A Litrature Review on Running Shoes and Biomechanics.doc

8/14/2019 A Litrature Review on Running Shoes and Biomechanics.doc

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Title Page

Title: A Literature Review on Running Shoes and Biomechanics

Author: David Ramocki DPT, CSCS

Address: 7 !emlock Ave" #arwick, R$ %&''(

)*mail: DaveRamo+hotmail"com

Phone : -%*./*%0&.

$nstitution: 1one 2$nde3endent4

#ord Count: &,('

So5tware 6sed: icroso5t #ord &%%.

Acknowledgements: I would like to acknowledge Professor Ken Holt of Boston University for

his guidance in writing this paper. I would also like to acknowledge Marathon Sports Boston!for providing the shoes which appear in the figures of this paper.


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Contents

"#stract $

%. Introduction $

$. &esearch li'itations ((. )o'ponents of a shoe *

*. &unning shoe research +*.% Midsole hardness +

*.%.% &earfoot 'otion ,*.%.$ -orce peaks and loading rates

*.%.( Muscle /M0 and 'eta#olic cost 1

*.$ Midsole 'aterial 2*.( 3arus4valgus 'idsole %5

*.* 6orsional rigidity and longitudinal 'idsole stiffness %%

*.+ Insoles %$*., Heel counter %$

*. Heel flare %(

*.1 Sole height %**.2 )urved last %**.%5 )o'#ined varia#les %+

*.%% Shoe properties and foot structure %,

+. 7iscussion %+.% Philosophies of running shoe prescription %1

+.$ -uture research $5

,. )onclusion $%

A8stract

6here e8ist 'any different theories regarding how different running shoe properties will

affect one9s #io'echanics and how running shoes should #e prescri#ed for runners to eli'inate

inury and enhance perfor'ance. "lthough there have #een nu'erous a'ounts of researchwhich have e8a'ined running shoes and their effect on a runner9s #io'echanics; the evidence is

still lacking on what running shoe characteristics should #e prescri#ed for a given runner. In

order to esta#lish what has #een e8a'ined in running shoe research; a full literature review will#e presented which includes running shoe varia#les such as: 'idsole duro'etry; 'idsole

angulations; heel flare; heel counter; 'idsole 'aterial; 'idsole torsional rigidity; insoles; sole

height; co'#ined varia#les; and the interaction of shoe properties with foot structure. )o''ontheories and ideas for how to prescri#e a running shoe as well as li'itations to these approaches

will #e discussed. )urrent research li'itations and ideas for the direction of future research willalso #e discussed; and an overview of the construction of running shoes will #e descri#ed.

" $ntroduction

5= seek 'edical care?%@?%@. It has also #een reported that A > of all runners sustain an inurywhich reCuires a change in practice and4or perfor'ance ?$@. "lthough there 'ay #e 'any risk

$


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entire lower e8tre'ity is 'oving. Solely relying on the su#talar oint 'ay #e 'isleading. -or

e8a'ple; if a runner has a certain foot structure such as a rearfoot varus!; he4she 'ay try to

co'pensate for the pronatory forces upon i'pact #y keeping the hip internally rotated andsu#talar oint supinated throughout the stance phase of gait. Internal hip rotation is considered a

nor'al coupling with su#talar pronation; yet in this case the internal hip rotation is coupled with

su#talar supination. Solely relying on su#talar oint 'otion; especially for short periods of ti'e;'ay not #e a relia#le indicator of how the hip; knee; and 'idtarsal oints are 'oving.

related inuries; etc. In reality; the 'aority of people running are not free of

pain; do not have Fnor'alG lower e8tre'ity architecture; and have had 'any running>relatedpro#le's in the past. 6herefore; caution should #e used when atte'pting to generalie the results

of these studies to the average runner.

." Com3onents o5 a Shoe

In order to #etter understand the research which has #een conducted on running shoes; itis necessary to #eco'e acCuainted with the anato'y of a running shoe. 6his is also i'portant if

we are to 'anipulate certain shoe varia#les in an atte'pt to co'ple'ent a runner9s anato'ical

lower e8tre'ity structure. Please refer to -igure % while reading the description of eachco'ponent of the shoe.

Dast6he construction of a shoe #egins with the last. 6he last is the #asic fra'e of the shoe

upon which all other co'ponents are placed. 6he last 'ay #e #oard; slip; or co'#ination>lasted.

If the 'aterial of the upper part of the shoe is sewn directly onto the top of the 'idsole withnothing covering it; then the shoe is said to #e slip>lasted. If there is a #oard overlying this

stitching; then the shoe is said to #e #oard>lasted ?%$@. If the shoe has a #oard overlying the

stitching on the posterior portion of the 'idsole; then it is said to #e co'#ination lasted. 6his

can #e visualied #y re'oving the insole and e8a'ining the inside portion of the shoe. " #oard>lasted shoe 'akes a shoe 'ore rigid; which is #elieved to reduce the a'ounts of pronation; yet

*


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this has not #een confir'ed with scientific research. " running shoe9s last 'ay also #e straight;

curved; or se'i>curved. 6his curvature designates the adduction of the forefoot portion of the

shoe. " shoe with a curved last will have the forefoot portion adducted relative to the rearfootportion; whereas a straight last will have little4no forefoot adduction?%(@. )urved lasts tend to #e

slip>lasted; and if a shoe is #oard>lasted; it usually has a straight last?%*@.

