Spanish version of the Swedish Occupational Fatigue Inventory (SOFI): Factorial replication, reliability and validity

ARTICLE IN PRESS

0169-8141/$ - se

doi:10.1016/j.er

�CorrespondE-mail addr

(J.L. Gonzalez

International Journal of Industrial Ergonomics 35 (2005) 737–746

www.elsevier.com/locate/ergon

Spanish version of the Swedish Occupational FatigueInventory (SOFI): Factorial replication, reliability and validity

Jose Luis Gonzalez Gutierreza,�, Bernardo Moreno Jimenezb,Eva Garrosa Hernandezb, Almudena Lopez Lopeza

aUniversidad Rey Juan Carlos, Facultad de Ciencias de la Salud, Avda. Atenas s/n, 28922 Alcorcon (Madrid), SpainbUniversidad Autonoma de Madrid, Facultad de Psicologıa, Ctra. de Colmenar km. 15, 28049 Madrid, Spain

Received 10 April 2004; received in revised form 25 September 2004; accepted 2 February 2005

Available online 15 April 2005

Abstract

This paper presents the adaptation to Spanish of the Swedish Occupational Fatigue Inventory (SOFI) (Ahsberg,

Gamberale and Kjellberg, 1997), an instrument for the multidimensional evaluation of work-related fatigue. A total of

240 nurses working in eight special attention units responded to a pool of 25 items about their level of fatigue after

work. Proposed SOFI structure (Ahsberg, 2000) was tested by means of Confirmatory Factor Analysis, and the data

demonstrate an acceptable fit to the theoretical five-factor model (with lack of energy defined as a general latent factor

representing much of the variance of the items) when the number of items was reduced to 15. Alpha coefficients were

calculated, and high internal consistency values were obtained for most of the subscales. Convergence was also

evaluated by calculating correlations between the SOFI subscales and a number of independent indices. All five

resulting subscales make up a promising 15-item instrument for the evaluation of work-related fatigue in the Spanish

language.

Relevance to industry: A reliable and valid instrument for the multidimensional evaluation of work-related fatigue

may be of great importance to an understanding of the origin and development of work-related disorders. This study

presents the adaptation to Spanish of the SOFI, a highly promising instrument, given the lack of multidimensional

instruments adapted to the Spanish language for the measurement of work-related fatigue.

r 2005 Elsevier B.V. All rights reserved.

Keywords: Perceived fatigue; Swedish occupational inventory; Validity; Reliability; Factorial replication; Questionnaire

e front matter r 2005 Elsevier B.V. All rights reserve

gon.2005.02.007

ing author. Fax: +3491 4888831.

ess: [email protected]

Gutierrez).

1. Introduction

Fatigue has been identified as one of thecommonest problems in developed countries(Lewis and Wessely, 1992), and a serious threat

d.

www.elsevier.com/locate/ergon

ARTICLE IN PRESS

J.L. Gonzalez Gutierrez et al. / International Journal of Industrial Ergonomics 35 (2005) 737–746738

to quality of life when it becomes chronic orexcessive (Piper, 1989). In spite of this, the conceptis ill-defined, fundamentally due to the inclinationto refer in the same linguistic terms to the presenceof different conditions (Ahsberg, 1998). Insome cases, this lack of definition has led authorsto exclude the phenomenon from scientific discus-sion (Munscio, 1921). Nevertheless, it is morefrequently considered as a multidimensional con-struct that differs among different levels ofresponse.

Bills’ (1934) approach has been the most widelyaccepted in this respect. He drew a distinctionbetween three aspects of fatigue: physiologicalfatigue (reduction of physical capacity), objectivefatigue (reduction in work) and subjective fatigue(feelings of weariness). Following the proposal ofthis author, most of the operative definitions havebeen grouped in bodily changes (Bigland-Ritchie,1984; Christensen, 1962; Eidelman, 1980), changes

in performance (Bartlett, 1953; Browne, 1953;Hemingway, 1953; Mital et al., 1994; Welford,1953) and perceptual changes (Britton, 1983; Piper,1986; Wessely et al., 1998).

Each of these three levels of response in fatigueis associated with a specific method of evaluation.Physiological parameters, such as muscular activ-ity (EMG) (Hagberg, 1981; Hagg et al., 1987;Malmqvist et al., 1981), blood pressure and heartrate (Bystrom et al., 1991; Kilbom et al., 1983),oxygen consumption (Gamberale, 1972), cerebralactivity (Torsvall and Akerstedt, 1987), melatoninlevel (Akerstedt et al., 1982), urinary cortisol(Melamed and Bruhis, 1996), and changes incritical flicker fusion frequency (Rey and Meyer,1980) have been used as indicators of physiologicalmanifestations of fatigue.

Behavioural manifestations, mainly in the formof deterioration in performance (Bartlett, 1943),have been studied, for example, through thecalculation of reaction times (Kjellberg et al.,1996), or error rate during tasks (Henning et al.,1989).

