I planted myself behind a bush about a quarter-mile from the starting line, and wound up getting slow-motion video (300 frames/sec) of 169 barefoot runners, and 42 runners wearing Vibram Fivefingers shoes (other footwear were represented as well, but sample sizes were small). My goal was to compare foot strike patterns between these two groups, as well as to compare patterns to those observed in other studies published on recreational runners wearing typical cushioned shoes.

I didn’t really do much with the video for a few years. I’d had some students analyze some of it for a senior research project, but the data needed some work if it was going to be publishable. Last Spring I met Martyn Shorten, head of the Runner’s World Shoe Lab, and we were chatting about our mutual interest in filming road races to look at form. When I told him about the NYC dataset he urged me to publish it, and put me in touch with Daniel Lieberman and Irene Davis. They were organizing a special edition of the Journal of Sport and Health Science on the topic of barefoot and minimalist running. They encouraged me to analyze and submit the data for publication – it was the push I needed, and I got it done.

The article I wrote was just published on-line – you can read the full text here. Here are the key points (note – midfoot strike means simultaneous contact of the heel and base of the fifth metatarsal):

1. For barefoot runners: 59.2% were forefoot strikers, 20.1% were midfoot strikers, and 20.7% were rearfoot strikers.

2. For minimally shod runners: 33.3% were forefoot strikers, 19.1% were midfoot strikers, and 47.6% were rearfoot strikers. Yes, almost 50% of the runners wearing Vibram Fivefingers contacted first on the heel.

3. The foot strike distributions were significantly different between the two groups.

4. Foot strike distributions for both groups differed from previously reported distributions in shod road runners (where ~90% of runners tend to heel strike).

What does all of this mean? Here’s my take on the significance of these results:

1. Barefoot runners are less likely to heel strike on asphalt than both minimally and traditionally shod runners. That being said, some barefoot runners (about 1 in 5) do continue to contact initially on the heel. This could be due to a lack of experience with barefoot running for some subjects observed. Anecdotally, my experience is that some people will immediately switch to a forefoot strike when you take their shoes off, others do not. Research suggests that for some people foot strike may change with experience. It could also be the case that a mild heel strike as typically exhibited by the barefoot runners is not a problem on a hard surface.

2. It is not easy to quantify and I did not attempt to do so in the paper, but the heel strikes observed in barefoot and minimally shod runners were typically not characterized by the extreme dorsiflexion you sometimes see in traditionally shod runners. For example, you don’t tend to see this type of pattern:

I’ve previously written about the fact that not all heel strikes are the same – we are beginning to realize that there is a lot of variation in how forces are applied even with the category we refer to as a “heel strike.”

3. The minimal shoe pattern differed from the barefoot pattern. Why? First, it’s possible that the Vibram runners were less experienced and thus opted to wear shoes rather than run barefoot in this “barefoot” race. Thus, they may not have had as much time to adapt their form. Second, the Vibram shoes may have provided enough cushion to make a heel strike on asphalt comfortable. Third, it may be that some factor other than a lack of cushioning is responsible for the reduced frequency of heel striking in barefoot runners. For example, a shoe sole also provides resistance to abrasion/friction with the ground. Removing that sole may require modifications of form to prevent damage to the plantar skin that are not required even when wearing a very minimal shoe.

What I’ve come to realize over the past several years is that determination of foot strike is multifactorial – I don’t think there is one right answer that applies to all conditions (and we now have evidence that some habitually barefoot humans heel strike a lot). The specific foot strike adopted by a given runner likely depends on some mix of footwear, running surface, running speed, running experience, etc. If you want to maximize the likelihood of observing a forefoot strike, I think you look at an experienced runner who is A) barefoot, B) has previous experience running barefoot, C) is running at a relatively fast pace, and D) is running on a hard surface like and asphalt road. That doesn’t mean that all runners under those conditions will forefoot strike, but I think the combo is most likely to encourage a form change from what we typically see in conventionally shod runners.

I elaborate on these points in a lot more detail in the actual paper, which you can read here. If you have any questions/thoughts, feel free to leave a comment.

A new study was just published on-line by Medicine & Science in Sport & Exercise that looks specifically at the influence of speed on foot strike. Previous research has suggested that some runners (not all) migrate foot strike from the heel toward the midfoot/forefoot as they run faster,  and this new study provides additional evidence to support this observation. But, it also goes beyond that finding and proposes the identification of a new foot strike type. I find this study quite compelling as it relates to my own running experience and shoe preferences!

