Barefoot running – do or don’t? A scientific approach

To barefoot, or not to barefoot? That is the question.

Before this article, I had an attitude towards barefoot running that reflected what the shoe mafia, the shoe pusher, the geek, the barefoot hippie and the shoe hippie have manipulated me into believing about barefoot running.

I couldn’t be satisfied with that. Where was the scientific evidence?

I hope the article sparks some thoughts for you.

Conclusions first

Based on 31 scientific studies, I have come to the following overall conclusion:

Do what works for you. If barefoot running has made you injury-free, then you should definitely continue. If you are happy as a heel-lander and you run in traditional running shoes, there is absolutely no need to worry, quite the opposite.

The studies had the following conclusions:

1. Historically, the vast majority of world records over time have been set in running shoes.
2. Currently, the elite primarily train in running shoes.
3. Barefoot running promotes mid- and/or forefoot landing
4. Your movement pattern changes from running in running shoes to running barefoot
5. Higher speed leads to landing further forward on the foot
6. Barefoot running increases not the running economy
7. 100 grams lighter running shoes optimize your running economy by 1.2-3.1%
8. Barefoot running gives not better running economy than running in 150 gram lightweight running shoes
9. A 0 mm drop is not more optimal compared to a 4 mm drop
10. A 10mm drop is more economical than running in shoes with a 45mm or 70mm drop
11. There is uncertainty about whether heel landing or midfoot/forefoot landing is most effective. However, there are most indications that heel landing is most effective.
12. A 5% increase in cadence gives you 3-4% less ground contact time
13. A 5% increased cadence reduces stress on knees and hips
14. It is not It has been proven that faster cadence, and thus reduced stress on the knees and hips, results in fewer injuries. The hypothesis is that your body adapts to the extra pressure
15. Forefoot landing reduces stress around the knee
16. Forefoot landing reduces stress around the hips
17. Most barefoot runners will land on their midfoot or forefoot.
18. Heel-landers land harder than forefoot-landers
19. Barefoot runners experience extra strain around the ankle joint
20. Barefoot runners experience extra stress around the Achilles
21. Running shoes reduce the strain on all joints
22. Running in running shoes causes injuries
23. Running barefoot causes injuries
24. The more kilometers you run, the greater the risk of injury.
25. The more intensively you train, the greater the risk of injury.
26. There is not evidence that increased impact forces (load) increase the risk of injury
27. Running on softer surfaces does not reduce injury risk
28. Softer insoles do not reduce the risk of injury
29. Barefoot running requires a minimum of 8 minutes of acclimatization and most likely longer.
30. Biomechanics are different from barefoot running to running in minimalist shoes
31. You can change your running style

It is coincidental that there are 31 conclusions and 31 studies. Many of the studies have multiple conclusions. In addition, many of the studies have similar conclusions and are intended to support points.

The interesting things about barefoot running

Here you get my version without bias from others with financial interests:

• Skomafian makes products based on market demand and not what works best.
• The shoe pusheris responsible for the daily sale of the shoe mafia’s products.
• The Fyssen sells insoles to optimize the performance of running shoes.
• Barefoot hippie has a community where he sells barefoot running courses.
• The Shoe Hippie sells minimalist running shoes.

Their raison d’être is contingent on each other.

Why did barefoot running become so big?

Barefoot running escalated in 2009 and experienced its heyday already in 2011 and 2012.

What happened? I’m no expert, but 2 events occurred:

1. The release of Born to Run af C. McDougall, which became a New York Times bestseller.
2. The explosion of Vibram FiveFingers’ massive marketing machine.

Since 2011, things have gone one way. Guess which one?

Barefoot running is a fad, as is the case with chi running, pose running, the paleo diet, high fat low carb diets, etc.

For a period of time, running shoes became more and more technology-heavy. The shoes became heavier and heavier. There was a natural protest and before long, barefoot running, as the opposite extreme, became popular.

The thoughts behind barefoot running

Humans are created naturally and should move naturally. Humans do not need unnatural shock absorption, stability, control and protection.

I will now walk you through the scientific basis of barefoot running..

What do the world’s best runners do?

