A few days ago a friend on Facebook posted a video that examines neuroplasticity as it relates to riding an unusual bike. As I watched it I kept thinking about the parallels to changing one’s running form. I also kept thinking about how amazing the human brain is – watch the video below, it’s well worth it!

We saw this process play out with the minimalist running trend – it took off like a rocket, but the reality is that though science has shown that people do typically run differently in minimal shoes, they are not the same as running barefoot, and injury rates among those transitioning into minimal shoes aren’t any different than those who continue to use a traditionally cushioned running shoe (though the types/location of injuries likely differ).

Over the past few years the hot trend in running has been maximal cushioning. Shoes like those made by the brand Hoka One One have been very popular, and sales are booming. However, to date there has been very little scrutiny of these shoes by the scientific community. That doesn’t mean that scientists are ignoring them, it just means that any data that has been collected has yet to be published (again, science is slower than trends).

Yesterday a friend (thanks Marc!) sent me the abstract of one of the first studies I have seen to look at how maximalist shoes affect running form. The abstract is of a presentation from the annual meeting of the American College of Sports Medicine. The lead author is Matthew Ruder from the Spaulding National Running Center at Harvard Medical School, and the title of the study is “Effect of Highly Cushioned Shoes on Ground Reaction Forces during Running.”

The study included five runners who ran in both highly cushioned and traditional running shoes. The abstract does not report what the highly cushioned shoe was, but Craig Payne indicates that it was the Hoka Stinson (see image below) in a thread on Podiatry Arena. They found that vertical impact peak, instantaneous vertical impact loading rate, peak medial force, and peak vertical force did not differ between the two shoes. Average vertical loading rate (VALR) was greater in the highly cushioned shoes, and peak lateral force was lower in the highly cushioned shoes. Regarding the latter, the authors suggest it could reduce the pronatory moment on the foot (i.e., less force forcing the foot into pronation, maybe due to the soft cushioning). They also note that higher VALR has been linked to injury (e.g., tibial stress fracture).

Now, these results need to be interpreted with caution – this was a conference presentation and not a published paper, and the sample size of five runners is tiny (they indicate that they plan to increase the sample). The results are also highly dependent on which shoes were chosen for the experiment – I don’t know what the traditional shoe was, and some of them have quite a bit of soft cushion under the heel. However, it is interesting, and somewhat surprising, to find that a big, cushy shoe like the Hoka Stinson (assuming that it is correct that the Stinson was the shoe they used) yielded a higher impact loading rate than a traditional running shoe, and that most other variables did not differ.

One thing I disagree strongly with is the opening sentence of an article on Medscape that discusses the study (you need to create a free membership to read it). It reads: “Highly padded maximalist shoes could increase the risk of running injury, researchers say.” This is a great example of bad journalism – the study did not look at injuries at all, it looked at forces. Furthermore, there remains considerable debate about whether impact forces are a major factor in causing running injuries. For example, running with a forefoot strike in minimal shoe can reduce vertical impact loading rates, but research has not found that running in minimal shoes reduces injury rates relative to traditional shoes. And peak vertical force, which I presume is the force at roughly midstance (the active peak), did not differ between the shoes. Some would say that the latter is far more likely to contribute to injury risk since forces are typically much higher during the active peak.

So does this mean it’s time to ditch your maximalist shoes? No, just as there is as yet no compelling data that running in minimal shoes is more dangerous than running in a traditional shoe, we don’t yet have any evidence that maximal shoes actually increase your risk of injury. And my guess is that there may be things going on above the foot in maximal shoes – for example, I suspect less knee flexion in a shoe like a Hoka due to the soft, thick, cushy sole. This could have benefits for the knee. So for now, I continue to say that different shoes will alter how forces are applied to the body, and it remains a matter of finding the best match for you as an individual.

1. Barefoot running is different and no shoe perfectly replicates the barefoot condition. Running barefoot, particularly on a hard surface, increases the likelihood that a runner will adapt a midfoot or forefoot strike. Running barefoot will also generally result in an increased stride rate and decreased stride length.

2. Running in a shoe with no cushioning will simulate some aspects of barefoot running, but will not necessarily simulate the barefoot condition perfectly. This might in part be due to the ability of any type of sole, even one with no cushioning, to reduce friction between the foot and the ground and thus reduce plantar skin abrasion.

3. Running in a “minimal” shoe with a moderate amount of cushioning is unlikely to alter form very much, particularly foot strike. In other words, if cushioning is present, a heel striking runner is unlikely to move to a midfoot or forefoot strike.

A new study was just published on-line in the journal PLOS One that adds additional support to some of what I have written above (full text available here). Here’s the Abstract:

Comparison of Minimalist Footwear Strategies for Simulating Barefoot Running: A Randomized Crossover Study

Karsten Hollander, Andreas Argubi-Wollesen, Rüdiger Reer, Astrid Zech

Published: May 26, 2015, DOI: 10.1371/journal.pone.0125880

Abstract

Possible benefits of barefoot running have been widely discussed in recent years. Uncertainty exists about which footwear strategy adequately simulates barefoot running kinematics. The objective of this study was to investigate the effects of athletic footwear with different minimalist strategies on running kinematics. Thirty-five distance runners (22 males, 13 females, 27.9 ± 6.2 years, 179.2 ± 8.4 cm, 73.4 ± 12.1 kg, 24.9 ± 10.9 km.week^-1) performed a treadmill protocol at three running velocities (2.22, 2.78 and 3.33 m.s^-1) using four footwear conditions: barefoot, uncushioned minimalist shoes, cushioned minimalist shoes, and standard running shoes. 3D kinematic analysis was performed to determine ankle and knee angles at initial foot-ground contact, rate of rear-foot strikes, stride frequency and step length. Ankle angle at foot strike, step length and stride frequency were significantly influenced by footwear conditions (p<0.001) at all running velocities. Posthoc pairwise comparisons showed significant differences (p<0.001) between running barefoot and all shod situations as well as between the uncushioned minimalistic shoe and both cushioned shoe conditions. The rate of rear-foot strikes was lowest during barefoot running (58.6% at 3.33 m.s^-1), followed by running with uncushioned minimalist shoes (62.9%), cushioned minimalist (88.6%) and standard shoes (94.3%). Aside from showing the influence of shod conditions on running kinematics, this study helps to elucidate differences between footwear marked as minimalist shoes and their ability to mimic barefoot running adequately. These findings have implications on the use of footwear applied in future research debating the topic of barefoot or minimalist shoe running.

