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Evaluation of a workplace redesign of a grocery checkout system
Ergonomics and Aerosol Technology
PII: S0003—6870(97)00016-1
Applied Ergonomics Vol. 29, No. 4, pp. 261—266, 1998 ( 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0003—6870/98 $19.00#0.00
Evaluation of a workplace redesign of a grocery checkout system Anja Johansson1, Gerd Johansson1, *, Peter Lundqvist2, Ingrid As kesson3, Per Odenrick1,4 and Roland Akselsson1,4 1
Department of ¸und Institute of ¹echnology, P.O. Box 118, SE-221 00 ¸und, Sweden Department of Agricultural Biosystems and ¹echnology, Swedish ºniversity of Agricultural Sciences, P.O. Box 88, 945, SE-230 53 Alnarp, Sweden 3 Department of Occupational and Environmental Medicine, ¸und ºniversity Hospital, SE-221 85 ¸und, Sweden 4 Change@¼ork, P.O. Box 118, ¸und ºniversity, ¸und, Sweden 2
(Received 5 June 1996; in revised form 6 March 1997)
The aim of this study was to evaluate the effects on the working postures and movements of a cashier when two different locations of the scales (one to the left of the cashier, the other under the conveyer belt in front of the cashier) were used in a grocery checkout system. Two cashiers (of average stature and short stature) were videotaped while working, in both sitting and standing working positions. Analysis of the video tapes was performed using the WOPALAS method and video observations. The results of the study show that the design of the checkout system with the scales under the conveyer belt provides a more favourable working position for both the taller and the shorter cashier. Additionally, the results indicate that a standing position is more favourable than a sitting one for the taller cashier while for the shorter cashier the sitting position is better. ( 1998 Elsevier Science Ltd. All rights reserved. Keywords: checkout system, scales, evaluation, working postures, movements
Introduction
gdahl, 1990; Hinnen et al, 1992). An increased risk of developing carpal tunnel syndrome has also been reported (Margolis and Kraus, 1987; Morgenstern et al, 1991; Osorio et al, 1994). The work of a supermarket cashier includes manual handling of large quantities of articles during each working day, often combined with a stressful workplace which may cause exposure to some of the above-mentioned risk factors for the development of musculoskeletal disorders. In a study of the neck and shoulder muscle activity, Lannersten and Harms-Ringdahl (1990) found that work with scanners and pen readers caused higher loads than conventional keyboard operation in the trapezius, infraspinatus and thoracic erector spinae muscles. Standing positions showed lower muscle activity at all load levels than did sitting positions. However, the main problems identified were the repetitive handling and the constant static load. To decrease the musculoskeletal load, several authors have suggested that the cashier alternates between sitting and standing positions (Lannersten and HarmsRingdahl, 1990; Ryan, 1989). A further improvement can be achieved by combining the checkout work with other kinds of work in the shop (Hinnen et al, 1992). Alternatively, Baron and Habes (1992) have suggested placing the weigh scales under the conveyer belt.
Work-related musculoskeletal disorders are recognised as a major occupational problem. An association between stressful working postures and movements and the development of musculoskeletal disorders in the neck and upper extremities is now widely acknowledged in the literature (Kuorinka and Forcier, 1995). Some risk factors have been suggested to be of special interest, for example joint positions such as constrained postures, positions close to extremes, and steep forward bending of the head. Furthermore, high repetitiveness, high force, high static muscle and joint load can compound the problems (Stock, 1991; Winkel and Westgaard, 1992). In recent years, musculoskeletal disorders among supermarket cashiers have been reported in several studies (Ryan, 1989; Baron and Habes, 1992; Harber et al, 1992). The symptoms are commonly found in the neck and the upper extremities, especially the left arm (Baron and Habes, 1992; Harber et al, 1992). The introduction of laser scanners for price registration seems to have further increased the problems (Lannersten and Harms-Rin-
*Author to whom correspondence should be addressed 261
Evaluation of a workplace redesign. A. Johansson et al.
