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Job rotation as a factor in reducing physical workload at a

refuse collecting department

P. PAU L F . M . K UIJER*, BAR T VISSER and H AN C . G . K EMPER

ERGOcare, Faculty of Human Movement Sciences and Institute of Research

in Extramural Medicine (EMGO), Faculty of Medicine, Vrije Universiteit

Amsterdam, Van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands

Keywords: Job design; Job rotation; Physical workload; Refuse collecting;

Manual materials handling.

The eect of job rotation on the physical workload was investigated for male

employees working at a refuse collecting department. Before the introduction of

job rotation, an em plo yee worked as a stree t sw eeper, as a ref use colle ctor or as a

driver. After the introduction of job rotation, every employee was allowed to

alternate between two of the three possible jobs during the day, i.e. refuse

collecting /street sweeping, refuse collecting/driving or street sweeping/driving.Two non-rotation groups (i.e. refuse collectors and street sweepers) and two

rotation groups (i.e. refuse collectors/street sweepers and street sweepers/drivers)were mutually compared. The physical workload was determined by measuring

the perceived load, energetic load and postural load during a full working day.

Job rotation resulted in a signicant decrease of t he perceived load and energetic

load and a slight decrease of the postural load. The results indicate that the total

amount of work performed by means of job rotation resulted in an overall

reduced physical workload of the employees of the refuse collecting department.

1. Introduction

Manual materials handling is considered to be a major cause of musculoskeletal

disorders, sickness, disability and high costs (Badger 1981, Mital et al. 1993). A great

number of variables (and their interactions) inuences the risk of these health

hazards. Although there is a general agreement that variables such as the weight of

handled objects or the time during which the tasks are performed are of primary

importance, there is rarely an eort made to establish the relationship between

la bo rat ory a nd eld s tu di es c on ce rn in g p hys ic al w or klo ad a nd t he o ns et o f

musculoskeletal disorders. Therefore, in order to prevent the onset of musculoskeletal

disorders, it is probab ly most eective to try to aect several variables sim ultaneously.

Possible preventive measures can be divided into ve categories: (1) engineering

m o di cat io ns ( e.g. w or ks ta tio ns ), ( 2) o rg an iza tio n o f w o rk ( e. g. w o rk/restschedules), (3) personal protective equipment (e.g. clothing), (4) training (e.g. work

methods) and (5) adm inistrative con trol (e.g. em ployee selection). The starting point

of an ergonomics intervention, to reduce the risk of musculoskeletal disorders,

should always be to strive for a redesign of the workplace. There are, however, jobs

that do not have a specic workplace layout, e.g. refuse collecting. The redesign is

mainly limited by the w ay the refuse is collected. Recent studies show that the use of

mini-containers is less physically demand ing for the refuse collectors than the use of

*Author for correspondence.

ERGONOMICS, 1999, VOL . 42, N O. 9, 1167 1178

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polythene bags (Frings-Dresen et al. 1995a, de Looze et al. 1995). U nfortunately, in

a historic city such as Amsterdam, the use of mini-containers is not possible for a

large part of the city due to architectural aesthetics and the number of inhabitants

per km2

. Therefore, to reduce the physical workload of collecting polythene bags, it

i s p ro ba bly m o st e e ct ive t o t ry t o c han ge t he o rg an iz at io n o f t he w or k b y

introducing job rotation. Job rotation can be dened as `regular, alternating betweendierent jobs within an organization on basis of a scheme or spontaneously on basis

of a personal appointment.

Although job rotation is often used to enhance the skills of employees and to

reduce monotony in daily work, it can also be used as a means to alternate between

dierent types of mechanical loads or to alternate between high and low energetic

loads of dierent jobs. Especially jobs with a dynamic type of work and great

dierences in muscular activities should be able to benet from this principle

(Jonsson 1998). Although job rotation is often advocated, only a few studies report

its possible eects. In a study on the physical workload of long-line bank shing,

Rodahl and Vokac (1977) found that the crew has resorted to their own job rotation

system. Although the study was not designed to evaluate the eect of job rotation, it

was concluded that contrary to general belief, bank shing need not be unsuitable

for older shermen, provided that an eective system for job rotation is provided.