Methods

In a nutshell, the study authors recruited 35 runners and had them run trials at 3 speeds (12:04 min/mile, 9:38 min/mile, 8:03 min/mile if I did the math correctly) in each of four different footwear conditions. The footwear conditions (see image at top of post) were barefoot, shoe with no cushion (Leguano), shoe with moderate cushion (Nike Free 3.0), and standard running shoe (Asics 2160). They recorded the following biomechanical variables during each trial: ankle angle at footstrike, knee angle at footstrike, stride frequency, step length, frequency of rear-foot strikes.

Results

Barefoot running was significantly different from all other footwear conditions (including the shoe with zero cushion) for three of the five variables measured. When barefoot, runners exhibited reduced ankle dorsiflexion at contact (flatter foot strike), increased stride frequency, and reduced step length. Barefoot runners still exhibited a heel strike about 60% of the time, which was similar to the zero-cushion shoe condition. In cushioned shoes, heel striking was observed about 90% of the time.

When subjects ran in the shoe with zero cushion (Leguano) they exhibited reduced ankle dorsiflexion at contact, increased stride frequency, reduced step length, and lower frequency of heel striking relative to both cushioned shoe conditions.

The cushioned minimal shoe (Nike Free 3.0) differed from the standard shoe (Asics 2160) in that the runners exhibited increased stride rate and reduced step length. Ankle angle and frequency of heel striking did not differ between the two cushioned shoes.

Knee angle at foot strike did not differ between any of the footwear conditions (barefoot included).

Commentary

The results of this study suggest a gradation of effect of running footwear on form. None of the shoes mimicked the barefoot condition perfectly, even the minimal shoe with no cushion. When barefoot, the runners had the smallest amount of ankle dorsiflexion, a higher cadence, and a shorter stride. The zero cushion shoe yielded similar results to barefoot for foot strike, and had intermediate values for ankle angle. Stride rate decreased incrementally from the zero cushion shoe to the standard shoe, and step length increased incrementally from the zero cushion to the standard shoe.

This study by Bonacci et al. found a similar reduction in stride length and increase in stride rate in the Nike Free relative to a traditionally cushioned shoe, so it does appear that a moderately cushioned shoe may induce some amount of form change in the direction of barefoot running. That being said, retention of a heel striking gait in such shoes can lead to increases in impact forces over traditional footwear.  Although the importance of impact forces to injury risk remains a source of debate, it seems prudent to suggest that care should be taken when migrating toward shoes with moderate cushion.

One of the disadvantages of this study is that it looked at immediate change in runners who were not familiar with running in minimal footwear, so we can’t know for sure if changes from the standard shoe might become more apparent with time and additional adaptation to such shoes.

In my own research I have found that barefoot runners on asphalt are more likely to midfoot or forefoot strike compared to runners in the minimally cushioned Vibram Fivefingers. Combined with results from the study discussed here (and others), these findings support my belief that barefoot running is different from running in any kind of shoe, and that although a zero or minimally cushioned shoe can alter form in the direction of barefoot running, it may never perfectly simulate what happens when you take your shoes off. At the same time, running in a minimal shoe is different than running in a more traditional shoe, but it might take removal of most or all of the cushioning to elicit major changes in running form (at least in the short term).

In my recent review of the Nike Free 5.0 I cited a study that compared running biomechanics in the Nike Pegasus and the Nike Free 3.0. This research has been out for awhile, but I never wrote about the paper. Since I’ve been running a bunch in various Nike Free shoes lately, I thought I’d write up a summary.

The study is authored by Richard Willy and Irene Davis and is titled “Kinematic and kinetic comparison of running in standard and minimalist shoes.” It was published in 2014 in the Journal Medicine & Science in Sport & Exercise. Here is the Abstract:

Abstract

PURPOSE: The purpose of this study was to determine whether running in a minimalist shoe results in a reduction in ground reaction forces and alters kinematics over standard shoe running. The secondary purpose of this study was to determine whether within-session accommodation to a novel minimalist shoe occurs.

METHODS: Subjects were 14 male, rearfoot striking runners who had never run in a minimalist shoe. Subjects were tested while running 3.35 m·s(-1) for 10 min on an instrumented treadmill in a minimalist and a standard shoe as three-dimensional lower extremity kinematics and kinetics were evaluated. Data were collected at minute 1 and then again after 10 min of running in both shoe conditions to evaluate accommodation to the shoe conditions.

RESULTS: Shoe-time interactions were not found for any of the variables of interest. Minimalist shoe running resulted in no changes in step length (P = 0.967) or in step rate (P = 0.230). At footstrike, greater knee flexion (P = 0.001) and greater dorsiflexion angle (P = 0.025) were noted in the minimalist shoe. Vertical impact peak (P = 0.017) and average vertical loading rate (P < 0.000) were greater during minimalist shoe running. There were main effects of time as dorsiflexion angle decreased (P = 0.035), foot inclination at footstrike decreased (P = 0.048), and knee flexion at footstrike increased (P = 0.002), yet the vertical impact peak (P = 0.002) and average vertical loading rate (P < 0.000) increased.

CONCLUSIONS: Running in a minimalist shoe appears to, at least in the short term, increase loading of the lower extremity over standard shoe running. The accommodation period resulted in less favorable landing mechanics in both shoes. These findings bring into question whether minimal shoes will provide enough feedback to induce an alteration that is similar to barefoot running.