Study Abstract:

Relationship between Running Speed and Initial Foot Contact Patterns

Breine, Bastiaan; Malcolm, Philippe; Frederick, Edward C.; De Clercq, Dirk

Abstract

Purpose: This study assessed initial foot contact patterns (IFCP) in a large group of distance runners and the effect of speed on the IFCP.

Methods: We determined the strike index, to classify the runners in IFCP groups, at 4 speeds (3.2, 4.1, 5.1, 6.2 m[BULLET OPERATOR]s-1) by measuring center of pressure (COP) with a 2 m plantar pressure plate. Such a system allows a direct localization of the COP on the plantar footprint and has a low threshold value (2.7 N[middle dot]cm-2) resulting in more accurate COP data at low ground reaction forces than when obtained from force plate.

Results: The IFCP distribution evolves from mostly initial rearfoot contact (IRFC) (82%) at 3.2 m[BULLET OPERATOR]s-1 to more anterior foot contacts with about equal distribution of IRFC (46%) and initial midfoot or forefoot contact (IMFC+IFFC) (54%) at 6.2 m[BULLET OPERATOR]s-1. About 44% of the IRFC runners showed atypical COP patterns with fast anterior displacement of the COP along the lateral shoe margin. Apart from the different COP patterns, these atypical IRFC were also characterized by a significantly higher instantaneous vertical loading rate than the typical IRFC patterns.

Conclusion: The IFCP distribution changes were due to intra-individual alterations in IFCP at higher speeds. That is, 45% of the runners made one or even two ‘transitions’ towards a more anterior IFCP (and 3% shows some other type of transition between initial foot contact styles as speed increases). Although, 52% of the runners remained with the same IFCP.

(C) 2014 American College of Sports Medicine

Methods

The authors recruited 55 runners and had them all wear the same model of cushioned, neutral running shoe (Li Ning Magne). Specs for this shoe were reported as follows for a US size 10: forefoot width 11.2 cm, heel width 9 cm, sole length 31.8 cm, heel thickness 2.9 cm, a heel toe offset of 1.15 cm, and impact testing results following ASTM F-1976-06 procedures of ~950 N or peak g of ~11.5 g. (I wish specs like this were reported for all shoes!)

The authors viewed using a single shoe for all subjects as being a more controlled situation than letting the runners wear their own shoes. I agree to an extent, but I do worry a bit about studies that put runners in novel footwear without allowing enough acclimation time (only a 5-10 warmup in the new shoe completed here). The authors acknowledge this possible limitation and they report that an initial “questionnaire did not indicate a systematic difference in habitual shoe type between different IFCP (initial foot contact pattern) groups.”

Each runner ran along a 25 m trackway at 4 speeds: 3.2 m/s (8:22/mile), 4.1 m/s (6:32/mile), 5.1 m/s (5:15/mile), 6.2 m/s (4:19/mile). The trackway was fitted with a force plate mounted with a pressure plate on top. This is a unique approach in that the added pressure plate is more sensitive at detecting smaller forces associated with initial contact and thus is more accurate at defining initial contact location.

The authors defined foot strike using the Strike Index (SI), which divides the foot into thirds from heel to toe. This is a standard method to classify foot strike in the lab, but I do agree with Daniel Lieberman who described his concerns about the ability to accurately classify forefoot strikes using SI:

“…strike index…uses the center of pressure at landing relative to maximum shoe length, with a RFS being less than 33%, a MFS between 34% and 66%, and a FFS as 67% or higher (4). This index, however, is arbitrary with respect to the foot’s anatomy. My observation is that the 4th and 5th metatarsal heads are often less than 67% of the foot’s length, leading one to classify FFS and MFS landings in the same category.”

Results

Foot strike patterns for the left foot at each speed were classified as follows:

Foot strike patterns for the right foot at each speed were classified as follows:

These results agree with expectations based on previous research in that some, but not all, of the runners shifted from a rearfoot strike to a mid or forefoot strike with increasing speed (variation once again!). The left-right asymmetry at the fastest speed is curious, not sure what to make of that. In my own Manchester marathon foot strike study I did find that “..asymmetrical runners tended to heel strike more often on the left side, forefoot or midfoot strike on the right side.” But, that was at a considerably slower pace than 6.2 m/s.

