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International Journal of Industrial Ergonomics 40 (2010) 698e709

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International Journal of Industrial Ergonomics

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The effect of occupational whole-body vibration on standing balance: Asystematic review

Ramakrishnan Mani, Stephan Milosavljevic*, S. John SullivanCentre for Physiotherapy Research, School of Physiotherapy, University of Otago, PO Box 56 Dunedin, New Zealand

a r t i c l e i n f o

Article history:Received 16 October 2009Received in revised form7 May 2010Accepted 27 May 2010Available online 23 June 2010

Keywords:Whole-body vibrationBalancePostural controlOccupationSeatedInjury preventionVehicle driving

* Corresponding author. Centre for Physiotherapytherapy, University of Otago, P.O. Box 56, Dunedin 90479 7193; fax: þ64 3 479 8414.

E-mail addresses: manra029@student.otago.acmilosavljevic@otago.ac.nz (S. Milosavljevic), sjohSullivan).

0169-8141/$ e see front matter � 2010 Elsevier B.V.doi:10.1016/j.ergon.2010.05.009

a b s t r a c t

Adverse health effects from exposure to occupational whole-body vibration (WBV) are common amongdrivers. In particular some researchers consider that there is kinaesthetic and balance disturbance fromWBV exposure in the workplace and this might be one of the aetiological factors responsible for occu-pational low back pain in drivers. The purpose of this study was to undertake a critical review of theliterature to determine whether exposure to seated occupational WBV can affect standing balanceperformance in an actual or simulated occupational environment. Specific keywords and MeSH terms forthree major areas included WBV, balance and occupation. These were used to conduct a systematicsearch of the following databases; PubMed, EMBASE (Ovid), Medline (Ovid), CINAHL (EBSCO), AcademicSearch Complete (ASC), AMED, Scopus, Web of Science, Science Direct, Proquest, Cochrane library(OVID),IEEExplore and ProQuest Dissertations and thesis, Google Scholar, WorldCat and related conferenceproceedings. Five articles met the inclusion criteria and were assessed for quality. Two were field studiesconducted on actual vehicles (a long haul freight truck and a bulldozer), while the other three werelaboratory studies simulating the characteristics of the following vehicles; long-haul-dump vehicle,underground mine shuttle car, and helicopter. The systematic review scored the methodological qualityof the included articles with an average and standard deviation of 76 �12.3% (range 59- 93%) indicativeof high quality. Three of the five studies (two field and one laboratory) found evidence for seated WBVdecreasing standing balance performance while two laboratory studies did not find such effects. Thusthere is modest evidence to suggest there is a decrease in standing balance performance followingexposure to seated occupational WBV.Relevance to industry: This systematic review suggests that balance deficits may exist immediatelyfollowing exposure to occupational seated WBV and may predispose driver/operator to low back injuryduring manual material handling tasks immediately post driving.

� 2010 Elsevier B.V. All rights reserved.

1. Introduction

The effects of whole-body vibration (WBV) on the human bodyhave beenwidely investigated. Evidence suggests exposure to WBVin standing may be a useful intervention to increase bone mineraldensity (Rehn et al., 2008), muscle strength (Rehn et al., 2007) andathletic performance (Jordan et al., 2005) as well as improvebalance (Wunderer et al., 2008). Conversely occupational WBV insitting has also been linked to low back pain (LBP), altered

Research, School of Physio-54, New Zealand. Tel.: þ64 3

.nz (R. Mani), stephan.n.sullivan@otago.ac.nz (S.J.

All rights reserved.

peripheral nervous system function, visual and vestibular distur-bances (e.g. motion sickness, giddiness and disturbed balance), aswell as prostate and gastrointestinal problems (Miyashita et al.,1992; Seidel and Heide, 1986; Bonney, 1999; Zahov andMedzhidieva, 2005)

Maintenance of balance in upright and adapted postures isimportant during most functional activities requiring control ofboth gravitational and acceleration forces. Postural and equilibriumcontrol of balance are respectively maintained by extensor activityin the stance limb(s) as well as inter-segmental stability of the body(Huxham et al., 2001). Although maintenance of balance duringstanding depends on descending motor commands from thecentral nervous system, it cannot be achievedwithout sensitive andaccurate input of somatosensory (muscle, joint, skin and pressurereceptors), visual and vestibular systems (Collins and De Luca,1993). Any alteration in the physiology of these sensory systems

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will result in alteration of postural and equilibrium control mech-anisms of the body and likely lead to a loss, or disturbance, ofbalance. Balance disturbance is considered to be a risk factor inmany fall related injuries, particularly in an occupational setting,leading to fractures and soft tissue injuries of the spine andextremities (Gauchard et al., 2001; Vouriot et al., 2004).

Falls in drivers are also considered a significant occupationalinjury, particularly in the transportation industry (Bureau of LaborStatistics, 2006). There is also a strong association between vehicleoperation and LBP (Waters et al., 2008). Occupational WBV exertsa substantive influence in vehicle environments and the aetio-logical mechanisms behind these falls/injuries appear to be multi-factorial. Several authors propose that there is strong associationbetween occupational WBV and LBP (Bovenzi and Hulshof, 1998;Lings and Leboeufyde, 2000; Pope et al., 1998; Tiemessen et al.,2008) Purported injury mechanisms from such WBV exposureinclude; disc degeneration, spinal muscle fatigue due to cyclicmuscular activity, delayed spinal muscular response to sudden loadand altered spinal proprioception (Bluthner et al., 2002; Lamis andWilson, 2008; Li et al., 2008). Conversely, other studies have foundno evidence to suggest that exposure to motorized vehicle WBVleads to accelerated disc degeneration and have also noted that noevidence currently exists to link WBV to herniated lumbar discs(Battie et al., 2002, 2009; Palmer et al., 2008) Given this ques-tionable link other mechanisms could be implicated in the rela-tionship between WBV and LBP. One such mechanism could be thedecrease in balance due to WBV exposure, also thought to bea contributing factor to falls while exiting from a vehicle (Nicholsonand David, 1985). Severe trunk postures have been identifiedamong truck drivers during non-driving tasks (e.g. ingress/egress)and also during manual material handling (Okunribido et al., 2006;Olson et al., 2009), and such postural demands interacting withWBV induced balance disturbances may predispose an individualto spinal injury.