Rationale and Methods

Many runners choose a moderately cushioned shoe to transition toward more minimal footwear figuring that it is a safer approach than jumping right into a shoe with no cushion at all. Because of this, the authors were interested in determining if running in a cushioned “minimalist” shoe might more closely simulate barefoot-like running mechanics than a more traditionally cushioned shoe. To address this, they recruited 14 heel-striking runners and had them run in both the Nike Pegasus and the Nike Free 3.0. The Pegasus has about 20mm more cushion in the heel, and the cushioning in the Peg is also significantly softer than that of the Free. Each runner ran two 10-minute trials on an instrumented treadmill, one in each shoe, and biomechanical measures were recorded near the beginning and end of the trials to see if acclimation time to the shoes had any effect.

Results

Contrary to expectations, step rate (both shoes just under 170 steps/min), step length, and foot inclination at foot strike did not differ between the two shoes. Even more unexpected was the fact that ankle dorsiflexion, vertical impact peak, and vertical loading rate were all significantly higher in the Nike Free 3.0.

Comparisons from the beginning to the end of the 10 minute run did not reveal any acclimation differences between the two shoes. In both the Pegasus and the Free 3.0 runners did not alter step length or rate, foot inclination and ankle dorsiflexion decreased, knee flexion at foot strike increased, and vertical impact peak and loading rate increased over the course of the run.

Commentary

Contrary to expectations, runners in the Nike Free 3.0 exhibited higher impact and loading rates compared to when they wore the Nike Pegasus. Furthermore, they did not exhibit changes typical of barefoot runners such as reduced step rate and stride length, or reduced foot inclination at initial contact that is indicative of adopting a midfoot or forefoot strike. In plain terms, the Nike Free 3.0 didn’t do a good job of simulating barefoot running. Rather, wearing the barefoot-inspired shoe resulted in a more impactful stride.

So what might be going on here? The authors suggest that “In order to see a change in footstrike pattern that simulates barefoot running, the shoes may need to be as minimal as possible.” In other words, the Nike Free 3.0 has enough cushion that it does not encourage alteration of the running stride in the direction of barefoot running. However, it has less cushioning than a traditional shoe and is firmer than the Pegasus so continuing to heel strike in a shoe like this results in increased impact loading. I should point out that I have observed that almost 50% of runners in the minimally cushioned Vibram Fivefingers continue to heel strike, so it may be that no shoe really does a perfect job of encouraging a barefoot-like stride.

The authors further point out that loading rates in the Free 3.0 exceeded those reported for runners with a history of tibial stress fractures. Other research has found that transitioning into Nike Frees increases injury risk to a greater degree than transitioning into the Nike Pegasus or the Vibram Fivefingers (injury risk in the latter two did not differ). We don’t know for sure if increases in impact loading might explain the increased injury risk in Frees (it could be their extreme flexibility or some other factor), but the combined results of these studies suggest that caution is warranted when beginning to run in a flexible, moderately cushioned shoe like the Nike Free 3.0. At the very least, runners should pay attention to running form when transitioning into a moderately cushioned shoe as they will not provide the same level of protection for a runner with a high-impact stride.

In this post we’ll take a look at another study on foot strike, in this case the influence of surface hardness on foot strike type in habitually shod runners who were asked to run barefoot in the lab. The study, led by Allison Gruber, was published in 2013 in the journal Footwear Science. They were interested in trying to determine whether pain associated with a barefoot heel strike on a hard surface might trigger a shift to a midfoot or forefoot strike.

Here is the abstract (full text is available here):

Footfall patterns during barefoot running on harder and softer surfaces

Allison H. Gruber^a, Julia Freedman Silvernail^a, Peter Brueggemann^b, Eric Rohr^c & Joseph Hamill^a*

Footwear Science, Volume 5, Issue 1, 2013, pg 39-44

Abstract

It has been suggested that the development of a thick, soft midsole of running shoes over the past 30 years has been primarily responsible for the majority of runners adopting a rearfoot or heel-toe footfall pattern thus deviating from a more ‘natural’ forefoot pattern. The purpose of this study was to determine the freely chosen footfall pattern when running barefoot on a harder versus a softer surface. Forty habitual rearfoot runners performed two running conditions: barefoot over a harder surface and barefoot over a softer surface. Three-dimensional motion analysis and ground reaction force data were collected to measure the ankle angle, vertical impact peak and strike index. The kinematic and kinetic parameters were used to confirm the footfall pattern in each condition. Only 20% per cent of the participants ran with a midfoot or forefoot pattern on the soft surface whereas 65% of the participants ran with a midfoot or forefoot pattern when running on the hard surface. Out of the 80% of participants that maintained a rearfoot pattern on the soft surface, 43% of these participants ran with a midfoot or forefoot pattern on the hard surface. These results suggest that, while running barefoot, the hardness of the running surface may be a significant factor causing an alteration in a runner’s footfall pattern.

Methods

The researchers recruited 40 habitually shod runners who were confirmed to be rearfoot strikers in their typical training shoes. They had each runner run trials in the lab along a 25 m runway equipped with a force platform. Trials included two conditions: 1) concrete runway with no cushioning (the hard surface); 2) runway covered with 20mm EVA foam mats to simulate characteristics of a shoe midsole (the soft surface). Foot strike patterns and a variety of other biomechanical measurements were recorded for each subject in both conditions.

Results

On the soft surface 80% of the runners ran with their usual heel-striking pattern, 17.5% ran with a midfoot strike, and one person ran with a forefoot strike. On the hard surface, 35% of subjects ran with a heel strike, 27.5% ran with a midfoot strike, and 37.5% ran with a forefoot strike. Statistical analysis confirmed that there was a significant shift in foot strike patterns between the hard and soft surfaces.

Commentary

What I liked about this study was that it asked and tested a simple question: What happens if habitually shod heel strikers run barefoot on a hard vs. a soft surface? What they found is that runners tended to shift to a midfoot or forefoot strike on concrete, but most continued to heel strike on the cushioned surface. This suggests that the presence of cushioning allows runners to heel strike comfortably and could indicate why heel striking is commonly observed in shod runners on hard surfaces, whereas barefoot runners tend to shift to a midfoot or forefoot strike on hard surfaces. Moving to a midfoot or forefoot strike allows the Achilles tendon and calf muscles to assist in attenuation of impact forces and could make running on hard surfaces more comfortable.