262
The aim of this study was to evaluate the effects on the working postures and movements of a cashier when two different locations of weigh scales were used in the same checkout system as that investigated by Lannersten and Harms-Ringdahl (1990). A location of the scales to the left of the cashier was compared with a location under the conveyer belt, in front of the cashier. The effects of sitting and standing working positions and of different body sizes of the cashiers were also studied.
Experimental design The experiments were performed in a laboratory using a commercially available supermarket checkout system (UK 90, manufactured by ABO METALL AB Jo¨nko¨ping, Sweden). The checkout system, with a non-adjustable working height of 90 cm, is designed for both sitting and standing working positions. It was equipped with a flexible chair which each cashier was able to adjust to a comfortable height and sitting position.
Figure 1 The two arrangements of the checkout system, with the scales to the left (a) and under the conveyer belt (b). Articles are supplied from the right. Only the middle part of the checkout system is shown. (A"scanner, B"scales, C"cash-box, D"cash register and E"cashier)
The checkout system had a vertical scanner and an adjustable cash-register keyboard. The scales of the original version of the system were located to the left of the cashier and the cash-box between the cashier and the conveyer belt. In the modified checkout system, the scales were removed and relocated under the conveyer belt just in front of the cashier. When an article is not registered by the scanner, the conveyer belt automatically stops, the cashier registers the article code and the article is weighed; then the belt automatically starts again. As the scales to the left were removed, the original cash-box, 18]49 cm, could be replaced by another with a depth of 15 cm and a width of 52 cm. The layouts of the two checkout system designs are shown in Figure 1. Two female cashiers with several months of daily experience ('6 months) using the checkout system in question (vertical laser scanner and the scales to the left) but with different anthropometric data were selected to participate in the study. No attempt was made to standardise their working technique. Both were righthanded and had no history of musculoskeletal disorders. One cashier (no. 1) was of medium stature (height 170 cm, weight 60 kg, age 21 yr) while the other (no. 2) was shorter (height 153 cm, weight 60 kg, age 25 yr). Ju¨rgens et al (1990) estimated the stature for a female North-European population; the values were 158.5, 169.0 and 179.5 cm for the 5-, 50- and 95-percentile, respectively. Twenty-five different grocery items (average weight 0.8 kg) with a total weight of 19.7 kg were used during the study. The prices of 17 articles were registered by the scanner while the other eight (average weight 1.1 kg) required weighing. The proportion of articles needing to be weighed was chosen to be higher than normally expected in order to detect better, any differences due to the location of the scales. The positions and orientations of of each article were marked on the conveyer belt to allow the experiment to be repeated with the same initial positions. For each cashier, both standing and sitting positions were studied and analysed for the two locations of the scales. Each experimental situation was repeated five times. When the working cycle started, all the articles were placed in the same initial positions on the conveyer belt and the cashier registered these. A working cycle lasted about 90 s. In Table 1, the properties of the experimental sequence are shown. During each experiment the cashier was videotaped from behind, from the left side and from above.
Table 1 Description of the experimental design. The cycle time is shown as mean value (SD) Experimental situation
Cashier number
Number of cycles
Position
Position of the scales
Average cycle time [s]
Scanning failures per cycle
1 2 3 4 5 6 7 8
2 1 2 1 2 1 1 2
5 5 5 5 5 5 5 5
Sitting Sitting Standing Standing Sitting Sitting Standing Standing
Left Left Left Left Conveyer belt Conveyer belt Conveyer belt Conveyer belt
93.1 87.6 81.9 83.2 87.1 99.6 76.3 73.0
0—2 4—7 2—4 1—14 1—4 3—14 1—5 0—3
(8.3) (5.7) (2.8) (5.0) (11.0) (14.4) (3.0) (2.0)
Evaluation of a workplace redesign. A. Johansson et al.