Finally, perceived fatigue has been assessed byuni-dimensional scales, including a single questionabout how tired the person feels (Goldmark, 1912;Lee et al., 1991; Monk and Folkard, 1985; Oberget al., 1994; Okogbaa et al., 1994; Rabinach, 1992;

Rimehaug and Svebak, 1987; Schaeffer et al.,1995). Within this perspective, Borg has developedseveral rating scales that have been correlated withphysiological responses and physical load, amongthem his successful Rating of Perceived Exertion(RPE; Borg, 1970, 1998) and CR-10 (Borg, 1982,1998). Another interesting instrument is theFatigue Severity Scale (FSS; Lichstein et al.,1997), which provides an exclusive score onseverity of fatigue by means of nine items.These instruments allow researchers to obtain

an estimation of the intensity of perceived fatigue,but do not offer information about its quality. AsAhsberg (1998) points out, even if the sameintensity of fatigue can be perceived after differentwork tasks, the perception of fatigue may beof a different nature. A multidimensional ap-proach to fatigue allows the simultaneous evalua-tion of intensity and quality of perceived fatigue(Kinsman and Weiser, 1976). Prominent amongthe instruments developed from this perspective isthe Multidimensional Fatigue Inventory (MFI;Smets et al., 1995, 1996), designed for use withinthe clinical context and employed in the evaluationof fatigue in cancer patients. The validity of thisquestionnaire was examined through confirmatoryfactorial analysis, and the five factors wereinterpreted as General fatigue, Physical fatigue,Mental fatigue, Reduced motivation and Reduced

activity. Another instrument of great interest forclinical practice is the Piper Fatigue Self-Report

Scale (Piper et al., 1989), initially developed for theevaluation of patients exposed to radiotherapytreatment. This instrument proposes seven dimen-sions of fatigue: Temporal, Intensity, Affective,Sensory, Evaluative, Associated symptoms andRelief. Finally, the FACES questionnaire (Shapiroet al., 2002), allows the evaluation of five dimen-sions of fatigue: Fatigue, Energy, Consciousness,

Energized and Sleepiness. Reliability and validityof the instrument, for a sample of 372 patientswith sleep disorders, were satisfactory.Despite the above-mentioned studies, and with

some exceptions, no systematic attempt has beenmade to develop self-report scales for the evalua-tion of perceived fatigue in occupational settings.As Ahsberg (1998) points out, it is not clear towhat extent fatigue characteristics are, as factors

ARTICLE IN PRESS

J.L. Gonzalez Gutierrez et al. / International Journal of Industrial Ergonomics 35 (2005) 737–746 739

associated with the process of disease, correspondto the factors present in the process of work-related fatigue. The characteristics of fatiguechange depending on the specific contexts, andseveral studies have been carried out with the aimof identifying meaningful dimensions involved inthe perception of work-related fatigue.

The qualitative aspects of fatigue most fre-quently described have been physical fatigue andmental fatigue (Chalder et al., 1993; Grandjean,1979), while other aspects of the construct usuallystudied are sleepiness (Gillberg et al., 1994) anddiscomfort (Cameron, 1996). A study amongrailroad workers identified two dimensions offatigue: Weakened activation and Weakened moti-

vation (Kashiwagi, 1969). On the other hand,Matthews and Desmond (1998) identified fourbasic dimensions of fatigue as result of exposure toa simulated driving task: Boredom, Visual fatigue,Malaise and Muscular fatigue, while Saito andKashiwagi (1970) extracted the following dimen-sions from a pool of 30 fatigue symptoms in asample of 9575 industrial workers: Drowsiness and

dullness, Mental symptoms, and Projection of

physical disintegration. These dimensions wereused later in a study with 17,789 participants, inwhich the first dimension (Drowsiness and dullness)proved to be common to a great variety ofprofessions, whereas the second (Mental symp-

toms) and third (Projection of physical disintegra-

tion) were found to be present in mental andphysical activities, respectively (Yoshitake, 1978).

Ahsberg et al. (1997) have developed theSwedish Occupational Fatigue Inventory (SOFI),a multidimensional instrument for measuringfatigue based on self-reports. This questionnaire

Table 1

Description of the fatigue dimensions proposed by the Swedish Occu

Dimension Description

Lack of energy This dimension describes general fee

Physical exertion This dimension describes whole-bod

certain extent, the sign of metabolic

Physical discomfort This dimension describes more local

workload

Lack of motivation This dimension describes feelings of

Sleepiness This dimension describes feelings of

proposes five dimensions extracted from 95 verbalexpressions describing feelings of fatigue that wererated by 705 workers from 14 different professions(including two groups of students). These dimen-sions were labelled as Lack of energy, Physical

exertion, Physical discomfort, Lack of motivation

and Sleepiness (see Table 1).According to the authors, the underlying

structure of the instrument corresponds to a newqualitative and quantitative description of thephysical (physical exertion and physical discom-fort) and mental (lack of motivation and sleepi-ness) dimensions of perceived fatigue. Togetherwith these, the factor ‘‘lack of energy’’ correspondsto a fatigue dimension with both physical andmental characteristics (Ahsberg, 1998).Originally, the SOFI (Ahsberg et al., 1997) was

made up of 25 expressions (five for each dimen-sion) related to physiological, cognitive, motor andemotional responses. Depending on the researchintentions, participants were asked to rate on an11-point scale the extent to which the expressionswere describing their own feelings at that moment,during the last few minutes, when they were mosttired, and so on.The instrument was subsequently revised by