Upper

6he upper portion of the shoe refers to the covering of the superior portion of the shoe?%[email protected] is usually 'ade of nylon; although other 'aterials such as leather 'ay #e attached to it?,@. 6he

va'p is the portion of the upper covering of the shoe which e8tends fro' the toes to the 'id>arch area. 6he re'ainder of the upper fro' the 'id>arch to the posterior aspect of the shoe is

called the Cuarter. 6he toe #o8 is the area in the front of the shoe which contains the toes?%(@. 6he

area where the upper portion of the shoe 'eets the 'idsole is called the featherline?,@. 6hetongue covers the dorsu' of the foot and provides protection fro' the laces ?%+@. 6he posterior

surface of the upper has a heel counter with the "chilles pad fle8 notch! located directly

superior to this. 6he heel counter is a 'olded piece of plastic or polyurethane which is 'oldedand placed in the heel area to supposedly contain the calcaneus and prevent unwanted

'ove'ent. 6he heel counter 'ay e8tend #eyond the heel area to the postero>'edial aspect of

the shoe?%,@. 6he covering of the heel counter is referred to as fo8ing. cell foa'!. 6his is what 'akes for the light>weight; high shock>a#sor#ing

Cualities of the /3". 6he disadvantage is that with repetitive use; the gas #u##les slowly

#eco'e e8pelled and the /3" e8hi#its decreased shock>a#sor#ing a#ility?%$@. 6he 'idsole can#e co'pressed into 'any different densities which can create soft or hard shoes. Many shoe

'anufacturing co'panies have incorporated other 'aterials into the 'idsole in the atte'pts to

#etter a#sor# shock; such as the airsoles found in Jike shoe; gel in "sics shoes; etc. 6he insolesockliner! of a shoe is the re'ova#le lining of cushioned 'aterial which is pri'arily for co'fort

and friction>reduction. 6he insole is usually 'ade fro' neoprene foa'; polyethylene foa'; or

viscoelastic 'aterials?%*@.

-" Running Shoe Research

-" idsole !ardness

Much of the research that has #een perfor'ed on running shoes has e8a'ined the effects

of varying the 'idsole hardness duro'etry!. 6he duro'eter of a shoe is deter'ined through theuse of an i'pactor device which involves dropping an o#ect of known 'ass fro' a

predeter'ined height to calculate the resistance of the 'aterial against penetration. -ro' this

test; the 'idsole is given a Shore value fro' % to %55; with the harder 'idsole receiving a higherscore. 6he 'aority of running shoes have 'idsole densities which have a Shore value which

ranges #etween *5 5.

+


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Many shoe co'panies have incorporated a dual density 'idsole a 'idsole of $ different

densities!; which usually has a higher Shore value on the 'edial aspect of the posterior 'idsole

See -igure $!.


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research lends credi#ility to the idea that hyperpronators should #e prescri#ed a F'otion controlG

shoe which has a hard 'idsole. However; a 'ain pro#le' with this research is that there see's

to #e an interaction effect #etween an individual9s structure and the running shoe. Because arunner9s structure likely dictates how his4her gait will adapt to a shoe; it is i'portant that future

research e8a'ine which aspects of a runner9s structure are responsi#le for such gait changes.

"nother pro#le' with such findings is that it is not known which varia#les of pronation are 'oststrongly correlated to running inuries. If pronation velocity is 'ore of a risk factor for inury

than 'a8i'al a'ount or ti'ing of pronation; then this 'ay indicate that harder running shoes arenot advantageous. If total a'ount of pronation is 'ore i'portant in ter's of running inuries;

then softer shoes would #e disadvantageous. If ti'ing of pronation is a significant risk factor;then 'ore research is needed which e8a'ines the pronation angle at ter'inal stance4preswing; as

none of the afore'entioned studies have investigated this varia#le.

*.%.$ -orce Peaks and Doading &ates

-orce peaks during the contact phase of running have #een studied using force platfor'swhich provide such infor'ation as contact force also referred to as initial force peak or passive

force peak! and propulsive force also referred to as second force peak!; as well as rate of

loading?$5@. 6his infor'ation reveals how 'uch force each aspect of the foot is #earing. Suchinfor'ation can provide insight into a#nor'al loading patterns which are #elieved to #e relatedto running inuries. "dditionally; knee fle8ion velocity and a'ount have also #een studied

usually in co'#ination with force plate studies! with the assu'ption that an increased

a'ount4rate of ti#ial advance'ent over the foot is correlated with an increased contact force4rate."n interesting finding across several of these studies was that the 'a8i'al vertical

contact peak force was not statistically different #etween soft and hard 'idsole shoes and even

less for the hard shoes!. In one study?$5@; it was found that when su#ects engaged in runningacross a force platfor' in harder shoes; there was a trend for decreased i'pact force peaks;

although this was not statistically significant. It was also found that while the ti'e of occurrence

for #oth the i'pact force peak and 'a8i'al loading rate decreased when switching fro' the

shoes of a (+ to *+ Shore duro'etry value; they re'ained the sa'e for the Shore $+ to (+duro'etry values. Milani and Hennig?%@si'ilarly used a force platfor' to show that su#ects

wearing harder shoes e8hi#ited a decreased i'pact force peak yet a shorter ti'e to reach this

value; although this study did not provide specific infor'ation regarding the shoes or thestatistical tests. " si'ilar study?%2@found decreased initial vertical i'pact peaks with a higher

loading rate when su#ects ran in harder shoes; although the relia#ility and validity of this study

are Cuestiona#le. )larke et al.?$(@also found a longer ti'e to peak vertical i'pact peak in thesofter shoes; #ut no differences in a#solute force 'agnitudes #etween the soft and hard shoes;

although the vertical propulsive force was significantly higher in the softer shoes.

In a study #y right et al.?$*@; a 'odel of a hu'an leg was created using kine'aticinfor'ation fro' a sa'ple of 2 'ales in the atte'pts to esta#lish whether or not the kine'atic

adaptations to loading forces could #e perfor'ed passively. It was found that their resultscoincided with other authors; in that there was no difference #etween peak i'pact forces

#etween hard and soft shoe groups; and that the rate of loading was higher for the harder shoes.Hennig et al.?$+@investigated the i'pact force varia#les as well as the perception of hardness for

differing 'idsole hardnesses while ground running using sensory transducers and a force

platfor'; and again it was found that the first vertical force peak was lower for the hard shoes.However; the peak pressures in the heel were higher and the forefoot #ore 'ore weight with the

hard shoes.

6he results of these studies suggest that the i'pact force peaks are si'ilar #etween shoeswith hard and soft 'idsoles. However; the loading rates appear to #e less for softer running

shoes. 6hese studies suggest that either the hardness of the 'idsole does not influence i'pact


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force peaks; or that the foot 'ust #e 'aking kine'atic adaptations to decrease the i'pact force

when running in shoes with a hard 'idsole. 6he results of these studies suggest that if initial

i'pact is a factor for running inuries; then there will not #e a significant difference #etweenshoes of differing 'idsoles. However; if loading rates are a factor for inury; then a softer

'idsole which is co''only prescri#ed! would #e #eneficial.

