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Foot Strike

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Foot Strike is the way the foot lands while running, and the best Foot Strike pattern is both controversial and unclear. It seems likely that other factors beyond the simplistic classifications of forefoot, midfoot or rear Foot Strike are important, especially [[Cadence]] and [[Overstriding]]. My suggestion is to focus on optimizing [[Cadence]] and reducing [[Overstriding]] rather than directly trying to change your Foot Strike pattern.
=Foot Strike classifications=
While running, the way the foot lands is often classified as ForeFoot Fore Foot Strike (FFS), MidFoot Mid Foot Strike (MFS) or Rear Foot Strike (RFS), though there is variation in these definitions<ref name="Daoud-2012"/>.
* In FFS, the forefoot lands first and can either be followed by the heel landing later or by the heel remaining above the ground.
* Generally MFS has the outside edge of the middle of the foot landing first, but some definitions include the locations from just in front of the heel to just behind the forefoot. After this edge lands, the foot flattens and both forefoot and heel are in contact with the ground.
* RFS is where the heel of the foot lands first, followed by the forefoot. This pattern can vary from a landing on the extreme back of the heel with the forefoot elevated through to a nearly MFS landing where the heel touches down just before the forefoot. In some cases the bulk of the landing forces are absorbed by the heel, where in other cases the bulk of the landing force is absorbed by the forefoot. RFS is often termed Heel Strike.
There is also a suggestion that the point of maximum loading should be used to determine foot strike instead of the initial contact point. This is because some runners may make only light contact with the heel, sometimes referred to as "proprioceptive heel strike".
==Strike Index==
A more precise approach to Foot Strike is to measure the position of the center of pressure of the initial contact of the foot<ref name="AltmanDavis2012"/>. This strike index is then this position as a percentage of the length of the foot.
While Strike Index is a good measure of Foot Strike, it requires sophisticated equipment to measure the pressure the foot makes as it lands. A simpler approach is to look at the angle of the foot as it touches down, called Foot Strike Angle (FSA). It is practical to evaluate FSA with [[High Speed Video Analysis]]. A study compared the two approaches and found there was a good correlation between Strike Index and FSA<ref name="AltmanDavis2012"/>. Note in the graph below the wide range of strike indexes for RFS, from nearly 0 (the extreme back of the heel) to close to the 33% mark, which is well in front of the heel bone.
[[File:Foot Strike Angle.jpg|none|thumb|500px|A graph of Foot Strikes, with each point showing Strike Index against Foot Strike Angle<ref name="AltmanDavis2012"/>. A Foot Strike Angle of 0 degrees means the foot is level with the ground on first contact. The color coding indicates the visual categorization of the Foot Strike.]]
=Measuring Evaluating Your Foot Strike=It seems intuitively obvious that a runner will know how their foot lands. However, it seems that runners are actually relatively poor at evaluating their foot strike. A study of 60 runners found that only 70% knew their foot strike<ref name="GossLewek2015"/>, while another study found that only 44% of recreational runners and 57% of collegiate cross-country runners knew their foot strike<ref name="Bade-2016"/>. This is in line with a study of 87 runners that showed only 69% were correct in their identification of their foot strike<ref name="Goss-2012"/>. Personally, I suspect that the extremes of foot strike are relatively easy to distinguish. A forefoot runner whose heel never touches the ground is pretty obviously a forefoot runner. Likewise, many runners are quite obviously extreme heel strikers. Between those extremes that becomes far more uncertainty, and a more objective measure becomes valuable. I think there are a few options for evaluating your Foot Strike:* High speed video can be quite effective, and the cameras are becoming far more accessible. The iPhone 6 and later will do 240 frames per second, which is enough to give a good evaluation of your foot strike.* There are a number of [[Running Sensors]] that will detect your Foot Strike. I've found [[RunScribe]] make Footpods that can measure to be quite accurate when compared with high-speed video, though I've also had promising results from [[Foot StrikeSHFT]]. * A common approach has been to look at the wear pattern on the sole of your running shoes. However, I've come to believe that this is extremely misleading as well as the movement wear on the bottom of your shoe has a far more to do with abrasion than it does pressure. For instance, I make initial contact with the ground with my heel, and when descending steeply, I tend to scrape the extreme edge of the heel. So, if you look at the outsole of my shoes you'd conclude that I am an extreme heel strike runner, but that's not an accurate conclusion.* Perhaps the cheapest, easiest, and most useful approach however is to look at how the cushioning of your running shoes degrades. I've found consistently that my running shoes become compressed under the ball of my foot after , which indicates this is the area of greatest loading. I have relatively little compression over the rest of the shoe, including no real compression under the heal, which suggests that I am a "proprioceptive heel strike" runner. I've found that I can see this degradation of the shoes cushioning most easily in the removable insole.[[File:Insole Wear and Foot Strike.jpg|none|thumb|300px|This is an insole where I've marked the area of compression, which is under the ball of my foot. It's hard to photograph the compression, but the it's quite obvious to the touch.]]