Recent evidence suggests that subjects with LBP have alteredhip movement strategies, increased sway in antero-posteriordirection, increased spinal displacement and reduced posturalcontrol (Della Volpe et al., 2006; Henry et al., 2006; Jacobs et al.,2009; Mok et al., 2004, 2007). Thus deficits in postural controland balance may be factors associated with LBP and WBV may beone aetiological mechanism creating such balance disturbance.Interestingly some studies have found exposure to seated WBV caninduce disturbances in standing balance (Manninen and Ekblom,1984; McKay, 1972) and thus occupational WBV could bea contributing factor for the initiation or maintenance of LBP in

Table 1List of search terms.

Search terms category WBV Balance/related terms

MeSH/subject terms/subject headings/CINAHL headings

Vibration,random vibration

Postural balance, equilibrium, balance,posture, postural, stabilometry posturoginner ear, vision, ocular, labyrinthmechanoreceptors, proprioception.

Keywords Whole-bodyvibration

postural control, postural stability, postustabilization, postural effects, postural swpostural equilibrium, body balance, bodybody posture, body equilibrium, equilibrbalance, posture, stabilometry, posturogrinner ear, vision, mechanoreceptors

drivers. Although this appears plausible, the mechanism support-ing a link between WBV, balance disturbance and risk of low backinjury has yet to fully investigated.

There is a need to review the research literature investigatingthe effects of seated WBV on standing balance in an occupationalsetting. The aim of this systematic review is to determine whetherexposure to seated WBV can affect standing balance of individualsin an actual or simulated occupational environment. Although twofurther studies investigating the effects of seated WBV havemeasured head and shoulder movements (using head mountedstrain gauges and photo-optic cranio-corpography) to evaluate thebalance performance (Hornick et al., 1961; Zahov and Medzhidieva,2005) post exposure, their reliability has not been established. Inaddition methodological concerns with the use of photo-opticcranio-corpography have been identified in the literature (Hozmanet al., 2008). The focus of the current study has been to investigatethe centre of pressure derivatives of balance performance that havebeen recorded from a force plate or similar apparatus, the reliabilityof which is well established and commonly used in research andclinical environments (McKeon and Hertel, 2008; Visser et al.,2008).

2. Methodology

The systematic search was focussed on the literature pertainingto the effect of WBV on the standing balance of healthy individualsin an actual or simulated occupational environment. Electronicdatabases were searched to locate studies relevant to three keysubject areas of the research question namely; WBV, balance andoccupation. The search strategywas developed in consultationwitha senior librarian and designed as a comprehensive and sensitivesearch that would locate the widest spectrum of articles forconsideration. Based on the electronic database searched, thesearch terms entered were either keywords or database specificsearch terms (MeSH, subject terms, subject headings (SH), andCINAHL headings) in combination with keywords. Boolean opera-tors, ‘OR’ and ‘AND’ were used to combine within and between thesearch terms of the three subject areas respectively. The detailedsearch terms are listed in Table 1.

The search limits were; full text articles written in English,German or French, published from the earliest date available in thedatabase to May 2009. The systematic search strategy was con-ducted in selected electronic databases, namely; PubMed, EMBASE(via Ovid), Medline (via Ovid), CINAHL (EBSCO), Academic SearchComplete (ASC), AMED, Scopus, Web of Science, Science Direct,

Occupation/related terms

raphy,Occupations, work environment, workplace,occupational exposure, man-machine systems,human-machine systems, environmental exposure,occupational health, motor vehicles, off-road motor vehicles,automobiles, transportation, all-terrain vehicles,automobiles, buses, commercial vehicles, motorcycles,recreational vehicles, road-rail vehicles, trucks,engines, motorcyclists, motor vehicle drivers , automobile drivers,truck drivers, bus drivers, agriculture, forest machinery,soldiers, military personnel, armed forces,military service, aircraft industry,ships, railroads, aircraft, space craft, space flight

ralay,sway,

ium control,aphy,

workplace, occupation, occupational exposure, agriculture,motor vehicles, automobile driving, off-road motor vehicles,transportation, tractor driver, truck driver, military vehicle,all-terrain vehicle, military personnel, military vehicles,agricultural vehicles, farming vehicles, aircraft, helicopter,space flight, war vehicles

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Proquest, Cochrane library (via OVID) and IEEExplore. In addition,supplementary searches were also conducted as a part of thecomprehensive search strategy. They were ProQuest Dissertationsand thesis, Google Scholar, WorldCat, related conference proceed-ings (e.g. Proceedings of theHuman Factors and Ergonomics Society,American Conference on Human Vibration, Proceedings of theInternational Ergonomics Association Congress and Proceedings ofthe International Conference on Whole-Body Vibration Injuries),reference lists of the included articles were searched for relevantinformation together with a hand search of related journals.

2.1. Eligibility criteria

Inclusion criteria were:

1. An investigation of the effects of seated occupational WBV onstanding balance in healthy individuals, aged 18e75 years.

2. Conducted in either a fieldwork occupational setting or ina laboratory setting that simulated vibration characteristics ofa vehicle.

3. The outcome measure used to determine standing balance wasthe centre of pressure (COP) measures (or derivatives) obtainedusing any form of force plate/stabilometry technology.

4. Studies which used preepost experimental design wereconsidered.

2.2. Exclusion criteria

Exclusion criteria were:

1. An investigation of WBV on balance that was conducted ina laboratory without simulating vibration characteristics ofa vehicle.

2. Segmental vibration on balance performance.3. WBV (standing on a vibration platform) as an exercise inter-

vention to evaluate balance in healthy individuals, sports pop-ulation and in participants with Parkinsonism, Stroke, MultipleSclerosis and any other neuro-musculoskeletal disorders.

Articles obtained by the systematic search were exported toEndNote library X2 (Thomson corporation) and duplicates wereremoved. Exclusion of irrelevant articles took place using a threestep systematic a priori determined approach. The titles wereexamined for relevance, then abstracts were considered and finallythe full text article was retrieved and considered. If there was anyuncertainty about content, the article proceeded to the next step.Furthermore, any articles retrieved by hand search were assessedfor inclusion in a similar manner (Fig. 1).

2.3. Methodological quality

Quality analysis of the included articles was conducted inde-pendently by two researchers using a modified Downs and Blackquality index originally developed to assess the methodologicalquality of both randomised controlled trials and non-randomisedstudies (Downs and Black, 1998). This quality index has highinternal consistency, high test-retest reliability and good inter-raterreliability (Downs and Black, 1998). Similar to other research (Allaet al., 2009; Irving et al., 2006; Munn et al., 2009), a modifiedversion of the original index was used. The modified index used forthis review considered 17 out of 27 items from the original index.Items 8, 9,14,15,17,19,23,24,26 and 27 were omitted since theywerenot relevant to non-randomised control trials. If there was noindependent control group in the included studies, items 21 and 22were scored as not applicable (Appendix A).

