From Fellrnr.com, Running tips
no edit summary
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 Strike (FFS), MidFoot 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.
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 Foot Strike=[[RunScribe]] make Footpods that can measure [[ Foot Strike]], as well as the movement of the foot after Foot Strike.
=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 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"/>.
* 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"/>.
* 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 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 Strikers. ]]
=Limitations of the available science=
There are a number of limitations to the available science that should be noted.
<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 [http://www.worldcat.org/issn/00219290 00219290], doi [http://dx.doi.org/10.1016/0021-9290(87)90324-1 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 [http://www.worldcat.org/issn/02680033 02680033], doi [http://dx.doi.org/10.1016/0268-0033(95)00068-2 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 [http://dx.doi.org/10.3928/01477447-20110526-25 10.3928/01477447-20110526-25], PMID [http://www.ncbi.nlm.nih.gov/pubmed/21717998 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 [http://dx.doi.org/10.1152/japplphysiol.01437.2012 10.1152/japplphysiol.01437.2012], PMID [http://www.ncbi.nlm.nih.gov/pubmed/23681915 23681915]</ref>