Henderson (1992) developed a rotation scheme for poultry processing. Every job w as

rated on a scale ranging from low physical stress to unacceptably high physical

stress. These last jobs were not to be performed and were given a high priority for

ergonomic redesign. The guidelines for the job rotation scheme were that no back-to-back high stress positions were to be performed after each other and that each high-

stress job was preceded and followed by a low-stress job. Although no precise data

w ere a va il a ble, o bs er va tio ns i nd ic at ed t hat t he n um b er o f m u scu lo sk ele ta l

complaints had decreased. In a study on the design of check-out systems, Hinnen

et al. (1992) found that job rotation had a very benecial impact on the prevalence of

musculoskeletal disorders in cashier work with scanners.

The objective of this study is to investigate the eect of job rotation on the

physical workload of employees working at a refuse collecting department.

2. M ethod

2.1. Job rotation

Before the introduction of job rotation in a refuse collecting department, an employee

would start as a street sweeper, after a few years could become a refuse collector, and

could eventually become a driver of a dustcart or a sweeping machine. After the

introduction of job rotation, every employee was allowed to perform all three jobs.

Job rotation was introduced in the following manner. To reduce the physical

workload, rotation between jobs during the day was suggested. As most work was

performed in the m orning, employees rotated between jobs after the rst break in the

morning and after the lunch break. During the day, employees alternated between

two of the three possible rotation combinations, e.g. between refuse collecting and

street sweeping, between refuse collecting and driving a vehicle, or between street

sweeping and driving a vehicle.

2.2. Participants

T he s am p le in t his s tu dy c on sis ted o f m ale e mp lo ye es o f a r efu se c ollec ti ngdepartment. Sixteen employees voluntarily participated in this study. To increase

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the number of employees in each group, four of the six possible jobs were studied.

Eight employees worked according to a non-rotation scheme. The two most

physical demanding jobs were selected: four men worked as refuse collectors

(group RR) and four men worked as street sweepers (group SS). The other eight

employees worked according to a rotation scheme. The most and least physically

d em an d in g jo bs w ere s elec te d: fo u r m en w o rk ed a s r efu se c oll ec to rs/streets we ep ers ( gr ou p R S ) an d f ou r m e n w o rk ed a s s tre et s we ep er s/drivers (groupSD). Two employees of each group of four would start the day with one job; the

other two employees would start the day with the other job, e.g. two employees

would start the day with refuse collecting, then alternate to street sweeping and

nally nish the day with refuse collecting. The other two employees would start

the day with street sweeping, then alternate to refuse collecting and nally nish

the day with street sweeping.

The physical workload of the group of employees working according to a non-

rotation scheme was compared with that of the group working according to a

rotation scheme. The employees in each group were matched on age and did not

dier in height, body weight, sum of skinfolds, maximum oxygen uptake and

dierence between maximum heart rate and heart rate during rest. The dierent

variables were determined during a test in a laboratory (Kemper et al . 1990)

(table 1).

Table 1. Mean, standard deviation (SD) and range of age, height, body weight, sum of

skinfolds, maximum oxygen uptake (VO 2m ax ) and dierence between maximum h eart rate

and heart rate during rest (Hfm a x Hfr e s t ) of the refuse collectors (RR), street sweepers

(SS), refuse collectors/street sweepers (RS) and street sweepers /drivers (SD).

RR SS RS SD Signicance

Age (years)

SD

Range

34

6

29 42

34

7

28 42

33

6

26 40

35

15

26 58

ns

Height (m)

SD

Range

1.78

0.02

1.76 1.81

1.73

0.05

1.76 1.87

1.77

0.04

1.68 1.84

1.73

0.03

1.68 1.76

ns

Weight (kg)

SD

Range

75.5

4.2

72.1 81.6

76.3

13.7

63.7 91.6

76.9

8.0

66.0 85.4

70.9

7.6

65.8 82.0

ns

Skinfold (cm)

SDRange

10.9

1.69.7 13.2

9.2

3.84.3 12.6

16.7

6.210.7 22.0

8.3

3.75.7 13.6

ns

VO 2m ax (ml kg 1

mi n 1

)

SD

Range

44.0

4.0

40.0 49.2

44.2

9.2

36.4 54.3

42.3

9.3

31.5 52.4

49.6

11.4

38.0 59.7

ns

Hfm a xHfr e s t (beats min 1

)

SD

Range

109

13

98 127

107

19

89 123

116

20

93 134

107

17

87 123

ns

ns, Not signicant.