In order to operationalize item 5 and 23, a list of confoundingfactors of balance performance and WBV transmission was devel-oped based on previous studies. They were classified into coreconfounders namely: age (Hegeman et al., 2007; Hytonen et al.,1993; Prieto et al., 1996), practice sessions prior to formal balancetesting (Nordahl et al., 2000; Tjernstrom et al., 2002; Warren et al.,2006), standardisation of standing posture (Chiari et al., 2002) andother confounders namely sex, height, weight, period of nonvibration exposure prior to formal exposure session and previousWBV exposure. This item scored “yes”, if the study defined/mentioned three core confounders and three or more otherconfounders; “partially”, if the study defined/mentioned three coreconfounders and one or two other confounders; and “no”, if thestudy defined/mentioned less than three core confounders. Foritem 13, the scoring was based on where the study was conducted.This item scored “yes”, if the study was conducted in a fieldworkbased occupational setting, scored “partially”, if it was conducted ina laboratory setting simulating an occupation in terms of vibrationparameters/seating/posture/noise, and scored “no”, if it was con-ducted in a laboratory setting simulating an occupation partially ornot at all. For the purpose of this review, a study was considered ofhigh quality if it scored >75% of the total criteria, 50e74% asmoderate quality and <50% as low quality.

2.4. Whole-body vibration exposure assessment

A second criteria list was used to evaluate the nature of theWBVexposure in the included simulated laboratory studies. This criterialist was a modified version of the 7 item scale developed by Rehnet al. (2007) and used to rate the quality of the whole-bodyvibration intervention in previous systematic reviews (Rehn et al.,2007, 2008). An 8th item (participant contact with the steeringwheel/back rest/foot rest) was included as it was thought toinfluence the transmission of and thus the effects of WBV on thehuman body (Appendix B) and scored 3 points, if the study speci-fied all the three contact areas. The presence of each item wasscored as a point with a maximum of 12 points (6th and 8th itemsscored 3 points) indicating sufficient (complete) information forthe replication of the particular WBV parameters. Item 6a and 6bscores were not applicable as it was considered not relevant for thissystematic review. If any itemwas not relevant it was scored as notapplicable. For the purpose of this review, a studywas considered ofhigh reproducibility if it scored 8 or more points, 6 or 7 points asmedium reproducibility and 5 or <5 as low reproducibility.

2.5. Data extraction and analysis

The following data were extracted from the included articles forfurther descriptive analysis: objective of the study, study design,characteristics of participants, source of vibration, study setting,WBV parameters and exposure duration, balance task andmeasurement, outcome measures, statistical analysis, results andconclusion. For the quantitative analysis, the COP measures(measure of standing balance), the primary dependent variable,were analysed for homogeneity.

The scores obtained from the quality analysis, vibrationassessment and the data extraction by the two researchers werecompared. If there was a disagreement then a third researcher (SM)repeated the procedure and the final consensus were achieved interms of scoring and data accuracy.

3. Results

The search strategy and article screening process are illustrated inFig.1. A total of1415articleswere identifiedby the searchstrategyand

Retained after abstract screening - 5

Excluded: title screening - 968

Excluded: abstract screening -143

Hand searching of reference lists - 7

Excluded after abstract and full text screening: narrative review, no full text, laboratory studies, local vibration

Excluded after abstract and full text screening: laboratory studies, standing exposure.

Hand searching of relevant journals by titles screening - 6

Total number of articles found - 1415

Retained after title screening -148

Excluded: duplicates - 299

Retained after duplicates - 1116

Electronic databases: PubMed, EMBASE, Medline, CINAHL, Academic Search Complete, Scopus, Web of Knowledge, Science Direct, Proquest, AMED, Cochrane Library & IEEExplore

Supplementary searches: WorldCat, Google Scholar, conference proceedings & Proquest Dissertation & thesis databases

Database specific search terms / keywords for WBV, Balance & Occupation

Nil

Final number articles included in this review - 5

Nil

Retained after full text screening - 5

Excluded: full text screening - nil

Fig. 1. Search strategy & article screening process.

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downloaded in to an EndNote� library. Of these, 299 duplicates wereremoved leaving 1116 articles. On examining the titles, 968 articlesdid not meet the criteria and were excluded. The abstracts of the 148remaining articles were examined and 143 articles did not meet thecriteria andwere excluded. This resulted in five articles satisfying theinclusion criteria. Although hand searching of reference lists of theincluded articles and relevant journals identified another 13 articlesof interest none of these met the final criteria for inclusion.

Two of the included articles were field studies conducted in anactual occupational setting while the remaining three were con-ducted in laboratory settings described as simulating the specificdemands and vibration characteristics associated with a designatedoccupational task. Detailed information extracted from the fivestudies is presented in Tables 2 and 3. The results of the qualityanalysis and WBV exposure assessment of the five articles is pre-sented in Tables 4 and 5, respectively.

Although all the studies used the COP as a common outcomemeasure to demonstrate the effects of WBV on balance, they useddifferent variations (e.g. area, distance, frequency) of the measure(Table 6). This heterogeneity did not permit anymeaningful poolingof the data. Hence, summary statistics were not calculated.

4. Discussion

The aim of this systematic review was to determine whetherexposure to seated WBV in an actual or simulated occupationalenvironment affects standing balanceperformance. Threeoutoffivestudies (2,field; 1, simulated laboratory) demonstrated a decrease instanding balance post exposure to WBV, while two simulatedlaboratory studies reported no changes in standing balance. Theaverage methodological quality score (�standard deviation) was76% (�12.3%) (Table 4). Consensus was reached between the inde-pendent reviewers for all articles. All simulated laboratory studieshad high reproducibility grading in terms of sufficient (complete)information on specific WBV exposure parameters (Table 5).

4.1. Study design

All studies employed preepost experimental designs with allparticipants providing standing balance scores pre and post expo-sure to WBV in sitting. Two studies employed a control group(Martin et al., 1980; Oullier et al., 2009) while in two other studiessubjects served as their own control (Cornelius et al., 1994; Santos

Table 2Summary of field studies: the effect of WBV exposure on balance.