Ahsberg (2000) using confirmatory factorial ana-lysis, and the number of expressions in eachdimension was reduced to four (the questionnairefinally consisted of 20 elements). Previously, inaccordance with the information from earlierresearch, two of the original expressions had beenreplaced by new ones. Finally, the response scalewas changed to one with seven points.The factorial validity of this new version was

better than that of the previous model (Ahsberg,

pational Fatigue Inventory (SOFI; Ahsberg et al., 1997)

lings of diminished strength

y sensations that may be the result of dynamic work and, to a

exhaustion

bodily sensations that may result from static or isometric

not being involved or enthusiastic

sleepiness

ARTICLE IN PRESS

Table 2

Distribution for the pool of 25 items initially proposed for the

adaptation process

Dimension Proposed items

English Spanish

Lack of energy Overworked Habiendo

trabajado en

exceso

Worn out Agotado

Exhausted Exhausto

Spent Desgastado

Drained Extenuado

Physical exertion Sweaty Sudoroso

Breathing heavily Respirando con

dificultad

Palpitations Con palpitaciones

Warm Con calor

Out of breath Sin aliento

Physical Tense muscles Con los musculos


2000). Concurrent and discriminant validity wereassessed by comparing the scores obtained bydifferent types of worker (teachers, firemen,cashiers, bus drivers and engineers) on eachdimension. Internal consistency of the subscaleswas satisfactory, with Cronbach’s alphas of over.80, especially for Lack of energy (.92), Lack ofmotivation (.92) and Sleepiness (.89). Slightlysmaller values were obtained for Physical discom-fort (.81) and Physical exertion (.87).

The present work proposes to examine one ofthe ‘‘forgotten’’ areas within the Spanish-speakingcontext, given the lack of multidimensional instru-ments adapted to the Spanish language forthe measurement of work-related fatigue. SOFIhas been chosen because of the strength of itstheoretical structure, shown in a wide rangeof studies focusing on the improvement of theinstrument’s psychometric properties.

discomfort en tension

Stiff joints Con las

articulaciones

agarrotadas

Numbness Entumecido

Hurting Lastimado

muscularmente

Aching Dolorido

Lack of motivation Uninterested Falto de interes

Passive Pasivo

Listless Apatico

Indifferent Indiferente

Lack of

involvement

Falto de

implicacion

Sleepiness Sleepy Somnoliento

Falling asleep Durmiendome

Drowsy Amodorrado

Yawning Bostezante

Lazy Con pereza

2. Method

2.1. Sample

Two hundred and forty full-time nurses workingin eight special attention units participated in theadaptation of the instrument. Thirty individualswere taken from each of these units, representing12.5% of the sample. The average age was 35.41years (7SD 8.10), and the average experience inthe profession was 13.28 years (7SD ¼ 7.85);86.7% of the participants were women and13.3% were men. Average duration of continuouswork was 9.86 (7SD 6.31). Shift distribution wasrotating shift (42%), morning shift (20%), eveningshift (18.75%), night shift (8.75%) and extended24-h shift (10.42%).

2.2. Instruments

The adaptation process began with a review ofthe 25 items from the initial version of the SOFI(Ahsberg et al., 1997). One of the originalexpressions (‘‘taste of blood’’) had previously beenreplaced (by ‘‘warm’’), following the authors’recommendations (Ahsberg and Gamberale,1998) (see Table 2). In addition, ‘‘lack of concern’’

was replaced by ‘‘lack of involvement’’, due to itssimilarity with other expressions making up theLack of motivation scale (once translated intoSpanish). These 25 items, representing subjectivefeelings of weariness, were translated into Spanishby means of translation and back-translation(Brislin, 1986). The pool of translated items wasrated by the 240 nurses using an 11-point responsescale. Following the indications of the authors,who pointed out the need for participants’ ratings

ARTICLE IN PRESS


to be related to a particular moment in time or aspecific period, interviewees were asked to indicatetheir typical feelings at the end of the working day.