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Methods used for evaluation For ergonomic studies of the postures and movements of the whole body, the WOPALAS method (Lundqvist, 1990) developed from the OWAS method (Karhu et al, 1977; Karhu et al, 1981) was used. The WOPALAS method differs from the OWAS method in that it separates registrations for left and right arms and legs. It also has a more detailed registration of the arm positions and finally it uses more levels of weight and force registration. The WOPALAS method is based on work sampling techniques which provide both the frequency of each posture and the time spent in each. The method includes registration of the postures of the back, the arms, the legs and the head. The angles registered for the arms are the deviations from the body—that is, a combination of flexion and abduction. It is also possible to register the weights and forces handled. These forces come from, for example lifting or dragging grocery items. In this study, the body posture was registered every 3 s. The WOPALAS analysis was carried out by a researcher experienced with this method. For the evaluation of the different designs of the checkout system, it was important to study further, the postures and movements of the head and the left arm, and this was done using the VIRA method (Kilbom and Persson, 1987). As opposed to the WOPALAS method, VIRA uses continuous registrations for one body part at the time. A VIRA analysis was carried out for the flexion and the abduction of the left upper arm, and an analysis using the same principles as the VIRA method was carried out for the rotation of the head. A computer program developed for this purpose was used (Pinzke, 1994). The chosen angle intervals for the classification of the flexion and abduction of the left upper arm were in this case: neutral position (the arm is at 0°), (0°, 0—30°, 30—60°, and '60°. These angles refer to the angle between the projection in the sagittal (flexion) or frontal (abduction) plane of the upper arm studied and the line of gravity. The chosen angle intervals for the rotation of the head were: '45° left, 15—45° left, 15° left—15° right, 15—45° right, and '45° right. The VIRA analysis was carried out from video tapes played in slow motion (1/5 of normal speed) by manually registering the occurrence of a body part in a certain angle segment. A further refinement of the ergonomic evaluation of the work situation of the cashier was to use additional video observations to record the time spent in particular working positions as a percentage ofthe total time of a work cycle. The particular positions are: 1. The left lower arm is supported. 2. The left elbow angle is less than 30°, combined with a flexion angle for the left upper arm of more than 30° (Figure 2a). The choice of a flexion angle of 30° is based on the results from the work of Ja¨rvholm and Palmerud (1990). Such positions are hereafter abbreviated as ‘stretching’. 3. The left upper arm is close to the body and the left forearm is in external rotation of more than 30° (Figure 2b). This position is henceforth abbreviated as ‘external rotation’. All five working cycles of each experimental situation were analysed with all three methods. The duration of the
Figure 2 (a) Definition of elbow extension and arm flexion. (b) Definition of external rotation
working cycles varied between 71 and 121 s. The number of failures when the price was not registered by the scanner varied between 0 and 14 per working cycle. A failure required the cashier to re-scan the bar-code of the article until the price was registered.
Results All the results from the WOPALAS-analysis are summarised in Table 2. In Table 3, the results from the other video observations are presented. All the differences between the designs of the checkout system, the working positions (sitting, standing) and the cashiers are significant at at least the 5% level (p(0.05). For the statistical analysis unpaired t-tests combined with Mann—Whitney º-tests were used. Medium stature cashier (person no. 1) in a sitting position When the scales are placed under the conveyer belt, the WOPALAS-analysis shows f decreased occurrence of postures in the larger angle segments both for the left ('30°) and the right arm ('10°); f the cashier spends less time handling heavy (1.5—5.0 kg) articles during a working cycle; f a reduction in occurrence of the head in a twisted ('45°) position. The VIRA-method shows improvements for the left arm with the scales placed under the conveyer belt. The external rotation of the left arm is eliminated and the arm is in neutral position (0°), supported position or both for a substantial part (about 30%) of the working cycle. The results in Table 3 also show that the head is rotated more towards the left and less time is spent in the extreme angle intervals ('45°) when the scales are under the conveyer belt. Medium stature cashier in a standing position When the cashier is standing with the scales situated under the conveyer belt, the same kind of improvements as for sitting are found for both the arms and the head. Also the time of handling of articles weighing 0.5—1.5 kg is decreased in this case.