Author & year Objective of the study Study design Participants characteristics Source of vibration WBV parameters Exposure/rest duration

Oullier et al., 2009 To assess the level towhich exposure to WBVgenerated by bulldozersaffects postural balance

Two groupexperimental design

M e 24 ;F e 0; agerange:17e20 yearsHeight, weight & BMI e NSDriver group e 12 apprenticebulldozer operatorsControl/non-driver group e 12

Bulldozer Direction: NSType: NSFr e NSA e NS

Driving: 2� 2 h (4 h)Rest : 2 h between2 periods of driving

Ahuja et al., 2005 To investigate theeffect of WBV on thepostural stabilityof long haul freightdrivers, followingvibration exposure

Experimental pre-post M e 8; F e 1; Agerange:42e74 yearsHeight, weight & BMI e NSDriver group: Full timeLHF truck driversNo control group

LHF truck Direction: Tri-axialType: NSFr e NSA e NS

Driving 2.5 h� 3 (7.5 h)Rest: two 30 minintervals between threeperiods of driving

Balance task Measurementdevice/system

Balance testing Outcome measures Statistical analysis Results Authors’ conclusion

Bipedal to unipedalstance with EO & EC; 20 seach conditions�4 trials/1 minrest period between trialsTotal time: 10 min

Force platform(50� 50� 3 cm)Rematic Ltd,Saint-Etienne, France

T1 e Pre driving, T2 e

immediate post driving(1stexposure), T3 e

immediate post driving(2ndexposure)

AP & ML COPdisplacement (mm)Confidence ellipse area (%)Reference standard:bipedal stance

Non-parametric Wilcoxonsigned rank tests: compareacross conditions/T1, T2, T3Stance: bipedal, unipedalright, unipedal left,conditions : EO & EC

Driver group: significant(p< 0.05) increase of COParea (85% Of COPdisplacements) for allthree stance conditions &both vision conditionsNon-driver group :non-significant (p> 0.05)

Prolonged exposure toWBV alters the uprightstance of bulldozer drivers.

mCTSIB: StandingEO&EC/10 seach /two trials eachTotal time: NS

Neurocom� BalanceMaster� system

D1: vibration D2: sittingT1: Pre-exposure,T2: immediate post 1stexposure, T3: post1st 30 min rest,T4: immediate post2nd exposure,T5: post 2nd 30 min rest,T5: immediatepost 3rd exposure

AP & ML RMSsway (cm): 3 drivingperiods� 2 conditions(EO & EC)

Mixed ANOVA repeatedmeasures: differenceb/w EO & EC in 3driving sessions

Significant RMS AP swaywithin subjects in EO (p< 0.05)Significant RMS ML swaywithin subject’s in EO (p< 0.05)No significant RMS AP & MLwithin subjects in EC (p> 0.05)

Postural stability maybe impacted by exposureto WBV, similar to thatexperienced by LHFtruck operators.

NS, not specified; M, males; F, females; T, testing; D, day; EO, eyes open; EC, eyes closed; Fr, frequency; A, acceleration; mCTSIB, Modified Clinical Test of Sensory Interaction on Balance; COP, centre of pressure; AP, antero-posterior; ML, mediolateral; LHF, long haul freight.

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Table 3Summary of laboratory studies: the effect of WBV exposure on balance.

Author and year Objective of the study Study design Participants characteristics Source of vibration/ Simulationcharacteristics

WBV parameters Exposure/rest duration

Santos et al., 2008a, b To evaluate the acuteeffects of seated WBVexposure on balance

Repeatedmeasures design

M e 12 , F e 0; mean age:22 years, height: 1.8� 0.1 m,weight �77� 9 kg,BMI e <30 kg/m2

Vibration group-12 Control/novibration group (sitting) e 12

Suspension seat mounted onvehicular simulator of LHDvehicles, vibration spectrumsignature from the minessteering wheel, posturesof related activities

Direction e Z,Type: random,Fr e 0.5e20 Hz, PeakF e 2.7 Hz, A e 0.86 m/s2

WBV: 60 min, novibration/sittinge 60 min

Cornelius et al., 1994 Does exposure to WBV atfrequencies similar tomine operators impair posture

Experimental designRepeated measures design

M e 6, F e 0; age range:22e45 years, height,weight BMI e NSVibration group e 6Control/no vibrationgroup(sitting) e 6

Carrier frameVibration platformReproduction of actualshuttle car vertical vibrations

Direction e Z, type: NS,Fr e 7e12 Hz, A e 0.5 m/s2

WBV: 40 min,no vibration/sitting: 40 min

Martin et al., 1980 Effects of long-term, solidtransmitted WBV onpostural adjustmentscharacteristics

NS M &F e 20; age range:18e46 yrs, Height,weight & BMI e NSVibration group: 10,control group: 4

Heavily cushioned helicopterpilot seat bolted to platform,vibration generated byvertical hydraulic pump(Sud Aviation Air 35e20)

Direction e Z, type: NS,Fr e 18 Hz, A e 0.5 g(platform); knee e 0.18,thorax e 0.065 gand forehead e 0.1 g

WBV:30 min,HTV e 30 min,LV e 30 min,HV e 30 min,No vibration/sitting: 30 min

Balance task Measurement device Balance testing Outcome measures Statistical analysis Results Authors’ conclusionStanding EC/1 min/

8 trials/few secs restbetween each trialTotal time: 15 min

Force plate (90� 90 AMTI,Watertown, MA), samplingfrequency 100 Hz

D1: vibration, D 2: sittingT1: pre-exposure,T2:immediatepost 60 min exposure,T3: recov 20 min,T3: Recov 40 min,T4: recov 60 min

AP & ML COP time series signals:area-CE(mm2); MFREQ (Hz);MPF (Hz); MVELO (mm/s)

Repeated measures: 2 wayANOVA: 2 vibrationconditions� 5measurement period

No statistically significantmain condition effects orcondition� period interactionsSignificant preepostperiod effects was observed(except MFREQ-AP)

WBV did nothave any effecton balance

Standing EO &EC/2 min each/1 trialTotal time: 4 min

Rectangular force platform(AMTI Model OR6-6-1)Sampling at 20 Hz

Baseline: 2D/1wkprior to actual testD1: vibration EO,D2: vibration EC,D3: no vibration EO,D4: no vibration ECT1: pre-exposure,T2: immediate post exposure(40 min), T3: after 5 minof sitting (post exposure)

X & Y direction RMS COPdisplacement ; COParea & velocity

ANOVA: PT1 e BT;PT2 e BT; PT2 e PT1

Statistically not significantfor all the variables e RMS ML& RMS AP sway, area& velocity (p< 0.10)

Postural stabilityis not affected byexposure to WBVfrequencies similarto thoseexperienced whileoperating amining vehicle.