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2.3. Physical w orkload

The physical workload was determined by measuring the perceived load, energetic

load and postural load during a full working day.

Perceived load was dened as the mean rate of the perceived fatigue and the

mean rate of the perceived exertion during a w orking day. Every hour, the employee

rated the perceived fatigue (Borg and Borg 1987) and the perceived exertion(Meijman et al. 1986).

Energetic load was dened as the mean heart rate during the working day,

represented as a percentage of the heart rate reserve (A strand and Rodahl 1986).

This was done to prevent possible biases due to age dierences between employees.

The heart rate was continuously registered by means of a small computerized

recorder (Sporttester PE 3000; Polar Electro, Finland).

Postural load was dened as the time during which exion of the trunk was > 45 8

and elevation of one or two of the upper arm(s) was > 60 8. Only two variables and a

total of ve categories within variables were observed to increase the validity and

reliability of the observations of the posture (B eek et al. 1992, De Looze et al. 1994,

Frings-Dresen e t al . 1995b). The position of the trunk and the upper arms were

recorded by means of TRAC (Task Recording and Analysis on Computer) on a

multi-moment basis during the tasks of refuse collecting and street sweeping. TR AC

was originally developed at the Robens Institute of Health and Safety (Un iversity of

Surrey, Guildford, UK) (Ridd et al. 1989) and adapted by the Coronel Institute and

ERGOcare (Frings-Dresen and Kuijer 1995). Every 15 s, at an audible cue, an

observation was made and recorded on a pocket computer (Psion Organiser II;Psion, UK (Beek et al. 1992).

2.4. Confounding variables

Measurements were carried out during the normal daily routine of the employees,

thereby several confounding variables might inuence the results. For this reason, a

second observer performed a task analysis on a real-time basis. Possible confounding

variables, such as the duration of the tasks and the number of objects handled, were

registered by means of TRAC during each full working day. The following variablesand categories within variables were observed: task (e.g. refuse collecting, street

sweeping or pausing), activity (e.g. walking, sweeping or shovelling), load handled

(e.g. polythene bag, broom or shovel) and number of bags lifted per lift (e.g. 1, 2 or

5) (Frings-Dresen et al. 1995a).

2.5. Data analysis

Mean perceived load, mean energetic load and mean postural load were calculated

for each employee and consecutively for each group over a full working day. The

testing of a dierence between the groups regarding the physical workload and the

confounding variables was done by using an ANOVA and subsequently with a post-

ho c F -test. Testing of a dierence between two groups was performed with an

unpaired t-test.

The eect of the dierent confounding variables on the physical workload

w as t es ted w it h a s te pw is e m u lt ip le r eg ress io n a nal ys is. T he c on fo un din g

variables included in the stepwise multiple regression analysis are presented in

table 2.

Statistical analysis was performed with the software package StatView SE+ G(Abacus Inc.). p< 0.05 was considered statistically signicant.


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3. R es ult s

3.1. Physical workload

In table 3, the results of the four groups are summarized. Job rotation has an eect

on the perceived fatigue (RP F) and the perceived exertion (RP E) during the w orking

day (F= 7.48, d.f. = 3,12, p = 0.004; F= 9.3, d.f. = 3,12, p = 0.002). The group of

refuse collectors rate the perceived fatigue and the perceived exertion higher than the

other groups during a working day. The RPF and RPE of the other three groups donot dier signicantly during a working day.

Job rotation has an eect on the energetic load (F= 6.47, d.f. = 3,12, p = 0.008).

The heart rate reserve (% HRR) of the group of refuse collectors is signicantly

higher than that of the other groups during a working day, while % HRR of the

other three groups do not dier signicantly during a working day.