The results of history: running shoes versus barefoot

It’s always interesting to see what the world’s best are doing.

• Abebe Bikila water in the 1960 Olympics at the marathon distance in a time of 2:15:16.2 in bare feet (the fastest time set without shoes)
• Bruce Tulloh won the European Championships in 5000m in 1962 in bare feet

2 great achievements. But since 1960 all world records in marathon made in running shoes.

The most recent was when Dennis Kimetto ran 2:02:57 in 2014 in a pair of running shoes with a profile of approximately 18 mm in the forefoot and approximately 28 mm in the heel.

Also in 5000m, 10000m and half marathons, the fastest times are achieved in running shoes (which are rarely flat, by the way).

Why don’t the elite run barefoot?

If you are a running enthusiast and get the chance, you should go to Iten in Kenya. This is where the world’s elite runners gather, and you can train with them.

No one in bare feet.

In fact, Vibram FiveFingers once sponsored 300 shoes.

The result?

Nobody used them.

Here are a few explanations:

Reason #1: It’s too risky

The potential improvement is very small compared to the effort required.

There are 52 weeks in a year. Typically, an elite runner is sick or injured for 4 of them. Missing 4 weeks of training can be disastrous.

Converting to barefoot running requires a long period of adaptation. It takes years to be able to run 150-200 kilometers a week in bare feet.

#2: The elite are already efficient runners

When you run 200 kilometers a week, your body will adapt to the environment. Running economy will automatically improve. Your body is amazing.

#3: Shock absorption is necessary

I give the floor to the great Steve Magness:

“If Galen Rupp has just done a long track workout in spikes and his calves are completely beat up, then they’re not going to do any of the cushioning job they normally do. So you throw on some heavy, padded trainers and let the legs recover”.

#4: The elite already train in “minimalist shoes”

They just call them everything else that isn’t as trendy as “natural running shoes”, “barefoot shoes”, etc. They call them, for example: competition shoes, spike shoes, etc.

The type of shoe that is very light and has no shock absorption.

They train in these shoes during their fast training sessions. Why? It’s faster. Quite simple.

But training in them for every workout is too demanding on the body.

In addition, the majority of professional runners train barefoot. There are many reasons for this – for example, strength of the foot, ankle joint and surrounding muscles.

Does barefoot running promote mid- and forefoot landing?

Yes, barefoot running promotes mid- and forefoot landing

A large part of the argument for the benefits of barefoot running is that you land further forward on your foot.

The logic is that if you add extra material under your heel, but not your forefoot, you will have a shorter path to the ground from your heel. All other things being equal, this will promote heel landing.

But others may have a different logic than you, so we support the argument with a collection of studies that clearly proved that Running barefoot promotes landing further forward on the feet.

Barefoot enthusiasts also believe that, in addition to the smaller heel, running barefoot forces the body to land further forward on the foot. The claim is based on the fact that the body will feel how hard and painful a heel landing is, and thereby automatically convert to a midfoot or forefoot landing.

One study analyzed the effect of switching from running in traditional running shoes (which are not defined in the method) to running in minimalist running shoes with a 0 mm drop and 9 mm thick sole. The result was that The lions’ movement pattern immediately changes to staying further forward on their feet..

This was also confirmed by another study.

At least as interestingly, it was concluded that The runners over an 8-minute period in the minimalist shoes gradually landed further and further forward in the shoes..

Last but not least, it is unequivocally proven that higher speed leads to landing further forward on the foot. You can test that yourself.

References/studies:

1. Is there Evidence to Support a Forefoot Strike Pattern in Barefoot Runners? A Review
2. Surface effects on ground reaction forces and lower extremity kinematics in running
3. Effect of time during a running session with minimal footwear
4. Biomechanical and physiological comparison of barefoot and two shod conditions in experienced barefoot runner.

Does barefoot running provide optimized running economy?

There is no evidence that barefoot running optimizes running economy, quite the opposite.

Running economy is trendy. A fancy word that gets a lot of attention. In 5 years it will be gone and instead the focus will be on something completely different. Just like with diets. High carb, high fat-low carb, paleo, the egg diet, high protein, etc.