=Foot Strike science=
The optimum Foot Strike is unclear given the available evidence.
* Two studies showed no difference in [[Running Economy]] between FFS and RFS<ref name="Perl-2012"/><ref name="Cunningham-2010"/>.
* A study compared the [[Running Economy]] of habitually FFS and RFS runners when running both FFS and RFS<ref name="Gruber-2013"/>. The runners were relatively fast, with a typical training pace of 7:15 min/mile and running 28 miles/week. The FFS group actually consisted of both FFS and MFS runners, and there were 14 MFS and only 4 FFS runners in the FFS group, with 19 in the RFS group. Each group was tested at slow (9:00 min/mile), medium (7:40 min/mile) and fast (6:45 min/mile) paces with both FFS and RFS. The results were:
** Using their habitual footstrike foot strike the FFS were very slightly more efficient at medium and fast speeds, but this was not statistically significant. (Estimating from the graphs, this is ~1 mg/kg/min.)
** At the slow and medium speed the FFS group using either FFS or RFS and the RFS group running RFS used the same oxygen, but the RFS group running FFS was less efficient. (So if you're a RFS runner, you're likely to be less efficient when running FFS until you get used to it, at which point you'll be back to your prior efficiency.)
** At the fast speed both groups were less efficient with a FFS.
* Runners tend to shift from RFS to MFS or FFS as they run faster, with runners becoming predominantly FFS at faster than 4:30 min/mile and predominantly RFS as 5:15 min/mile or slower<ref name="KellerWeisberger1996"/><ref name="NiggBahlsen1987"/>.
* One study found that habitually barefoot endurance runners are predominantly FFS, with some MFS but fewer RFS, though the pace evaluated was quite fast (5:15-4:30 min/mile)<ref name="LiebermanVenkadesan2010"/>. Another study showed that at endurance running speeds, habitually barefoot runners were 83% RFS, 17% MFS and none were FFS<ref name="LuciaHatala2013"/>. At faster speeds, this changed, and at around 5 min/mile pace there were 43% RFS, 43% MFS and 14% FFS, then above 4 min/mile the breakdown changed again to 40% RFS, 60% MFS, and no FFS<ref name="LuciaHatala2013"/>.
* The Foot Strike patterns of runners were evaluated at an elite half marathon in Japan, and 74.9% were RFS, 23.7% were MFS and 1.4% were FFS<ref name="Hasegawa-2007"/>. For the fastest 50 runners the Foot Strikes were 62.0% RFS, 36.0% MFS, and 2.0% FFS. This does not indicate what the best Foot Strike is, but does give some indicate of what Foot Strike is used by the best runners.
* A study trained 20 runners in the pose method that uses a FFS along with other modifications to the [[Running Form]] including a higher [[Cadence]]<ref name="Arendse-2004"/>. The pose method resulted is less vertical movement, which may be the result of the FFS, the higher cadence, or both. The pose method reduced the eccentric load on the knee, but increased it in the ankle compared with MFS and RFS. This suggests that the pose method may help reduce the stress on the knee, but at the cost of additional stress on the calf and Achilles tendon.