Job rotation has an eect on the time during which exion of the trunk is > 45 8

(F= 37.03, d.f. = 3,12; p = 0.0001) . F lexion o f the trun k o f > 45 8 occurs

signicantly more often for the group of refuse collectors than for the other threegroups. Flexion of the trunk of > 45 8 also occurs more often for the group of refuse

collectors/street sweepers than for the groups of street sweepers and street sweepers/drivers. The last two groups do not dier signicantly.

Job rotation has no eect on the time during which elevation of an upper arm is

> 60 8.

3.2. Confounding variables

Mean, standard deviation (SD) and range of the possible confounding variables of

the four groups are summarized in tables 4 and 5. The group of refuse collectors

perform the task `refuse collecting and the activity `carrying du ring a longer period

than the group of refuse collectors/street sweepers (t = 4.41, p = 0.002; t = 3.87,p = 0.004).

The group of refuse collectors lift m ore than twice the am ount of bags during a

w ork in g day t han the gr ou p of r efu se co llecto rs/s tr eet s we ep ers (t = 6.37,p< 0.001). Job rotation has no eect on the period during which street sweeping

takes place.

Jo b r ot at io n h as a n e e ct o n t he p er io d t hat e m plo ye es d riv e (F= 7.27,d.f. = 3,12, p = 0.005). The group of refuse collectors and the group of refuse

Table 2. Possible confounding variables included in the stepwise multiple regression analysis

to explain the physical workload.

Variables Categories within variables

Task (min) refuse collecting, street sweeping,

driving, pausing, non-working time,

other tasks, length of working day

Activities (min) carrying, sweeping

Objects handled total number of bags collected during

the day, number of bags collected

per min during refuse collecting

Workload during refuse

collecting and street sweeping

% VO 2m ax , % HRR


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collectors/street sweepers drive during a shorter period than the group of streetsweepers and the group of street sweepers/drivers.

Job rotation has an eect on the non-working time. The period performing non-

work-related tasks is less for the group working according to a non-rotation schemethan for the group working according to a rotation scheme (F= 3.66, d.f. = 3,12,

p = 0.047).

J ob r ot at io n a ls o h as a n e e ct o n t he l en gt h o f a w o rk in g d ay (F= 7.27,

d.f. = 3,12, p = 0.005). The working day of the group of refuse collectors is shorter

than of the other three groups. The other confounding variables to not dier

signicantly between the four groups.

3.3. Eect of confounding variables on physical workload

The results of the stepwise multiple regression analysis of the physical workload

during refuse collecting and street sweeping are presented in table 6.

The physical workload during refuse collecting can be explained by only a few

variables. The results show that the rated perceived fatigue and the rated perceived

exertion can be explained for respectively 91% (F= 58.5, p< 0.001) and 87%

(F= 40.3, p< 0.001) by the variable `time carrying bags. The energetic load during

refuse collecting can for 76% be explained by the variables `time trunk > 45 8, and

`length of the working day (F= 7.9, p< 0.05). Th e postural load of the trunk du ring

refuse collecting can for 81% be explained by the variable `number of bags handled(F= 58.5, p< 0.05).

Table 3. Mean, standard deviation (SD) and range of the rated perceived fatigue (RPF),

rated perceived exertion (RPE), percentage of `heart rate reserve (% HRR), time during

which exion of the trunk was > 45 8 and elevation of one or two of the upper arm(s) was

> 60 8 of the refuse collectors ( RR), street sweepers (SS), refuse collectors/street sweepers(RS) and street sweepers/drivers (SD) during a full working day.


RPF

SD

Range

2.0

0.9

1.1 3.0

0.8

0.3

0.6 1.2

0.3

0.1

0.2 0.4

0.6

0.6

0.0 1.4

RR> SS,RS, SD

RPE

SD

Range

54.2

22.4

23.8 77.5

27.7

6.0

20.6 33.1

11.1

4.0

5.7 14.4

19.5

7.6

11.3 27.5

RR> SS, RS, SD

% HRR

SDRange

36.4

7.527.4 43.9

22.6

5.016.6 28.9

23.8

4.517.9 28.0

1.55

9.26.0 28.1

RR> SS, RS, SD

Trunk> 458 (min)

SD

Range

44.6

6.8

38.9 52.5

5.0

6.4

0.5 14.4

22.0

8.3

11.9 30.5

2.6

2.7

0.4 6.4

RR> SS, RS, SD

RS> SS, SD

Arm(s)> 608 (min)

SD

Range

9.5

3.7

5.0 12.8

24.4

6.8

19.6 34.3

14.4

9.2

5.1 25.9

16.4

7.5

8.8 25.8

ns

ns, Not signicant.