The results here could also explain why habitually barefoot or minimally shod people like the Daasanach, Tarahumara, or Hadza children and adult women have been observed to heel strike while running slowly on natural sand/dirt surfaces, whereas experienced Kalenjin runners moving fast tend to midfoot or forefoot strike on such surfaces. It might also explain why approximately 50% of runners in Vibram Fivefingers have been observed to contact on the heel when running on asphalt – there may be just enough cushion present in minimal shoes to allow this to be done comfortably if the pace is not too fast.

One interesting finding here was that 20% of the runners switched from their typical heel strike in shoes to a midfoot or forefoot strike even on the soft surface. The authors reported in their Discussion section that some of these subjects had previous experience with barefoot running, and that they indicated that they were more comfortable with the MFS/FFS when running barefoot. In other words, previous experience running barefoot could have led to development of modified form in this condition (similar to the role of experience in the Hadza runners). I would also suggest that even though cushion is present in both conditions, plantar sensation when running barefoot on a mat vs. with a shoe on the foot might differ and could explain some of these changes.

One other interesting finding was that 35% of subjects continued to heel strike when running barefoot on concrete. The authors suggest that the lab runway may not have been long enough to induce discomfort necessary to trigger a change in foot strike. However,  I have observed a similar proportion of barefoot runners heel striking on asphalt during a race, so length of the runway may not have been the only factor. It may be that a move to a less prominent heel strike could make barefoot heel striking comfortable enough for some runners, or it could be that some runners need more experience before adopting a different foot strike when barefoot on a hard surface.

As with most studies, this one provides some answers but also raises new questions. For example, I wonder if there is an individually specific threshold combination of speed and surface hardness that triggers a shift in foot strike to attenuate the impact forces associated with a heel strike? Also, why do some people shift but others do not? How much experience is required for a shift to occur, and are there some people who will never shift their foot strike? What role does plantar sensation or abrasions with the ground surface play in determining foot strike? To me, the continual search for answers to questions like these is what makes science so much fun.

In this post we’ll take a look at another study that examined foot strike patterns in a population that habitually wears minimal footwear. This study, led by Herman Pontzer, looks at Hadza hunter-gatherers from Tanzania, Africa. Like the traditional Tarahumara huaraches, the Hadza tend to mostly wear minimal sandals made out of repurposed tire rubber.

The Hadza are an interesting group in which to study running form since adult males and females exhibit a division of labor. Adult females spend the day gathering foods like berries and tubers, whereas adult males hunt game and collect honey. Both groups walk a lot, and though running is not a common practice, it is presumed that males engage in running more frequently during hunts. This difference allows for some insight into the role of running experience in contributing to variation in running form.

Here’s the abstract to the study (full-text available here):

Foot strike patterns and hind limb joint angles during running in Hadza hunter-gatherers

Herman Pontzer, Kelly Suchman, David A. Raichlen, Brian M. Wood, Audax Z.P. Mabulla, Frank W. Marlowe

Journal of Sport and Health Science

Volume 3, Issue 2, June 2014, Pages 95–101

Abstract

Background

Investigations of running gait among barefoot and populations have revealed a diversity of foot strike behaviors, with some preferentially employing a rearfoot strike (RFS) as the foot touches down while others employ a midfoot strike (MFS) or forefoot strike (FFS). Here, we report foot strike behavior and joint angles among traditional Hadza hunter-gatherers living in Northern Tanzania.

Methods

Hadza adults (n = 26) and juveniles (n = 14) ran at a range of speeds (adults: mean 3.4 ± 0.7 m/s, juveniles: mean 3.2 ± 0.5 m/s) over an outdoor trackway while being recorded via high-speed digital video. Foot strike type (RFS, MFS, or FFS) and hind limb segment angles at foot strike were recorded.

Results

Hadza men preferentially employed MFS (86.7% of men), while Hadza women and juveniles preferentially employed RFS (90.9% and 85.7% of women and juveniles, respectively). No FFS was recorded. Speed, the presence of footwear (sandals vs. barefoot), and trial duration had no effect on foot strike type.

Conclusion

Unlike other habitually barefoot populations which prefer FFS while running, Hadza men preferred MFS, and Hadza women and juveniles preferred RFS. Sex and age differences in foot strike behavior among Hadza adults may reflect differences in running experience, with men learning to prefer MFS as they accumulate more running experience.

Methods

The researchers traveled to Tanzania and recruited 26 Hadza adults (15 men, 11 women) and 14 juveniles (mean age = 8.6 years) to run trials while being recorded by a high-speed camera. The subjects ran along a hard-packed sand/silt trackway cleared of shrubs and loose rocks. Ankle, knee, and plantar foot angles were measured at initial foot contact from the video sequences. Some of the adults ran barefoot, others ran in minimal sandals. All of the juveniles ran barefoot.

Results

For adult males, 86.7% were midfoot strikers while running, and 13.3% were heel strikers. For adult females, 9.1% were midfoot strikers, and 90.9% were heel strikers. For juveniles, 14.3% were midfoot strikers, and 85.7% were heel strikers.

No significant differences in foot strike patterns were found between barefoot and minimally shod adults (though non-significant, heel striking was actually more frequent in the barefoot condition). Speed was not found to significantly influence foot strike (though the sample was small for this subset of data). No forefoot striking was observed in any of the trials. Joint angles did not differ between the groups.

Commentary

What I like about this study is that it may provide some evidence that running experience has an influence on the development of certain aspects of running form, in this case foot strike. Hadza children overwhelmingly tend to heel strike when barefoot, as do adult Hadza women. In contrast, adult Hadza males tend to midfoot strike when running. The authors write the following as a potential explanation of this pattern:

“This pattern of foot strike usage suggests running experience may be important in developing foot strike preferences. As children learn to walk and their gait matures, RFS develops as a normal part of the walking gait cycle;²⁰ thus RFS is the behavior learned first. As the musculoskeletal system and motor control develop further during adolescence, experience running barefoot or minimally shod may lead to a preference for MFS or FFS during running, perhaps in response to the high impact forces²¹ experienced when running with RFS. Individuals who rarely run might not have the same accumulated experience of high impact forces due to RFS, and thus never switch from RFS to MFS or FFS for running.”