As a step in testing the validity of the SOFIadaptation, the NASA-TLX Effort and Frustra-tion subscales (Hart and Staveland, 1988) wereadministered without the usual weighting phase,these having been satisfactorily used by authorssuch as Nygren (1991), Hendy et al. (1993) orMoroney et al. (1995). NASA-TLX is a multi-dimensional self-reported assessment techniquethat provides an estimation of the overall workloadassociated with task performance. The assessmentis comprised of the relative contribution of sixunderlying psychological factors to overall work-load: mental demand, physical demand, temporaldemand, performance, effort (mental and physical)and frustration level. NASA-TLX has been foundto be the most valid measure of subjective work-load, to have the highest user acceptance, and tohave the smallest between-subject variability(Vidulich and Tsang, 1986; Byers et al., 1988; Hartand Wickens, 1990; Hill et al., 1992). NASA-TLXratings have also been shown to be sensitive toexperimentally manipulated levels of workload andto be more reliable than other subjective techniques(Aretz et al., 1996). Finally, in addition to theapplication of the NASA-TLX Effort and Frustra-tion subscales, information on the usual durationof participants’ shift was recorded.

2.3. Statistical treatment of data

To test the five-factor structure of fatigueproposed by Ahsberg (2000) in the revision of

Table 3

Swedish occupational Fatigue Inventory (SOFI): Summary of ma

hypothesized model is compared to the one-factor model, the revised m

model, and the revised model with 15 manifest variables is compared

Model w2/df diff w2/df Dw

One-factor, 25 var. 2146/275 — —

Hypothesized, 25 var. 861/249 1285/26 49

Revised, 20 var. 495/148 366/101 3

Revised, 15 var. 205/72 290/76 3

Note: w2/df ¼ relative chi-square, RMSEA ¼ root mean square

AGFI ¼ adjusted goodness of fit index.

SOFI, confirmatory factor analyses were per-formed by means of the Structural EquationModelling (Crowly and Xitao, 1997; Mueller,1996). The covariance matrix was analysed usingthe maximum likelihood estimation method(Hoyle, 1995). Internal consistency of the sub-scales was evaluated by calculating their alphacoefficients. Finally, in order to analyze theconvergent validity of the instrument, intercorrela-tions between the SOFI subscales and the NASA-TLX Frustration and Effort subscales werecalculated, as well as between the SOFI subscalesand normal shift duration.

3. Results

As a start, two Confirmatory Factor Analyseswere preformed with the purpose of testing thefive-factor structure of fatigue proposed by Ahs-berg (2000) in the revision of SOFI. Initially, asimple one-factor where the 25 variables (items)were related to one latent factor was confirma-tively tested. This model assumes that fatigue is acoherent concept consisting of only one dimen-sion, and the results showed a very unsatisfactoryfit to the data (Table 3). Then, the hypothesizedmodel (25 observed variables and four latentvariables plus an additional general latent vari-able) was tested. The results showed that thistheoretical model was significantly better ascompared to the one-factor model, but stillunsatisfactory. GFI was lower than .90, AGFIwas less than .80 and RMSEA is over .08,indicating a need to re-specify the model (v.g.

ximum likelihood confirmatory factor analysis results. The

odel with 20 manifest variables is compared to the hypothesized

to the revised model with 20 manifest variables

2/Ddf RMSEA p GFI AGFI

.17 .00 .48 .38

.42 .10 .00 .77 .70

.62 .10 .00 .83 .75

.81 .08 .00 .90 .83

error of approximation, GFI ¼ goodness of fit index,

ARTICLE IN PRESS


Chin, 1998; Hair et al., 1995; Segars and Grover,1993). Consequently, internal correlations, factorloadings, and t-values for each manifest variablewere analysed and a revised model was formu-lated, including 20 manifest variables distributedin the same way as in the previous case. Again,results showed an unsatisfactory adjustment to thedata. In consequence, a new revised model withonly 15 items was formulated (again, distributed infour latent variables plus an additional generallatent variable). The results indicated an accepta-ble, even if not wholly satisfactory, fit to thedata. Relative chi-square (w2/df), w2-difference(Dw2/Ddf), RMSEA, GFI and AGFI values,revealed that the 15-variables model was signifi-cantly better than the three previous models

Worn out

Exhausted

Drained

Breathing heavily

Palpitations

Warm

Stiff joints

Numbness

Aching

Listless

Passive

Indifferent

Sleepy

Falling asleep

Yawning

0.65

0.92

0.77

0.29

0.24

0.27

0.49

0.45

0.54

0.25

0.19

0.08

0.31

0.24

0.36

0.63

0.55

0.32

0.67

0.63

0.42

0.69

0.89

0.68

0.92

0.78

0.80

Lack of energy

Factor loadings

Factoloadin

α 0.82

α 0.55

α 0.80

α 0.81

α 0.91

Fig. 1. Swedish Occupational Fatigue Inventory (Spanish version): c

loadings, correlations between factors, and the reliability of each fact

(Table 3). Fig. 1 represents the factor solutionwith 15 items distributed in four latent variablesplus an additional general latent variable. Thisfinal solution corresponds with the model pro-posed by Ahsberg (2000): a general dimension(Lack of energy) and some specific dimensions offatigue (Physical exertion, Physical discomfort,Lack of motivation and Sleepiness).Correlations between all the factors were

moderate, except for that between Physical exer-tion and Physical discomfort, which was slightlylarger (.80). A close examination of the analysisresults showed that all the items loaded in theirexpected target factors. However, the item ‘‘In-different’’ loaded minimally (.08) on the expectedLack of energy factor, and the item ‘‘Warm’’

Physical exertion

Physical discomfort

Lack of motivation

Sleepiness

0.80

0.47

0.55

0.44

0.22

0.17

r gs

Correlations

onfirmatory factor analysis with 15 manifest variables. Factor

or (Cronbach alpha, a), are shown.

