Analysis

In the video below I noticed two things that may be significant.  This runner is predominantly a forefoot striker even at slow speeds.  Quite rare.  She essentially reaches out for the ground with her forefoot.  If you notice her knee it is actually quite extended just before foot strike.  This is not normal. See a kinematic review of running here. There is usually quite a bit of knee bend before landing and of course on impact.  Simply, this runner overstrides with a forefoot strike. She does this both in shoes and in socks.  This position is similar to the Straight Leg Raise test with a peroneal nerve bias and it may be contributing to the "funny" feeling in the leg.  A review of running biomechanics with video can be seen here.


I can't rule out exertional compartment syndrome but I also can't confirm that with ease as the test would take over 3 months to get here in Toronto.  And Andy Franklyn-Miller (UK sports doc with a great deal of experience studying this type of thing -  website here) would suggest that this test is even questionable for this condition and we might even want to question the condition itself.  So I keep the exertional compartment idea in my head and look at other possibilities.

Why I question the compartment syndrome is the positive response I get when I stress the superficial  peroneal nerve with neurodynamic testing.  I don't believe that this is a classic response for exertional compartment syndrome suggesting to me that we have an altered neurodynamic on our hands.


- explain pain, always explain pain

- at home - every hour, 5-6 nerve sliders for the peroneal nerve (video below but don't dorsiflex the foot)

- running changes: this is tough but our runner is working on a midfoot strike and is trying to cue the idea of landing behind her (this is impossible but it can get the idea across).

- I also treat the "container" of the nerve.  I do gentle soft tissue work (I used to be an  A.R.T guy but I am much gentler now and don't believe the theory they propose) along the entire sciatic nerve. I think that I am really the nervous system and ultimately influence the muscle and the peripheral nerves with my manual therapy.  You can explain this treatment anyway you like. I choose a neural based explanation rather than thinking that I am digging out adhesions.

- I believe runners should be strong.  And not just runner strong - athlete strong. This runner has had previous high hamstring tendinopathy/tearing (or possibly sciatic nerve or all the little nerves back there irritation) so she is on a heavy resistance training program for everything.  I don't emphasize anything - I just train for balance, capacity and variety.  She gets exercises like one leg deadlifts, deadlifts, squats with bands, hip thrusts, hip airplanes, bridges, clamshells, one leg squats, one leg lateral wall squats, nordic hamstrings, push ups, suitcase carries etc.  Click here for a "hamstring" injury for runners sample program for videos

Is she better?

Sorry, don't know yet.  Just started.  Any ideas please let me know.  I can say that after I gently treat the region around the sciatic, tibial, peroneal nerve we are able to decrease the sensitivity associated with the SLR testing. This is a good sign. I am cautiously optimistic.

Rate of impact loading not consistently different in shoes versus forefoot barefoot running

Audience: Runners and TherapistsBackground: Changing running form, particularly through the aid of minimalist or barefoot running, is often proposed to change the type of forces that the body experiences during running.  This in turn may influence of risk for injuries.

Source of information: Zadpoor et al (2011), Lieberman et al (2010) and Squadrone et al (2010)

I love the idea that there exists a proper way to do something.  In sport or any movement this can be considered ideal form (I consider form to be the dynamic equivalent of posture). I question whether there is an ideal way to do something but it still fascinates me.  Barefoot running and minimalist running is garnering a lot of attention because of some research suggesting how it can change the stride characteristics of a runner.  And how it changes the characteristics without the person really consciously trying to change their form is also interesting.  It is proposed that barefoot running is natural…and the feedback that your feet receive from the ground will automatically cause you to modify your stride to a proposed more ideal technique.  If we extend the excellent biomechanics research (which the authors of those papers caution against but others in the lay press still do) we might argue that the differences that exist in changing running mechanics lead to fewer injuries.  See my previous post (click here) comparing the differences in running mechanics during  barefoot running, shod running with a heel strike and shod running with a forefoot strike.

