299BrJ Sports Med 1997;31:299-303

Original articles

Hazard of deceptive advertising of athleticfootwear

Steven Robbins, Edward Waked

AbstractObjectives-Athletic footwear are associ-ated with frequent injury that are thoughtto result from repetitive impact. No scien-tific data suggest they protect well. Expen-sive athletic shoes are deceptivelyadvertised to safeguard well through"cushioning impact", yet account for123% greater injury frequency than thecheapest ones. This study tested thehypothesis that deceptive advertising cre-ates a false sense of security with users ofexpensive athletic shoes, inducing attenu-ation of impact moderating behaviour,increased impact, and injury.Methods-Fifteen young healthy male vol-unteers confronted four surfaces: a bareforce moment platform, and three with thisplatform covered by identical shoe solematerial made to appear different andadvertised divergently. Advertising mes-sages suggested superior impact absorp-tion and protection (deceptive message),poor impact absorption and high injuryrisk (warning message), and unknownimpact absorption and safety (neutral mes-sage). Ground reaction forces were re-corded for 10 barefoot footfalls, accordingto a protocol requiring stepping forwardfrom perch to a surface 4.5 cm below.Results-Impact varied as a function ofadvertising message (p

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incorporating new features that protect,and more advanced safety technology, yetepidemiological data indicate that users ofmore expensive shoes are injured morefrequently. Expensive shoes accounted for123% greater frequency of injury than thelowest cost models, regardless of manufac-turer, after correcting for previous injury,training mileage, and sex, factors influencinginjury frequency.`5 This suggests that impactis greater when consumers use more expensiveathletic shoes, and we can think of nothingother than the effect of advertising that mightaccount for it.As an explanation of the higher injury

frequency when humans use expensive athleticshoes, we hypothesise that deceptive advertis-ing suggesting good protection against impactpersuades users to eschew cautious behaviour,resulting in higher impact. We tested this in anexperiment in which the independent variablewas the advertising message deceptively de-scribing the same shoe sole material made toappear different as either effective protection,unsafe, or of unknown safety. The dependentmeasure was impact.

MethodsSUBJECTSA random sample of 15 healthy young menwith a mean (SD) age of 31 (4.2) years partici-pated in this study on a voluntary basis. Allwere selected from the general population andparticipated actively in sports and leisureactivities. Mean (SD) body mass and heightwere 75 (9.2) kg) and 175 (7.8) cm, respec-tively. All were free of conditions affecting theirability to walk, run or balance.

SOLE INTERFACE MATERIALThe sole interface material covering the topsurface of the force moment platform consistedof a 2.5 cm thick layer of ethyl-vinyl acetate(EVA), Shore Al0 in hardness. EVA is thepolymer material most commonly used infootwear soles. Sole conditions differed only inthe colour of the fabric encasing the EVA solematerial. This envelope ensured subjects couldnot identify the material within it.

MESSAGES FOR SHOE SOLE ADVERTISINGDeceptive messageThis message resembled advertisements usedto promote athletic footwear in periodicalsavailable to us. It included pseudoscientificgraphs and tables, and athlete endorsementsuggesting superior impact absorption and sta-bility. We used the terms "advanced technol-ogy" and "state of the art", to describe the sole.We stated that this technology is incorporatedin the most expensive athletic shoes currentlyon the market.

Warning messageThis message was based on pre-experimentalevaluation of user opinions, indicating thatusers believed that athletic shoes were effectivein protecting against injury, that expensiveshoes protected better than cheap ones, andthat new technology has resulted in more pro-

tective shoes. We concluded that contrastingnotions from the deceptive message wouldconstitute warning. The shoe sole was de-scribed as associated with frequent injuriesfrom excessive impact and instability. Subjectswere told that this material was old technologyand used only in cheap running shoes.

Neutral messageThis shoe sole material was described as neverused in shoe soles previously, and impossible topredict how it might influence either impactabsorption or stability.

FORCE MOMENT PLATFORMA unique force moment platform was used.This force moment platform is 500 mm' in areaand 150 mm high. It is capable of measuringpeak loads of up to 10 000 N with a resolutionof 1 N for forces and 0.1 Nm for moments. Themaximum acquisition/ transmission rate foreach load sensor is 500 Hz. A high speed (115kbaud) serial link transmits data from forcemoment platform to host computer, which cal-culates various performance indices andrecords data to disk. A graphical user interfaceallows operator to view time history of theforces, moments, and centre of force.