ARTICLE IN PRESS


yielded a moderate loading on Physical exertion(.32). Consequently, Cronbach alpha for Physicalexertion was low (a ¼ :55).

According to the result of the factor analysis,the five factors were interpreted as subscales, andin order to obtain a simple measure of eachsubscale, the means of the ratings were calculatedfor each subject. Table 4 presents means, standarddeviations and kurtosis indexes of each subscale ofthe SOFI.

Convergent validity of the SOFI was assessed bycalculating the Pearson correlations between sub-scale scores and independent scores for relatedconstructs (NASA-TLX subscales of Effort andFrustration, and shift duration). As Table 5 shows,in most of the cases the SOFI subscales correlatedsignificantly with the proposed constructs.Furthermore, certain patterns of correlationssupporting the differentiation among subscaleswere observed. For example, Effort (NASA-TLX)

Table 4

Descriptive statistics: means, standard deviations and kurtosis

indexes.

Mean SD Min Max Kurt.

Lack of energy 5.00 2.42 .00 10.00 �.82

Physical exertion 2.52 1.77 .00 8.33 .19

Physical discomfort 3.37 2.40 .00 9.33 �.58

Lack of motivation 2.26 2.04 .25 8.33 �.05

Sleepiness 2.82 2.65 .00 10.00 �.10

Table 5

Convergent validity of SOFI subscales. Pearson correlations

between SOFI subscales, NASA-TLX subscales of Effort and

Frustration, and shift duration

Subscales Effort

(NASA-TLX)

Frustration

(NASA-TLX)

Shift duration

Lack of

energy

.349** .302** .178**

Physical

exertion

.250** .155* .043

Physical

discomfort

.258** .295** .120

Lack of

motivation

.102 .303** .152*

Sleepiness .169** .256** .504**

*po0:05; **po0:01:

showed a special relationship with the physicalaspects of fatigue (Physical exertion and Physicaldiscomfort), as well as with Lack of energy. On theother hand, Frustration (NASA-TLX) was espe-cially correlated with Lack of motivation. Finally,as expected, Shift duration was particularlyassociated to Sleepiness.

4. Discussion

The present results offer encouraging prelimin-ary support for the reliability and validity of theSpanish version of the SOFI. The data in thisstudy demonstrate an acceptable fit to the pro-posed theoretical five-factor model with Lack ofenergy defined as a general latent factor represent-ing much of the variance of the items (Ahsberg,2000). Neverthless, fit is not wholly satisfactory, asin the work of Ahsberg (2000) occurred. This wasinterpreted by the author appealing to the lessernumber of occupations in her sample, as comparedwith the sample employed in her first study(Ahsberg et al., 1997). In the same way, thepresent analysis was based on a sample consistingexclusively of nurses. In this regard, the use of asample made up of workers from the sameoccupation (with similar demands) may hinderthe fit to the model. Besides, the number of items isreduced to 15, with three items in each factor. Inspite of this, alpha coefficients indicated thepresence of high levels of reliability for thesubscales, exceeding the minimum criterion(a ¼ :502:70) recommended for research instru-ments (Anastasi, 1988), except in the case ofPhysical exertion (a ¼ :55). The low alpha valuefor Physical exertion is attributable to the proble-matic fit of the item ‘‘Warm’’ on this dimension.With a view to testing the fit of the model in a

sample composed by a greater number of occupa-tions, it would seem essential to develop furtherstudies using heterogeneous Spanish samples withdifferent demands (Ahsberg, 2000). In addition,these new studies should try to increase thereliability of the Physical exertion by means ofthe addition of new items and examining thepossible suppression of the item ‘‘Warm’’. In turn,increases in the number of items per subscale,

ARTICLE IN PRESS


avoiding the loss of the practical implications oflimited number of items in the questionnaire, shouldimprove the content validity of the subscales.

Finally, on examining convergent validity,positive results were also yielded, since almost allthe subscales were positively associated with thelevel of perceived physical and mental effort, aswell as with the level of frustration generated bythe task, measured by means of the NASA-TLXsubscales. Effort (NASA-TLX) showed a specialrelationship with the physical aspects of fatigue(Physical exertion and Physical discomfort),as well as with Lack of energy. Frustration(NASA-TLX) was especially correlated with Lackof motivation. Similarly, as was expected, exceptPhysical discomfort and Physical exertion, theremaining subscales were related to the usualduration of shift, and especially Sleepiness.