Standing EC/30 s/6 trials /15 s restbetween each trialTotal: 4 min

StabilometerSampled at1000 Hz bandwidthchart paper recorder& a magnetic tape

D1: vibration, D2: sittingT1 e pre-exposure,T2 e immediate post30 min exposure,T3 e 30 min after30-min vibration period

ML & AP components ofpostural forces(amplitude& velocity)

Amplitude & velocityhistograms; SI e posturalforce mean variationamplitude histogramsTests of significance

WBV: 2-fold increase(3e8 kg) in force oscillationamplitude & velocity inforward & lateral directionSignificant e WBV & LVcompared to HTV & HVControl: no deviation

WBV & LV appliedto the body alterspostural control thanHTV & HV.

NS, not specified; M, males; F, females; T, testing; S, sessions; EO, eyes open; EC, eyes closed; LHD, long haul dump; LV, leg vibration; HTV, head trunk vibration; HV, head vibration; COP, centre of pressure; CE, confidence ellipsearea; MFREQ, median power frequency; MPF, mean frequency; MVELO, mean velocity; Fr, frequency; A, acceleration; D, day; BT, before treatment; PT1, immediate post treatment; PT2, 5 min post treatment; SI, semi-inre-quartiles; AP, antero-posterior; ML, mediolateral; Z, vertical.

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Table 4Methodological quality rating of included studies.

Studies Item number Quality rating

1 2 3 4 5 6 7 10 11 12 13 16 18 20 21 22 25 Total (%)

Oullier et al., 2009 Y Y Y Y N Y Y Y N N Y Y Y Y N Y N 76 HighAhuja et al., 2005 Y Y Y Y N Y Y N Y Y Y Y Y U N/A N/A N 80 HighSantos et al., 2008a, b Y Y Y Y N Y N Y N N Y Y Y Y N/A N/A N 73 ModerateCornelius et al., 1994 Y Y Y Y Y Y Y Y Y Y P Y Y Y N/A N/A N 93 HighMartin et al., 1980 Y Y Y Y N Y Y N N N P Y N U Y Y N 59 Moderate

Y, yes; N, no; P, partially; U, unable to determine; N/A, not applicable; high, >75%; moderate, 50e74%; low, �50%.

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et al., 2008b). A fifth study (Ahuja et al., 2005) did not employa control condition. In those studies where subjects experiencedboth the experimental and control conditions there was adequatetime (1 day to week) to allow for a washout period reported to lastfor approximately 30 min (Martin et al., 1980). The sample size waslow (<10) in two studies (Ahuja et al., 2005; Cornelius et al., 1994)and acceptable (12e24) in the others (Martin et al., 1980; Oullieret al., 2009; Santos et al., 2008b).

4.2. Study participants

In four of the studies participantsweregenerallyyoung tomiddleaged (18e46 years) (Cornelius et al.,1994;Martin et al.,1980;Oullieret al., 2009; Santos et al., 2008b) while in one study (Ahuja et al.,2005), they were somewhat older (42e74 years). Participants weregenerally males, reflective of the occupational workforce of trans-portation operators; however one field study included a singlefemale, while one laboratory study included an undefined numberof female participants. Professional and apprentice drivers partici-pated in the field studies (Ahuja et al., 2005; Oullier et al., 2009) andin one laboratory study(Cornelius et al., 1994) whereas in the othertwo laboratory studies healthy male individuals participated. Priorand accumulated exposure to vibration in the professional drivers/operators group may have modulated the vibration response of thesystem and consequently balance.

All studies fully, or partially, incorporated screening procedurefor disorders (e.g. vestibular disorders, abnormal vision) known toaffect balance performance together with the monitoring of drugusage/alcohol consumption, and previous injury/pathology of lowerlimb/spine. Specific vestibular testing designed to exclude personswith vestibular disorders, an important consideration in balanceassessment, was carried out in only one study (Martin et al., 1980).

4.3. WBV and other exposure characteristics

SeatedWBV exposure characteristics (e.g. frequency, magnitudeof acceleration, direction, type, duration of exposure and othervariables) are considered important variables which may deter-mine the extent of alteration in balance (Tiemessen et al., 2008). Inthe simulated laboratory studies, the generatedWBVwas similar tothe vibration characteristics of a specific vehicle in terms offrequency and acceleration (long haul dump vehicles, undergroundmining vehicles, helicopter). The laboratory studies used vibrationfrequencies within the range from 0.5 to 20.0 Hz and with

Table 5Results of the criteria list of WBV exposure assessment.

Author & year Damping Magnitude Direction Frequency Type Duration A

Santos et al 2008 Y Y Y Y Y NACornelius K.M

et al 1994N Y Y Y Y NA

Martin et al., 1980 Y Y Y Y N NA

Y, yes (item specified); N, no (item not specified); NA, not applicable; high reproducibili

accelerations ranging from 0.9 to 4.9 m/s2.The range of describedvibration frequencies included the reported resonant frequencies(4.0e8.0 Hz) of the spine (Lewis and Griffin, 1996). The two fieldstudies (Ahuja et al., 2005; Oullier et al., 2009) did not specificallyreport the frequency and accelerations associated with the partic-ular environment and vehicle.

The two field studies exposed their participants to periods ofWBV ranging from 4.0 to 7.5 h of bulldozer and long haul freight(LHF) truck driving respectively in a real time driving environment.In contrast the laboratory studies exposed their participants tobetween 30 and 60 min of seatedWBV in a single session. Althoughthe evidence is inconclusive for doseeresponse relationship, it isgenerally assumed that longer exposure durations lead to a greatermagnitude of health effects on the system (Bovenzi, 2009). Little isknown about threshold exposure dose that will influence or predictbalance performance, or how long such an effect can last (Lamisand Wilson, 2008; Li et al., 2008; Martin et al., 1980). The gener-ated vibration was in the vertical direction (Z-axis) in all thesimulated laboratory studies whereas it is assumed to be multidi-rectional in the field studies. Studies report that vertically directedvibration will produce stronger seat to head transmission (Egeret al., 2008) and thus influence the extent of the biodynamicresponses (accelerations) of the head, neck and trunk and relatedsensory organs. It can be assumed that vibration generated in thefield studies would demonstrate variable frequency and accelera-tion response (random vibration) as it was generated by a realworking vehicle in a working environment. Although Santos et al.(2008b) used random vibration (0.5e20 Hz) the other two labora-tory studies did not describe the waveform characteristics of theirvibration parameters.