The question is…What is the link to injury reduction?  Update, well after this post was written a paper did come out looking at running technique and injuries.  I'm sure this is the first of many to come.  See it here at Alex Hutchinson's blog (

Recap of changes in mechanics with barefoot running

First a quick recap of how barefoot running changes the loading when the foot strikes the ground.  Lieberman’s work is excellent and a video is seen below.  When the foot first strikes the ground (particularly in heel to toe running) there is an Impact transient or collision force.  Notice the first big peak in the picture below. This force is then slightly decreased and then the ground reaction force starts to increase again as we push off of the ground.  The second big peak is called the Active peak.  The force pushing against the ground then decreases as the foot leaves the ground.  See the picture below.

What Lieberman demonstrated was that the Collision force or that initial impact transient peak was significantly reduced when running barefoot and forefoot striking for habitually barefoot runners.

Lieberman wrote the following (emphasis is mine):

“At similar speeds, magnitudes of peak vertical force during the impact period (6.2 ± 3.7% (all uncertainties are s.d. unless otherwise indicated) of stance for RFS runners) are approximately three times lower in habitual barefoot runners who FFS than in habitually shod runners who RFS either barefoot or in shoes (Fig. 2a). Also, over the same percentage of stance the average rate of loading in FFS runners when barefoot is seven times lower than in habitually shod runners who RFS when barefoot, and is similar to the rate of loading of shod RFS runners (Fig. 2b). Further, in the majority of barefoot FFS runners, rates of loading were approximately half those of shod RFS runners”.

a, b, Magnitude (a) and rate of loading (b) of impact transient in units of body weight for habitually shod runners who RFS (group 1; open boxes) and habitually barefoot runners who FFS when barefoot (group 3; shaded boxes). The rate of loading is calculated from 200 N to 90% of the impact transient (when present) or to 6.2 ± 3.7% (s.d.) of stance phase (when impact transient absent). The impact force is 0.58 ± 0.21 bodyweights (s.d.) in barefoot runners who FFS, which is three times lower than in RFS runners either barefoot (1.89 ± 0.72 body weights (s.d.)) or in shoes (1.74 ± 0.45 body weights (s.d.)). The average rate of impact loading for barefoot runners who FFS is 64.6 ± 70.1 body weights per second (s.d.), which is similar to that for shod RFS runners (69.7 ± 28.7 body weights per second (s.d.)) and seven times lower than that for shod runners who RFS when barefoot (463.1 ± 141.0 body weights per second (s.d.)). The nature of the measurement (force versus time) is shown schematically by the grey and red lines. Boxes, mean ± s.d.; whiskers, mean ± 2 s.d.

Interesting?  The RATE of loading is not different when heel striking in shoes when compared with forefoot barefoot striking.

I think this is a very interesting finding and I certainly don’t fully understand its implications.  Where it may be relevant is the research that looks at impact forces and injury risk.

A recent review paper (click here) by Zagpoor (2011) found that peak impact loading was not related to the occurrence of stress fractures in the lower extremity but that the RATE of loading was related to the occurrence of stress fractures.   So, the variable that is changed so greatly with barefoot running and forefoot striking does not appear related to injury risk in the studies that we have to date (it still might be, I’m not ready to rule it out) but the variable that shows no difference between the forefoot barefoot group and the rearfoot shod runners is related to injury. Cool…maybe?…I don’t know.

A final caveat.

What I don’t know from these studies is how an individual’s loading profile changes when going from rearfoot shod to a barefoot running gait that was trained over a long period (or forefoot running).  I would wager that on an individual basis we might have an argument that we can change the rate of loading when going to barefoot or forefoot striking.  In fact, I know that this can be done with simply giving feedback on loading and asking individuals to run softer.  Dr. Irene Davis (click here) has shown that this type of feedback can change loading rates.  Her work did not investigate kinematics so I don’t know how her patients changed their stride but I would surmise that many are taking a smaller stride and probably landing more midfoot.

Final caveat, I actually asked Dr. Davis about Lieberman's finding.  She believes that a couple people were outliers in the study and this dramatically increased the rate of loading for the group average.  This certainly seems feasible considering the low numbers in the study population.