Improving running economy is super interesting. But how do you do it? And is barefoot running better at improving running economy?

The weight of running shoes and optimal running economy

Heavier running shoes place greater demands on oxygen uptake = poorer running economy. That’s why you use lightweight running shoes when you run competitively.

In competition, you compromise on cushioning and support in exchange for higher speed.

The studies conclude that 100 grams reduces running economy by 1.2 – 3.1%.

However, there are other studies that prove that Barefoot runners do not have better running economy than running in 150 gram heavy running shoes.

Heel to toe drop and optimal running economy

I have previously written a very detailed post about The effect of heel-to-toe drop on your running training, injury risk and running economy.

Science has, very significantly, concluded the following:

1. 0 mm drop is not better for running economy compared to a 4 mm drop
2. 10mm drop is more economical than 45mm drop and 70mm drop.

Other studies that I have referenced also conclude that competition running shoes with a lower drop and lower weight are less demanding and thus provide optimized performance.

Heel landing versus mid- and forefoot landing

Several studies indicate that heel landing is more effective than midfoot and forefoot landings. In fact, it has been shown that heel landers run 5-9% more efficiently.

The reason is hypothetical. One suggestion might be that midfoot and forefoot landings place greater demands on the musculature, but heel landings place greater demands on the joints and bones.

However, the study is contradicted by other studies, which conclude that there is no difference in the utilization of maximal oxygen uptake for runners who land on their heel and runners who land on their forefoot.

Cadence and optimal running economy

There is also much discussion about the optimal cadence during running. It is known that mid- and forefoot running in the vast majority of cases increases cadence, which is associated with positive results. An increased cadence typically results in 3-4% shorter ground contact time and reduces the strain on the knees and hips.This has been proven many times.

However, it has not been proven that increased load increases the risk of injury. The question is whether the joints adapt to the extra load, just as your feet do when you run on harder surfaces. More on that later.

References/studies:

1. The Acute Effects of Heel to Toe Drop on Running Economy
2. Running Economy and kinematic differences among running with the foot shod, with the foot bare, and with the bare foot equated for weight
3. Effect of Shoes’ Heel Height on the Energy Cost during Jogging
4. Rearfoot striking runners are more economical than midfoot strikers
5. Economy and rate of carbohydrate oxidation during running with rearfoot and forefoot strike patterns
6. The concurrent effects of strike pattern and ground-contact time on running econonmy
7. Effects of footwear and strike type on running economy
8. Athletic Footwear, Leg Stiffness, and Running Kinematics.
9. Quantifying foot kinematics inside athletic footwear: a review.

Does forefoot landing reduce the stress on landing?

The load on the knees and hips is reduced, while the load on the ankle joint and Achilles is increased. It’s like exchanging one injury for another.

A large part of the basis for barefoot running is that it is said to promote mid- and forefoot landing, which is correct.

Daniel Lieberman, a big proponent of barefoot running, published a study in which he analyzed the movement patterns and loading of barefoot runners, who naturally land on their forefoot, and runners who were used to running in running shoes, who landed on their heel.

The conclusions were:

• Barefoot runners typically land on the forefoot, second most often on the midfoot, and rarely on the heel.
• Forefoot landings generate a less forceful accelerating shock when landing on a treadmill compared to heel landings in bare feet and than heel landings in running shoes.

What I wonder about is that the maximum force that the runners land with in Lieberman’s study is the same whether the runners land in bare feet or in running shoes.

It makes me question where the measurements were taken. The whole foundation of running shoe cushioning is to spread the shock out over the foot, which is not the case here.

In addition, the figure clearly shows how the heel landing in running shoes and the heel landing in bare feet initially achieve the same force impact, which I also question.

Last but not least, it should be mentioned that the study was only conducted at speeds of 4-6 m/s.

I have not been able to find answers to my questions in the full publication of the study, nor in various forums online.

Nevertheless, here you will find a series of videos for a heel landing and a forefoot landing, where you can see how the force impacts in running shoes and in bare feet.