In all the studies, participants were either partially or totallyexposed to other specific components of the cab design such as;seating, suspension, back rest, arm rest, steering wheel, and noise,some of which are thought to be potential factors influencing thetransmission of WBV. It has been reported that exposure to noisealone and/or in combination with WBV can induce balance distur-bances (Juntunen et al., 1987; Manninen and Ekblom, 1984). Partici-pantswereexposed to steeringwheelvibration inonlyone laboratorystudy (Santos et al., 2008b) which would have increased the likeli-hoodofheadandneck accelerations (Nishiyamaet al., 2000) and thuspresumably influence the sensory systems located within the headand neck (visual, vestibular and neck muscles) regions.

Although there were similarities in WBV exposure parameters,only Santos et al. (2008b) required participants to adopt prescribed

Duration B Duration C Posture Contact: backrest/steering/foot rest

Totalscore (/10)

Reproducibilitygrading

NA Y Y Y 9 HighNA Y Y Y 8 High

NA Y Y Y 8 High

ty, 8, >8 points; moderate, 6 and >6; low, 5 and <5.

Table 6COP measures.

Author & year AP measures ML measures Area/units Mean velocity/units RMS sway/units Median powerfrequency/units

Mean frequency/units

Oullier et al., 2009 Y Y Y/(%) N Y/(mm) N NSantos et al., 2008a, b Y Y Y/(mm/s) Y/(mm/s) N Y/(Hz) Y/(Hz)Ahuja et al., 2005 Y Y N N Y/(cm) N NCornelius et al., 1994 Y Y Y/(sq/cm) Y/(cm/s) Y/(cm) N NMartin et al., 1980 Y Y N N Y/(SI) N N

Y, yes (used); N, no (not used); SI, semi inter-quartiles.

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driving postures such as trunk flexion and, sustained and dynamicneck rotations to either side, in an effort to simulate a variety ofwork related tasks throughout the exposure periods. Evidence alsosuggests that driving speed can alter the magnitude of vehiclevibration (Tiemessen et al., 2008) and thus it may indirectly influ-ence the extent of biodynamic responses and also the nature ofstimulation of body segments, however this was controlled in onlyone of the field studies (Ahuja et al., 2005).

4.4. Balance tasks

In a clinical setting, several sensitive balance tasks (Tyson andConnell, 2009) are chosen to test balance (e.g. forward reach,Berg Balance scale) whereas in a research setting using balancetesting devices (e.g. force plate technology), the common balancetasks executed by participants are bipedal stance either with eyesopen or eyes closed (static balance), the limits of stability test andsingle leg stance and common functional tasks like sit to stand andstep and quick turn test (self perturbed dynamic tasks) (Visser et al.,2008). The balance measurement tools vary from a clinical method(Yelnik and Bonan, 2008) to instrumented testing (force platetechnology) which is considered to be superior at identifyingbalance deficits (McKeon and Hertel, 2008).

In the studies included in this review, the balance task used toassess the effects ofWBVwasbipedal stance ona force platformeitherwith the eyes open (EO) or with eyes closed (EC) or both. Oullier et al.(2009)alsorequiredtheirparticipants toperformabipedal tounipedalstance transition as the balance task, simulating the elements of theexiting task from a bulldozer. Standing balance trials ranged from oneto eight trials for each of the EO and EC conditions with trials lastingfrom 10 s to 2 min in the included studies. As has been previouslyreported, reliability of trial duration and the number of trials to beconsidered in a balance testing session variedwidely (Carpenter et al.,2001; Pinsault and Vuillerme, 2009; Santos et al., 2008a).

The standardisation of standing posture is an important factorthat decreases the variability in balance performance between andwithin subjects. All studies controlled the standing posture by thefollowing methods: standardising the foot position (Chiari et al.,2002; Kirby et al., 1987; McIlroy and Maki, 1997), the subject waseither barefooted or wore standardised shoes (Menant et al., 2008),focussing on a target/white wall in EO condition, and controllingthe upper limb posture. In one study (Oullier et al., 2009), bipedal tounipedal stance transition period and the leg to be lifted werestandardised by specific time and instructions.

Participant’s cognition/attention can also affect the balanceperformance (Donker et al., 2007; Woollacott and Shumway-Cook,2002) and this variable was not controlled in all the studies. Prac-ticing or repetition of balance trials may induce an adaptivepostural control strategy due to a consolidation process (learning)within the system (Fransson et al., 2004; Tjernstrom et al., 2002;Warren et al., 2006), indicating the importance of establishinga baseline pre-exposure balance measurement on an individual.However, only Cornelius et al. (1994) reported using a practice trialto establish a measure of normal, stable balance before exposure.

4.5. Balance measurement occasion

Both field studies measured balance pre and immediately postWBV exposure but only one field study (Ahuja et al., 2005) evalu-ated balance between the driving sessions to determine the timedependent effects of balance over each driving shift. This givesinsight in to the possibility of injury occurrence due to disturbancesin balance immediately post exposure or at the end of the day dueto cumulated effects of vibrations. All the laboratory studies(Cornelius et al., 1994; Martin et al., 1980; Santos et al., 2008b)evaluated balance over-time in addition to an immediate postexposure measurement. These included 5 min post exposure(Cornelius et al., 1994), 30 min post exposure (Martin et al., 1980)and on intervals up to 60 min (Santos et al., 2008b) respectively inorder to further understand the attenuating aspects of WBVexposure on balance.

Balance measurements were conducted immediately after WBVexposure, where the participants stepped on to a force plate posi-tioned near to the vibration platform (Cornelius et al., 1994; Martinet al., 1980) or directly from the real vehicle, avoiding interveningcontact with any surfaces (Ahuja et al., 2005). This immediatebalance testing was argued to test for vibration related effectswithout resetting any altered sensory inputs basically from the feetputatively caused by vibration. In Santos et al. (2008b) and Oullieret al. (2009) study, the information regarding the immediatelybalance testing following vibration/no vibration exposure was notspecified.

