This article was downloaded by: [The University of Manchester Library]On: 20 December 2014, At: 21:12Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

ErgonomicsPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/terg20

The perception of exertionF. GAMBERALE aa National Board of Occupational Safety and Health, Ekelundsvagen 16 , S-171 84 Solna,SwedenPublished online: 30 May 2007.

To cite this article: F. GAMBERALE (1985) The perception of exertion, Ergonomics, 28:1, 299-308, DOI:10.1080/00140138508963137

To link to this article: http://dx.doi.org/10.1080/00140138508963137

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of theContent.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

ERGONOMICS, I~85, VOL. 28, NO. I, 299-308

The perception of exertion

By F. GA¥BERALE

National Board of Occupational Safetyand Health,Ekelundsviigen 16,S-171 .84 Solna, Sweden

In the study of physicalwork a multiplicityof methods have been used to measureexertionand fatigueat theperceptual level. In recentyears,howeyer, the assessmentof perceived exertion and subjectivefatigue during physical work has reliedalmostexclusively on four psychophysical measurement techniques: (i) ratio scaling, (ii)categoryscaling, (iii)rating scalesand (iv)acceptabilityscaling.This paper.providesa descriptionof these measurement techniques,a review of the major experimentalresultsobtained by their application to the study of physicalwork, and a discussionof the use of perceived exertion data as a criterion in the assessment of manualmaterials handling.

1. IntroductionAlthough subjective reactions to physical work have often been found to correlate

with work intensity and work performance, until recently they have not been seriouslyconsidered as constituting a possible basis for criteria in the assessment of manualmaterial handling. The reason for the neglect of subjective reaction in favour of better­defined physiological indicators ofexertion is that these reactions have been difficult todefine and measure. Some ofthe difficulties are probably simply due to a certain lack offamiliarity with the use of 'sophisticated' psychophysical methods on the part of thephysiologists. However, most of the difficulties are fundamental and are connectedwith the nature of the measurement itself. Being a privately experienced event,perceived exertion, or any other subjective reaction to physical work, can only bemeasured indirectly through the use of self-report techniques. Thus, it is important tobe aware of the fact that the individual's report of perceived exertion or experiencedfatigue constitutes only a distal reaction. The extent to which this distal reaction is areflection of the proximal reaction, i.e. the reaction within the individual organism,relies very heavily on the adequacy of the measurement procedure used. Therefore, thepractical usefulness of the assessment of subjective symptoms cannot be evaluated ingeneral terms. The applicability of subjective symptoms as criteria in the assessment ofmanual material handling will always depend on a series of elements which affect thereliability and validity of the measurement, e.g. (i) the type of subjective reactionobserved, (ii) the way in which the reaction is observed and recorded, (iii) the extent towhich the reaction varies systematically in different work operations, (iv) how well thereaction correlates with work intensity and work performance and (v) how well itcorrelates with the physiological and neurological events.

An analysis of the literature on this topic clearly suggests that no one singlesubjective reaction, measurement method or experimental strategy is more adequatethan others in every condition and for all purposes. However, in recent years theassessment of perceived exertion or related symptoms of subjective fatigue duringphysical work has relied almost exclusively upon psychophysical measurementtechniques. Four of these techniques have been used more systematically than others in

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

300 F. Gamberale

several studies and have produced interesting results. These four techniques will bedescribed in the present paper which will also review the main results attained throughtheir application. The paper concludes with a discussion of the applicability of thesetechniques in the assessment of manual material handling.

2. Ratio-scaling techniquesThe application of psychophysical methods has shown that for a great number of

sensory and perceptual dimensions, the functional relationship between subjectivesensory or perceptual magnitude and the physical dimension being manipulatedappears to approximate a power function. The general formula for such a relationshipis presented by Stevens [592] as 'I' = KC1>", where 'I' is the magnitude of sensation, C1> isthe physical stimulus intensity and K and n are parameters characteristic of the type ofexperience being scaled. If this power function is expressed in logarithmic terms,log 'I' = n(1og C1» + log K, the result is simple linear equation. Thus, when plotted onlog-log co-ordinates, the exponent of the power function constitutes the slope of astraight line. An exponent greater than 1·0 indicates that the perceptual intensity is apositively accelerated function of the physical stimulus, while an exponent less than 1·0indicates that the function is negatively accelerated.

