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[[File:The myth of arches and shoe types.jpg|none|thumb|500px|This image probably originated with the "The Running Shoe Book"<ref name="runningshoebook"/>.]]
=Impact & Injury=
The relationship between impact and injury is less clear than one might suppose. It has been suggested that while excessive impact can result in injury, lower levels of impact are the [[Supercompensation| stimulus for improved strength and performance]]<ref name="Hreljac-2004"/><ref name="Nigg-1997"/> (See . [[SupercompensationFile:Footstrike Impact.png|none|thumb|300px|Footstrike impact metrics.]]There are various ways of evaluating impact, and not all studies use the same metric or are not clear on which metric is used. * Active Peak is the greatest force or acceleration detected during foot strike. * Peak Impact is the greatest force seen during the initial landing.* Loading Rate is how rapidly the forces build up and can either be averaged over parts of this section of the graph or an instantaneous peak can be used. (That would be peak rate of change of impact, not peak impact.) * In addition, impact is sometimes normalized to body weight. There is evidence that the impact seen in running does not result in injury:
* Impact forces are not related to injury rates in epidemiologic studies<ref name="Nigg-1997"/>.
* The A study of three runners found that impact forces at the heel are not related to the forces at common injury sites such as the ankle, Achilles, or knee.<ref name="Scott-1990"/>.
* A study of 131 runners showed that injury rates were highest in those with the lowest impact levels<ref name="Bahlsen1988"/>.
* The impact forces of 210 notice runners were evaluated for the symmetry of their impact forces and their subsequent injury rates<ref name="Bredeweg-2013"/>. The injured runners had greater symmetry than the uninjured, and there was no difference between the impact forces on the injured side compared with the uninjured side. (However, see the results on the companion study below).
* Another study of the 210 notice runners mentioned above found that Loading Rate was related to the injury rate of male (but not female) runners, though the female runners had a higher Loading Rate than the males<ref name="Bredeweg-2013-2"/>. However, when time spend running was considered, the relationship between Loading Rate and injury disappeared.
* A review of the available research in 2007 found no relationship between impact and injury rates<ref name="van Gent-2007"/>.
* A review of the available research in 1992 found no evidence that injury rates were related to hard or soft surfaces<ref name="van Mechelen-1992"/>. (Of course, you can't assume too much about the impact rates from the surface.)
However, there is also some evidence of a relationship between higher impact and injury:
* A study that compared 20 runners who had never been injured with 20 runners that had prior injuries found that peak impact rates were higher in those that had been previously been injured<ref name="Hreljac-2000"/>.
* A study of five female runners who had previously had a stress fracture showed higher peak impact forces than subjects without stress fractures<ref name="GrimstonNigg1994"/>.
* A meta-analysis of 13 studies found that while there was no correlation between rates of stress fracture and impact, there was a relationship for the rate of loading<ref name="Zadpoor-2011"/>.
* A study of 20 female runners with a previous tibial stress fracture showed they had high rates of impact, but not greater peak impact than matched controls<ref name="Milner-2006"/>.
It seems possible that Loading Rate is related to stress fractures, but it seems unlikely that impact is related to other injury types. (It's estimated that stress fractures account for 0.7% to 20% of clinical injuries<ref name="Fredericson-2006"/>.)
=Pronation, Arch Height & Injury=
The evidence for the correlation between pronation and injury is rather mixed. This is compounded by the use of arch height as a proxy for pronation.
* A meta-analysis of 5 studies showed that motion control shoes can reduce pronation when compared with barefoot or simple cushioned shoes, but only by about 2%<ref name="Cheung-2011"/>.
* A study compared a Motion Control shoe (MC) with a Cushioned shoe (CT) with 20 high arched (HA) and 20 low arched (LA) runners<ref name="Butler-2006"/>. The motion control shoe was the New Balance 1122 and the cushioned shoe was the New Balance 1022. The change in pronation (in degrees) is shown below.
{| class="wikitable"
!
! CT
* A study of 10 male runners compared "normal" running shoes with and without a 10 degree orthotic wedge showed the orthotic reduced pronation by 6.7 degrees<ref name="PerryLafortune1995"/>.
* A study of 25 inexperienced, over-pronating female runners looked at differences in pronation in motion control and cushioned shoes, before and after a 1.5 Km (~1 mile) run<ref name="CheungNg2008"/>. These runners only averaged 2.1 Km (1.3 miles) per week and had pronation of more than 6 degrees. The Motion Control shoes reduced pronation by 3.3 degrees before the run, but after just this short run the Motion Control shoes made no difference. The motion control shoes were Adidas Supernova Control and the cushioned shoes were Adidas Supernova Cushion. The results are shown below:
{| class="wikitable"
!
! CT
** Runners in the traditional shoes had a lower incident of injury (#4/32 runners) than the partially minimalist (#12/32 runner) or minimalist (#7/35 runners).
** The only statistically significant difference in pain scores for the shoe conditions was in shin and calf pain, with runners in the partially minimalist and minimalist shoes having greater pain scores than the traditional shoes. However, the underlying data is a little more complex. Below are shown the pain scores before and after the trial for each shoe type. As you can see, the pain goes up by the greatest percentage for the partially minimalist, but this rise is from a much lower initial level. The absolute level of pain is lowest for the partially minimalist condition, making this study tricky to interpret.