TESTING PROTOCOLWritten consent was obtained both beforebeginning the experiment and followed theethical guidelines for human experimentationset by the Helsinki Declaration. Subjects wereconfronted with four surface interface condi-tions in a counterbalanced order: a bare rigidforce moment platform, and three with thisplatform covered by identical impact absorbingshoe sole material. The advertising messageswere presented in writing and graphics. Beforeeach surface condition, the advertising messagewas read by the subject and re-read by thetechnician. No message was presented for thebare force moment platform. Impact testingconsisted of 10 consecutive barefoot footfallimpacts recorded on the force moment plat-form for each surface condition. Subjects wererequired to step forward from perch to asurface 4.5 cm below, and land on one foot, asshown in figure 1. Subjects were debriefed atthe end of the experiment to assess any subjectbias regarding the experiment and its protocol.Included in the debriefing were questions con-cerning the credibility of claims made bymanufacturers of modern athletic shoes con-cerning protection against injuries, andwhether subjects were aware of any reports oradvertisements contrary to these claims.

DATA ANALYSISOne way analysis ofvariance was performed foreach dependent measure using the three mate-rial conditions as independent variables. Posthoc tests were performed for significant F val-ues only. Differences between the bare plat-form surface condition and the three othermaterial surface conditions were assessed usingt test with Bonferroni adjustment to correct fortype I error. Statistical significance for all testswas set at 0.05.

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Hazard of deceptive advertising of athletic footwear

1 KItS

Figure I Schematic representation of experimental set up for dynamic footfall testing. Subject stepped down onto forcemoment platform, which was either bare, or covered by athletic shoe sole material. He balanced on one foot afterfoot contactwith platform. Subjects were barefoot with gaze straight and arms to side.ResultsImpact varied in relation to advertising claims(F (2, 28)=96.87, p

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This finding is expected as all incorporate solesmade of similar materials, and produce compa-rable impact enhancing instability.'8-2' Thereare no data supporting the notion that athleticfootwear are capable of protecting againstinjury through cushioning of impact.Without any significant difference in impact

absorption between footwear, one would an-ticipate that users of athletic footwear wouldexperience no difference in injury frequency inrelation to model and manufacturer. It comesat some surprise however that Marti found thatexpensive shoes accounted for 123% greaterinjury frequency than lowest cost models,regardless of manufacturer, after correcting forprevious injury, training mileage, sex, andalmost everything hypothesised to be associ-ated with injury.5 Furthermore, runners whoexpressed strong brand preference had asignificantly greater chance of being injuredthan those who had no brand loyalty. This sug-gests that footwear products may be useddifferently in relation to cost based on expecta-tions of protection as communicated throughadvertising. As an explanation of injury fre-quency in relation to athletic footwear cost, wehypothesised that advertising affects usercaution, thereby inducing users to adjustimpact moderating behaviour in relation toperceived risk inferred by the advertisingmessage-higher impact with expensive mod-els that are assumed to be safe, and lowerimpact with inexpensive models that arepresumed dangerous.

In this experiment impact amplitude variedas a function of advertising message, with thewarning message resulting in lower impactthan the deceptive one, 110% BW versus 121%BW, respectively (p=0.03 1). With repetitivefootfalls, impact amplitude declined and in-creased in relation to the warning and decep-tive message, respectively (p

Hazard of deceptive advertising of athletic footwear 303

One limitation of this experiment is thatexperimental conditions differed from naturalconditions-stepping off a perch differs fromhow footwear products are used during loco-motion. Shock absorbing materials have beenshown to influence impact similarly whethertested by humans stepping from a perch orduring actual locomotion. For example,McNitt-Gray found during landings from aplatform,"5 and Nigg during running,'6 thatimpact increases as interfaces become softer.This suggests that this limitation should notinfluence our conclusions.

In summary, pre-existing beliefs of protec-tion against injury formed through deceptiveadvertising of athletic footwear attenuates usercaution thereby amplifying impact. This mayexplain the 123% higher injury frequencyassociated with more expensive shoes.5 Accord-ingly, deceptive advertising of protective de-vices is a public health hazard and must beeliminated. Humans are less cautious evenwhen they use truthfully advertised productsbecause of excessively positive attitudes towardnew products and wrong impressions of thestandards of truth in advertising throughgovernment regulation.

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