Greg Lehman

Differences in impact loading in older runners

Repost:  I originally posted this in October 2011 but lost it in the great porn/spam database hack debacle of January 2012. Purpose: To highlight some key differences in impact loading in older runners versus younger runners

I’ve been meaning to write this post forever and thought I could provide some amazing insight into the study in respect to all of the other great research on running mechanics out there.  Well, I can’t.  I suck.  The study is beautiful enough as it is so I thought I should share it and document the findings for myself as well as any readers.

Sicco Bus (2003) performed a study entitled ” Ground Reaction Forces and Kinematics in Distance Running in Older-Aged Men”.  The author looked at joint kinematics (how joints move) and ground reaction forces (the loads that travel from the feet into the body) in young men and older men (55-65) while running on a track.  The groups ran at both a self selected running speed (SRS) and a controlled speed (CRS). For simplicity here is a picture of the main results:

Interesting Points from these results

  • -the younger runners ran faster at self selected speeds (duh, but not duh for me because I smoked by older runners on a daily basis - never judge a runner by age, sex or size)
  • -even at the same speed older runners had both higher peak impacts (expressed relative to body weight) and higher loading rates
  • -older runners had shorter strides and a higher stride rate (1.38 Hz) well short of the “magical” but unfounded 180 steps per minute.
  • -older runners tend to have greater knee flexion at the time of foot strike but then they had less flexion (range of motion) while they bent their knee during the load absorption phase of landing and subsequently toeing off.
  • -older runners also had smaller amounts of ankle range of motion

Digested Take Home Points

What I find most interesting about this paper is the finding that even when running at the same speed  the younger runners had less impact peak and less loading rates.  It should also be highlighted that the older runners tried to do the stride modifications typically recommended to lower their impact forces and rates (e.g. increase stride rate and reduce stride length) but still had more impact forces at the same pace as the younger runners.  It would be interesting to see how high their kinetic/loading variables would be if they ran with the same stride variables as the younger runners.

What we don’t know is why older runners had more impact forces…and to my knowledge no study has occurred in the past 8 years answering this.  What it does strongly suggest is that the method most commonly espoused to influence loading rates and loading impact levels (e.g. changing stride rate and stride length) did not cut it.  Nor was it correlated with the kinetics.  And lets not forget, the big question is whether it even matters.

Kinematically (aka, how your movements look) the differences in knee joint range of motion is significant.  Older runners have less of range of movement but still have higher degrees of force through their joints.  This suggests greater stiffness in their knees and ankles.

Final Take Home Points

This is a very neat study and I would encourage you to read the entire thing as the discussion is very detailed.  But don’t conclude that older runners are more prone to injury because there is more loading and higher loading rates. . .  And for the love of tempo runs don’t stop running.  You don’t stop running because you get old, you get old because you stop running.  I stole that quote, please inform me of  the source.

Related Posts on the Web

1. From Alex Hutchinson's super blog at Runner's World Sweat Science:

Barefoot, forefoot strike and heel strike - a biomechanics summary

Audience: Runners and therapistsPurpose: To summarize the biomechanics of running strike pattern and shod conditions

I feel like in the blogosphere and the popular running media that there is a love affair with all things barefoot.  Barefoot running is associated with forefoot striking and there appears to be changes in the biomechanics associated with alteration in running form when compared with heel striking.  However, the research gets presented as if it is very neat in tidy when in fact it is quite murky.  This post is a work in progress.  It attempts to summarize some of the work comparing barefoot running with shod running and the work that compares forefoot striking and rearfoot striking while running in shoes.  I hope that I have conveyed that the results are quite conflicting.  Hence, what a pain it was to try to summarize this work.

This post will be updated consistently. Please view it as a work in progress.

A. Changes when going from shod to barefoot running

Kinematic changes

-there is a trend to shift  from rearfoot striking to landing more on the midfoot or forefoot

-an increase in step frequency (e.g. more steps per minute)

-a decrease in step length (Divert et al 2008, Squadrone 2009)

-the foot is more plantar flexed (i.e. the toes point down at contact) and there is a greater degree of ankle motion (Pohl and Buckley 2007, Lieberman et al 2010)

-a decrease in the amount of peak pronation or calcaneal eversion (Morley et al 2010) which is most evident in runners who pronate a great deal.  Going barefoot decreases peak eversion from 10.3 degrees to 6.7 degrees in moderate pronators and from 14.8 degrees to 9.2 degrees in super pronators.