In psychophysical studies the subjective reactions are measured using direct-scalingmethods, i.e. methods for obtaining direct judgements of subjective qualities on a ratioscale. These methods are either estimation methods, in which the subject estimates therelative magnitude of physical stimuli, or production methods, where the subjectmanipulates the physical stimuli to reflect a given subjective relation.

Both estimation methods and production methods have been used to study theperception of physical work. However, because they are much easier to use andprobably even more reliable, estimation methods, including ratio estimation [207) aswell as magnitude estimation [591), have generally been preferred to productionmethods.

In ratio estimation the subject is asked to estimate the percentage magnitude of astimulus in relation to a standard. In magnitude estimation the subject will match anumber directly to the perceived magnitude of a stimulus in reference to a standardstimulus which has given a numerical magnitude. For both of these direct-scalingmethods the basic assumption is that the subject is able to match his perceptions withnumbers. Numerous empirical studies have shown that subjects are able to performthis task and that the subjective scale obtained is a ratio scale.

Previous psychophysical studies clearly indicate that the perceived intensity ofmuscular effort follows the psychophysical power law. Thus, Stevens and Mack [589]obtained a power function with an exponent of I·7 when scaling subjective force, asexerted in the squeezing of a handle. Borg and Dahlstrom [88) investigated musclarwork carried out on a bicycle ergometer and obtained an exponent of 1·6. Exponents ofthe same magnitude were also found by Eisler [202] in relating subjective force tophysical force both for involving large muscle groups, i.e. exerting a force against a footpedal, and for work involving small muscle groups, i.e. squeezing a handgrip. A powerfunction with an exponent of \·6 was also obtained by Gamberale et al. [239] in aninvestigation of the subjective experience associated with external resistance tobreathing. Perceived etTort depends not only on the intensity of physical workperformed but also on the duration of the work. When investigating the combinedeffects of the two factors Stevens and Cain [588] and, later, CatTarelli et al. [III] foundthat the increase of effort with time also followed a power function. The exponent of

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

Industrial back pain in Europe 301

this function was shown to depend on the type of work investigated as well as on itsintensity.

To give a more concrete example of the application of ratio scaling to the study ofperceived exertion, some of the results ofa recent study by Ljungberg et al. [378] will bereferred to in more detail.

In this investigation five brewer's draymen with several years of occupationalexperience were studied in the laboratory during horizontal lifting work, whichsimulated an order filling task at a brewery. The task consisted of lifting a caseapproximately 1·1 m horizontally at a height of 60 em. In order to facilitate repeatedlifting, a treadmill was used to return the case after each lift. The subjects worked at agiven lifting rate with cases weighing 67, 100, 133, 167 and 200% of a case weight,which they had individually chosen as constituting the maximum amount that theycould lift without strain and discomfort. After 11 min of work at each load, eachsubject was asked to give a magnitude estimation of the workload. The estimations.were made by having the subject indicate a number equivalent to the perceivedworkload in relation to the immediately preceding workload, which was alwaysassigned the value 10.The sequence ofworkloads was chosen in such a way that when asubject had compared each load with the immediately preceding load, he hadperformed all possible pairwise comparisons between the loads. Since the sequence ofthe workloads was also performed in the reversed order a complete matrix of relativecomparisons between case weights was obtained for each subject. On the basis of thesematrices, a scale of perceived workload was calculated for each subject according toEkman [207]. Using the same methods, a subjective scale was also calculated for allsubjects on the basis ofa ratio matrix ofgeometric mean values. The results of this partof the investigation are illustrated in the table and figure 1.