* The evaluation of 52 competitive middle and long distance collegiate athletes found that RFS runners were 2.6 times more likely to have a mild repetitive strain injury and 2.4 times more likely to have a moderate repetitive strain injury than FFS<ref name="Daoud-2012"/>.
* Analysis of 240 female RFS runners found that runners were injured over a two year period had higher impact forces than those that were not injured<ref name="Davis-2010"/>. No analysis of other Foot Strike patterns was performed.
* Most<ref name="LiebermanVenkadesan2010"/><ref name="Arendse-2004"/><ref name="Cavanagh-1980"/>, but not all<ref name="Laughton-2003"/> studies show that RFS have higher impact forces than FFS. Note that impact force tends to increase with pace<ref name="LuciaHatala2013"/><ref name="KellerWeisberger1996"/>, and impact is reduced with a higher [[Cadence]]<ref name="Heiderscheit-2011"/><ref name="Mercer-2003"/><ref name="Hamill-1995"/>.
* One study found that some runners made initial contact with the heal (RFS), but it was midfoot when the foot became loaded<ref name="BreineMalcolm2013"/>. About a quarter of runners that made initial contact at the rear had the maximum loading occur midfoot. This raises a question around the classification of foot strike; should we consider the initial contact point or the point of maximum loading?
* There have been a few studies looking at foot strike patterns in races. This research does not indicate the optimal Foot Strike, but it gives some idea of prevalence.
** The Foot Strike patterns of 415 runners were evaluated at an elite half marathon in Japan, and 74.9% were RFS, 23.7% were MFS and 1.4% were FFS<ref name="Hasegawa-2007"/>. For the fastest 50 runners the Foot Strikes were 62.0% RFS, 36.0% MFS, and 2.0% FFS.
** Analysis of 286 runners at the 10K point of the 2009 Manchester (US) marathon showed 87.8% were RFS, 3.1% MFS, and 1.4% FFS (7.7% were asymmetric)<ref name="LarsonHiggins2011"/>. At the 32K point the mixture had changed, with more RFS (93%) and midfoot (3.5%). No runners were FFS at the 32K point, though 3.5% were asymmetric. This study showed no relationship between pace and foot strike, but the runners in this race did not have the faster elite runners.
** A study of 1991 runners at 8Km mark of the 2011 Milwaukee Marathon showed that 93.7% were RFS, but faster runners were more likely to be FFS<ref name="Kasmer-2013"/>.
** In a 50K trail race 85% were RFS at the 8KM point<ref name="KasmerLiu2013"/>.
** RFS Runners in a 100 mile trail race made up 80% @ 16K, 89% @ 90K, and 84% @ finish<ref name="Kasmer-2014"/>. The non-RFS runners had more muscle damage (CK levels) than RFS runners at the latter two stages.
* There is almost no research into the effect of changing Foot Strike patterns. There is a report of two runners that had stress fractures in their foot after changing from RFS to MFS, but they also changed to FiveFingers as well<ref name="Giuliani-2011"/> .
* I found not no studies that looked at strike pattern and cadence to evaluate the interactions between these two factors. It seems possible to me that RFS is more common with runners who have a lower cadence, and that many of the negative implications of RFS are actually due to a low cadence. However, this is pure supposition at this point.[[File:Footstrike forces.png|none|thumb|500px|The forces of barefoot forefoot and rear Foot Strikes<ref name="LiebermanVenkadesan2010"/>. Note the initial spike in force for the rear Foot Strike, which is occurs at a faster rate (steeper line) than in foreFoot forefoot Strikers. ]]
=Limitations of the available science=
There are a number of limitations to the available science that should be noted.