In conclusion, the resulting adaptation toSpanish includes 15 expressions related to physio-logical, cognitive, motor and emotional responses,through which five basic fatigue dimensions (Lackof energy, Lack of motivation, Sleepiness andPhysical discomfort and Physical exertion) can bemeasured. Reliability of the instrument wassatisfactory, and examination of convergence alsoyielded encouraging results. Nonetheless, it seemsnecessary to undertake new studies based on moreheterogeneous samples (in relation to work de-mands), in order to test the fit of the model in asample composed by a greater number of occupa-tions, as well as with the aim of improve thereliability of the Physical exertion subscale. Gath-ering new data on the instrument’s reliability andconvergent and divergent validity seems alsonecessary. In any case, this adaptation constitutesa highly relevant product, bearing in mind theprevious lack of adequate tools for measuringwork-related fatigue in the Spanish languagecontext.

References

Ahsberg, E., 1998. Perceived fatigue related to work. Tryckt ho

CM Gruppen, Solna, Sverige.

Ahsberg, E., 2000. Dimensions of fatigue in different working

populations. Scandinavian Journal of Psychology 41,

231–241.

Ahsberg, E., Gamberale, F., 1998. Perceived fatigue during

physical work: an experimental evaluation of a fatigue

inventory. International Journal of Industrial Ergonomics

21, 117–131.

Ahsberg, E., Gamberale, F., Kjellberg, A., 1997. Perceived

quality of fatigue during different occupational tasks.

Development of a questionnaire. International Journal of

Industrial Ergonomics 20, 121–135.

Akerstedt, T., Gillberg, M., Wetterberg, L., 1982. The circadian

covariation of fatigue and urinary melatonin. Biological

Psychiatry 17, 547–554.

Anastasi, A., 1988. Psychological Testing, sixth ed. McMillan,

New York.

Aretz, A.J., Johannsen, C., Ober, K., 1996. An empirical

validation of subjective workload ratings. In: Proceedings of

the Human Factors Society 40th Annual Meeting. Human

Factors and Ergonomics Society, Philadelphia, PA,

pp. 91–95.

Bartlett, F., 1943. Fatigue following highly skilled work.

Proceedings of the Royal Society—Series B 131, 247–257.

Bartlett, F., 1953. Psychological criteria of fatigue. In: Floyd,

W., Welford, A. (Eds.), Symposium on Fatigue. H.K. Lewis

and Co., London, pp. 1–5.

Bigland-Ritchie, W.J., 1984. Changes in muscle contractile

properties and neural control during human muscular

fatigue. Muscle & Nerve 7, 669–699.

Bills, A., 1934. General Experimental Psychology. Longmans,

Green and Co., New York.

Borg, G., 1970. Perceived exertion as an indicator of somatic

stress. Scandinavian Journal of Rehabilitation Medicine

2–3, 92–98.

Borg, G., 1982. A category scale with ratio properties for

intermodal and interindividual comparisons. In: Geissler,

H.-G., Petzold, P. (Eds.), Psychophysical Judgment and the

Process of Perception. VEB Deutscher Verlag der Wis-

senschaften, Berlin, pp. 25–33.

Borg, G., 1998. Borg’s Perceived Exertion and Pain Scales.

Human Kinetics, Champaign.

Brislin, R.W., 1986. The wording and translation of research

instruments. In: Lonner, W.L., Berry, W. (Eds.), Field

Methods in Cross-cultural Research. Sage Publications,

Beverly Hills, CA, pp. 137–164.

Britton, D., 1983. Fatigue. In: Yasko, J. (Ed.), Guidelines

for Cancer Care. Raven Publishing Company, Reston,

pp. 33–37.

Browne, R., 1953. Fatigue, fact or fiction? In: Floyd, W.,

Welford, A. (Eds.), Symposium on Fatigue. H.K. Lewis and

Co., London, pp. 137–142.

Byers, J.C., Bittner, A.C., Hill, S.G., Zaklad, A.L., Christ, R.E.,

1988. Workload assessment of a remotely piloted vehicle

(RPV) system. In: Proceedings of the Human Factors Society

32nd Annual Meeting. Human Factors and Ergonomics

Society, Santa Monica, CA, pp. 1145–1149.

Bystrom, S., Mathiassen, S., Fransson-Hall, C., 1991. Physio-

logical effects of micropauses in isometric handgrip exercise.

European Journal of Applied Physiology and Occupational

Physiology 63, 405–411.

ARTICLE IN PRESS


Cameron, J., 1996. Assessing work-related body-part discom-

fort: current strategies and a behaviorally oriented assess-

ment tool. International Journal of Industrial Ergonomics

18, 389–398.

Chalder, T., Berelowitz, G., Pawlikowska, T., et al., 1993.

Development of a fatigue scale. Journal of Psychosomatic

Research 37, 147–153.