As shown in the table and figure 1 the relation between the magnitude estimate ofperceived workload and case weight (objective load) is satisfactorily described by thepsychophysical power function. The exponents of the individual's function variedbetween 1·44and 2·45, indicating that a doubling of the case weight would result in anapproximately three- to fivefold increase in perceived workload.

In summary, the application of ratio-scaling techniques to the study of physicalwork can provide a detailed description of the relationship between the perceived andthe physical level ofexertion. There is strong empirical evidence that perceived exertionis a positively accelerated function of the workload. Although there are inevitableinterindividual differences, on the average, the exponent of the function will fall withina limited range (1. 5-1,9) irrespective of the type of work performance or the musclegroups involved.

Magnitude estimates of perceived workload (ME) as a function of case weight in horizontallifting of cases (from Ljungberg et al. [378]).

Subject Function R2

I ME=0·010kg!·643 0·9692 ME~0'032kg!'444 0·9913 ME=0.015 kg!'702 0·9894 ME =0·006 kg2-06! 0·9795 ME=O.OII kg N 49 0·998

Total ME=O.OII kg l '86O 0·997

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

302 F. Gamberale

Magnitude estimation (ME)

5

ME -o.om,"60 R' -0'" /

/~/ Case - weight kg

10 20

2

3

4

O........=- -----.---....Jo

Figure 1. Magnitude estimation of perceived workload (ME) as a function of case weight. Theplotting and curve fitting were performed on the basis of average values for the fivesubjects. (from Ljungberg et al. [378]).

3. Category scalingAs an alternative to the ratio-scaling techniques, subjects can be instructed to rate

the perceived intensity ofa stimulus on a category scale with equal intervals. The use ofthese scales involves procedures were the subjects work with numerical categories. Thesubjects are usually presented one low and one high stimulus to define the ends of thepsychological continuum. The category scales were originally believed to be ratioscales. However, it has been shown [203] that values obtained with a category scale donot plot as a linear function of magnitude-scale values. According to Ekman andKiinnapas [208] the category scale is closely matched by a logarithmic transformationof the magnitude scale.

Category scales have been used to collect estimates of subjective effort duringprolonged physical exercise and endurance tasks. The technique used was developedby Caldwell [113] for use with an isometric handgrip task. The procedure consists ofletting the subjects indicate when, in an endurance task, they perceive the expenditureof 1/5, 2/5, etc., of their available effort or when, in the same self-paced fashion, painintensity attained values of 1-5.

Using this technique, Cladwell [113],Caldwell and Smith [114],Menzer et al. [414]and Lloyd et al. [380] have obtained a linear relationship between time on an isometrictask and subjective estimates, of both pain intensity and perceived effort expended.Using the same technique, subjective estimates ofeffort were also found to be linearly

.related to endurance time during treadmill performance [379].It has been suggested [331] that the self-paced rating procedure used in the above­

mentioned studies might have contained a timing artifact, in that the subjects mighthave been judging elapsed time rather than effort expended. The relationship betweensubjective estimates and time on the task 'would attain a spurious linearity if, assuggested by Kinsman and Weiser, the subjects of these studies were matching intervalson the time dimension. .

The suggestion ofspurious linearity is indirectly supported by the result ofa recentexperiment [330], in which static exercise was performed as a 900 elbow flexion at 25%of maximal voluntary contraction force, either until exhaustion, or for a duration of20-80% of maximal endurance time. In this experiment the subjects were requested torate effort expended after the exercise had been interrupted by the investigator.

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

Industrial back pain in Europe

100 ,., ellorlexpended

80

60

40

20

% of max, endurance time

303

20 40 60 80 100

Figure 2. Mean values and standard errors (N ee 18)for the rating of perceived effort expendedduring static concentrations from Kilborn et al. [330]).

Furthermore, the subjects rated effort expended only once at the end of eachsubmaximal test and only one submaximal test was performed each experimental day.This procedure was adopted in order to minimize the possible effect of time on theratings. Under these conditions, the relation of perceived effort expended and time ontask, as shown in figure 2, was no linear.