-the time it takes to get to maximal calcaneal eversion decreases in barefoot

-total eversion distance is increased with barefoot running.  Even though there is less pronation the foot starts in a greater degree of inversion when barefoot.  Therefore, the heel travels a greater distance when striking the ground to reach maximal eversion/pronation.

Force or Impact changes

-a decrease or complete reduction in the impact peak (aka. impact transient) when the foot strikes the ground but the push off peak is unchanged. A shod heel strike vertical ground reaction force can be seen in this video from Dr. Lieberman:

In the following graph notice how the first "bump" is lower in the barefoot and forefoot condition when compared with the rear foot shod condition (Divert 2008).

Ummm, is the initial impact transient eliminated with Barefoot running?

The initial impact transient is not always eliminated with barefoot running. While, other researchers (Lieberman 2010) show that the initial impact peak or impact transient is completely washed out rather than just decreased this is not always seen. Dr Lieberman's work is fantastic and his argument is beautifully laid out.  His website is here (

He also provides this video showing the impact transient loss when running barefoot and forefoot striking.

In the study by Divert (2008)  three out of the 12 subjects continued to demonstrate an impact transient. This difference may be due to the fact that other studies investigate youths who have always run barefoot while in the above graph (from Divert 2008)  the subjects were just learning to run barefoot and may have not run a sufficient number of steps for the body to adapt and modify its kinematics.   In effect, the sample used in the above study may have  not had enough time to learn how to run barefoot to eliminate that impact peak.

Nonetheless, below is a graphic by Dr. Lieberman showing the loss of the impact transient with barefoot forefoot striking

In contrast to Dr. Lieberman's work, other studies have also looked at habitually barefoot runners and have NOT found a complete loss of the impact peak, albeit a reduction was found when running barefoot or in Vibrams versus a standard shoe. Squadrone (2009) compared barefoot, shod and Vibram wearing runners in athletes who have had extensive experience running barefoot (3 of them having completed a marathon barefoot).  In the following graph notice how the impact transient is still greatest with shoes, decreases with barefoot and is most modified with Vibrams (VF).  Most importantly, notice how the impact transient still exists.  These authors did not calculate the slope of this impact transient so it can not be directly compared with the work of Lieberman et al (2010).

How can this impact transient still exist in minimalist or barefoot runners?

One difference between Lieberman's group and Squadrone's group may be the degree of plantar flexion in the ankle that occurs at footstrike in both groups.  In Squadrone's group the ankle is at 94 degrees - this means about 4 degrees of plantar flexion.  In Lieberman's group the plantar flexion in habitually barefoot Kenyan youths is around 14 degrees.

This is an important point which leads to a main thesis of this article.  It implies that barefoot or minimalist running alone is NOT A SUFFICIENT condition to obliterate your impact transient during foot strike.  In fact, if you run barefoot in a heel to toe fashion you will see an increase in the impact transient.  This was seen in the work by De Clercq (2000) who compared barefoot versus shod but made everybody still run with a heel strike.  This was found a decade later by Dr Lieberman.  De Clerq found this:

Not to be too confusing but the above authors also measured foot dorsiflexion at impact and found an ankle angle of around 94 degrees (4 degrees of plantarflexion) with a sole angle around 12 degrees (I believe the sole angle is the angle of the entire foot relative to the flat ground).  Zero degrees would be flat while 12 degrees means the toes are pointing up relative to the ground (this is my interpretation, it was not explained in the article). This ankle angle in the barefoot condition is similar to the Squadrone's study of 94 degrees yet we see an impact transient as well as a greater rate of force development in the barefoot condition.  My interpretation here is that while the ankle was slightly plantarflexed the heel still came down first (i.e. the sole angle was still pointing up).  I don't know what the sole angle was in the Squadrone study but it  certainly might help explain the difference between studies.

Bottom line about barefoot.

Obviously barefoot running is no panacea for eliminating an impact transient.  Additionally, there are other factors associated with barefoot running (e.g Kinematic variables: stride rate, stride length, ankle range of dorsiflexion, range of pronation) that may influence many of the kinetic variables (e.g. impact transient, ground reaction forces).  And most importantly how does it relate to injury and performance?