It is very possi#le that since shoes of increasing 'idsole hardness see' to e8hi#it lessi'pact force; there 'ust #e kine'atic changes during gait to help decrease the kinetic forces at

i'pact. Initial pronation 'ay #e a solution to decreasing the initial i'pact forces; as severalstudies have shown that running in harder shoes leads to a faster initial pronation?%1; %2@.

"nother proposed 'echanis' is that the knee fle8ion will #e greater or occur faster withthe harder running shoes. However; results of testing knee fle8ion velocity and a'ount have not

revealed this to #e the case.


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duro'etry values. It was found that #etween shoes; 'uscles; and su#ects; the /M0 intensities

changed #efore heel contact with the ground. 6he authors reported that this change in /M0

intensity through different lower e8tre'ity 'uscles supports the idea that 'uscles are tuned tocontract differently when the 'idsole hardness is varied. 6hus #y 'anipulating the 'idsole

density; one 'ay alter the need for certain 'uscle use #efore contact with the ground. However;

this study relied on a sa'ple of , su#ects; and there was no consistent pattern of 'uscle use#etween shoe conditions suggesting that 'uscle use for differing 'idsoles is su#ect specific!.

6he results of these studies suggest that 'anipulating 'idsole duro'etry alone does notresult in differences in 'eta#olic cost. However; if increasing the duro'etry of a shoe leads to

increased shoe weight; than this can certainly lead to an increased 'eta#olic cost. It isinteresting that 'uscle use did change when the 'idsole hardness was 'anipulated. If a

consistent pattern can #e shown regarding which 'uscles #eco'e overworked with differing

'idsole duro'eters; then this could help to decrease 'any running inuries. However; the'uscle responses to differing shoes are likely to #e su#ect specific.

-"& idsole aterial

6here have #een several studies conducted which have e8a'ined the effects of changing

the 'idsole 'aterial on a runner9s gait. 6he 'aority of the investigators integrated an air>pocket into the 'idsole; and used o8ygen consu'ption as an outco'e 'easure. "s statedearlier; the 'idsole is usually co'posed of ethylene vinyl acetate /3"!.

In a study #y -alsetti et al.?$2@; #lood 'easure'ents were taken fro' su#ects #efore and

after a %+ 'ile run to e8a'ine the effects of running in a fir'>soled versus an air>soled runningshoe. 6he post>run #lood values for the air>soled group showed increases in he'atocrit; 'ean

cellular volu'e; and 'ean cellular he'oglo#in. 6his suggests that the air>soles resulted in less

red #lood cell da'age. "dditionally; the white #lood cell count was twice as high in the fir'>soled shoes as co'pared to the air>sole group; suggesting that the fir'>sole condition had 'ore

stress placed upon the' during the run. However; the weight of each shoe was not provided #y

the authors; and the shoes pro#a#ly had other design differences other than the 'idsole 'aterial.

In a si'ilar study?(5@

; the o8ygen cost of running was e8a'ined in conventional shoesversus running in shoes with an encapsulated air>cushioned 'idsole. It was found that the

o8ygen consu'ption was $.,= less on average for the air>soled group; and no su#ects had lower

o8ygen consu'ption levels for the conventional shoe. It was interesting to note that the shoeswith the air>soles actually weighed 'ore than the fir'>soled shoes. e#ster et al.?(%@found

contrasting results in that there were no differences in 3tension strain values or rates. In another study?((@shockattenuation characteristics were assessed using ti#ial acceleration para'eters #etween su#ects

perfor'ing fil'ed>tread'ill running in different shoes. 6he * shoe conditions were: a! 7ou#le

density /3" with cantilever outsole #! 7ou#le density /3" c! "ir>filled cha'#ers within adou#le density /3" d! /ncapsulated dou#le density /3". 6he investigators found no

2


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differences for peak ti#ial acceleration or ti'e to peak ti#ial acceleration across shoe conditions;

and the knee fle8ion4e8tension differences were not found to #e significantly different.

6he results fro' these studies suggest that air>filled 'idsoles are not effective inreducing lower e8tre'ity shock when running. Unfortunately; no other kine'atic data was

recorded; so no results on a'ount and rate of pronation when running in air>soled shoes can #e

revealed."side fro' research which has e8a'ined air>filled 'idsoles; there were several studies

which e8a'ined altering the 'idsole 'aterial of a running shoe. Morgan et al.?(*@designed ashoe which had a car#on fi#er 'aterial which was 'olded to for' a leaf spring within the

'idfoot of the 'idsole and an elastic strap was configured which attached fro' the calcaneal>area of the shoe and wrapped around the distal leg near the 'alleoli. 6his shoe was co'pared

with a conventional shoe with FstandardG 'idsole and outsole 'aterials. dyna'ic shoe!; and the third a single unit /3" foa'. /ach runner perfor'ed'ultiple trials of running across a force platfor' while wearing reflective skin 'arkers.

"lthough there were su#tle differences in loading rate and 'agnitude; there did not appear to #e

a significant difference when co'paring the control shoe single unit /3" foa'! to either of the*>colu'ned 'idsole shoes; and little can #e generalied fro' this study.

Jigg et al.?(,@e8a'ined the effects of changing the heel 'aterial within a shoe. 6he two

shoes which were used differed only in the heel9s 'idsole 'aterial which was either hard andvisco>elastic; or softer and less visco>elastic. Both lower e8tre'ity 'uscle /M0 and o8ygen

consu'ption were used for outco'e 'easures for su#ects perfor'ing tread'ill running. 6here

were no group differences #etween the two shoes for either of the two outco'e 'easures; yet

there were 'any individualied differences #etween the two shoes.

-". 9arus9algus idsole

"nother varia#le that has #een studied with running shoes has to do with the angulation

of the 'idsole. Several studies have e8a'ined the effects of varying the valgus and varus angle

of the 'idsole configuration. It should #e noted that only studies that e8a'ined actual shoe'odifications were included in this review; as there are other studies which have reviewed the

effects of differing orthoses9 angulations on gait.