Subjects tended to overestimate effort expended as related to endurance time. Thisoverestimation was statistically significant (p<O·OOI) for each condition correspond­ing to 50, 60, 70 and 80% of TmBI" The average degree of overestimation in allsubmaximal tests was also calculated for each subject. Effort expended was overes­timated by 15 of the 18 subjects (p = < 0·008; two-tailed binominal test). The resultsclearly indicated a tendency for the subjects to underestimate their maximal staticendurance capacity during the task.

As mentioned above, a category scale with numerical values from I to 5, has beenused to collect estimates of pain intensity using the self-paced technique. The value of 1was defined as constituting the first noticeable perceptible pain and the value of 5 asintolerable pain, i.e. the pain perceived at the end of the endurance task. In theexperiment by Kilborn et al. [330] reviewed previously, subjects were also required torate pain intensity on a 5-point rating scale ranging from 'no pain' to 'intolerable pain'.In this experiment at maximal endurance time no subject rated perceived pain using thehighest pain intensity of the scale, which clearly indicated that perceived pain on .thelocal muscles was not the primary factor limiting endurance in the task. Consideringthese results, it seems clear that perceived pain intensity, especially if assessed atsubmaximal endurance time, would be a poor predictor of the static endurancecapacity of the individual.

The use of category scales in the study of perceived exertion during physicalexercise has produced results somewhat less convincing than those obtained by the useof ratio-scaling techniques. The relation between perceived effort expended and timeon task in prolonged physical work or endurance task is not as well explored anddocumented as, e.g. the relation between perceived exertion and workload. In part, thismay be due to peculiarities associated with category scaling.

4. Rating scalesThe rating scales is the most commonly used measurement instrument in psych­

ology. Although both the rating scale and the category scale imply the use ofa number

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

304 F. Gamberale

ofcategories, the two should not be confused. In the rating scale no assumption is maderegarding the distance between the different categories, and the rating values obtainedare considered to be on the ordinal level.

By far the most frequently used scale for rating the degree of perceived exertionduring physical work is the RPE scale (rating scale ofperceived exertion) developed byBorg [84]. The scale, printed in a quarto format, is as follows:

67 very, very light89 very I~ght

1011 Fairly light1213 Somewhat hard1415 Hard1617 Very hard1819 Very, very hard20

The RPE scale has been developed on the basis ofempirical data from work on thebicycle ergometer. 'In fairly young to middle-aged people (25 to 45 years old), workingat moderate to high intensity levels, the heart rate roughly corresponds to 10 times theRPE value' [86].Thus, according to Borg, the relation between RPE and heart rate forwork on the bicycle ergometer is linear. Consequently, RPE is also a linear function ofthe physical workload. This linear relationship has been confirmed by severalinvestigators (for a review see ref. [331D.

The fact that RPE is found to be a linear function of the physical workload shouldnot be interpreted as conflicting with the results of the previously psychophysicalstudies, in which perceived exertion was found to be a positively accelerated function ofthe workload. It is important to observe that the form of the relation obtained whenRPE values are plotted to the corresponding values of heart rate of the workload,depends largely on the specific characteristic of the rating scale itself, i.e. the number ofcategories, the verbal definition, etc. To obtain a linear relationship between the RPEand workload was in fact one of the objectives in the construction and development ofthe scale. This objective was achieved by a careful choice of verbal categories.

In spite of the metrical limitation of the rating scale compared with the ratio scales,RPE has been the most frequently employed method for the assessment of subjectivequalities during physical work. Thus, a substantial literature has become availableconcerning the significance of perceived exertion as measured by the RPE scale. SinceRPE values could be used as a complement to the circulatory responses duringexercise, and in fact the scale was constructed with this objective, it is of special interestto observe when changes in the physiological responses are not followed by corre­sponding changes in RPE.