So lets look at these other variables.  Very simply, barefoot running seems to shift someone from being a Heel striker to being a forefoot striker.  A small amount of research has investigated the differences while running in shoes with a rearfoot versus a forefoot strike pattern.

Can changing your foot position at foot strike influence Kinematics and Kinetics?

They sure can, please read more.  Dr Irene Davis has been involved in much of this research but there is surprisingly little published.  Dr. Davis' published work often cites her unpublished lab findings when comparing a Rearfoot strike (RFS) with a forefoot strike (FFS).  Some of what I cite below will refer to Dr. Davis' statements (Williams et al 2000 or Laughton et al 2003)  in her introduction or discussion instead of her actual data (which I can not get a hold of).

Kinematic and Kinetic Changes when moving from a rearfoot to forefoot strike


- forefoot strikers have increased calcaneal eversion excursions and eversion velocity (McClay and Manal 1995a/b) but end up with less maximal calcaneal eversion (aka pronation)

- the foot lands with greater ankle plantar flexion and is in greater inversion at foot strike in the Forefoot strike condition.

--increased knee internal rotation velocity in Forefoot strike conditions (Williams et al 2000)

Changes in Leg Stiffness

-According to the work of Laughton et al (2003) forefoot strikers have greater leg stiffness in general but less ankle stiffness.  They have less ankle stiffness because there is more time and range of motion for the ankle to bend. Essentially, there is more time for the ankle to spread out the joint torque during impact because the ankle moves a through a larger range with the forefoot strike (remember, the foot contacts the ground with the toes down in plantar flexion) (Laughton et al 2003).  These authors also found that the knee does not flex as much in the forefoot strike condition as in the rearfoot strike conditions (30 degrees versus about 34 degrees) therefore there is greater overall leg stiffness.

-Conversely, according to the work of Lieberman et al (2010) forefoot strikers have greater leg compliance (defined as the drop in the body’s centre of mass relative to the vertical force during the period of impact) meaning there is also greater Knee flexion as well as ankle flexion when striking with the forefoot.

Inconsistent changes in Impact Force with forefoot strike

Dr Lieberman's website has an excellent video that shows modifications in the impact transient when striking with a forefoot in shoes.  Unfortunately, this kinetic information is not accompanied with a great deal of kinematic information.

Dr Lieberman has shown the loss of the impact transient in the following video:

However despite this decrease in the impact transient documented in the video  the one other study that investigated Shod running and changes in foot strike pattern show different results.

A review of Laughton et al (2003)

These authors compared rearfoot and forefoot strikers ground reaction forces and found the following:

-There is less peak tibial positive acceleration in the rearfoot strike condition

-The average peak vertical ground reaction force, the anteroposterior peak GRF (i.e. the braking force),and average anteroposterior GRF load rates were significantly greater for the FFS pattern than for the RFS pattern

-Average and instantaneous vertical GRF load rate (i.e. the impact transient), however, did not differ significantly between the FFS and RFS patterns. the Laughton study the forefoot striking runners were different than your typical forefoot strikers.  You might actually call the TOE runners because when their forefoot struck the ground they were not allowed to let their heel strike the ground.  This is not what happens with barefoot/forefoot running.  This may account for the differences in loading.

Is this getting CONFUSING?

What I take from this is that forefoot striking can certainly decrease the loading rates on the foot/shank to a similar extent as barefoot running.  But again, it is not a SUFFICIENT condition.  I would guess that it might even be possible to train yourself to run with a heelstrike but in such a manner that you decrease your impact transient.  Work out of Dr. Davis' lab that gives feedback to individuals on their tibial shock shoes that people can learn to run softer and decrease the impact transient. In these studies (click here) no advice is given to forefoot strike and individuals wear neutral shoes.  They are merely asked to run softer and are given feedback.

I don't have a definitive answer for why the Laughton study shows no change in the impact transient yet Lieberman's work shows a significant decrease in the loss of the impact transient.  My hunch is that other kinematic variables may influence the loading through the foot.   One explanation may be that if in the Laughton study there was no difference in the stride length when shifting to a forefoot strike from heel strike then this may account for the lack of a loss of the impact transient (couple this with the lack of the heel being allowed to lower to the ground - a type of impact absorption and this may explain our differences).