{| class="wikitable"
! Time
! Traditional
<ref name="Boling-2009">MC. Boling, DA. Padua, SW. Marshall, K. Guskiewicz, S. Pyne, A. Beutler, A prospective investigation of biomechanical risk factors for patellofemoral pain syndrome: the Joint Undertaking to Monitor and Prevent ACL Injury (JUMP-ACL) cohort., Am J Sports Med, volume 37, issue 11, pages 2108-16, Nov 2009, doi [http://dx.doi.org/10.1177/0363546509337934 10.1177/0363546509337934], PMID [http://www.ncbi.nlm.nih.gov/pubmed/19797162 19797162]</ref>
<ref name="Nigg-1997">Nigg, Benno M. "Impact forces in running." Current Opinion in Orthopaedics 8.6 (1997): 43-47.</ref>
<ref name="Bahlsen1988">author Alexander Bahlsen, The Etiology of Running Injuries: A Longitudinal, Prospective Study, 1988</ref>
<ref name="Johnston-2003">CA. Johnston, JE. Taunton, DR. Lloyd-Smith, DC. McKenzie, Preventing running injuries. Practical approach for family doctors., Can Fam Physician, volume 49, pages 1101-9, Sep 2003, PMID [http://www.ncbi.nlm.nih.gov/pubmed/14526862 14526862]</ref>
<ref name="Heil1992">Barbara Heil, Running Shoe Design and Selection Related to Lower Limb Biomechanics, Physiotherapy, volume 78, issue 6, 1992, pages 406–412, ISSN [http://www.worldcat.org/issn/00319406 00319406], doi [http://dx.doi.org/10.1016/S0031-9406(10)61525-8 10.1016/S0031-9406(10)61525-8]</ref>
<ref name="Frederick 1985">Frederick , E. C. The energy cost of load carriage on the feet during running. In: Winter, D.A., R. W. Norman, R. P. Wells, K. C. Hayes, and A. E. Patla (Editors), Biomechanics IX-B Human Kinetics Publ., Champaign, IL, pp.295-300, 1985</ref>
<ref name="DibSmith2005">Mansour Y Dib, Jay Smith, Kathie A Bernhardt, Kenton R Kaufman, Kevin A Miles, Effect of Environmental Temperature on Shock Absorption Properties of Running Shoes, Clinical Journal of Sport Medicine, volume 15, issue 3, 2005, pages 172–176, ISSN [http://www.worldcat.org/issn/1050-642X 1050-642X], doi [http://dx.doi.org/10.1097/01.jsm.0000165348.32767.32 10.1097/01.jsm.0000165348.32767.32]</ref>
<ref name="Milner-2006">CE. Milner, R. Ferber, CD. Pollard, J. Hamill, IS. Davis, Biomechanical factors associated with tibial stress fracture in female runners., Med Sci Sports Exerc, volume 38, issue 2, pages 323-8, Feb 2006, doi [http://dx.doi.org/10.1249/01.mss.0000183477.75808.92 10.1249/01.mss.0000183477.75808.92], PMID [http://www.ncbi.nlm.nih.gov/pubmed/16531902 16531902]</ref>
<ref name="van Mechelen-1992">W. van Mechelen, Running injuries. A review of the epidemiological literature., Sports Med, volume 14, issue 5, pages 320-35, Nov 1992, PMID [http://www.ncbi.nlm.nih.gov/pubmed/1439399 1439399]</ref>
<ref name="Bredeweg-2013-2">SW. Bredeweg, B. Kluitenberg, B. Bessem, I. Buist, Differences in kinetic variables between injured and noninjured novice runners: a prospective cohort study., J Sci Med Sport, volume 16, issue 3, pages 205-10, May 2013, doi [http://dx.doi.org/10.1016/j.jsams.2012.08.002 10.1016/j.jsams.2012.08.002], PMID [http://www.ncbi.nlm.nih.gov/pubmed/22921763 22921763]</ref>
<ref name="Bredeweg-2013">SW. Bredeweg, I. Buist, B. Kluitenberg, Differences in kinetic asymmetry between injured and noninjured novice runners: a prospective cohort study., Gait Posture, volume 38, issue 4, pages 847-52, Sep 2013, doi [http://dx.doi.org/10.1016/j.gaitpost.2013.04.014 10.1016/j.gaitpost.2013.04.014], PMID [http://www.ncbi.nlm.nih.gov/pubmed/23673088 23673088]</ref>
<ref name="Fredericson-2006">M. Fredericson, F. Jennings, C. Beaulieu, GO. Matheson, Stress fractures in athletes., Top Magn Reson Imaging, volume 17, issue 5, pages 309-25, Oct 2006, doi [http://dx.doi.org/10.1097/RMR.0b013e3180421c8c 10.1097/RMR.0b013e3180421c8c], PMID [http://www.ncbi.nlm.nih.gov/pubmed/17414993 17414993]</ref>
<references/>
[[Category:Science]]
[[Category:Injury]]