Heels in running shoes:

Forefoot landing in running shoes

Heels in bare feet

Forefoot landing in bare feet

Science has the following unambiguous conclusions:

• Heave landings land harder. This means that the collision with the surface occurs faster.
• Heelers typically experience stress around the knee joint or hip joint.
• Barefoot runners experience extra stress around the ankle joint and Achilles tendon.
• Running shoes reduce the strain on all joints

Read the next section, where you are guaranteed to be surprised by how the increased force does not mean an increased risk of injury.

References/studies:

1. Foot strike patterns and collision forces in habitually barefoot versus shod runners
2. Forefoot Strikers Exhibit Lower Running-Induced Knee Loading than Rearfoot Strikers
3. Barefoot Running and Hip Kinematics: Good News for the Knee
4. Variation in Foot Strike Patterns during Running among Habitually Barefoot Populations
5. Impact attenuation during weight bearing activities in barefoot vs. shod conditions: A systematic review
6. The Effect of Running Shoes on Lower Extremity Joint Torques
7. Gait retraining to reduce lower extremity loading in runners

Does barefoot running cause fewer injuries?

There is no significant evidence that barefoot running reduces injury rates compared to running in running shoes. There is also no evidence that midfoot or forefoot running reduces injury rates compared to heel landing.

There is a lot of rivalry between the running shoe industry and the barefoot training industry. But there is one thing they can agree on:

• Running in running shoes causes injuries
• Running barefoot causes injuries

Isn’t the solution just to stop exercising?

This section is undoubtedly the most important, as it is often used as a basis for argument by barefoot hippies.

To date, there have been no studies with a robust design that have demonstrated a reduced risk of injury when running barefoot compared to running in running shoes.

What is known about the risk of injury is the following:

• Running training causes injuries
• The more kilometers you run, the greater the risk of injury.
• The more intensively you train, the greater the risk of injury.

Impact forces and injury risk

In the previous section, it was concluded how heel landings landed more forcefully than midfoot and forefoot landings. However, there is no evidence that the increased load increases the risk of injury (explanation follows).

It is proven that Running on harder surfaces does not increase the risk of injury.

It is further proven that Softer insoles do not reduce the risk of injury.

Surprised?

So am I.

Vivobarefoot published a study that “finally confirmed that barefoot is best”. I have written about their false marketing in this post.

In the study, they looked at cross-country runners who landed on their heel and runners who landed on their forefoot and concluded that heel landings suffered more injuries. But does this also apply to asphalt? Or do factors such as slope, softness of the surface (lots of mud) and training volume also have an influence?

Vertical loading force

Now it gets a bit technical, but in simple terms, vertical loading force is the force you land with in your vertical movement.

There are studies that point in both directions. However, there is consensus that the maximum vertical impact force is the same for heel and forefoot landings.

The FiveFingers-sponsored Harvard professor has shown how increased loading forces lead to more injuries. However, this contradicts Benno Nigg’s research findings, which concluded that low impact forces did not mean lower injury risk.

At first glance, your logic probably says that a harder impact equals a greater risk of injury (however, this has not been proven).Nigg explained impact forces very well:

“input signals that produce muscle tunning shortly before the next contact with the ground to minimize soft-tissue vibration and/or reduce joint and tendon loading”.

In Jutland, this means that the extra shock alone is a signal to the body to build itself stronger..

Pribut has also mentioned that the increased force is a signal to the bone cells to produce extra bone (basically explained).

This is very consistent with the result you read earlier about how the body adjusts its shock absorption depending on the surface you train on.

References/studies:

1. Impact forces in running
2. The relationship between lower-extremity stress fractures and the ground reaction force. A systematic review
3. Do impacts cause running injuries? A prospective investigation
4. Foot Strike and Injury Rates in Endurance Runners: A Retrospective Study
5. Injury Reduction Effectivenss of Selecting Running Shoes Based on Plantar Shape
6. Relation between running injury and static lower limb alignment in recreational runners
7. Clinical effectiveness of customized sports shoe orthoses for overuse injuries in runners: a randomized controlled study
8. Foot Bone Marrow Edema after 10-week Transition to Minimalist Running Shoes
9. Incidence and determinants of lower extremity running injuries in long distance runners: a systematic review
10. Effect of foot posture, foot orthoses and footwear on lower limb muscle activity during walking and running

Does barefoot running require getting used to and to what extent?