What is missing in this review

- research investigating whether individuals could wear standard running shoes yet still be trained to run in a manner that mimics all of the kinematics of barefoot, forefoot strike running.

-any research investigating the theory (I stress theory) that running in shoes influences plantar foot proprioception which in turn negatively influences running - this belief is very common and is always written about in a superficial  manner.  Yet there is not a lot of research investigating it.  I will reserve an opinion.

-a full body kinetic analysis comparing all the different foot conditions of running.

-long term studies investigating changing stride mechanics on injury prevalence and running efficiency

-I purposefully left out the good research investigating the POSE technique

Clinical Relevance - What I tell my patients

I think it is too early to give barefoot running the gold medal and switch everyone to minimalist shoes but I am certainly open to the idea.  Runners were still getting injured with minimalist shoes in the 1970s (see a pdf review here: Am J Sports Med-1978-James-40-50 running injury overview from 1978 surprisingly good we know nothing new)

Barefoot or forefoot strike running may be an excellent adjunct to the recreational runner as a training stimulus.  It can be used as a form of strength training or rehabilitation.

No research has looked at the impact transients with runners who run much slower than what is studied in these papers.  Most of these papers have the slowest runners running 5 minute kilometres (an 8 minute mile).  The vast majority of your recreational runners do not run this pace.  If you run at 25 minute 5 km you will probably be in the top 10% of a large race (for example, at the 2010 Goodlife Marathon 5 km a 25 minute result put you 178th out of 2721) and the top 15% if you keep that pace up for a marathon.  So, do we want to be telling all our runners to covert to a forefoot strike, minimalist shoe or barefoot based on the research of relative elites? the only correct :) answer is -----I have no idea.

Good luck piecing this all together and stay tuned for more updates.

Greg Lehman

Toronto Physiotherapist


Squadrone R, Gallozzi C. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runners. J Sports Med Phys Fitness. 2009 Mar;49(1):6-13.

Divert C, Mornieux G, Freychat P, Baly L, Mayer F, Belli A. Barefoot-shod running differences: shoe or mass effect? Int J Sports Med. 2008 Jun;29(6):512-8. Epub 2007 Nov 16.

Pohl MB, Buckley JG.Changes in foot and shank coupling due to alterations in foot strike pattern during running.Clin Biomech (Bristol, Avon). 2008 Mar;23(3):334-41. Epub 2007 Nov 19.

Morley JB, Decker LM, Dierks T, Blanke D, French JA, Stergiou N. Effects of varying amounts of pronation on the mediolateral ground reaction forces during barefoot versus shod running. J Appl Biomech. 2010 May;26(2):205-14.

Lieberman DE, Venkadesan M, Werbel WA, Daoud AI, D'Andrea S, Davis IS, Mang'eni RO, Pitsiladis Y.Foot strike patterns and collision forces in habitually barefoot versus shod runners. Nature. 2010 Jan 28;463(7280):531-5.

Carrie A. Laughton1, Irene McClay Davis2, and Joseph Hamill Effect of Strike Pattern and Orthotic Intervention on Tibial Shock During Running JOURNAL OF APPLIED BIOMECHANICS, 2003, 19, 153-168

Williams DS, McClay IS & Manal K: Lower extremity mechanics in runners with converted forefoot strike pattern. Journal of Applied Biomechanics, 16(2): 210-218, 2000.

McClay, I., & Manal, K. (1995a). Lower extremity kinematic comparisons between forefootand rearfoot strikers. In K.R. Williams (Ed.), Conference Proceedings: 19t Annual Meeting of the ASB, Stanford, CA (pp. 211-212). Davis, CA: UC–Davis.

McClay, I., & Manal, K. (1995b). Lower extremity kinetic comparisons between forefootand rearfoot strikers. In K.R. Williams (Ed.), Conference Proceedings: 19th Annual Meeting of the ASB, Stanford, CA (pp. 213-214). Davis, CA: UC–Davis.