<ref name="GossLewek2015">Donald L. Goss, Michael Lewek, Bing Yu, William B. Ware, Deydre S. Teyhen, Michael T. Gross, Lower Extremity Biomechanics and Self-Reported Foot-Strike Patterns Among Runners in Traditional and Minimalist Shoes, Journal of Athletic Training, volume 50, issue 6, 2015, pages 603–611, ISSN [ 1062-6050], doi [ 10.4085/1062-6050.49.6.06]</ref>
<ref name="NiggBahlsen1987">B.M. Nigg, H.A. Bahlsen, S.M. Luethi, S. Stokes, The influence of running velocity and midsole hardness on external impact forces in heel-toe running, Journal of Biomechanics, volume 20, issue 10, 1987, pages 951–959, ISSN [ 00219290], doi [ 10.1016/0021-9290(87)90324-1]</ref>
<ref name="KellerWeisberger1996">TS Keller, AM Weisberger, JL Ray, SS Hasan, RG Shiavi, DM Spengler, Relationship between vertical ground reaction force and speed during walking, slow jogging, and running, Clinical Biomechanics, volume 11, issue 5, 1996, pages 253–259, ISSN [ 02680033], doi [ 10.1016/0268-0033(95)00068-2]</ref>
<ref name="Giuliani-2011"> J. Giuliani, B. Masini, C. Alitz, BD. Owens, Barefoot-simulating footwear associated with metatarsal stress injury in 2 runners., Orthopedics, volume 34, issue 7, pages e320-3, Jul 2011, doi [ 10.3928/01477447-20110526-25], PMID [ 21717998]</ref>
<ref name="Gruber-2013">AH. Gruber, BR. Umberger, B. Braun, J. Hamill, Economy and rate of carbohydrate oxidation during running with rearfoot and foreFoot Strike patterns., J Appl Physiol, May 2013, doi [ 10.1152/japplphysiol.01437.2012], PMID [ 23681915]</ref>
<ref name="BreineMalcolm2013">Bastiaan Breine, Philippe Malcolm, Edward C. Frederick, Dirk DeClercq, Initial foot contact patterns during steady state shod running, Footwear Science, volume 5, issue sup1, 2013, pages S81–S82, ISSN [ 1942-4280], doi [ 10.1080/19424280.2013.799570]</ref>
<ref name="LarsonHiggins2011">Peter Larson, Erin Higgins, Justin Kaminski, Tamara Decker, Janine Preble, Daniela Lyons, Kevin McIntyre, Adam Normile, Foot strike patterns of recreational and sub-elite runners in a long-distance road race, Journal of Sports Sciences, volume 29, issue 15, 2011, pages 1665–1673, ISSN [ 0264-0414], doi [ 10.1080/02640414.2011.610347]</ref>
<ref name="Kasmer-2013">ME. Kasmer, XC. Liu, KG. Roberts, JM. Valadao, Foot-strike pattern and performance in a marathon., Int J Sports Physiol Perform, volume 8, issue 3, pages 286-92, May 2013, PMID [ 23006790]</ref>
<ref name="KasmerLiu2013">Mark E. Kasmer, Xue-cheng Liu, Kyle G. Roberts, Jason M. Valadao, The relationship of foot strike pattern, shoe type, and performance in a 50-km trail race, Journal of Strength and Conditioning Research, 2013, pages 1, ISSN [ 1064-8011], doi [ 10.1519/JSC.0b013e3182a20ed4]</ref>
<ref name="Kasmer-2014">ME. Kasmer, JJ. Wren, MD. Hoffman, Foot strike pattern and gait changes during a 161-km ultramarathon., J Strength Cond Res, volume 28, issue 5, pages 1343-50, May 2014, doi [ 10.1519/JSC.0000000000000282], PMID [ 24149763]</ref>
<ref name="Bade-2016">MB. Bade, K. Aaron, TG. McPoil, ACCURACY OF SELF-REPORTED FOOT STRIKE PATTERN IN INTERCOLLEGIATE AND RECREATIONAL RUNNERS DURING SHOD RUNNING., Int J Sports Phys Ther, volume 11, issue 3, pages 350-5, Jun 2016, PMID [ 27274421]</ref>
<ref name="Goss-2012">DL. Goss, MT. Gross, Relationships among self-reported shoe type, footstrike pattern, and injury incidence., US Army Med Dep J, pages 25-30, PMID [ 23007933]</ref>

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