In a study by Pandolfet al. [468], changes in temperature were found to affect heartrate but not RPE. In another study [238] the heat gain resulting from wearing anunventilated gas-protective suit during simulated fire fighting and gas accident

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

Indus-trial back pain in Europe 305

practice, as well as during exercise on a bicycle ergometer, brought about aconsiderable increase in heart rate which was not followed by a corresponding increasein RPE. According to the latter authors, heat load does not have an impact uponperceived exertion comparable to the physiological strain it produces. Thus, 'heat loadwill create conditions in which a person will overestimate his physical endurance. Anoverestimation of this kind could be a determinant factor in the occurrence of cases ofexhaustion and collapse observed in fire-fighting and other extreme situations' [238].Provided that exercise on the bicycle ergometer is performed at the same workload, e.g.100W, different pedalling rates produce the same heart rate. However, Henriksson et01. [273] and Pandolf and Noble [469] have reported that pedalling at a rate of 30 or40 rpm resulted in higher RPE than at a rate of 60 or 80 rpm. Ekblom and Goldbarg[204] and Sjoberg and Frankenhaeuser [573] used autonomic blocking drugs to affectheart rate during physical work. While heart rate changed in the expected direction as aresult of the drugs, RPE was unaffected. Pandolfet al. [468]and Morgan [430] reportedthat while heart rate was unchanged during the course of work on a bicycle ergometer,RPE tended to increase after 5 min of work. Similar results were obtained byLjungberg et 01. [378]during horizontal lifting work. RPE collected after 4 and 13minof work, respectively, showed a significant increase while heart rate did not display anynoticeable differences. Finally, Gamberale et al. [240] showed that at the same heartrate exercise on a bicycle ergometer was perceived by a group of women as moredemanding during menstruation than during either the premenstrual or post­menstrual phase. The changes in RPE during the menstrual cycle were interpreted asdue to motivational factors.

Many investigations have shown that the relationship between RPE and heart rate, is highly dependent upon the type of physical task involved. At a given heart rate, RPE

is lower for running than for work on the bicycle ergometer [55, 204] or for walking[455]. Arm exercise also gives higher RPE at the same heart rate than cycling [204,236]or pushing a wheel barrow.

Besides the RPE scale, other rating scales have been used for the measurement ofperceived exertion. However, not one of these scales has shown the same versatility,'parsimony and validity as the RPE scale.

5. Acceptability scalingTo determine the load-handling capacity of industrial workers, some investigators

[43, 129, 577, 579, 5801 have systematically collected estimates of workload duringdifferent manual material-handling activities standardized in the laboratory. Themethod used, which here will be called the RAL method (rating of acceptable load),resembles in some respects one of the basic psychophysical methods, i.e. the method ofadjustment, used to determine perceptual threshold. The procedure is to ask the subjectto adjust his work-load, i.e. the weight of lift, to the maximum amount that he canperform without straining himself, or without becoming unusually tired, weakened,overheated or out of breath [576]. Following the procedure used in the method ofadjustment, the subject on one occasion will start with a heavy weight and on anotheroccasion with a light weight. The two results are then averaged.

The results ofa series of studies in which the RAL method has been used, have beensummarized and integrated by Snook [576]. In his report Snook presents a series oftables indicating the maximum weights predicted to be acceptable to 10,25, 50 and90% of the working population. Similar tables have also been published by Ayoub et01. [51], who combined their own data with the data generated by Snook [576]. At the

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

306 F. Gamberale

present time there is no general agreement concerning the validity of the recommend­ations represented by these tables. However, according to Snook 1576], a proper use ofthe tables in designing the job to fit the workers can reduce the occurrence of industriallow-back injuries more effectively than selecting the worker for the job, or training theworker to lift properly. .