In a study #y Holden and )avanagh?(@; the free 'o'ent of ground reaction M9! was'easured #y having su#ects run over a force platfor' when wearing a shoe with either a

neutral; varus; or valgus 'idsole varus 'idsole was raised 'edially; the valgus 'idsole wasraised laterally!. It was found that the 'a8i'u' free 'o'ent of ground reaction M9! and net

angular i'pulse increased when switching fro' varus to neutral to valgus 'idsoles. However;while M9 was consistent #etween each su#ect and shoe condition; there were differences in

M9 #etween su#ects of the sa'e shoe condition. 6his suggests that su#ects of differing lower

e8tre'ity structure will respond differently to differing shoe properties.In a study #y Milani et al. ?(1@; su#ects with internal shoe>pressure 'onitors were fil'ed

while running across a force platfor' wearing shoes with either a neutral; 1 degree varus; or 1

degree valgus 'idsole. It was found that the 'a8i'al pronation and pronation velocity was lessfor the varus shoes and higher for the valgus shoes. -or the valgus 'idsole condition; increased

lateral rearfoot loads and first ray contri#ution was found; and the takeoff angle was found to #e

%5


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(.1 degrees of pronation on average. )onversely; the varus 'idsole condition e8hi#ited

increased 'edial 'idfoot loads and fifth 'etatarsal contri#ution #ut no statistically significant

differences in takeoff supination angles when co'pared to the neutral 'idsole condition!. 6hissuggests that the valgus 'idsole created increased pronation values which led to an increased

'edial forefoot loading response.

In another study?(2@; su#ects perfor'ed tread'ill running while wearing a shoe with aneutral; %5 degree varus; or %5 degree valgus 'idsole. 6he results showed that the a'ount of

pronation increased when 'oving fro' the varus to neutral to valgus shoes; which is consistentwith the afore'entioned studies. Brauner et al.?*5@confir'ed these results in showing that

running shoes with progressive increases in varus angulation led to decreases in total pronationa'ount and 'a8i'al pronation velocity.

6he results of these studies provide evidence that shoes with a varus 'idsole create less

total pronation values; whereas valgus 'idsoles create higher pronation values.


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stiffness 'easures control shoe: %1 J''; stiff shoe: (1 J''; stiffest shoe: *+ J''! were

used for this e8peri'ent. It was found that there were no significant differences in /M0 or

kine'atic varia#les. 6he


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shoes with 'ore fle8i#le heel counters; the 'ove'ent #etween the heel counter and calcaneus

was not significantly different.

6hese results suggest that heel counter rigidity is not effective in controlling rearfoot'otion; as a rigid heel counter would #e necessary to prevent calcaneal 'ove'ent; yet the rigid

heel counter in this study was not shown to contain the calcaneus. It should #e noted that the

three shoes used for this study had differing properties and that heel counter rigidity was notcontrolled.

-"7 !eel lateral portion of the outsole See -igure 2!. 6he

lateral heel flare of a shoe has #een studied #ecause it is #elieved that with an increased lateralheel flare; there e8ists a greater lever ar' #etween where the shoe contacts the ground and thesu#talar oint?*@. Because of this; it is #elieved that a larger lateral heel flare will result in higher

pronation values due to the larger 'o'ent ar' of the pronatory torCue. "lthough there have not

#een any studies perfor'ed with regards to 'edial heel flare; there are shoes availa#le whichprovide this See -igure *!. -ro' a 'echanical standpoint; it would 'ake sense that a s'all

lateral heel flare and a larger 'edial heel flare would help to co'#at e8cessive pronation.

6he studies which have varied the lateral heel flare of a shoe see' to show differingresults with regards to its effects on pronation and other kine'atic para'eters. In one study?*1@;

su#ects ran across a force platfor' with ( differing lateral heel flares $+ degrees; neutral; and

rounded!. /ach su#ect had #one pin 'arkers as well as shoe 'arkers. It was found that there

were no effects #etween conditions on ti#io>calcaneal rotation or shoe eversion; and inversion#etween the flare conditions was not statistically different for each su#ect. However; there were

significantly different touchdown inversion values for each flare condition #etween differing

su#ects. 6he #one pins showed there to #e different eversion velocities for differing flareconditions with no consistent pattern #oth a'ongst and #etween su#ects. 6he authors concluded

that the eversion para'eter 'easures appeared to #e highly su#ect specific.


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increase with increasing heel flare. "s is the case with 'any other shoe varia#les; 'ore research

is needed. "lso; there 'ay very well #e a significant interaction effect #etween heel flare and

foot type; as was seen with the study #y Stacoff et al.?*1@. Also see results of the effects of lateralheel flare in the Combined Variables section.

-"' Sole !eight

Nerosch et al.?*2@e8a'ined the effects of su#ects perfor'ing tread'ill running in a shoewith a negative sole versus a conventional shoe. " negative sole i'plies that the construction of

the 'idsole is done in such a way that the toes are placed higher than the heel within the shoe.6he negative>soled shoe had a sole height of $+ '' at the toes and %5 '' at the heel; as

opposed to the control shoe which had a sole height of %5 '' at the toes and $5 '' at the heel.

Su#ects were assessed with regards to fil' kine'atics; and also anterior ti#ial intraco'part'entpressures. 6he ti#ial co'part'ent pressure was 'onitored using a co'part'ental pressure

'onitor with a slit catheter and lancet needle. It was found that su#ects wearing the negative>

soled shoe had an average of 1 degrees less dorsifle8ion at heel strike. 6he su#ects with thecontrol shoe had a 'ean plantar fle8ion of %, degrees 5.% seconds! following heel strike as

opposed to the negative>soled group which had a 'ean of , degrees 5.%5 seconds!. 6he control

shoe group had significantly higher peak co'part'ental pressures as co'pared with thenegative>soled shoe.