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Neither the stepwise multiple regression analysis o f the postural load of the arm /shoulder nor the stepwise multiple regression analysis of the physical workload

during street sweeping resulted in an unambiguous explanation.

4 . D iscu ssio n

4.1. Job rotation

The aim of the introduction of job rotation was to divide equally the physically

demanding work of refuse collecting among the employees during the day. The

results show that this target has not been fully accomplished. For instance, the total

number of bags collected by the non-rotation group is more than twice as much as

that of the group of refuse collectors/street sweepers. This result is probably no t dueto a lesser number of bags placed on the street during those days. A more plausible

explanation is the lack of ne tuning between the two groups of refuse collectors /

street sweepers. During the measurement period each day, only one employee wasob serve d. T he colle ag ue w ith w ho m h e rotates d uring the day w as n ot

Table 4. Mean, standard deviation (SD) and range of the possible confounding variables

used in the stepwise regression analysis of the perceived load, energetic load and postural

load.


Refuse collecting

(min)

SD

Range

172.6

39.0

127.6 222.8

71.0

24.5

36.5 89.0

RR> RS

Street sweeping

(min)

SD

Range

153.2

38.3

111.9 204.2

88.6

52.6

36.6 155.6

99.2

34.3

68.5 140.6

ns

Driving (min)

SDRange

90.5

14.172.3 106.0

153.1

39.0121.6 207.1

75.8

39.034.9 125.5

177.7

44.8111.5 210.7

RR< SS SD

RS< SS SD

Pausing (min)

SD

Range

72.1

18.6

50.8 96.3

108.5

39.2

73.9 160.2

76.5

34.2

28.7 104.0

95.0

40.6

40.0 134.6

ns

Non-working

time (min)

SD

Range

10.6

10.8

1.2 22.1

41.6

52.7

11.2 120.1

113.3

78.2

58.1 228.6

85.6

20.0

63.1 102.6

RR< RS SD

Other tasks (min)

SD

Range

18.6

10.3

7.9 31.0

10.1

6.2

5.6 19.2

33.7

34.7

1.5 82.4

13.7

6.2

7.1 21.6

ns

Working day

(min)

SD

Range

364.5

18.6

341.6 381.3

466.4

8.3

459.7 478.0

459.0

13.0

440.3 470.2

471.3

10.4

456.8 479.7

RR< SS RS SD

ns, Not signicant.


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simultaneously observed. The standard deviation and the range of the variables

`non-working time and `total number of bags collected of the group of refuse

collectors/street sweepers compared with the group of refuse collectors indicate thatthe non-observed refuse collectors/street sweepers might have collected more bagsthan they should. This result hampers the d rawing of co nclusions. Despite this fact, a

f ew c om m en ts c an s till b e m ad e o n t he e e ct o f jo b r ot at io n o n t he p hy sic al

workload.

Refuse collecting is the m ost physically dem anding task due to the h igh energetic

and postural load. Job rotation seems to have no eect on the intensity w ith whichthis task is performed. The number of bags collected per minute, the percentage of

Table 5. Mean, standard deviation (SD) and range of the possible confounding variables

used in the stepwise regression analysis of the perceived load, energetic load and postural

load.