Evaluation of a workplace redesign. A. Johansson et al.
264
Table 2 Percentage distribution of working postures according to the WOPALAS-analysis for the different locations of the scales (xN "mean value, s"standard deviation). Furthermore, the percentage distribution of the weights handled are shown Person no. 1 Sitting Left Conveyer x6 s x6 s Back Straight 100 Left arm 0—10° 15.5 10—30° 28.9* 30—90° 55.7* Right arm 0—10° 72.7* 10—30° 23.9* 30—90° 3.3 Head T wisted ('45°) 16.0* Weights handled (kg) 0—0.5 45.1 0.5--1.5 47.6 1.5--5.0 7.3*
0
100
Person no. 1 Standing Left Conveyer x6 s x6 s
0
100
0
3.4 7.0 5.2
17.3 37.9* 44.7*
5.8 4.3 3.0
18.4* 44.0 37.7*
5.7 3.7 7.5
1.6 4.6 3.5
96.0* 4.0* 0
2.7 2.7 0
91.5* 8.5* 0
6.1 6.1 0
0
2.2
0*
6.4 5.3 4.3
0
46.4 51.8 1.8*
0
8.8 7.8 2.8
51.9* 41.8* 6.3*
100
0
37.1* 47.8 15.1*
8.6 7.8 2.8
Person no. 2 Sitting Left Conveyer x6 s x6 s
Person no. 2 Standing Left Conveyer x6 s x6 s
100
100
0
100
5.3 4.1 6.7
25.0 38.6 36.4
2.1 4.0 3.4
28.0 39.3 32.6
100* 0* 0
0 0 0
81.3* 18.1* 0.6
2.1 2.7 1.3
100* 0* 0
0
0
11.6*
3.7
3.9 3.9 0
58.0 35.5 6.5*
11.8 12.0 2.4
71.7* 28.3* 0*
0.8* 61.2 38.8 0*
0
0
100
0
5.7 4.9 3.9
14.3* 43.4 42.3*
2.7 4.1 4.3
24.0* 44.2 31.8*
3.0 4.1 5.1
0 0 0
92.9* 7.1* 0
4.1 4.1 0
99.2* 0.8* 0
1.7 1.7 0
1.7
2.8*
1.6
2.4 2.4 0
48.1* 41.9* 9.9*
7.5 6.5 2.5
0* 64.3* 34.9* 0.8*
0 6.7 6.6 1.7
*indicates significant differences between the mean values for different locations of the scales (p(0.05)
Table 3 Percentage distribution of the time spent in a working position according to the video observations for the different locations of the scales (xN "mean value, s"standard deviation)
Upper left arm Flexed (0° +0° (neutral) 0—30° 30—60° '60° Abducted (0° +0° (neutral) 0—30° 30—60° '60° Head Rotated '45°left 15—45° left 15° left—15°right 15—45° right '45° right Left arm Supported Stretched External rotated
Person no. 1 Sitting Left Conveyer x6 s x6 s
Person no. 1 Standing Left Conveyer x6 s x6 s
Person no. 2 Sitting Left Conveyer x6 s x6 s
Person no. 2 Standing Left Conveyer x6 s x6 s
34.6* 2.1* 32.3 28.2 2.8*
2.1 2.3 4.3 4.6 1.4
1.8* 37.0* 35.7 25.0 0.5*
2.3 4.7 5.8 4.8 0.2
37.5* 7.5* 44.0 11.0 0