They point out that the only two adolescents who were classified as midfoot strikers were the two oldest boys in the group, and suggest that:

“…the change in foot strike behavior by Hadza men may develop as they learn to hunt and track wild game. While Hadza men do not typically engage in endurance running, it is likely that they run more often as they learn to hunt than their female counterparts do in learning to gather plant foods. Indeed, our measurements of travel speeds used while out of camp on forays, taken using wearable GPS devices,¹⁶ indicate that men use running speeds approximately twice as often as women.”

These results have implications with regard to the interpretation of two other studies of foot strike patterns among habitually barefoot Africans. In Daniel Lieberman’s well known study of foot strike patterns among habitually barefoot Kenyans he found that the overwhelming majority exhibited midfoot or forefoot strikes while running. The Kalenjin subjects that he filmed were experienced runners, and it’s worth noting that they were running quite fast. In contrast, habitually barefoot Daasanach adults tend to heel strike at slower running speeds (though frequency of midfoot/forefoot striking increased at faster speeds). Unlike the Kalenjins, the Daasanach rarely run. Thus, in addition to speed differences, differences in running experience could partially explain the differences in foot strike patterns observed between the two groups.

For me, the most surprising result in this study was the pattern observed for the Hadza children. If you asked me how I thought a group of kids who are typically barefoot or shod only in a pair of sandals would strike the ground when running barefoot, I would have guessed an overwhelming majority would be mid- or forefoot strikers. This study demonstrated the exact opposite – almost all were heel strikers. If you think heel striking is abnormal or bad, just think about that for a second. It’s not as simple as saying that barefoot runners forefoot strike, or that kids never land on their heels. It’s more likely that foot strike is determined by a number of factors, among which are experience, speed, surface properties, footwear, fatigue, and so on.

I’ll finish by saying once again that I don’t believe there is a perfect or “natural” running form that applies under all circumstances. Rather, form is determined by properties of the individual and the characteristics of their immediate running environment. There are things that many people could do better (e.g., reduce overstriding, better hip stabilization), but to say that every person should run a certain way simply does not sync with the range of variation we see, even in populations that are habitually barefoot or minimally shod.

Personally, I view foot strike as one aspect of running form that varies with a range of factors. These factors would include running speed, running experience, surface hardness, surface incline, fatigue, footwear type or the lack thereof, etc. For example, I think we tend to see a shift more toward the forefoot side of the spectrum when experienced runners run fast on hard surfaces, particularly if barefoot. We see a shift more toward the heel strike side when inexperienced runners run slowly on soft surfaces or in heavily cushioned footwear. Mix and match these factors and we can get a variety of different foot strike types, and it’s unlikely that any one set of conditions will yield identical responses in all runners exposed to them (because people are variable).

As an example of the influence of both external variables on running foot strike and individual variability within the same condition, I thought it might be interesting to take a look at a research study that was published last year. Authored by Daniel Lieberman, the study takes a look at foot strike patterns among traditionally shod and conventionally shod Tarahumara Native Americans from Mexico (full text is available here). The running prowess of the Tarahumara was made famous by Christopher McDougall in his book Born to Run. That book, published in 2009, was largely responsible for kicking off the form and footwear debates that ensued over the following years, and the Tarahumara thus make for a great running form case study.

Here’s the abstract of the study:

Strike type variation among Tarahumara Indians in minimal sandals versus conventional running shoes

Daniel Lieberman

Journal of Sport and Health Science, Volume 3, Issue 2, June 2014, Pages 86–94

Abstract

Purpose

This study examined variation in foot strike types, lower extremity kinematics, and arch height and stiffness among Tarahumara Indians from the Sierra Tarahumara, Mexico.

Methods

High speed video was used to study the kinematics of 23 individuals, 13 who habitually wear traditional minimal running sandals (huaraches), and 10 who habitually wear modern, conventional running shoes with elevated, cushioned heels and arch support. Measurements of foot shape and arch stiffness were taken on these individuals plus an additional sample of 12 individuals.

Results

Minimally shod Tarahumara exhibit much variation with 40% primarily using midfoot strikes, 30% primarily using forefoot strikes, and 30% primarily using rearfoot strikes. In contrast, 75% of the conventionally shod Tarahumara primarily used rearfoot strikes, and 25% primarily used midfoot strikes. Individuals who used forefoot or midfoot strikes landed with significantly more plantarflexed ankles, flexed knees, and flexed hips than runners who used rearfoot strikes. Foot measurements indicate that conventionally shod Tarahumara also have significantly less stiff arches than those wearing minimal shoes.

Conclusion

These data reinforce earlier studies that there is variation among foot strike patterns among minimally shod runners, but also support the hypothesis that foot stiffness and important aspects of running form, including foot strike, differ between runners who grow up using minimal versus modern, conventional footwear.

Methods

Lieberman traveled to Mexico and collected kinematic data from 20 Tarahumara. Twelve of these individuals wore only traditional huarache sandals (see photo at top of post for image of huaraches), and eight wore conventional running shoes. After a five minute warmup, subjects were filmed while running 15 meters along a flat, natural surface free of grass and rocks. Each subject ran the 15 m trials until three usable videos were recorded for each. A variety of biomechanical variables were measured from the video sequences.

Results

Minimally shod Tarahumara that ran their trials in huarache sandals exhibited the following foot strike patterns: 40% midfoot strike, 30% forefoot strike, 30% heel strike. In contrast, Tarahumara in conventional running shoes landed on the heel 75% of the time and on the midfoot 25% of the time. No forefoot strikes were observed in the conventionally shod runners. Of the other biomechanical variables measured, only overstride angle differed – minimally shod runners tended to land with the ankle in a position more underneath the knee at ground contact.

Commentary

These results demonstrate two things to me:

1. Footwear does have an influence on foot strike. Those Tarahumara who typically wear conventional shoes and ran their trials in this type of shoe tended to heel strike 75% of the time. This is consistent with other studies that have found that 75% or more of traditionally shod runners land first on the heel.