4.6. Outcome measures and data analysis

All studies used various derivatives of COPmeasures but did notreport the reliability of the measures (Santos et al., 2008a).Research suggests that mean velocity, RMS distance, meanfrequency, centroid frequency of the COP were the measures thatidentified age-related changes in both eyes conditions and differentbetween eye conditions in both young and elderly subjects (Prietoet al., 1996; Schmid et al., 2002).Out of all measures, mean velocitywas the most reliable and a sensitive measure to differentiate age-related changes in balance performance (Lin et al., 2008; Prietoet al., 1996). All the studies included in this review used eitherone or some of the above mentioned COP measures and Corneliuset al. (1994) and Santos et al. (2008b) study used mean velocity toidentify standing balance performance (Table 6).

Three studies (2 field, 1 laboratory) reported a vibration inducedincrease in COP derivatives (area, RMS sway and velocity) indi-cating abnormal balance performance in both the eyes open andclosed conditions (Ahuja et al., 2005; Martin et al., 1980; Oullieret al., 2009). Ahuja et al. (2005) observed a reverse effect with EOcondition showed more postural sway than EC. Such observationssuggest an abnormal visual input induced by seated WBV (Ahujaet al., 2005). Another interesting phenomenon noticed by Ahujaet al. (2005) was a time dependent increase with each drivingshift indicating a cumulative effect of vibration on the system.During post 1st exposure standing balance testing, Oullier et al.

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(2009) observed no significant changes (COP area %) between EOand EC conditions in both driver and non-driver group. Martin et al.(1980) observed a marked enlargement of vertical force amplitudehistograms in both x and y directions and also significant absolutevalue of mean deviation of postural equilibrium forces post expo-sure to seated WBV in all the subjects. However, analysis of 30 minpost vibration exposure measurement was not completed for allthe participants signifying that washout period of WBV could notbe determined (Martin et al., 1980).

The two simulated laboratory studies reported no significantchanges in COP derivatives of; area, velocity, mean frequency,median power frequency(Santos et al., 2008b) and RMS sway, areaand velocity (Cornelius et al., 1994) indicating no disturbance inbalance performance. However Cornelius et al. (1994) found anincrease in RMS sway in the antero-posterior direction immediatelypostWBV exposure that was still evident after 5minutes of recovery,indicating a decrease in standing balance performance. SimilarlySantos et al. (2008b) found COP ellipse area and median powerfrequency significantly increased immediately post vibration expo-sure that was still evident 20e40min later. Another noteworthyfinding observed during the recovery period measurements (20, 40and 60min) was a decreasing pattern in mean velocity and medio-lateral median power frequency in both vibration/no vibrationconditions. The possible reason for this observed decreasing patterncould be the adaptive postural control strategy induced due torepetition of balance trials (n¼ 8), despite the study considered thereliable number of trials (Santos et al., 2008a) and observed a non-significant differences across the pre and post exposure trials.Although (EMG recorded) voluntary and reflex activity of the trunkextensors was also measured by Santos et al. (2008b) the order ofpost vibration tests (reflex EMG, voluntary EMG, and balance) werenot specified and thus any delay in testing balance performancemayhave diluted any measurable differences in balance parameters.

Inaddition tothefivestudies included in this review, inwhich threedemonstrated alterations in balance, a small number of WBV labora-tory studies have also demonstrated an alteration in upright bodysway, an increase in sagittal stabilography and increased amplitude ofpostural sway followingexposure toWBVfrequencies ranging from1.4to 11.2 Hz and accelerations from 1.0 to 2.1 m/s2 (Bastek et al., 1977;Manninen, 1986, 1988; Manninen and Ekblom, 1984; Seidel et al.,1980). A recent field study conducted on a group of overgroundmachineryoperators incoalminesdemonstratedperipheralvestibularbalance disorders evaluated by using photo-optical cranio-corpog-raphy (Zahov and Medzhidieva, 2005).A further laboratory reportsuggests that there is no changes in body equilibrium on exposure tolow frequency, high amplitude, longitudinal and transverse whole-body vibration in a laboratory setting measured the body sway bya head mounting device connected to a strain gauge (Hornick et al.,1961). A previous literature review on WBV has also suggested thatbalance is affectedduring and after exposure to low frequency (<1 Hz)and also to higher frequencies (>15 Hz) WBV measured by stabilo-metric investigations (Kjellberg andWikstrom, 1985).

Although the results of these laboratory studies help in theunderstanding of the effects ofWBV on balance, the results may notbe directly applicable to real world conditions. Field studies areconsidered to be more challenging and advantageous over labora-tory studies in terms of actual exposure of the participant to specificoccupational factors including vehicle set up (vehicle vibration, seat,cabin, suspension, type of tyre /inflation, track condition/vehiclespeed and postural demands) (Salmoni et al., 2008; Tiemessen et al.,2008). Although laboratory based research can help simulate someof the characteristics of the specific vehicle, variations in vibrationmagnitude due to changes in surface and vehicle speed and otherassociated factors are very difficult to simulate. In accepting a needfor ecological validity for study design, field studies and description

of simulated fieldwork conditions conducted in the laboratory metthe inclusion criteria for this review. Studies that did not attempt tosimulate or describe field based effects were excluded.

The findings from this systematic review indicate that distur-bances in standing balance usually occur immediately post expo-sure to WBV and may be due to effects on the balance sub-systemsand suggest a cumulative effect of WBV exposure. This highlightsthe probabilities of injuries/falls immediately following exposureand also possibly at the end of the working day.

4.7. Possible mechanisms of balance disturbances

Seated whole-body vibration can influence the various sensoryinputs (visual, vestibular, somatosensory) through biodynamicresponses (accelerations) of the head, neck and trunk due to wellestablished transmission from seat to head (Paddan and Griffin,1998) and may also be due to upper limb transmission (Donget al., 2005; Mirbod et al., 1997). This seated WBV can be consid-ered as a collection of local vibrations influencing several bodysegments including the spine (Li et al., 2008), feet (Barbieri et al.,2008; Kavounoudias et al., 1999a,b, 1998, 2001), back (Schmidet al., 2005; Arashanapalli and Wilson, 2008), gluteus muscle(Duclos et al., 2007), upper limb (Tanaka et al., 2004), and also thehamstrings, collectively resulting in disturbances of balance.