Yes, running in minimalist shoes takes getting used to – as is expected for barefoot running

A study examined how long it takes to get used to running in minimalist shoes with a 9 mm sole and a 0 mm drop from heel to toe.

Runners who came from regular shoes changed their running style to flat shoes over 8 minutes.

The takeaway from this is that you can’t jump into a pair of minimalist shoes and think you’re immediately running optimally. Your body adapts to the conditions.

What happens after 8 minutes? Does the body adapt further? The study doesn’t show anything about that.

References/studies:

1. Effect of time during a running session with minimal footwear

Is barefoot running different from running in minimalist running shoes?

Yes, barefoot running puts pressure on different joints and muscles than minimalist shoes do.

In a study of biomechanics, highly trained runners were tested running barefoot compared to running in minimalist shoes without a heel-to-toe drop (=zero drop).

The results were as follows:

• Barefoot running had 11% less flexion in the knee joint at mid-stance (when the entire foot is placed on the ground during running)
• Barefoot running had a 24% reduction in knee work effort (=less strain on the knee)
• Barefoot running had a 19% increase in work effort in the ankle joint and Achilles.

So – reduced pressure on the knees and increased pressure on the ankle and Achilles when running barefoot compared to running in minimalist running shoes.

References/studies:

1. Running in a minimalist and lightweight shoe is not the same as running barefoot: a biomechanical study

Can/should I change my running style?

Jack Daniels tests for optimal running economy

Jack Daniels. One of the world’s most recognized running experts of all time. He has said many wise things, including:

“I have tested runners’ economy of running with their hands in their pockets, on their hips, folded on top of their heads, etc., and it always costs more than when using a normal arm swing”

Pointe?

Do what feels most natural to you.

Bill Rogers’ change of running style

Bill Rogers. The world’s best marathon runner in the late 1970s. He was tested by a running expert who wanted to improve his running style.

The result?

Rogers used more oxygen than ever before.

Pointe?

Don’t try to change your natural running style. Over time, your body will adapt to its personal optimum.

Min personlige holdning

Warning.

This is my personal opinion. You have yours, I have mine.

My overall stance is: Do what works for you.

If you avoid injuries by running barefoot, you should definitely keep doing it. If running in running shoes with a 15 mm drop makes you happier, then do it.

My secondary position is: focus on what makes a difference.If you can optimize your running economy by 2%, that’s great, but wouldn’t a second opinion on your running program make a bigger difference?

Me versus the barefoot enthusiast

God, there are so many people who want to persuade me to run barefoot.

The argument of fewer injuries

As the salesperson says (and yes, he is a salesperson who is trying to sell me an overpriced course): “I can reduce your risk of injury”, or “my clients run more efficiently”. For example, Lone who says: “I tried barefoot running, and after that I no longer have injuries in my knees and hips like I used to. I also run faster than before”.

Nice one Lone.

And to the seller: Where do you get it from?

How do you measure your results?

It is obvious that if you ask your patients to reduce their training volume from 70 kilometers per week in running shoes to 10 kilometers per week in bare feet, you also correct the risk of overtraining, overuse injuries and many other factors.. You don’t isolate barefoot running versus running in running shoes. It’s obvious that I get fewer injuries from running 10 kilometers a week than from running 70 kilometers a week.

“I can follow you, but my clients also become faster marathon runners”

Okay mate, super cool for them. Are you sure it’s because they’re learning chi-running, pose-running, flat-footed running, forefoot landing, arm swings or whatever else you’re teaching them, or is it because you’re adjusting their training structure?

The barefoot advocate: “The science is clear – barefoot running is best”

Respect for the barefoot experts who use science.

But please, do it right now.

You’re absolutely right, science supports barefoot running… At least in the one study you highlight, where the study design was completely crap.

The one study that the vast majority of barefoot enthusiasts mention was done at Harvard University.

Wow, Harvard. It must be done.

It was Daniel Lieberman’s study that “finally confirmed the existence of barefoot running”.