Total number of

bags

SD

Range

1556

229

1256 1779

57 2

20 8

292 783

RR> RS

Number of bags

per min

SD

Range

9.2

1.2

7.5 10.3

8.0

0.6

7.4 8.8

ns

Carrying (min)

SDRange

85.4

22.060.2 113.6

37 .2

11.720.1 46.2

RR> RS

Sweeping (min)

SD

Range

97.6

21.9

76.4 128.2

58.3

35.4

25.4 107.4

56.8

18.4

40.8 77.7

ns

% VO2 m a x refuse

collecting

SD

Range

61.5

11.8

45.1 72.4

61 .0

13.5

47.8 78.2

ns

% VO2 m a xsweeping

SD

Range

41.5

13.8

30.3 57.0

38.4

8.5

30.8 57.0

35.6

13.6

20.4 51.0

ns

% HRR refuse

collecting

SD

Range

60.9

12.3

43.4 70.6

59 .3

14.2

43.4 75.4

ns

% HRR sweeping

SD

Range

41.3

20.7

17.6 68.0

37.0

6.1

30.3 43.7

33.0

11.8

17.5 45.4

ns

ns, Not signicant.


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the heart rate reserve and the percentage of the VO 2 m a x during refuse collecting donot dier between the group of refuse collectors and the group of refuse collectors /street sweepers. The time during which the bags are collected does dier between the

two groups. This is due to job rotation and the lesser number of bags collected by the

group of refuse collectors/street sweepers. Therefore, it is not surprising that thephysical workload is the highest in the group of refuse collectors.

However, one result is very remarkable and points out the positive eect of job

rotation on diminishing the physical workload. When comparing the physical

workload of the group of refuse collectors/street sweepers with the groups of streetsweepers and street sweepers/drivers, only the postural load of the trunk diers. Therated perceived fatigue, rated perceived exertion, energetic load and postural load of

the arm/shoulder do not dier between both groups. Two possible explanations canbe formulated.

First, the change in tasks led to dierent postures and activities and, therefore, to

a more heterogeneous physical workload. Lifting and throwing of bags is probably

more strenuous for the lower back than sweeping with a broom. On the other hand,

sweeping might be more strenuous for the shoulder and upper arm due to the

prolonged static workload. Furthermore, van Dieen and Oude Vrielink (1994)

showed that job rotation might change more than only the temporal aspects of work.

While not changing the (peak) intensity of the work, job rotation may have a positive

eect on the energy storage in the segments. Owing to the viscoelastic behaviour of

biological structures, van Dieen and Oude V rielink (1994) found a decrease in energy

storage up to 24% . Therefore, it is not unreasonable to assume that the sam e amou nt

of work performed while working according to a rotation scheme might result in an

overall lower physical workload of the employees com pared with the same amount

of work performed according to a non-rotation scheme. Moreover, the relationshipbetween work output and fatigue might not be linear but exponential (Kilbom 1995).

Table 6. Explained variance (r2

) of the perceived load, energetic load and postural load

during refuse collecting and street sweeping.

Refuse collecting Street sweeping

Variable r2

Variable r2

Rated perceived fatigue

(RPF)

carrying 0.91

Rated perceived exertion

(RPE)

carrying 0.87

Percentage heart rate

reserve (% HRR)

trunk> 458working day

0.76

Postural load of the trunk

(time trunk > 458 [min])

number of bags 0.81

Postural load of the

upper arms (time arm(s)

> 608 [min])

, No unambigu ou s explan atio n.


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Above a certain amount of work, fatigue rises more quickly. Therefore, job rotation

between more and less strenuous work might result in preventing the crossing of a

`fatigue threshold, the point where a more or less linear increase of the worktask /workload relationship starts to increase exponentially.

Secondly, job rotation results in a more com plete job. The em ployee is enabled to

perform a larger part in the process of refuse collecting. Several studies report thatthe perceived load depends on more than only the physical workload (Borg 1978).

Other relevant factors are `task aversion and `motivation. The enrichment of the

job mak es the jo b less mono to nous an d the refore might dec rease task aver si on an d

increase the motivation of the employee. This increase of intrinsic job satisfaction

probably results in a reduction of the perceived load.