The investigators who have developed and used the RAL method to determine themaximum acceptable workload in lifting tasks, consider their method to be apsychophysical method [576]. The use of the term psychophysical instead of psycho­logical can be questioned since it is not evident that the subject in the RAL method isscaling sensory or perceptual stimuli. On the contrary, it is obvious that the subject'sprevious experience with lifting tasks will influence his choice of workload. Conse­quently, we should consider his choice as being a cognitive response rather than aperceptual response. Of course, the users of the RAL method are aware of this fact,since they point out the importance of using industrial workers as subjects whenstudying industrial tasks [576].

Independent of their validity, the estimates of subjective workload collected byusing the RAL method undoubtedly present some difficulties of interpretation. Thesewill be illustrated by reference to the previously described investigation by Ljungberget al. [378]. The results of the application of the RA L method in this investigation areshown in figure 3.

As shown in figure 3 it only took subjects 5-10 min to find a case weight which alsobecame their final weight after 1hour of lifting work. The preferred weight was aboutthe same in the two trials indicating good test-retest reliability. However, theinterindividual variation was large and there was no covariation between preferredweight, muscle strength and aerobic power or body size. Furthermore, there was noobservable relation between preferred weight and perceived exertion as measured bythe RPE scale. These results suggest that the choice of the case weight was not governedby crude somatic factors or by known biomechanical factors. A further question raisedby this investigation regards the representativeness of values based on standardizedlifts.

In a study of vertical lifting with the same instructions and comparable lifting rate,

30 Case - weight kg

20

10

~ """"\~~ • ~----~ 1696.'320

~./":::---- _ _ _ '202 12.06'" -.-~- --- - ,_--- ".2" .1020~~'W---== ---~q-r- -" - - - 10 ~~ _ 10 2,)

.'" --- q oQo Q/ __ --..0- -- --t'-- - ----<r- --q.- ~ 4 630~ 528

Time. rnmo I I Io W ~ ~

Figure 3. Individualchanges in the preferredcase weightfor the five subjectsduring I hour ofliftingat a standard rate. Each subject is representedby one symbol. The subject startedeither with 2Skg in the case (unbroken lines) or with Skg (dashed lines). The table on theright lists individual mean values (starting with 5 or 2Skg) for preferred case weights atthe standard (35s) and the double (18 s) liftingrates after 60 min work (from Ljungberget al. [378]).

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

Industrial back pain in Europe 307

Snook et al. [580] showed that, in lifting from the floor to a height of 25 em, subjectspreferred to work with about twice as heavy a case as in the present study. This isattributable to the fact that the lifting task used in the present study was performedhorizontally to simulate a kind of lift which is very common in working life. Therecommendations by Snook [576] or those by Ayoub et al. [51] are based uponexperiments with vertical lifting in optimal work positions. Lifting according to such'recommendations may lead to overload if applied uncritically in working life.

6. Concluding remarksThe present paper has dealt with the four main techniques available for measuring

subjective reactions during physical work performance. Examples of their applicationto the study of physical work have also been presented. By now, it should be clear thatno one of these techniques can be considered as being generally superior to the others.However, each of these techniques has specific characteristics which makes it moreappropriate than the others for certain purposes, These characteristics can make thesame technique quite unsuitable for other purposes.

Undoubtedly, the best method for studying how subjective sensations in a physicaltask vary with variation in stimulus intensity is a ratio-scaling method, i.e. magnitudeestimation. As a matter of fact, an adequate description of the relation betweenperceived exertion and workload for a specific physical task can hardly be obtained byapplying the other techniques. In practical settings where absolute comparisonsbetween different work situations are needed or when interest is focused on interindi­vidual or intraindividual comparisons, the use of a rating scale can have clearadvantages compared with magnitude estimation or other techniques. Category-scalingtechniques have been applied to the study ofphysical work almost exclusively to collectestimates of effort or pain in prolonged exercise or endurance tasks. Since the ratio­scaling properties of the category scale can be questioned, other methods, for example,a simple rating scale, would probably have fulfilled the same purposes. The use of theRAL method seems to be confined to situations where manual material-handlingactivities have been evaluated and where norms aimed at the prevention of manualhandling injuries have been generated. The use of the RAL method is based on theassumption that the worker is able to indicate with some accuracy the highestworkload which is tolerable to him. Furthermore, it is assumed that the workloadsaccepted by workers in conditions which simulate real work, are below the loadsleading to manual handling injuries. Although the validity of these assumptions hasnot yet been assessed, the RAL method is very attractive in its simplicity and deservesserious attention.