6his study suggests that the use of a negative>soled shoe 'ay help to decrease the

intraco'part'ental pressures in the anterior ti#ial co'part'ent while running; and hence

decease anterior Fshin splintsG for certain runners. 6he authors of this study #elieve that this isdue to the decreased a'ount of eccentric dorsifle8ion which is reCuired #y the ti#ialis anterior

'uscle upon initial contact. However; 'ore studies will need to #e perfor'ed to provide 'ore

support for this concept; as this was the only study which e8a'ined this aspect of a running shoe.&einsch'idt and Jigg?+5@e8a'ined the effects of varying the heel height of a running

shoe to esta#lish if shoes with a higher heel would decrease the plantar>fle8ion 'o'ent

throughout the stance phase of gait; and hence decrease the a'ount of tension on the "chilles

tendon for runners who are prone to "chilles tendonitis. -or each of the five different shoeconditions which were used; the forefoot sole had a height of 5.1 c'; whereas the heel had a

height of $.%; $.*; $.; (.5; and (.( c' for each of the respective shoe conditions. It was found

that heel height did not have a significant effect on 'agnitude or ti'e of occurrence for'a8i'u' plantar> fle8ion 'o'ents. 6he results of this study suggest that altering heel height

does not affect the a'ount of stress which is placed through the "chilles tendon when running;

yet 'ore studies will need to #e conducted to confir' these results.

-"/ Curved Last

6here has yet to #e any pu#lished research to date that has co'pared the effects of

running in a straight versus a curved last. 6he curvature of a last can #e seen #y viewing theinferior aspect of the shoe See -igure +!. It is a co''on #elief that shoes with a curved last

should #e prescri#ed for high>arched runners with little pronation range of 'otion; and straightlasts should #e prescri#ed for hyperpronators.

Several authors have speculated that a curved last will create 'ore pronation due to the

lack of 'edial arch support?+%; %(; %$; +$@. -rederick?+%@reports that he has conducted unpu#lishedresearch which shows that straighter lasts have 'ore 'edial support and a wider heel #ase; and

reduce 'a8i'u' pronation. )learly; research needs to #e pu#lished which e8a'ines the

differences #etween last configuration #efore anything can #e concluded.

%*


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-"% Com8ined 9aria8les

6here are several studies in which the authors chose to investigate the effects of

'anipulating several varia#les of a shoe to see how the gait para'eters would change.However; do to the co'ple8ity of researching several varia#les at once; interpretation and a

generaliation of an overall 'essage regarding the effects of 'anipulating shoe varia#les

#eco'es difficult.In a study #y Jigg and Bahlsen?+(@; 'idsole hardness and lateral heel flare were varied to

'easure the pronation4supination and i'pact forces of su#ects running across a force plate.

6hree shoes of differing 'idsole constructions %! single density 'idsole of Shore (+

duro'etry; $! 5 duro'etry 'idsole 'ounted atop a Shore *5 duro'etry; (! Shore (+ 'aterialon the 'edial 'idsole and Shore $+ on the lateral 'idsole! were used; and three different heel

flares %, degrees; neutral; and rounded! were added to each of these three conditions. It was

found that for the %, degree flare; the $ndshoe showed high initial shoe and oint pronationwhereas the third shoe showed low initial oint pronation. 6he neutral and rounded heel flared

conditions did not show significant differences for each of the three shoe conditions. It was also

found that for all shoe conditions; having a rounded flare led to a decreased inversion angle attouchdown; whereas for the %, degree flare condition; shoes % and $ showed the highest initial

inversion angles at touchdown. )onsistent with past research; shoe ( softest 'idsole! had the

highest vertical i'pact peak and rate across all flare conditions.

6his study suggests that when a shoe has a large heel flare; a soft lateral 'idsole helps todecrease the pronation; and that shoes with a neutral or rounded heel flare 'ay not #e affected #y

varying 'idsole hardness with regards to the a'ount of initial pronation. 6his study also

showed there to #e 'uch individual difference #etween shoe>type.In a study #y )larke et al.?+*@; (, pairs of shoes were constructed with the co'#inations of

three different varia#les: Heel flare neutral; %+ degrees; and (5 degrees!; 'idsole duro'etry $+;

(+; *+ Shore values!; and heel height %5 '' 'idsole; %5 '' 'idsole with %5 '' heel lift; %5

'' sole with $5 '' heel lift; and $5 '' sole with %5 '' heel lift!. 6he 'a8i'al pronation;total rearfoot; and ti'e until the 'a8i'u' velocity of pronation 'otion increased with the softer

shoe conditions; although there were no significant differences #etween the 'ediu' and hardduro'eter shoes for the 'a8i'al pronation and total rearfoot 'otion. It was also found that

shoes with the neutral heel flare had significantly greater 'a8i'al pronation and total rearfoot

'otion as co'pared with the other two flare groups; which differs fro' the results #y Jigg et al.?+(@. 6he neutral flare condition was also found to have a later ti'e until 'a8i'al velocity ofpronation as co'pared to the (5 degree flare condition. It was shown that as heel height

increased; the ti'e until 'a8i'al velocity of pronation increased as well. 6he authors also

stated that shoes with a soft 'idsole and neutral heel flare showed the greatest a'ount of'a8i'u' pronation as opposed to the shoes with hard 'idsole and (5 degree heel flare showed

the least.6hese two studies see' to have varying results. 6he study #y Jigg and Bahlsen?+(@see's

to support the idea that shoes with a large heel flare and soft 'idsole lead to less pronation; yet

no infor'ation is provided across flare conditions. 6he study #y )larke et al.?+*@supports the

idea that the large flare and hard 'idsole lead to less pronation. Jigg and Bahlsen?+(@also

showed that neutral4rounded heel flares are unaffected #y 'idsole hardness with regards torearfoot para'eters; whereas )larke et al.?+*@show that the shoe with the neutral heel flare led to

higher 'a8i'al pronation when co'#ined with a softer 'idsole.

6hese inconsistent results could very well #e due to each individual9s structuraldifferences. 6herefore; nothing can #e concluded at this ti'e fro' these studies; and 'ore

%+


16/34

research will need to #e perfor'ed #efore any conclusions can #e 'ade. However; fro' a

#io'echanical standpoint; it would 'ake sense that a large lateral heel flare with a hard 'idsole

would increase the resistance ar' of the torCue and create higher pronatory forces. 6his 'ay nothave #een revealed in these studies due to the potentially high variation in each su#ect9s foot

structure.