The authors also performed statistical analyses (a three-level linear regression for you stats folks) to test for a relationship between speed and strike index within individuals. They found a significant effect of speed on strike index (faster speed = increased strike index = contact further forward on the foot), with only 3.2m/s and 4.1m/s not being significantly different. This basically means that at the two slower speeds strike index remained pretty consistent, but once pace dropped to 5:15/mile initial contact moved forward on the foot, and then moved even further forward at the fastest speed.

One fascinating thing about the results is that the authors identified a group they referred to as transition runners. 37% of subjects shifted foot strike type once at a faster speed (mostly heel to midfoot), and a second group shifted twice as speed increased (heel—>midfoot—>forefoot). In contrast, 46% were heel strikers at all speeds, and 6% were midfoot strikers at all speeds. Again, there is variation among individuals in the way they alter stride with increasing speed. The authors point out that “These ‘transitional’ runners create the complex task of a shoe design that, both at low and high running speeds, is functionally adjusted for changes in IFCP.” Or, simply, that such gear shifting runners might be best served by choosing different shoes depending on the type of workout they plan to do.

One other fascinating result is that they found two subgroups of rearfoot strikers that could be distinguished based on the underfoot pressure patterns. One group (72% of rearfoot contacts) had “…a COP trajectory with the initial contact at the posterior lateral shoe sole side, after which the COP moves rapidly towards the midline of the shoe sole.” The pressure then moves forward and takes a bit longer to reach the forefoot. You might think of this as the typical heel-forefoot roll seen in many runners (I might call it a classic heel striking pattern).

In the other group (28% of rearfoot contacts), “initial contact was made in the rearfoot zone, immediately followed by a fast anterior COP movement along the lateral shoe margin into the midfoot zone, which was then followed by the COP moving medially in the midfoot zone.” The atypical heel striking group shifts pressure to the region under the metatarsals of the foot much faster than the typical heel strike.

The authors go so far as to propose founding “…the identification of the atypical IRFC as a distinct fourth IFCP” (forefoot, midfoot, and the two types of heel strike). Doing so would emphasize that all heel strikes are not the same, and perhaps more interestingly, might call into question studies that have lumped all heel strikers into a single group for comparative purposes. As a first step, the authors present data showing that contact time was longer in the typical rearfoot striking group than in all other foot strike classes (including atypical rearfoot strike), and that the atypical rearfoot strike group exhibited the highest vertical impact loading rate of any of the classes. 

Conclusions

I’d summarize the primary conclusions of this paper as follows:

1. Increasing running speed shifts the contact point on the foot forward. In some people this shift is significant enough that a change in discrete contact pattern is observed (e.g., heel to midfoot). Sometimes two discrete contact pattern shifts occur (heel—>midfoot—>forefoot). In some people there is no change in discrete contact pattern (e.g., they land on the heel at all speeds, but maybe slightly further forward on the heel when running faster). There is no single pattern applicable to all runners .

2. There are two types of heel strikers. One exhibits a slower heel-forefoot transition, which the authors term the “typical” heel strike. Overall contact time is longer in this group, but in a shoe with a cushioned heel the vertical loading rate is the same as in a midfoot or forefoot striker. The “atypical” heel strikers contact on the heel but pressure moves rapidly to the forefoot. Contact times is shorter than in a typical heel striker, but vertical loading rate is higher than in any of the other categories.

I’ll finish with some thoughts relating to the second conclusion.

I suspect strongly that my stride fits within this newly proposed atypical heel strike category, and further that this may be why I am very sensitive to firmness and amount of flare of the lateral portion of the sole of running shoes. Most of my shoe wear is a bit forward from the posterolateral corner of the heel (I used to chew that area up, not anymore), but not on the midfoot or forefoot (except maybe in very minimally cushioned shoes). Having run on a force-plate equipped treadmill I’ve been told my SI is a midfoot strike, but this did not utilize the more sensitive pressure pad method used here.