4.2. Guidelines

Frings-Dresen et al . (1995c) have formulated guidelines for the physical workload

of refuse collectors in The Netherlands. The guidelines are based on the energetic

load and the assumption that an overall energetic load of < 30% VO 2m ax is

acceptable for an 8-h working day. The guidelines are formulated in terms of the

acceptable duration of the period of refuse collecting and the amount of collected

refuse. The most stringent limit is formulated for refuse collecting of polythene

bags in a city by refuse collectors > 39 years of age. The maximal acceptable

period of refuse collecting and the maximal acceptable amount of collected refuse

for 90% (P 10 limit) of the refuse collectors > 39 years of age are respectively

1.7 h and 4000 kg. The group working according to a rotation scheme does notexceed the P 1 0 limit. The mean period of refuse collecting and the mean amount

of collected refuse are respectively 1.2 h and 4004 kg (an average bag of refuse

weighs around 7 kg; Kemper et al . 1990). The group working according to a

non-rotation scheme does exceed the P 10 lim it. T he m ean p er io d o f refu se

collecting and the mean amount of collected refuse are respectively 2.8 h and

10892 kg.

Although these results suggest that no further action is required to reduce the

physical workload in the group working according to a rotation scheme, tworemarks have to be made. First of all, the guidelines by Frings-Dresen et al. (1995c)

ar e b as ed o n a n e ner ge tic cr ite ri on b eca us e th er e is n o g en era ll y a cc ep te d

biomechanical criterion for an 8-h working day. De Looze et al . (1995) quantied

the biomechanical load on the back during the lifting and throwing of polythene

b ag s. A ve ra ge p ea k c om p re ss ion fo rce s r an ge d f ro m 3 34 1 t o 5 17 9 N . Th ese

compression forces exceed the NIOSH criterion for lumbar disc compression of

3400 N (Waters et al . 1993). Therefore, manually collecting polythene bags in the

conventional way remains a risky activity.

Second, the energetic acceptable peak load of 50% VO 2 m a x for 1 h (Kemper et

al. 1990) is exceeded by both groups working according to a rotation and a non-

rotation scheme. In this study, the mean energetic load during refuse collecting in

both groups is about 60% VO 2 m a x fo r > 1 h. A further reduction of the physical

w or klo ad in A m s te rd am c an b e a ch ie ve d b y lo ok in g fo r n ew w ay s o f r efu s e

collecting, e.g. by applying the METRO-system (citizens drop their refuse in

dustbins on the street that have large depots underground. The refuse from the

depots is then removed mechanically b y special dustcarts). A nother possible solution

is improving the present way of working, e.g. by creating refuse collecting points inevery street to which citizens brings their polythene bags. By designing these


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collecting points in such a manner that the dustcart can approach them easily, and

by heightening the collecting points, the period during which bags are carried and

when exion of the trunk occurs might be reduced and thus reducing the energetic

and biomechanical workload.

AcknowledgementsTh is s tu dy w as s up po rt ed na nc ia lly b y t he m u nic ip ali ty o f A m s terd am , in

particular by the `de Pijp district.

ReferencesA STRAND, P.-O. and RO D A H L, K. 1986, Textbook of Work Physiology: Physiological Bases of

Exercise (New York: McGraw-Hill).

BADGER, D . W . 1 9 8 1 , Work Practice Guide for M anual Lifting (Cincinnati: NIOSH, US

Department of Health Human Services).

BEE K, A. J. VAN DER, GAALEN , L. C. VA N and FRINGS-D RESEN, M. H. W. 1992, Working posturesand activities of lorry drivers: a reliability study of on-site observation and recording on

a pocket computer, Applied Ergonomics, 23, 331 336.

BOR G, G. 1978, Subjective aspects of physical and mental load, Ergonomics, 21, 215 220.

BOR G, G. and B OR G, P. 1987, On the Relations between Category and Ratio Scales and a Method

fo r Scale Tran sf ormat ion (Stockholm: Department of Psychology, University of

Stockholm).

BUCKLE, P. W., STUBBS , D. A., R A N D L E, I. P. M. and N ICHOLSON, A. S. 1992, Limitations in the

application of materials handling guidelines, Ergonomics, 35, 955 964.

DIE EN, J. H. VA N and O UD E VRIELINK, H. H . E. 1994, Mechanical behaviour and strength of the

motion segment under compression: implications for the evaluation of physicalworkload, International Journal of Industrial Ergonomics, 14, 293 305.