-" Shoe Pro3erties and


17/34

shoes #oth pre and post>fatigued states. It was also found that when running in the 'otion

control shoes; the rearfoot 'otion did not significantly change fro' pre to post>fatigue. hen

running in the neutral shoe; the rearfoot 'otion increased #y ,.+= fro' pre to post>fatiguedstates. 6his study differs fro' that of Butler et al.?+@in that this study showed an increase in

rearfoot 'otion when running in softer shoes whereas the previous study did not show a

significant difference in rearfoot 'otion when running in the cushion trainer shoe. )heung andJg?+2@perfor'ed a si'ilar study where a group of $+ runners with O , degrees of dyna'ic

pronation where tested with a 'otion control shoe "didas Supernova )ontrol! and a neutralshoe "didas Supernova )ushion! to esta#lish how well these shoes controlled pronation during

a %.+ k' tread'ill run. It was found that the runners wearing the neutral shoe had significantlyhigher a'ounts of pronation throughout the tread'ill run; whereas the runners wearing the

'otion control shoe did not show significant differences in their total pronation angles.

"dditionally; there were higher peak force values over the 'edial 'idfoot and first 'etatarsalheads throughout the run when running in the neutral shoes.

In a study #y egener et al?,5@; runners with a cavus foot>type where used to e8a'ine the

effectiveness of cushioned running shoes "sics 0el Ji'#us , and Brooks 0lycerine ( wereco'pared to the 7unlop 3olley control shoe! on plantar pressures at the whole foot; rearfoot;

'idfoot; and forefoot while perfor'ing over>ground running. 6he in>shoe Jovel Pedar>Q was

used to record plantar pressures. 6he -oot Posture Inde8 was used to deter'ine whichparticipants had a cavus foot>type. -or peak pressure 'easure'ents; the cushioned shoes led tosignificantly decreased peak pressure for the whole foot as well as for the rear4'id4fore foot

when co'pared with the control shoe. 6here was also a significant decrease in pressure ti'e

integrals when co'paring the cushioned shoes to the control; indicating a 'ore gradual loadingwhen running in the cushioned shoes. Interestingly; the force values for the cushioned running

shoes were higher at the 'idfoot and lower at the forefoot as co'pared to the control shoe. 6his

likely indicates that the cushioned shoes acted to spread the forces out over the entire foot;whereas the control shoe kept the contact forces consistent with the foot structure i.e. over the

rearfoot and forefoot!. 6he authors of this study also found decreased plantar pressure values in

the rearfoot when running in the "sics 0el Ji'#us ,; and decreased plantar pressure values in

the forefoot when running in the Brooks 0lycerine (. 6his 'ay #e significant when prescri#ingrunning shoes for runners with different foot>strike patterns i.e. rearfoot; 'idfoot; or forefoot>

strike pattern!; or for runners who develop pain and4or stress fractures in different areas of the

foot.6he results of these studies are generally in agree'ent with the co''on prescription

ideas which involve prescri#ing hard 'idsole F'otion controlG shoes to those who pronate

e8cessively; and prescri#ing soft 'idsole FcushionG shoes to those who have a cavus foot andhypopronate.

0"% Discussion

"lthough there has clearly #een 'uch research conducted in the real' of running shoes;there have not #een 'any studies which have looked at 'atching a runner9s 'echanics to a

specific running shoe. However; the trend has 'oved towards the categoriation of runners #yeither their arch type and4or dyna'ic gait presentation; and deter'ining how the different groups

of runners react to differing shoe properties.

6he research has given us so'e insight into 'atching a runner with a pair of runningshoes. 6he 'ain varia#les which appear to have an effect on a runner9s gait appear to involve

'idsole duro'etry and varus4valgus 'idsole angulations. Specifically; shoes with a harder

'idsole; varus 'idsole; and of the 'otion control category appear to li'it total pronation values;whereas shoes with a softer 'idsole; valgus 'idsole; and of the cushioned category appear to

increase total pronation values. In order to now understand how a running shoe prescription can

%


18/34

#e 'ade; an overview of co''on philosophies will #e e8a'ined. 6he philosophies regarding

running shoe prescription which will #e e8a'ined are those of running shoe store e'ployees

which will #e ter'ed the 0eneralist viewpoint!; the #io'echanical view which will #e #rokendown into su#talar>neutral #io'echanists Kine'atic viewpoint! and non su#talar> neutral

#io'echanists Kinetic viewpoint!.

0" Philoso3hies o5 running shoe 3rescri3tion

0eneralist 3iewpoint

6he foundation of this philosophy is that a runner is categoried as a hyperpronatoroverpronator!; neutral runner; or hypopronator supinator or under>pronator! and prescri#ed a

running shoe depending into which category a runner falls. 6here are several factors which leads

to this classification. " generalist will look at your arch height in non weight>#earing and then inweight#earing to esta#lish how 'uch arch collapse is present i.e. are you standing with a

pronated stance; a neutral stance; or a high>arched stance!. 6he generalist will also have the

runner run for a short distance to esta#lish whether or not that runner hyperpronates; is neutral; orsupinates.

If a runner is found to have a low arch in weight#earing and hyperpronates; he4she is

prescri#ed a 'otion control shoe which has a straight last and hard 'idsole. If the runner has anor'al arch in weight#earing and pronates #ut not e8cessively; he4she is prescri#ed a sta#ilityshoe which will have a se'i>curved last and 'ediu' duro'etry 'idsole. Dastly; if the runner

has a high arch in weight#earing and supinates throughout the gait cycle; he4she is prescri#ed a

cushion shoe which has a curved last and soft 'idsole configuration. Knapik et al.?,%@e8a'inedthis philosophy with 'ilitary recruits; #ut there were 'any confounding varia#les which

disallows any conclusions fro' #eing 'ade.