Independent of the specific technique used to measure it, perceived exertion shouldbe interpreted as constituting a 'summing up' of the influence from all structures understress during exercise. Of course, there is no objective counterpart of this perceptualphenomenon. However, it should be obvious to everyone that the perception ofexertion during physical work not only has a psychological validity, but it also reflectsreal conditions such as the interplay between the requirements of the job and thecapacity of the individual.

Dans l'etude du travail physique, on a utilise une multitude de methodes pour determinerI'effort et la fatigue au niveau perceptif. Ces dernieres annees, cependant, I'analyse de I'effortpercu et de la fatigue subjective au cours du travail physique a Ie plus souvent eu recoursexclusivement :i quatre techniques d'evaluation psychophysique: (I) utilisation des echelles de

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14

308 Industrial back pain in Europe

rapport, (2) utilisation des echelles de categoric, (3) echelles de jugernent et (4) utilisation desechelles d'acceptabilite. Cet article fournit une description de ces techniques, des principauxresultats obtenus atravers leur utilisation lors de I'analyse du travail physique. La discussionporte sur I'utilisation des donnees en tant que criteres de l'efTort percu dans I'analyse de larnanutention.:

1m Studium korperlicher Arbeit wurde eine Vielzahl von Methoden angewendet, urnAnstrengung und Errniidung auf der Wahrnehmungsebene zu messen. In den letzten Jahrenberuhte die Beurteilung von empfundener Anstrengung und subjektiver Errniidung wahrendkorperlicher Arbeit jedoch beinahe ausschlieBlichauf vier psychophysischen MeBtechniken: (I)Verhaltnisskalierung, (2) Kategorienskalierung, (3) Schatzskalen und (4) Akteptanzskalierung.Diese Arbeit gibt eine Beschreibung dieser vier MeBtechniken, einen Oberblick iiber bedeutendeexperimentelle Ergebnisse, die man aus ihrer Anwendung auf das Studium korperlicher Arbeit ­erhalten hat, und eine Diskussion iiber den Sinn von Daten empfundener Anstrengung als einKriterium fiir die Beurteilung manueller Materialhandhabung.

~1*{'F~O)liIf~I':10 p "t'9:lJ:vtv~}ld'::to ~t 6~)J tfif.~ I:: ~lIl~)iT 6 tzs»: ~ <O)niIdJ:Ffj \ '':' i1.-::!i ts; Up llltilil'li~1*{-'Fmr:pO)~)J~I::llf.~~ t O)fHiI!it;tl~ t f.., t'O)f!I;~~O) 4 -::>O)m~ml!+e~

t;.:1ll~;E$I.:tt?n>6o (l)l:t$R!l-:>~:t, (2);/)T:iI)-7..7-1)~J', (3lf¥5E.R.N, -fl"'C{4Iff:@:lilF;1l-::H10) 4 -::>l'1> 6. ::<j;:iR1BJtl'I;l:':'.t1. '? 0)1Il~;E$1': -::>~, "t'jzt'~, j;l;I1*1-'F~O)liIf~"':' h -?O)i1l~JEi~~ i(!jm-ro':' I:: I': J;? "t't,f}'?ho::tq~Ui~:!"H':"J~>"t'~~l,r.Jmll!1t!k~'1-'F~O)i(liilli'::toIH¥.i:I!::'_-::~)J~O)T-?~m",o':'I::'':-::>P''t'~iH~Too .

Dow

nloa

ded

by [

The

Uni

vers

ity o

f M

anch

este

r L

ibra

ry]

at 2

1:12

20

Dec

embe

r 20

14