I can’t help but question whether Vibram actually paid him to conduct the study.I wonder if Vibram had an incentive in the outcome, cf. their Vibram FiveFingers?

Get the point?

It’s fine to have industrial support for research results, but be extra careful.

My opinion on science – it doesn’t hold up

“Barefoot running is best”

“Science says…”

“Many studies conclude…”

And I could go on.

1. Which studies?
2. Have you read them yourself?
3. Do you have an understanding of research design?

There are many potential pitfalls in these studies (which I refer to myself in this article). Too many people misinterpret results and conclusions in studies. In addition, it is common to see conclusions taken out of context. .

Some of the risk elements of barefoot running studies (and studies in general) are:

• Often the investigations are short-term. If you prove how something improves over 5 weeks, it doesn’t mean it will be better in 5 years.
• The sample, i.e. how many people are in the test groups, is often very small.
• Typically, studies compare average values ​​for the groups.You are an individual runner, built individually. Can you use average values ​​for anything?
• A study is usually built with a base group that does what they have always done and a test group that does something new. To increase the validity of the study, it is necessary that the runners do not know which group they belong to, as this can be a placebo effect. This is why studies with pills always let all participants take pills, while the test group only gets a placebo pill without any expected effect. You can’t do a placebo group the same way with barefoot running. Either you’re wearing shoes or you’re not wearing shoes. You can’t do a trick that makes people think they’re actually wearing shoes when they’re not.
• There are very few studies on the effects of barefoot running.. It’s a niche, and only a few people are interested in it. It’s more important to cure cancer than it is to find out whether barefoot running is more beneficial than running in “normal” running shoes. This means that many studies simply replicate each other.
• Sponsored studies are valid in many cases, but I cannot help but question Lieberman’s and Kerrigan’s studies of barefoot running,when the studies are paid for by companies that sell barefoot running shoes.
• Studies that test one hypothesis tend to draw more general conclusions. So do the press. Imagine this. You do a study with 6 beginners. You let 3 of them train as they normally do and 3 of them you let them train barefoot. The ones who train barefoot tell you to reduce their training volume by 80%. After 4 weeks, 2 of the beginners who train normally have injuries, while only 1 from the ones who land on their forefoot. The story goes: “heel-landers have twice as many injuries as forefoot-landers”. Get the point? You cannot use an inductive method, as is done in many interpretations of studies.

Barefoot running is natural

Correct, it is significantly more natural to run barefoot than to use equipment.

However, it is not always the case that natural is best.

The argument often becomes that 30,000 years ago we were all running around and hunting wild animals in bare feet. All humans also followed all the Paleo principles. There were no politicians, there were no weapons, there was no industry and so on. And if so, humans rarely lived longer than 30 years.

What we did 30,000 years ago does not mean what is best.

1. Don’t you also wear a raincoat because it’s unnatural?
2. Don’t you also use surgeries when you get injured because it’s unnatural?

I feel very naturalistic myself, but it shouldn’t become a religious issue.

What is a natural running style?

Is it most natural to run as you feel it should be, or is it most natural to correct your running style to achieve a “natural running style”??

Is it best for all runners to land far forward on their foot?

Is it natural to correct something that the body naturally does?

What is a natural running style?

A barefoot advocate would probably say something like that this is the running style you would have if you ran and walked barefoot your entire life.

But is that also what is most natural now that that is not the case?

Is barefoot running for everyone?

Situations where even barefoot hippies advise against barefoot running:

• Not everyone is born the same. Genes can create challenges. For example, you were not born to run if your right leg is 5 cm longer than your left.
• How often do you move on uneven terrain? Everything is flat. The asphalt is flat, the floor of your house is flat, your garden is flat, etc.
• Whether you are of normal weight and weigh 70 kg, or severely overweight and weigh 150 kg, does not change anything about your foot structure. Obese people will, all other things being equal, put more strain on the body when you are in motion than normal weight people will. It is not natural to be severely overweight, which the body is therefore not used to.
• Your history has an impact on your risk of injury when running. If you have had surgery, for example due to a football injury, you can compensate for the damage in other muscles and joints, which will not always be a natural movement. This will increase the risk of injury.