6here are several key li'itations4criticis's of this philosophy. 6he #iggest li'itation isthat pronation is the varia#le which is treated instead of what is causing the pronation. It is

#elieved #y 'ost #io'echanists that certain foot structures are what lead to different gait patterns

see Kinetic viewpoint for ela#oration on this topic!; and there can #e different foot structures

which can lead to such gait patterns as hyperpronation or late pronation. 6reating allhyperpronators with the sa'e running shoe 'ay not #e appropriate. -or e8a'ple; a runner 'ay

e8hi#it a significantly pronated foot due to the intrinsic factor of a co'pensated forefoot varus;

or fro' an e8trinsic source such as fro' co8a valga which has led to a co'pensated genu varu';which will then lead to a varus attitude of the lower leg and foot towards the ground forcing the

foot into a pronated position. )onsistent with the li'itation to this philosophy is the reliance on

standing arch height. 6here 'ay #e runners who stand in a neutral position giving theappearance of a 'id>high arch! who have a co'pensated rearfoot varus defor'ity. 6his foot

structure will likely lead to hyperpronation and4or late pronation which is difficult to o#serve

dyna'ically; as a runner with this foot>type is already significantly pronated when the calcaneusis perpendicular with the distal %4( of the leg in stance.

6he second li'itation is that the generalist is forced to rely on watching a runner run for avery short distance; and 'uch like the li'itation to the running shoe research; this 'ay not #e the

runner9s true gait pattern. 6his #rings us to the third 'ain criticis' of this philosophy; which isthat ti'ing of the pronation is not e8a'ined only a'ount of pronation!. It is very co''on for a

runner to have a rearfoot or forefoot varus defor'ity See -igure ,! which 'ay lead to s'all

a'ounts of pronation very late into the gait cycle. 6his late pronation has the potential ofstressing the passive plantar fascia; spring liga'ent; I6 #and; etc! and dyna'ic ti#ialis anterior;

ti#ialis posterior; fle8or hallucis longus! 'echanis's of resupination. "dditionally; this late

pronation is difficult to o#serve and 'ay appear as supination to an untrained eye.

Kine'atic 3iewpoint

%1


19/34

6he key co'ponent to this philosophy is that a runner9s varus4valgus angulation of the

rearfoot and forefoot are what deter'ine how a runner9s gait pattern will e'erge. 6he

angulations of the rearfoot and forefoot are found #y placing the runner in a prone position on aplinth with his4her feet hanging off of the plinth. 6he e8a'iner9s hands palpate the talus over the

antero>'edial and anterolateral aspect of the talo>navicular oint; and the foot is inverted and

everted until the talus is dee'ed to #e neither adducted nor a#ducted See -igure !. 6his isknown as the su#talar>neutral position of the foot. hile #eing held in the su#talar>neutral

position; the runner9s varus4valgus angulations of the rearfoot and forefoot are deter'ined #y thee8a'iner; and the runner is then placed in the weight#earing position of resting stance to

esta#lish any co'pensations of the lower e8tre'ity. 6his position is #elieved to #e i'portant asthis #io'echanical theory ascertains that the foot will function 'ost efficiently when this

position of the foot is achieved during ter'inal stance. neutral

position does not take into account how the foot is striking the ground; and hence is not takinginto account the kinetic forces which are likely to dictate how the lower e8tre'ity will undergo

it9s loading response pattern.

Kinetic 3iewpoint

6he critical co'ponent of this philosophy is that the gait pattern which will e'erge for a

given runner co'es a#out #ecause of the kinetic forces which are created #y the angulations of

the foot when it first strikes the running surface?,$@

. Because #io'echanists who adhere to thistheory are concerned with the kinetic forces of the foot upon i'pact; they are not concerned with

e8a'ining the foot in it9s su#talar>neutral position. 6he e8a'iners who follow this philosophy

will place the runner in the prone position with his4her feet over the edge of the plinth; and havethe runner hold his4her feet in 5 to %5 degrees of dorsifle8ion as this is the position the foot will

#e in when it strikes the ground!. 'edial aspect of the shoe. Because neither of these running shoe

%2


20/34

characteristics is currently availa#le; then this runner would have to settle for a 'otion control

shoe with a hard 'idsole or #e prescri#ed an orthosis.

6he 'ain li'itation to this philosophy is that atte'pting to esta#lish e8actly how the footwill contact the ground and understanding how 'uch each oint of the lower e8tre'ity is

contri#uting to the way the foot strikes the ground is difficult. 6rying to o#ectively esta#lish the

a'ount of hip anteversion4retroversion; ti#ial varu'; rearfoot4forfoot varus; 'idtarsal 'o#ility;first ray position; etc. and trying to predict how these varia#les will relate to the position of the

lower e8tre'ity when it 'akes contact with the ground is a difficult task. "dditionally; slowerrunners will tend to #e rearfoot strikers and will likely achieve full foot co'pensation when the

foot is closer to %5 degrees of plantarfle8ion.

Prescription 7ecision

ith several different philosophies and little supportive evidence to each one; how doesone decide how to prescri#e the proper running shoeE Ironically; #ecause the only true

differences in running shoes which are on the 'arket today involve choosing #etween soft

cushion!; 'ediu' sta#ility!; or hard 'otion control! 'idsoles; the decision for prescription#eco'es very si'ilar regardless of which philosophy is used when 'aking a prescription. "fter

all; the 'aority of differences #etween 'ost running shoes today have 'ore to do with aesthetic

appeal than they do 'echanical properties. However; there will #e so'e differences inprescription #etween these different philosophies.

6he key feature of the kinetic philosophy is that principles of physics are used to e8plain

why a runner is undergoing a#nor'al pronation too 'uch or too late!. "dhering to the

generalist9s philosophy will lead one to try to treat pronation; instead of trying to understand thecause of the pronation?,$@. If one does not understand which intrinsic4e8trinsic aspects of the foot

are creating the a#nor'al pronation; then how can one know which aspects of the shoe should #e

custo'ied to an individual9s feetE "dhering to the kine'atic philosophy 'ay also #einco'plete #ecause physics is again not taken into account. -or e8a'ple; there 'ay #e two

different runners who #oth have a neutral rearfoot and %5 degree forefoot varus 'easured in

su#talar>neutral. &unner R% however; has %5 degrees of forefoot varus when 'easured in the

resting position which is 5 to %5 degrees of dorsifle8ion!; and runner R$ has $5 degrees offorefoot varus and %5 degrees of rearfoot varus when 'easured in the resting position. &unner

R$ will clearly have different values of pronatory torCue as co'pared with runner R%; and thus

need different running shoe properties. Until 'ore research #eco'es availa#le; it 'ay #e usefulto try to i'ple'ent aspects of #oth the kinetic and kine'atic philosophies at this ti'e.