This study found that vertical loading rate was highest in the atypical heel strike group (to which I think I may belong). About this the authors write the following (my comments in parentheses):

• “When running with an IFFC or IMFC the impact of running is partially attenuated by an initial ankle dorsiflexion movement.” (i.e., the ankle + calf muscles are involved and reduce loading rate)
• “With a typical IRFC this is done by the cushioning properties of both the heel’s fat pad and shoe midsole.” (i.e., a cushioned heel reduces loading rate)
• “A possible explanation for the higher VILR associated with an atypical IRFC could be that when running with an atypical IRFC neither of these ‘strategies’ of impact reduction are fully used. Initial contact is made with the rearfoot, limiting the possible use of an ‘ankle-dorsiflexion strategy’ and the early first metatarsal contact and the fast anterior COP movement indicates the limited use of the cushioning properties of the heel partition.”

This is brilliant. Most shoes are designed to cushion a typical rearfoot strike starting near the back of the shoe. A forefoot striker relies less on cushion and more on the calf muscles to slow the landing. An atypical contact can’t make use of either of these strategies if the shoe is not designed for it.

I find that shoes with a soft heel and firm forefoot work best for me. A shoe with an overly firm or rigid heel does not work well for me at all – I might describe the ride on pavement as jarring. Examples of shoes like this include the Mizuno Sayonara and Saucony Ride 7.  I can make such shoes feel comfortable by forcing a more pronounced heel strike or by getting up on my forefoot, but that requires conscious effort. I would be very interested to compare my vertical load rate in a shoe like the Sayonara to a shoe like the New Balance 1400v2 or Newton Energy. I’m really curious if identifying these heel strike patterns could lead to better shoe recommendations for runners, and might explain why a shoe that works well for one heel striker might not work well for another.

As always, lots of additional work needs to be done! 

Over the past few days I’ve been reading my way through the June 2013 issue of Footwear Science (sure to be found on a newsstand near you!). The issue is a compilation of presentation abstracts from the annual meeting of the Footwear Biomechanics Group that was recently held in Brazil. To be honest, I eat this stuff up, and this is probably the first periodical I’ll have gone through cover-to-cover in a few years. There are a ton of interesting studies in the issue (I hope to write about several of them), and one that I found particularly fascinating was titled “Initial foot contact patterns during steady state shod running.”

In the study, a group from Belgium led by Bastiaan Breine set out to examine foot strike patterns among runners using a novel measuring device. What they did was place a pressure sensing plate on top of a force plate so that both underfoot pressure tracings and force application could be recorded simultaneously.

Traditionally, foot strikes have been classified either visually (point of first contact between foot/shoe and ground) or by using a method known as the Strike Index. With the Strike Index, footstrike is classified by the location of initial contact as determined by center of pressure tracings under the foot. Using the this method, initial contact (IC) under the rear one-third of the foot would be classified as a heel strike, IC under the middle one-third would be classified as a midfoot strike, and IC under the anterior one-third would be a forefoot strike (which in my opinion is problematic since this requires a very anteriorly placed initial contact to score a forefoot strike).

The authors of this study observe that although pressure tracings might be recorded at initial contact, the actual forces at work might be very small and functionally irrelevant. So, in addition to scoring foot strikes by location of initial contact as determined by pressure tracings, they decided to also score foot strikes based on the location of maximal impact loading rate (impact loading rate is the rate of force application and is typically expressed in units of body weights/second). Max loading rate is functionally meaningful in that higher max loading rates have been linked to increased risk of injuries like stress fractures.

So what did they find? Using Strike Index only they found that 45 out of 55 runners were rearfoot strikers and the remaining 10 were midfoot strikers (same pattern on both feet). However, when they used the location of the instant of maximal loading rate to classify foot strikes they found that:

1) On the left foot, 11 of the 45 heel strikers were actually midfoot loaders, and 1 midfoot striker was a forefoot loader.

2) On the right foot, 13 of the 45 heel strikers were actually midfoot loaders, and apparently 2 heel strikers were forefoot loaders.

Below is a reproduction of their figure showing what the underfoot pressure tracings for the various strike patterns look like:

What you’ll note from the above diagram is that the blue and red tracings both originate on the rear, outer portion of the heel indicating initial heel contact. However, things differ from that point on. The blue line moves quickly forward along the outer margin of the shoe and peak impact loading rate actually occurs under the midfoot. The red line veers inward a bit and peak loading rate is squarely in the center of the heel. So, although the initial contact pattern is similar (both are “heel strikers”), the actual loading pattern is very different. The authors feel that those exhibiting a pattern like the blue line should not be considered heel strikers. If the proportions in their sample are reflective of the frequency with which these patterns might be found in the broader running population, it might mean that as many as 25-33% of “heel strikers” don’t actually load much at all under their heels!