2. Foot strike patterns are variable in Tarahumara runners wearing huarache sandals. Almost a third of them heel strike, and there is no overwhelmingly predominant pattern exhibited by this group. Lieberman himself writes: “…minimally shod Tarahumara runners appear to be best characterized as midfoot strikers who also employ forefoot and rearfoot strikes. These data therefore partially support but also modify earlier anecdotal reports that Tarahumara runners who use huaraches primarily FFS (forefoot strike).” As the source of these anecdotal reports, Lieberman cites McDougall’s book Born to Run and Scott Jurek’s book Eat and Run.

So here we have two levels of variability. Variability among groups due to the type of footwear typically worn, and variability within groups wearing similar kinds of footwear. It’s not as simple as saying that all huarache-wearing Tarahumara forefoot strike, and this suggests that there is no “perfect” or “natural” running form or foot strike that is or should be used under all circumstances by all people. Rather, running foot strike is dictated both by external influences (footwear here) and individual variation in response to a given set of conditions.

To me, this combo of adaptability and variability is what makes the study of human running form so fascinating – we are amazing and complex animals, and this is exhibited by both our incredible running ability as well as how we run.

If you enjoyed this post, you might also like this one on foot strike patterns in Hadza hunter-gatherers.

In this post we’ll take a look at another study that investigated the effects of a self-directed cadence training protocol on runners. Here’s the Abstract

Scand J Med Sci Sports. 2015 Feb 4.

In-field gait retraining and mobile monitoring to address running biomechanics associated with tibial stress fracture.

Willy RW1, Buchenic L, Rogacki K, Ackerman J, Schmidt A, Willson JD.

Abstract

We sought to determine if an in-field gait retraining program can reduce excessive impact forces and peak hip adduction without adverse changes in knee joint work during running. Thirty healthy at-risk runners who exhibited high-impact forces were randomized to retraining [21.1 (±1.9) years, 22.1 (±10.8) km/week] or control groups [21.0 (±1.3) years, 23.2 (±8.7) km/week]. Retrainers were cued, via a wireless accelerometer, to increase preferred step rate by 7.5% during eight training sessions performed in-field. Adherence with the prescribed step rate was assessed via mobile monitoring. Three-dimensional gait analysis was performed at baseline, after retraining, and at 1-month post-retraining. Retrainers increased step rate by 8.6% (P < 0.0001), reducing instantaneous vertical load rate (-17.9%, P = 0.003), average vertical load rate (-18.9%, P < 0.0001), peak hip adduction (2.9° ± 4.2 reduction, P = 0.005), eccentric knee joint work per stance phase (-26.9%, P < 0.0001), and per kilometer of running (-21.1%, P < 0.0001). Alterations in gait were maintained at 30 days. In the absence of any feedback, controls maintained their baseline gait parameters. The majority of retrainers were adherent with the prescribed step rate during in-field runs. Thus, in-field gait retraining, cueing a modest increase in step rate, was effective at reducing impact forces, peak hip adduction and eccentric knee joint work.

© 2015 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

What was unique about this study was that the researchers screened runners beforehand and only included those who exhibited high baseline impact loading rates. The value that constituted “high” corresponded to the average value for a cohort of runners with a history of tibial stress fracture. Thus, they were looking at runners who had impact loading rates that might put them at risk of injury and therefore might benefit most from a protocol that increases step rate.

Methods

The researchers measured a variety of biomechanical variables both before and after a cadence training protocol. The protocol consisted of 8 runs, during a portion of which subjects ran at a cadence target that was 7.5% higher than their baseline. The retraining utilized a faded-feedback design in which cadence feedback was provided during runs 1-3, 5, and 7. The rationale for this was that it might help subjects to internalize cadence changes if feedback was gradually removed.

Cadence feedback was accomplished by using a Garmin footpod that displayed real-time cadence on a GPS watch. A control group went through the same protocol but was not instructed to increase their cadence (it was not displayed on their watch). All subjects returned again 30 days after the end of the 8-run protocol to see if any changes would be retained in the absence of continued cadence training.

Results

After the 8 run protocol the gait retraining group exhibited significantly increased stride rate. Stride rate for this group was on average 166.5 steps/min at baseline, 180.8 steps/min post-training, and 180.6 steps./min 30 days post-training. This shows that the subjects had retained the new, higher stride rate even 30 days after feedback was removed.

The experimental group also exhibited significant reductions in instantaneous impact loading rate (-18.9%), average vertical loading rate (-17.9%), peak hip adduction (about 3 degrees less), and eccentric knee joint work (-26.9%). These changes were all retained 30 days later.

No differences between baseline, post-training, or 30 days post training were observed in the control group.

Comparisons between the two groups revealed that stride rate was significantly higher, and loading rates were significantly lower in the experimental group both post-training and 30 days post-training. Peak hip adduction and eccentric knee joint work did not differ between the groups.

Comments

I like this study because it provides additional evidence that runners can make lasting changes to their cadence outside of the lab/clinic setting, thus saving both time and money. Consistent with other studies, this one also shows that increasing cadence can alter biomechanical variables that have been associated with risk of injuries like tibial stress fractures, patellofemoral pain, and iliotibial band syndrome. I also like that they pre-screened subjects to include only those who exhibited baseline loading rates consistent with a population of runners with a history of stress fractures. Thus, they were looking at a population of runners who might benefit most from such an intervention.

Given the increasing number of devices that are capable of displaying running cadence (including both phone apps and GPS watches), the protocol here seems like a logical option that should be accessible to most runners. I routinely utilize the cadence function on my Garmin 620 (mainly out of curiosity), and the iSmoothRun app will give you this information on a phone. I haven’t actively attempted to retrain my own cadence, but if I were going to try I think I’d prefer going this route over using something like a metronome or music with a target tempo.

The missing link, however, continues to be the lack of interventional studies that take runners suffering from one of the injuries mentioned above through a gait retraining protocol like the one studied here. This will go a long way toward bridging the gap between gait retraining, resulting biomechanical changes, and their potential role in injury resolution. In the meantime, attempting to increase cadence a bit might be a worthwhile experiment if you suffer/have suffered from tibial stress fracture, PFPS, or ITBS.