0"&


21/34

Secondly; we should #e designing our studies so that runner9s are actually given a chance

to run in a given shoe for a 'atter of weeks to 'onths; and our outco'e 'easures should involve

such varia#les as a'ount of lower e8tre'ity pain; a'ount of distance which can #e ran #eforeonset of pain; etc. 0iven the fact that 'any runners are not a#le to run for the distances that they

would like #ecause of such overuse inuries as posterior ti#ial stress syndro'e; patello>fe'oral

pain syndro'e; anterior co'part'ent syndro'e; and plantar fasciitis ust to na'e a few!; thenwhy aren9t we 'easuring the running shoe9s a#ility to co'#at these pro#le's in a 'ore practical

and applied 'annerE

("% Conclusion

6he current research on running shoes has given us so'e insight into how adusting

certain running shoe properties 'ay influence a runner9s gait. e still need 'ore evidencewhich shows us why running inuries co'e a#out so that we 'ay #etter configure running shoes

to co'#at these pro#le's. "lthough there is no solid evidence on this 'atter; the principles of

#io'echanics will likely lead us in the proper direction when prescri#ing a running shoe. -ro' a#io'echanical standpoint; e8a'ining the kinetic forces which are created #y the interaction of a

runner9s rearfoot4forefoot varus angulations upon i'pact with the ground is #eneficial to

esta#lish why a#nor'al pronation is co'ing a#out; instead of trying to treat the pronation as acause of inury. e si'ply cannot treat hyperpronation or late pronation #y prescri#ing a

running shoe unless we e8a'ine why this a#nor'al pronation is co'ing a#out. It is this author9s

hope that future research will take into account a runner9s individual foot structure and try to

decipher which running shoe properties will #est co'ple'ent each foot structure.

$%


22/34

Re5erences

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+,. Butler; &N; 7avis; IS; Ha'ill; N. Interaction of arch type and footwear on running'echanics. "'erican Nournal of Sports Medicine $55, (* %$!: %221>$55+

+. Butler; &N; Ha'ill; N; 7avis; I. /ffect of footwear on high and low arched runners9

'echanics during a prolonged run. 0ait and Posture $55 $,: $%2>$$++1. )heung; &6; Jg; 0T. /fficacy of 'otion control shoes for reducing e8cessive rearfoot

'otion in fatigued runners. Physical 6herapy in Sport $55 1: +>1%

+2. )heung; &6; Jg; 0T. Influence of different footwear on force of landing duringrunning. Physical 6herapy $551 11 +!: ,$5>,$1

$*


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,5. egener; ); Burns; N; Penkala; S. /ffect of neutral>cushioned running shoes on plantar

pressure loading and co'fort in athletes with cavus feet. "'erican Nournal of Sports

Medicine $551 (, %%!: $%(2>$%*,,%. Knapik; NN; -eltwell; 7; )anha'>)hervak; M; et al. /valuation of inury rates during

i'ple'entation of the -ort 7ru' running shoe inury prevention progra'. U.S. "r'y

)enter for Health Pro'otion and Preventive Medicine; "#erdeen Proving 0round; M7$%5%5.


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Figure 1a: The anatomy of a running shoe

Figure 1b: Shoe insole

$,

Midsole Outsole

HeelCounter

Achilles Pad

Vam

Toe !o"

Tongue#acing

Featherline

$uarter

Fo"ing


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Figure -: The density of the midsole may be determined manually by grasing the toand bottom of the midsole bet&een the thumb and inde" finger to imlement the .inchtest*/ Although this &ill not gi(e an ob0ecti(e durometry number' a comarison may bemade bet&een different shoes to decide &hich midsoles ha(e a high or lo& density*

$1


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Figure : The shoe on the left e"emlifies a rounded heel flare &hich is characteristic ofmost running shoes on the mar)et today* The shoe on the right sho&s a rearfoot medialheel flare*

$2


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Figure 2: The cur(ature of the last may be found by turning the shoe o(er andimagining lines &hich bisect the anterior and osterior asect of the shoe* The t&oshoes on the left ha(e more of a cur(ed last configuration' &hereas the shoes on theright ha(e a semi3cur(ed and straight last configuration*

(5


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Figure 4: Common foot structures &hich are determined in the rone' non3&eightbearing osition* The neutral foot &ill ha(e both the calcaneus and metatarsal

head erfectly bisecting the distal tibia* The forefoot (arus deformity &ill ha(e thecalcaneus bisecting the distal tibia' but the metatarsal heads &ill be in(erted in relationto the tibia* The rearfoot (arus deformity &ill ha(e both the calcaneus and metatarsalhead in(erted as comared to the distal tibia* The to' right icture sho&s ho& theremay be (arying degrees of rearfoot and forefoot (arus structures*

(%

a5 6eutralFoot

b5 7earfoot and ForefootVarus 8More forefoot(arus5

c5 ForefootVarus

d5 7earfootVarus


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Figure 9: The subtalar neutral osition is found by lacing the runner in the roneosition &ith his,her distal leg hanging off of the table* The e(aluators thumb and inde"finger alate the antero3medial and antero3lateral asects of the talona(icular 0oint&hile the foot is in(erted and e(erted* The oint &here the talus feels to be neithere(erted nor in(erted is said to be the neutral osition of the talus* From this osition'

the degrees of rearfoot and forefoot (arus angulations may be determined* ;t should benoted that many biomechanists feel that e"amining the foot in


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Figure =a: Ha(ing a rearfoot (arus deformity &ill lead to larger amounts of ronatorytor>ue &hen the foot ma)es initial contact &ith the ground* ?hen the foot first ma)escontact &ith the ground' the le(er arm for the ronatory rotation is greater' and the foot

&ill generate high amounts of momentum as it ronates to meet &ith the ground* This&ill li)ely lead to e"cessi(e or late ronation during the runners gait cycle*

((


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Figure =b: Ha(ing a forefoot (arus deformity &ill li)ely lead to higher amounts ofronatory tor>ue late into the gait cycle* This laces the runner at ris) for late ronation*

(*

Documents

A Litrature Review on Running Shoes and Biomechanics.doc