My personal interest in this study is that I’m pretty sure that my foot strike tracing would be in the blue-line category, or somewhere between blue and green. I’m a mild heel striker if you look at me on film in most shoes, but when I was running on the force treadmill at Saucony HQ I was told by biomechanist Spencer White that I loaded under the midfoot. This would also seem to explain to me why my wear patterns nowadays originate at outside of the heel and extend forward along the lateral edge, whereas I used to absolutely destroy just the back-most corner of my heels. I suspect when I went through my running form experimentation phase a few summers ago I shifted my tracing from red to blue, and in some shoes (and barefoot) to green. I’m beginning to also wonder if this might explain why I’m so sensitive to heel-forefoot drop in running shoes – given my mild heel strike it seems to not take very much additional material under the heel to start messing with my stride. It would be very interesting to take this group of pseudo-heel strikers and examine how their stride changes with varying shoe properties.

Perhaps the biggest issue that this study might bring up is that any other studies that have compared heel strikers to midfoot or forefoot strikers may not have actually been comparing what they thought they were comparing – it really depends on how the heel strike was classified. If it was done by video or by Strike Index alone there may have been some midfoot loaders in the heel strike group…

The same approach is applied to the running foot strike – we classify foot strikes as forefoot, midfoot, or heel, but the reality is that there is a huge amount of variation within each of these categories. For example, some forefoot strikers bring the heel down after contact, others don’t. The distance of the foot from the center of mass at initial contact varies. Joint angles vary.

I’ve long said that all heel strikes are not created equal. Some people land with the foot angled 45 degrees to the sky with a virtually locked knee, others touch down just slightly back toward the heel with a more or less vertical shin. There are lots of variants in between.

Below is a photo compilation of foot strike variation from slow motion video (300 fps) that I shot at the 2009 Manchester City Marathon. You can see variation from heel strike down to midfoot as you look from top to bottom (I trimmed off the forefoot strikers to reduce the image size) – all are at the first moment of foot contact with the ground:

What you can see above is a lot of variation in foot dorsiflexion at contact, shin orientation, knee angles, and so on.

What we’ve lacked until now is a good sense of how the different flavors of heel strike differ in terms of the way forces experience during running. I was reading through a summary of studies to be presented at the upcoming ACSM meeting on Steve Magness’ blog (great post, check it out here) and came across a study titled “Influence of Different Rear Foot Strike Strategies on Impact Force During Running.” This study was conducted by John Mercer and Sarah Horsch at UNLV – it is currently only an abstract, so one must keep that in mind, it has not been published in a journal yet.

What Mercer and Horsch did was instruct runners to run over a force plate with either “an obvious heel strike (OHS) or subtle heel strike (SHS).” Instantaneously forced stride change studies like this need to be interpreted with caution, but what they found was that at a constant speed the runners exhibited an impact force in both conditions about 85% of the time, but that impact force was significantly higher in the obvious heel strike condition (1.68±0.54 BW for OHS vs. 1.55±0.44 BW for SHS; p<0.05). They conclude that “The unique observation of this study was that impact force was influenced by foot strike patterns that would both have been considered rear foot strike patterns.”

The significance here is that it shows that impact force can vary significantly even within a single foot strike category. You might look at the heel striking data and say “Well, forefoot strikers usually have no impact, so that must be the way to go.” Not necessarily. In a study where runners were told to forefoot strike without letting the heel come down, their tibial acceleration was actually higher than when they landed on their heels (study PDF here). Jay Dicharry often makes the point that in his clinic he sees forefoot runners with high impact, and heel strikers with low impact. And, another Abstract from the ACSM meeting reports no difference in self-reported injury rates between confirmed heel-striking and non-heel-striking US Army soldiers. This contrasts with an earlier finding that forefoot-striking Harvard runners were less prone to injury.

So even among forefoot strikers there is variation, and we have no consistent and conclusive evidence that one foot strike type is better than another from an injury prevention standpoint. What’s more, we really have no idea at what magnitude impact force becomes a problem. In fact impact force magnitude has not reliably been linked to injury as far as I’m aware. Rather, impact loading rate, which is the speed at which the force is applied, has been linked to stress fracture risk. Mercer an Horsch did not report on loading rates in their abstract. It might actually be the case that some impact is a good thing for stimulating bone strength via remodeling.