First off, for those who might not be familiar with the terminology, a medial post is a firmer wedge of midsole foam located on the inner side of the sole, typically under the heel/midfoot regions. You can see the medial post in the photo below as the region of gray, speckled foam:

The goal of a medial post is to limit pronation, or the inward rolling of the foot that occurs after initial contact with the ground. The thinking is that excessive pronation can cause injuries, and the medial post in a shoe like the 1500 can help to control this pronation. You’ll find a medial post in many shoes that are labeled as “stability” shoes, though some brands have other methods of trying to make shoes more stable.

So, does the presence or absence of a stability structure like a medial post influence my decision about whether to try a given running shoe? My answer is no, not at all. Personally, I’ve never felt that a medial post does much of anything, and I don’t put much stock in the categorization of shoes as “stability” or “neutral.” For example, the New Balance 1500 doesn’t feel a whole lot different than the New Balance 1600  (pictured below), and the latter lacks a medial post.

Even if stability elements do work, I’m not really convinced that controlling pronation is all that necessary in the first place – short of things like medial tibial stress syndrome and maybe a few other problems, I don’t think there is much strong evidence linking pronation to injury.

My feeling based on having run in a lot of shoes is that each shoe is a little bit different, and a neutral shoe with a firm sole might be just as (if not more) stable than a given stability shoe. I’ve recently run in “stability: shoes like the Saucony Fastwitch, Brooks PureCadence, and Saucony Mirage without issue. I just bought a pair of Asics DS Racers. When I first started running I ran in Brooks Adrenalines and Asics Kayanos. I’ve also run in a bunch of neutral shoes. There is a lot of variation in feel among these shoes, but rarely do I find it to be associated with their stability category. Individual feel is what matters most.

I will add one caveat – I do think there are some shoes that are unstable. Shoes that are too narrow in certain areas for a person’s foot, and shoes that are too soft in a particular area can cause excessive movement. For example, I didn’t like the narrow midfoot of the New Balance 5000, and the medial forefoot of the Nike Pegasus and some Hoka models are too soft and exacerbate my late stage pronation (I wind up caving in the medial border of the sole). But these are more individual shoe issues than differences among broader categories. (I’ll add that it’s worth considering whether a problem with a “category” was more a problem of a bad match with a single shoe than anything else)

I honestly think that for the most part stability and neutral are categories that exist more for marketing purposes than anything else. I’m not aware of any independent scale or test that allows you to determine exactly how stable a given shoe is versus another. However, having categories makes it easier to sell shoes, and some people will not run in a shoe outside of their prescribed category. Therefore, companies feel compelled to produce shoes labeled as stability or neutral to cater to these beliefs (even if the company doesn’t necessarily believe in the need for the categories…).

I’ll finish by saying that what is important to me when choosing a shoe is how a shoe feels on my feet while running and how it fits. I honestly could care less whether a shoe has stability elements.

How about you, do stability elements factor into your decision-making process when choosing a shoe?

One of the challenges with gait retraining methods employed in clinical settings is that the equipment required is not always accessible to runners outside of the clinic (e.g., accelerometers, force treadmills). This can require repeated, often costly appointments, especially if they are not covered by insurance. Cadence training has the advantage of being easy to do outside of the clinical setting using smartphone apps, metronomes, or fitness watches that can measure cadence in real time.

Questions that arise are whether runners can make lasting modifications to their running cadence on their own, whether those modifications might yield the same loading changes observed acutely in the lab, and whether there are any negative consequences to cadence change such as a loss of running efficiency. A recent study led by Jocelyn Hafer of the University of Massachusetts addressed each of these issues. Published in the Journal of Sports Sciences, the study looks at how a 6-week cadence training protocol effects running biomechanics and efficiency.

Here is the abstract of the study:

The effect of a cadence retraining protocol on running biomechanics and efficiency: a pilot study

Jocelyn F. Hafer, Allison M. Brown, Polly deMille, Howard J. Hillstrom & Carol Ewing Garber

Journal of Sports Sciences, Volume 33, Issue 7, 2015

Abstract

Many studies have documented the association between mechanical deviations from normal and the presence or risk of injury. Some runners attempt to change mechanics by increasing running cadence. Previous work documented that increasing running cadence reduces deviations in mechanics tied to injury. The long-term effect of a cadence retraining intervention on running mechanics and energy expenditure is unknown. This study aimed to determine if increasing running cadence by 10% decreases running efficiency and changes kinematics and kinetics to make them less similar to those associated with injury. Additionally, this study aimed to determine if, after 6 weeks of cadence retraining, there would be carryover in kinematic and kinetic changes from an increased cadence state to a runner’s preferred running cadence without decreased running efficiency. We measured oxygen uptake, kinematic and kinetic data on six uninjured participants before and after a 6-week intervention. Increasing cadence did not result in decreased running efficiency but did result in decreases in stride length, hip adduction angle and hip abductor moment. Carryover was observed in runners’ post-intervention preferred running form as decreased hip adduction angle and vertical loading rate.

Methods

In this study, researchers screened for runners with a cadence between 150 and 170 steps per minute, which is on the low end of the range of cadences typically observed (six runners were included in the study, so a relatively small sample size). They then had these runners train for 6 weeks with a goal of running at least 50% of their miles at a cadence 10% higher than their baseline. To accomplish this they could use either a metronome app or songs with tempos corresponding to the target cadence. A variety of metabolic and biomechanical measurements were taken before and after the training period to assess the effects of the retraining protocol. They also looked at immediate effects of increasing cadence at the outset to see if changes would be similar to those previously reported in the literature (they were).

Results

After the six week training protocol, the runners preferred cadence had increased significantly from around 166 steps/min on average to around 170 steps/min. Thus, though they did not adopt a full 10% increase through the training, cadence did increase significantly. Along with the preferred cadence increase, the runners also exhibited reduced ankle dorsiflexion at contact (less pronounced heel strike), reduced peak hip adduction angle (the thigh did not angle medially/inward as much), and reduced vertical loading rate. Running efficiency was not significantly different.