Chin, W.W., 1998. The partial least squares approach to

structural equation modelling. In: Marcoulides, G.A. (Ed.),

Modern Methods for Business Research. Lawrence

Erlbaum Associates, Mahwah, NJ, pp. 295–336.

Christensen, E., 1962. Muscular work and fatigue. In: Rodahl,

K., Horvath, S. (Eds.), Muscle as a Tissue. McGraw-Hill,

New York, pp. 176–189.

Eidelman, D., 1980. Fatigue: towards an analysis and a unified

definition. Medical Hypotheses 6, 517–526.

Gamberale, F., 1972. Perceived exertion, heart rate, oxygen

uptake and blood lactate in different work operations.

Ergonomics 15, 545–554.

Gillberg, M., Kecklund, G., Akerstedt, T., 1994. Relations

between performance and subjective ratings of sleepiness

during a night awake. Sleep 17, 236–241.

Goldmark, J., 1912. Fatigue and Efficiency. Russell Sage

Foundation, New York.

Grandjean, E., 1979. Fatigue in industry. British Journal of

Industrial Medicine 36, 175–186.

Hagberg, M., 1981. On evaluation of local muscular load and

fatigue by electromyography. Arbete och Hiilsa 24.

Hagg, G., Suurkula, J., Liew, M.A., 1987. Worksite method for

shoulder muscle fatigue measurements using EMG, test

contractions and zero crossing technique. Ergonomics 30,

1541–1551.

Hair, J.F., Anderson, R.E., Tatham, R.L., Black, W.C., 1995.

Multivariate Data Analysis with Readings. Prentice-Hall,

Englewood Cliffs, NJ.

Hart, S.G., Staveland, L.E., 1988. Development of NASA-TLX

(task load index): results of experimental and theoretical

research. In: Hancock, P.A., Meshkati, N. (Eds.),

Human Mental Workload. North Holland, Amsterdam,

pp. 139–183.

Hart, S.G., Wickens, C.D., 1990. Workload assessment and

prediction. In: Booher, H.R. (Ed.), MANPRINT: An

Emerging Technology. Advanced Concepts for Integrating

People, Machines and Organizations. Van Nostrand

Reinhold, New York, pp. 257–300.

Hemingway, A., 1953. The physiological background of

fatigue. In: Floyd, W., Welford, A. (Eds.), Symposium on

Fatigue. H.K. Lewis and Co., London, pp. 69–75.

Hendy, K.C., Hamilton, K.M., Landry, L.N., 1993. Measuring

subjective workload: when is one scale better than many?

Human Factors 35, 579–601.

Henning, R., Sauter, S., Salvendy, G., Krieg, E., 1989.

Microbreak length, performance, and stress in a data entry

task. Ergonomics 32, 855–864.

Hill, S., Iavecchia, H., Byers, J., Bittner, A.C., Zaklad, A.L.,

Christ, R.E., 1992. Comparison of four subjective workload

rating scales. Human Factors 34, 429–439.

Kashiwagi, S., 1969. Psychological rating of human fatigue. In:

Hashimoto, K., Kogi, K., Grandjean, E. (Eds.), Methodol-

ogy in Human Fatigue Assessment. Taylor & Francis,

Kyoto, pp. 17–21.

Kilbom, A., Gamberale, F., Persson, J., Anwall, G., 1983.

Physiological and psychological indices of fatigue during

static contractions. European Journal of Applied Physiol-

ogy 50, 179–193.

Kinsman, R., Weiser, P., 1976. Subjective symptomatology

during work and fatigue. In: Simonson, E., Weiser, P. (Eds.),

Psychological Aspects and Physiological Correlates of Work

and Fatigue. CC Thomas, Springfield, pp. 336–405.

Kjellberg, A., Skoldstrom, B., Andersson, P., lindberg, L.,

1996. Fatigue effects of noise on aeroplane mechanics.

Work & Stress 10, 62–71.

Lee, K., Hicks, G., Nino-Murcia, G., 1991. Validity and

reliability of a scale to assess fatigue. Psychiatry Research

36, 291–298.

Lewis, G., Wessely, S., 1992. The epidemiology of fatigue: more

questions than answers. Journal of Epidemiology and

Community Health 46, 92–97.

Lichstein, K.L., Means, M.K., Noe, S.L., Aguillard, R.N.,

1997. Fatigue and sleep disorders. Behavior Research and

Therapy 35, 733–740.

Malmqvist, R., Ekholmm, I., Lindstrom, L., et al., 1981.

Measurement of localized muscle fatigue in building work.

Ergonomics 24, 695–709.

Melamed, S., Bruhis, S., 1996. The effects of chronic industrial

noise exposure on urinary cortisol, fatigue, and irritability.

Journal of Occupational and Environmental Medicine 38,

252–256.

Mital, A., Foononi-Fard, H., Brown, M., 1994. Physical fatigue

in high and very high frequency manual materials handling:

perceived exertion and physiological indicators. Human

Factors 36, 219–231.