In addition to alterations in local structures/muscles,WBVcanalsoalter the other distant sensory structures/systems namely visual(Ishitake et al., 1998), vestibular (Suvorov et al., 1989), and neckmuscles (Dupuis,1989; Rehn et al., 2004, 2005;Wikstromet al.,1994)thereby influencing the maintenance of balance. These alteredsensory inputsmay in turndisturbmotoroutputs through local spinal(Roll et al., 1980), vestibulo-spinal (Santos et al., 2008b;Wilder et al.,1996) and vestibulo-ocular reflexes (Suvorov et al., 1989).

Seated WBV is likely to alter the standing balance via a range ofneurophysiological mechanisms. These disturbances may bemagnified or attenuated by altering the seat to head vibrationtransmissibility which in turn is dependent on key variables such asvibration characteristics (magnitude, frequency, waveform andassociated shocks), personal factors (age, weight and height),postural components (alterations of individual’s head, neck, upperback, lumbar, pelvis posture and associated back muscle activity),and seating related factors (presence of back rest and its tilt angle)(Paddan and Griffin, 1998).

Thus, seated WBV is likely to affect the various sub-systems ofbalance resulting in balance disturbances due to abnormal motorcontrol of the trunk and limbs. This would increase the vulnera-bility of soft tissue injuries to the spine and extremities (e.g. lowback injury) and it has been classically described as a “vibro-acoustic accident” (Manninen and Ekblom, 1984).

4.8. Strengths and Limitations

This is the first systematic review which has specificallyaddressed the issue of whether exposure to seated occupationalWBV can affect balance (actual or simulated occupational envi-ronment) in an individual. This review conducted an extensive,sensitive and comprehensive search strategy using a detailed list ofsearch terms in all relevant databases and also included a supple-mentary search (e.g. conference proceedings) component.

The limitations of this comprehensive review include theexclusion of relevant literature published in languages other thanEnglish, French and German (e.g. Russian) due to the unavailabilityof adequate translation services. Our literature search identifieda number of laboratory studies on WBV without simulation of anoccupational situation or vehicle, and which unfortunately did notmeet our pre-determined inclusion or selection criteria. The

Appendix A (continued)

Quality assessment Scoring

11. Were those subjects who were asked toparticipate in the study representativeof the entire population from whichthey are recruited?

12. Were those subjects who wereprepared to participate in the studyrepresentative of the entire populationfrom which they are recruited?

13. Were the staff, places, and facilitieswhere the patients were treated,representative of the treatment themajority of patients receive?

16. If any of the results of the study werebased on Data dredging, was made thisclear?

18. Were the statistical tests used to assessthe main outcomes appropriate?

20. Were the main outcome measures usedaccurate (valid and reliable)?

21. Were study subjects in differentintervention groups or were the casesand controls recruited from the samepopulation?

22. Were study subjects in differentintervention groups or were the casesand controls recruited over the sameperiod?

25. Was there adequate adjustment forconfounding in the analyses fromwhichthe main findings were drawn?

Scoring guidelines: For 5th and 23rd item: yes, 3 core confounders and three ormore other confounders; partially, 3 core confounders and one or two otherconfounders; and no, 3 core confounders but no other confounders, or less than 3core confounders.For Item 13: yes, 2; partially, 1; no, 0.

R. Mani et al. / International Journal of Industrial Ergonomics 40 (2010) 698e709 707

strength of the findings are somewhat limited as we did not poolthe data for the various measure of COP due to the limited number(2) of studies for which these were available.

Future investigations are warranted to explore the specificfunction of the vestibular apparatus on exposure to seated occu-pational WBV in a field set up in order to better understand effectsof the disturbances to the vestibular apparatus. Such studies shouldinclude fieldwork based experiments that explore the effects onfunctional and dynamic balance tasks (e.g. lifting) after exposure toseated occupational WBV in a real vehicle (Salmoni et al., 2008).

5. Conclusion

This systematic review is based on the cumulative findings offive publications (two field; three laboratory) where three of thestudies found evidence for seated WBV challenging standingbalance performance (bipedal/unipedal stance) while two labora-tory studies did not find such effects. Thus there is modest evidenceto suggest there is a decrease in standing balance performancefollowing exposure to seated occupational WBV. If such posturaldisturbances do occur from vibration induced changes to thesomatosensory, visual and vestibular pathways this may disturbdynamic balance following a period of vehicle driving. Thus it ismay be that kinaesthetic and balance demands of functionalposture will be adversely altered immediately following suchexposure and this may place the driver at risk of a possible injuryfrom falls or predispose them to accidents in occupational relatedtasks such as lifting, due to suboptimal movement strategies.Although this is considered a plausible argument further fieldworkbased research is required to verify such effects from exposure towhole-body vibration.

Acknowledgements

The authors would like to acknowledge assistance provided byPrasath Jayakaran (Ph.D. candidate) for secondary review of qualityanalysis and exposure assessment of the included studies; DavidJackson, Research Assistant in assisting data extraction from thestudies andCatherineRobertson, SeniorLibrarian,UniversityofOtagoin assisting with the design of the search strategy for this review.

Appendix A. Modified Downs and Black (1998) questionnaire.

Quality assessment Scoring

Serial no. Items Yes No/partial Unable todetermine

1. Is the hypothesis/aim/objective of thestudy clearly described?

2. Are the main outcomes to be measuredclearly described in the Introduction orMethods section?

3. Are the characteristics of theparticipants included in the studyclearly described?

4. Are the interventions of interest clearlydescribed?

5. Are the distributions of principalconfounders in each group of subjectsto be compared clearly described?

6. Are the main findings of the studyclearly described?

7. Does the study provide estimates of therandom variability in the data for themain outcomes?

10. Have actual probability values beenreported for the main outcomes?

Appendix B

Modified criteria list for evaluation of whole-body vibrationexposure

1. Damping is the footwear/suspension/seat cushion during WBVexposure specified?

2. Magnitude is themagnitude or amplitude of vibration specified?3. Direction is the direction of vibration specified?4. Frequency is the frequency of vibration specified?5. Type is the waveform of vibration specified?6. Duration

a. Is the duration of the individual exercise session specified?b. Is the number of exercise sessions specified?c. Is the full length of the exercise period specified?

7. Posture is the posture adopted during vibration exercisedescribed?

8. Is participant contact specified?a. steering wheelb. back restc. foot rest

Score guidelines: “yes”, Y; “no”, N; N/A, not applicable.Each yes yields one score, i.e. maximum of 12 (items 6 & 8, 3

points).

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