3.4 3.3 4.1 3.1 0
6.6* 38.1* 43.2 11.3 0.7
5.2 11.8 16.1 8.6 1.6
20.8* 20.0 34.1 23.0 2.0
2.7 4.2 5.4 3.8 1.5
0* 31.6 39.2 27.1 2.1
0 10.6 7.0 8.7 1.7
26.0* 6.2 44.0 23.2* 0.5*
10.0 4.2 6.0 9.8 0.6
9.4* 2.3* 76.5* 11.1 0.6
3.0 2.6 5.3 4.6 0.3
15.4* 32.5* 44.7* 6.2 1.2
3.1 4.0 7.5 3.2 1.3
15.6* 38.0 44.2* 2.3* 0
3.4 5.6 3.0 1.9 0
29.0* 44.7 26.3* 0* 0
2.4 8.9 8.3 0 0
25.7 19.0* 44.6 10.2 0.6
4.2 3.7 5.1 3.9 0.6
21.7 29.1* 42.3 6.6 0.3
6.7 8.7 7.8 3.2 0.4
28.3 7.5* 46.0 18.2* 0
3.4 4.3 6.6 2.2 0
17.6 12.1 32.6* 8.6 39.4 7.8 10.4* 4.8 0 0
0.5* 23.2* 39.8 25.8 10.6*
0.3 3.3 4.9 5.0 2.3
4.2* 35.4* 36.9 23.1 0.4*
1.5 4.8 2.4 4.2 0.3
1.1 15.0* 49.1* 22.0* 12.9*
0.9 3.3 6.6 4.2 2.4
3.7 47.7* 37.6* 10.6* 0.3*
3.1 2.2 5.0 6.6 0.6
1.4* 20.1* 42.9* 28.3 7.3*
0.6 9.6 11.1 8.1 4.0
5.5* 41.2* 23.0* 29.2 1.1*
2.2 4.0 3.0 6.0 0.8
2.6 12.1* 48.5* 29.4 7.4*
1.4 4.3 6.4 4.3 2.2
2.3 40.8* 26.3* 28.6 1.9*
3.5 7.3 6.5 2.9 1.3
1.8* 7.2 35.5*
3.7 1.4 3.2
32.4* 5.5 0*
5.1 2.0 0
0.6* 4.2 31.5*
1.3 2.3 3.6
7.5* 2.8 6.6*
1.2 1.4 3.4
15.1* 18.1* 17.3*
4.4 2.1 2.3
30.2* 22.4* 0*
10.7 1.8 0
4.4 27.6 20.3*
2.6 6.5 2.9
6.8 31.0 2.6*
2.8 4.7 2.5
0.2* 8.8 43.0 45.6* 2.3*
0.2 4.3 6.3 4.9 1.6
*Indicates significant differences between the mean values for the different locations of the scales (p(0.05)
The results further show that, for this cashier, the standing position is more favourable when evaluating the angle distributions of both the left and right arm. The left arm is in more of a neutral position when standing and the stretching movements are decreased.
In the standing position, the cashier is, however, only supporting the arm 8% of the time compared to 32% when sitting. The WOPALAS-analysis further shows more twisted positions for the head when sitting with the scales to the left and less handling of articles
Evaluation of a workplace redesign. A. Johansson et al.
heavier than 0.5 kg when standing using the scales beneath the conveyer belt. However, the same tendency for the head rotation cannot be observed from the video observations.
265
f exhibited more forward ‘stretching’ movements with the left arm, the difference was greater in standing positions.