So, the point I’m trying to make here is that saying “heel striking is bad” makes little sense since foot strike categories encompass a lot of variation. Some kinds of heel striking might be bad, other kinds might be just fine. You could be a forefoot striker and be exposing your tibia to more shock than if you were heel striking. There’s more to the running stride than simply which part of the foot first contacts the ground, and this is why I’ve moved away from focusing on foot strike except in certain very specific cases (e.g., I think a forefoot strike might help runners suffering from anterior compartment syndrome or chronic anterior shin splints).

As always, things are more complicated than a one size fits all prescription. Each individual is a bit different and needs to be handled accordingly.

(If you’re interested in a drier take on foot strike by me, here’s an article I wrote for Lower Extremity Review)

1. Traditional trainers with a large heel

2. Track flats

3. Barefoot

As reported on Science Daily:

“The researchers found that shoe type “dramatically” altered running biomechanics in the adolescent runners. When wearing cushioned heel trainers, the athletes landed on their heel 69.8 percent of the time at all speeds. With the track flats, the heel was the first point of contact less than 35 percent of the time; and when barefoot, less than 30 percent of the time. Shoes with cushioned heels promote a heel-strike running pattern, whereas runners with track flats and barefoot had a forefoot or mid-foot strike pattern.”

This study is of interest because it looks at adolescents (no info provided on exact ages), and it seemingly demonstrates that type of footwear can have an impact on how the adolescent foot contacts the ground. I’m actually surprised that patterns in the track flats were so similar to barefoot as my observations of adult runners in Vibram Fivefingers indicate that approximately 50% still heel strike on asphalt (this observation is based on analysis of video footage the 2011 NYC Barefoot Run), and this makes me wonder if maybe things change as we age (perhaps our form gets more ingrained and hard to change).

A sample size of 12 is very small, which is a concern when it comes to making comparisons, and hopefully they will add more subjects before the study goes through the publication process. The article also mentions something about performance, but doesn’t provide any data that specifically addresses performance differences between the conditions.

I don’t have much more to say since this is all second-hand from another site, but it seems like we are being constantly bombarded by studies that are making the foot strike issue seem even more complex than previously thought!

For some additional foot strike study coverage, see this article by Amby Burfoot on a study that looked at how running surface influences foot strike type.

Also, check out the current issue of Outside Magazine which contains an article that discusses the pitched battle between the minimal and traditional shoe camps – it’s sure to anger both sides!

A group of researchers had set up a study to look at foot strike patterns and stride characteristics of runners at several points in the race, and the post provides the text of an email summarizing their results (the blogger, Ian Sharman, had run in the race). In a nutshell, here’s what they found:

1. 80-90% of runners were heel strikers at all four locations where they analyzed foot strike patterns (10.2 miles, 56.1 miles, 56.4 miles, 100.1 miles). This is in-line with data I have published on marathon runners.

2. Excluding the downhill analysis point, stride length was longest at the earliest examination point (10.2 miles).

3. No relationship was observed between foot strike pattern and performance (I found the same among marathoners).

Making the likely assumption that all of these runners were shod, and that most were wearing somewhat cushioned shoes, these results don’t surprise me and are in line with my own findings on foot strike patterns among shod runners in a road marathon (I also did a bit of filming at the VT100 this year and would guess the results would have been similar there). It may turn out that in some of the locations heel striking in trail ultramarathoners was a bit less common than in road marathoners (I observed 88.9% heel strikers at the 10K point of a road marathon), but we’d need the raw numbers to address that (not just a range).

It’s also important to note that neither this nor my study examined variation among heel strikers – there is a great deal of variety in the amount of dorsiflexion at ground contact among heel strikers, and lower limb orientation is also highly variable – heel striking isn’t really a category so much as a spectrum that encompasses a wide range of variability.

What I like about studies like this is that they provide data on what runners in the “real world” do outside of an artificial lab environment. This study provides further evidence that when distance runners wear shoes, even those who run huge mileage on trails, they tend to land on their heels most of the time. The results don’t provide insight on whether heel striking is good or bad, and if anything they suggest that at least from a performance standpoint it doesn’t much matter how your foot contacts the ground. All of this contributes to my belief that as long as it’s not too extreme, it’s OK to be a heel striker!