FRINGS-D RESEN , M. H. W. and K UIJER, P. P. F. M. 1995, The TRAC-system: an observation

method for analysing work demands at the workplace, Safety Science, 21, 163 165.

FRINGS-D RESEN , M . H . W . , K EMPER, H . C . G . , STASSEN, A. R. A. , C ROLLA , I . F . A. M . a nd

M ARKSLAG, A. M. T. 1995a, The daily workload of refuse collectors working with three

dierent collecting methods: a eld study, Ergonomics, 38, 2056 2064.

FRINGS-D RESEN , M. H. W., K EMPER, H. C. G., STASSEN , A. R. A., M ARKSLAG, A. M. T., LOOZE,

M. P. D E and TOUSSAINT, H. M. 1995c, Guidelines for energetic load in three methods of

refuse collecting, Ergonomics, 38, 2065 2077.

FRINGS-D RESEN , M . H . W . , L EEUWEN, P. VA N, BOU W, A . a n d KUIJER, P . P . F . M . 1 9 9 5 b,Validation of posture registration based on visual observation at the workplace. In I.

Kuorinka (ed.), Prevention of Work Related Musculoskeletal Disorders (Montreal:

Institute de recherche en sante et en securite du travail de Quebec). 286 288.

HENDERSON, C. J., 1992, Ergonomic job rotation in poultry processing, 1992. In S. Kumar

(ed.), Advances in Industrial Ergonomics and Safety (London: Taylor & Francis), 443

450.

HINNEN, U., LA UBLI, T., G UGGENBU H L, U. and K RUEGER, H. 1992, Design of check-out systems

including laser scanners for sitting work posture, Scandinavian Journal of Work

Environment and Health, 18, 186 194.

JONSSON

, B. 1988, Electromyographic studies of job rotation, Scandinavian Journal of WorkEnvironment and Health, 14 (suppl. 1), 108 109.

KEMPER, H . C . G . , A ALST, R. VA N , LEEGWATER , A . , M AA S, S . a n d KNIBBE, J. J. 1990, The

physical and physiological workload of refuse collectors, Ergonomics, 33, 1471 1486.

KILBOM , A . 1995, Measurement and assessment of dynamic work, 1995. In J. R. W ilson and E.N. Corlett (eds), Evaluation of Human Work (London: Taylor & Francis).

LOOZE, M. P. DE , STASSEN A. R. A., M ARKSLAG, A. M. T., BORST, M. J., W OONING, M. M. and

TOUSSAINT, H. M. 1995, Mechanical loading on the low back in three methods of refuse

collecting. Ergonomics, 38, 1993 2006.

LOOZE, M. P. D E, TOUSSAINT, H. M., ENSINK, J., M A N G N U S, C. and BEE K , A. J. VAN DER 1994, The

validity of visual observation to assess posture in a laboratory-simulated, material

handling task, Ergonomics, 37, 1335 1343.


7/30/2019 Ergonomics 42 1999 1167-1178

12/12

M EIJMAN , T., Z IJLSTRA, F., KOMPIER, M., M ULDERS, H. and BROERSEN, J. 1986, Measurement of

eort. In D. J. Oborne (ed.), Contemporary Ergonomics (London: Taylor & Francis).

M ITAL, A., N ICHOLSON , A. S. and AY O U B, M. M. 1993, A Guide to Manual Materials Handling

(London: Taylor & Francis).

RID D, J . E . , N ICHOLSON, A . S . a n d M ONTAN, A. J. 1989, A portable microcomputer based

system for `on site activity and posture recording. In E. D. Megaw (ed.), Contemporary

Ergonomics (London: Taylor & Francis), 366 371.RO D A H L, K. and VOKAC, Z. 1977, Work stress in long-line bank shing, Scandinavian Journal of

Work Environment and Health, 3, 154 159.

W ATERS, T . R . , PU TZ -A NDERSON, V . , GAR G, A . a n d LAWRENCE, J. F. 1993, Revised NIOSH

equation for the design and evaluation of manual lifting tasks, Ergonomics, 36 , 749

776.


ergonomics 42 1999 1167-1178

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