Comments

Though the sample size was small (the authors admit this and refer to it as a pilot study in the title), it is encouraging to see that cadence training can lead runners to modify their form, and that changes can alter variables associated with injury (especially with the small cadence increase that they observed). Reduction in hip adduction angle could benefit those with patellofemoral pain or ITBS, and reduced vertical loading rate could benefit those with a history of tibial stress fracture. It’s also encouraging that these benefits are accrued without a hit to running efficiency.

I would like to see this study completed with a larger sample of runners, but it was encouraging the significant changes were found even with this small sample. I’d also like to see some analysis of which method of cadence training is most effective for a runner (music, metronome, real-time feedback via an app or watch).

All things considered, these results do suggest that increasing cadence is one option to consider for those experiencing ilitibial band syndrome, patellofemoral pain syndrome, or past tibial stress fracture. I also like that this is an intervention that runners can undertake on their own without the need to make repeated visits to a clinic. A useful next step would be an interventional study where runners experiencing one of these conditions undergo a cadence training program and symptoms are monitored before and after.

Hixson’s opening paragraph references my 2014 reader survey, emphasizing the point that four “maximally” cushioned shoes appear among the top 20 models. He then asks the following question “What happened with runners that made “fat and flat” shoes so popular, and in the process, push aside minimalism like some beefy schoolyard bully?”

Hixson makes some good points. For example, I agree that a lot of people who tried minimal went into it too fast and got injured in the process. Making a radical change in form or footwear requires a slow transition, and failure to do this is partly what led a lot of people to abandon minimal shoes. However, my major problem with the article is that it pits minimal against maximal and traditional shoes in a sort of us vs. them battle. I personally don’t see the need to polarize this debate any more. There is no convincing evidence that one type of shoe is better than any other, and in the absence of such evidence the best approach is to simply find what works best for you. Minimal, maximal, traditional, who cares? It’s just shoes, and being able to enjoy running is what it’s all about.

My personal feeling is that minimal went flat simply because people stopped buying minimal shoes. The reasons for this are probably many – people got hurt, minimal shoes last longer so you don’t need to buy them as often, Vibram Fivefingers were a funny-looking fad, running in minimal shoes really wasn’t the same as running barefoot. The fact is that if a product doesn’t sell, stores won’t carry it. If stores won’t carry it, companies will stop producing it. Simple as that. If everyone who went minimal had an incredibly positive experience, the trend would not have gone flat. Is there still a market for minimal shoes? Sure, and I hope they always remain an option since many people do genuinely run best in minimal footwear.

My own experience might be instructive here, and highlights why I still think the minimal movement was so important. I started running in 2007 and was told at a shoe store that I overpronate and thus needed stability shoes. I wore stability shoes for two years without issue, and in 2009 I started experimenting with minimal footwear after reading Born to Run. I ran quite a lot of miles in Vibram Fivefingers and minimal shoes like the Merrell Trail Glove. I had a very positive experience – I didn’t get hurt, I enjoyed running with less cushion, and I had fun experimenting with my form. But, perhaps most importantly, going minimal let me know that I wasn’t trapped in a life of stability shoes by my “diagnosis” as an overpronator. I was free to experiment, and I did. And in the process I was able to find what worked best for me.

Going minimal made me realize that I liked a wide toebox. I liked a flexible sole. I liked a lower drop. But I also realized that I liked a bit of cushion, and that I liked that cushion to be on the softer side. Not too much cushion, but just enough to provide comfort for long miles on the road. I found myself gravitating toward shoes like the Saucony Kinvara and New Balance 1400. Not minimal shoes, but not traditional or maximal either. I found a formula that worked best for me, and going minimal helped me to hone in on my sweet spot.

Minimal also led to experimentation by shoe companies and designers, and the outcome is that we now have an incredible diversity of shoes to choose from. Shoes like Hokas that combine aspects of minimalism with max cushion are part of that diversity. Just as I no longer feel pigeonholed into stability shoes, shoe walls no longer need to be organized into three narrowly-defined categories. There are tons of options available now, and this is a good thing. Minimalism was and is a good thing, it gave us the variety we have today.

In the past year I have run in Hokas, and I have run in a few traditional models. I liked the Hoka Huaka, but none are as good a fit for me as some of more trimmed-down models I have grown to prefer. That being said, I know lots of people who swear by maximal shoes like Hokas or the Altra Paradigm/Olympus. My wife went minimal and it didn’t work out well. She now runs in Hokas and cushioned Altras and is doing great. I know others who still swear by minimal shoes or barefoot. Different strokes for different folks – find what lets you enjoy running most and go with it.

Though I still appreciate a good footwear debate, and I enjoy following emerging science on the effects of footwear on things like form and running injuries, I honestly don’t think we will ever see any evidence supporting a single best shoe for all. It’s time to drop the us vs. them mentality when it comes to footwear and get back to just enjoying running.

I hope to get ahold of the text of this study, and had planned on writing about it myself as there are some clear issues with the interpretation of the results. However, Alex Hutchinson has already done the job and I thought I’d refer you to his take-down for an interesting and thoughtful read.

I particularly like this passage:

“Yes, the conclusion of the study (that “strenuous” jogging is as bad as being sedentary) is based on two deaths over more than a decade of follow-up. (Thank goodness a third person didn’t die, or public health authorities would be banning jogging.)”

Yes, their conclusion that strenuous jogging is as risky as being sedentary is based on two deaths. Alex expands on this, and addresses other issues as well. Head over to Runner’s World to read his full analysis.

Update: For another insightful look at this study, read this article by Larry Husten at Forbes.com. Love the final paragraph:

“Journalists and scientists have an obligation to fairly and accurately report the results of individual studies, and they have the further obligation to place those results in the context of what is already known in the field. By reporting the results of this one quite limited study with little or no critical perspective of its details or the larger context of the research, they have once again helped perpetuate the scientific illiteracy and innumeracy that is fast becoming one of the hallmarks of our time.”