Typical concerns about converting to barefoot running

• The skin on your feet can’t handle the extra wear and tear.If you start out slowly, your body will adapt to the environment and over time you will be able to run many kilometers on all kinds of surfaces.
• I have severe overpronation, which my running shoes help me control.. If you switch to barefoot running, you will land further forward on your foot, which, all else being equal, will reduce your pronation tendency.
• It is cold.. Barefoot running and running in minimalist shoes are not the same, but there are many similarities. You can train in lightweight competition shoes to approximate a natural running style.
• It hurts to run on asphalt and I don’t have the opportunity to run on grass.. Consider shoes with a minimal and very flexible sole as an alternative.

A concluding comment

1. Be critical when you hear: “studies show…”
2. Be critical in the store when the clerk gives advice on choosing shoes
3. Be critical when barefoot hippie criticizes running shoes and wants to sell you a course
4. Be critical when reading this article.
5. The level of knowledge is not sufficient to confirm many of the questions we have

And most importantly: listen to your body.

Referencer

I studied a total of 72 studies and selected the following 31. Omitted studies (41) were omitted for 2 reasons: 1) their scope was too small (the sample was too small) and/or 2) the studies were not relevant to the article.

1. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3497946/
2. http://www.ncbi.nlm.nih.gov/pubmed/11079523
3. http://www.tandfonline.com/doi/full/10.1080/10255842.2013.815924#.VEKt2vnLd5I
4. http://www.ncbi.nlm.nih.gov/pubmed/19188889
5. http://eprints.fortlewis.edu/162/2/Final_Paper-no_NB_reference.pdf
6. http://www.researchgate.net/publication/36278539_Running_economy_and_kinematic_differences_among_running_with_the_foot_shod_with_the_foot_bare_and_with_the_bare_foot_equated_for_weight_
7. http://maxwellsci.com/print/rjaset/v6-1531-1533.pdf
8. http://www.ncbi.nlm.nih.gov/pubmed/24002340
9. http://jap.physiology.org/content/early/2013/05/13/japplphysiol.01437.2012
10. http://www.sciencedirect.com/science/article/pii/S1440244013001382
11. http://www.ncbi.nlm.nih.gov/pubmed/22217565
12. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1748411/
13. http://www.tandfonline.com/doi/abs/10.1080/19424280.2012.735257?journalCode=tfws20#.VEVdefmUdSJ
14. http://barefootrunning.fas.harvard.edu/Nature2010_FootStrikePatternsandCollisionForces.pdf
15. http://journals.lww.com/acsm-msse/Abstract/publishahead/Barefoot_Running_and_Hip_Kinematics___Good_News.97917.aspx
16. http://journals.lww.com/acsm-msse/Citation/2013/12000/Forefoot_Strikers_Exhibit_Lower_Running_Induced.12.aspx
17. http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0052548
18. http://www.gaitposture.com/article/S0966-6362(12)00437-7/abstract
19. http://www.pmrjournal.org/article/S1934-1482%2809%2901367-7/abstract
20. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3014399/
21. http://journals.lww.com/co-ortho/Abstract/1997/12000/Impact_forces_in_running.7.aspx
22. http://www.clinbiomech.com/article/S0268-0033%2810%2900225-1/abstract
23. http://www.asbweb.org/conferences/2010/abstracts/472.pdf
24. http://journals.lww.com/acsm-msse/Abstract/2012/07000/Foot_Strike_and_Injury_Rates_in_Endurance_Runners_.17.aspx
25. http://journals.lww.com/nsca-jscr/Abstract/2009/05000/Injury_Reduction_Effectiveness_of_Selecting.1.aspx
26. http://bjsportmed.com/content/38/5/576.full
27. http://bjsm.bmj.com/content/45/12/959.abstract
28. http://journals.lww.com/acsm-msse/Pages/default.aspx?PAPNotFound=true
29. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2465455/
30. http://www.ncbi.nlm.nih.gov/pubmed/18922696
31. http://bjsm.bmj.com/content/early/2013/01/10/bjsports-2012-091837.abstract