Monk, T., Folkard, S., 1985. Individual differences in shiftwork

adjustment. In: Folkard, S., Monk, T. (Eds.), Hours of

Work. Temporal Factors in Work Scheduling. Wiley,

Chichester, pp. 227–237.

Moroney, W.F., Biers, D.W., Eggemeier, F.T., 1995. Some

measurement and methodological considerations in the

application of subjective workload measurement techniques.

The International Journal of Aviation Psychology 5,

87–106.

Munscio, B., 1921. Is a fatigue test possible? British Journal of

Psychology 12, 31–46.

Nygren, T.E., 1991. Psychometric properties of subjective

workload measurement techniques: implications for their

use in the assessment of perceived mental workload. Human

Factors 33, 17–33.

Oberg, T., Sandsjo, L., Kadefors, R., 1994. Subjective and

objective evaluation of shoulder muscle fatigue. Ergonomics

37, 1323–1333.

Okogbaa, O., Shell, R., Filipusic, D., 1994. On the investigation

of the neurophysiological correlates of knowledge worker

mental fatigue using the EEG signal. Applied Ergonomics

25, 355–365.

ARTICLE IN PRESS


Piper, B., 1986. Fatigue. In: Carrieri, V., Lindsay, A., West, C.

(Eds.), Pathophysiological Phenomena in Nursing: Human

Responses to Illness. W.B. Sanders & Co., Philadelphia, pp.

219–234.

Piper, B., 1989. Fatigue: current bases for practice. In: Funk, S.,

Tomquist, E., Champagne, M., Copp, L., Weise, R.

(Eds.), Key Aspects of Comfort. Springer, New York,

pp. 187–189.

Piper, B., Lindsey, A., Dodd, M., Ferketich, S., Paul, S.,

Weller, S., 1989. The development of an instrument to

measure the subjective dimension of fatigue. In: Funk, S.,

Tomquist, E., Champagne, M., Copp, L., Weise, R. (Eds.),

Key Aspects of Comfort. Springer, New York, pp. 199–208.

Rabinach, A., 1992. The Human Motor-energy, Fatigue and

the Origins of Modernity. University of California Press,

Berkeley.

Rey, P., Meyer, J., 1980. Visual impairment and their objective

correlates. In: Grandjean, E., Vigilani, E. (Eds.), Ergonomic

Aspects of Visual Display Terminals. Taylor & Francis,

London, pp. 77–83.

Rimehaug, T., Svebak, S., 1987. Psychogenic muscle tension:

the significance of motivation and negative affect in

perceptual-cognitive task performance. International Jour-

nal of Psychophysiology 5, 97–106.

Saito, Y., Kashiwagi, S., 1970. Factors underlying subjective

feelings of fatigue. Journal of Science Labour 46,

205–224.

Schaeffer, S., Darby, L., Browder, K., 1995. Perceived exertion

and metabolic responses of women during aerobic dance

exercise. Perceptual and Motor Skills 81, 671–700.

Segars, A.H., Grover, V., 1993. Re-examining perceived ease of

use and usefulness: a confirmatory factor analysis. MIS

Quarterly 17 (4), 517–525.

Shapiro, C.M., Flanigan, M., Fleming, J.A.E., et al., 2002.

Development of an adjective checklist to measure five

FACES of fatigue and sleepiness. Data from a national

survey of insomniacs. Journal of Psychosomatic Research

52, 467–473.

Smets, E., Garssen, B., Bonke, B., De Haes, J., 1995. The

multidimensional fatigue inventory (MFI). Psychometric

qualities of an instrument to assess fatigue. Journal of

Psychosomatic Research 39, 315–325.

Smets, E., Garssen, B., Cull, A., De Haes, J., 1996. Application

of the multidimensional fatigue inventory (MFI-20) in

cancer patients receiving radiotherapy. British Journal of

Cancer 73, 241–245.

Torsvall, L., Akerstedt, T., 1987. Sleepiness on the job:

continuously measured EEG changes in train drivers.

Electroencephalography and Clinical Neurophysiology 66,

502–511.

Vidulich, M.A., Tsang, P.S., 1986. Techniques of subjective

workload assessment: a comparison of SWAT and the

NASA-Bipolar methods. Ergonomics 29, 1385–1398.

Welford, A.T., 1953. The psychologist’s problem in measuring

fatigue. In: Floyd, W., Welford, A. (Eds.), Symposium on

Fatigue. H.K. Lewis & Co., London, pp. 183–191.

Wessely, S., Hotopf, M., Sharpe, M., 1998. Chronic Fatigue

and Its Syndromes. Oxford University Press, Oxford.

Yoshitake, H., 1978. Three characteristic patterns of subjective

fatigue symptoms. Ergonomics 21, 231–233.

Documents

Spanish version of the Swedish Occupational Fatigue Inventory (SOFI): Factorial replication, reliability and validity