Discussion Short stature cashier (person no. 2) in a sitting position For the shorter cashier, when the scales are under the conveyer belt the WOPALAS-analysis shows a reduction of the time the upper right arm is found in a position '10° out from the body, a reduction of the time the head is twisted and the time heavier articles are handled. The time the left arm is supported or in a neutral position is increased and the rotation of the left arm is reduced. A slight increase from 18 to 22% of the stretching of the left arm is registered using the scales beneath the conveyer belt. Moreover, for this cashier the head (see Table 3) is more rotated towards left when using the new scale location. Short stature cashier in a standing position The WOPALAS-analysis shows more obvious improvements for this work situation when using the scales beneath the conveyer belt. The time spent in the larger angle segment is reduced for both arms as the time spent handling articles heavier than 0.5 kg. The VIRA-analysis gives a decrease for the time the left arm is in the angle segment '30° for abduction but an increase for flexion. No significant change is found in ‘stretching’ the left arm when the scales beneath the conveyer belt are used. The external rotation movements of the left arm are also reduced and the head is more often rotated towards the left. Comparing sitting and standing position for the shorter cashier shows that the sitting position is superior for the left arm. There are more support and neutral positions for this arm, as well as less stretching and less time spent in several angle intervals '30°. However, the WOPALAS-analysis shows more twisted positions for the head for a sitting position when the scales are set to the left. Comparison of the two cashiers The average cycle times presented in Table 1 show that the work rates of the two cashiers are almost the same and that no significant change is found for the two different locations of the scales. When the working position is changed from sitting to standing the average work rate, however, seems to increase (the difference is statistically significant in three out of four working situations). Upon comparing the two cashiers we found that person no. 2. (shorter stature) f spent substantially less time in external rotation when the scales were located to the left, f supported her left arm more and had this arm in a more neutral position when sitting with the scales located to the left; in a standing position, the taller cashier (no. 1) had the arm in a neutral position more frequently; f had the upper left arm in the angle segment '30° more when standing and less when sitting;
The two cashiers were selected to represent, a person of medium stature in the distribution of North-European females and a very short stature. Both cashiers were very experienced working with the checkout system in question with the scales to the left, but neither had used the system with the scales under the conveyer belt. The observed differences between the cashiers are probably due to both different body constitutions and different working techniques. The shorter cashier worked using more flexed or stretched movements of the left arm, probably due to a shorter reach. She had less failures when using the scanner. Her working technique also differed from that of the taller cashier when weighing the articles. The taller cashier lifted the articles more and kept her left arm in a externally rotated position while weighing. The shorter cashier rested her left arm more when using the checkout system with the scales to the left. Whether these increased periods of resting the arm are due to a better working technique or to a greater need for rest caused by a higher work load is difficult to determine. The results of this study show that the design of the checkout system with the scales under the conveyer belt provides a more favourable working position for both the taller and the shorter cashier. The external rotation of the left arm decreased substantially, the time spent handling articles was reduced and the possibilities for resting the left arm or keeping it in a neutral position were greatly improved. The twisting of the head was also decreased when the scales were placed under the conveyer belt. The reduction in the handling of the articles is more pronounced for a standing working position. More daily work with the scales beneath the conveyer belt may further improve the cashiers’ work technique, which may decrease the musculoskeletal load but may increase the work rate. However, the improvements due to the placement of the scales are more evident for the taller cashier than for the shorter. The reason for a more twisted position of the head towards the left side when using the scales under the conveyer belt is that the cashiers position themselves closer to the register found to their right. Hence, when observing the articles on the belt, they twist their heads more towards the left. The most common working position for cashiers is sitting. In our case, the cashiers can partly adjust their sitting position by adjusting the chair. When standing they have, however, a fixed working height (conveyer belt 90 cm). The elbow height is an average 103 cm for a person of mean height 169 cm (Ju¨rgens et al, 1990; Lewin, 1969) and 95 cm for a person of 158.5 cm stature. A suitable working height for light manipulative tasks is 5—10 cm below elbow level (Grandjean, 1988). The extension of the articles means that the working height of the cashiers is approximately 5 cm above the conveyer belt. Therefore the height of the checkout system (90 cm) is suitable for the taller cashier but to obtain a more suitable working height for the shorter cashier the height of the checkout system should be about 10 cm lower.
266
Evaluation of a workplace redesign. A. Johansson et al.
Several authors (Lannersten and Harms-Ringdahl, 1990; Ryan, 1989) suggest alternating between sitting and standing positions during checkout work. Lannersten and Harms-Ringdahl (1990) showed for this check-out system, with the scales to the left, that the muscle activity in the neck and shoulders at all levels of load was lower when standing. In our study, the work rate increased slightly in the standing position, which may or may not cause a work situation with more stress depending on the organisation of the work. Additionally, the possibility of resting the left arm by supporting it is decreased. However, the results indicate that a standing position is more favourable than sitting for the taller cashier. For the shorter cashier, the sitting position is better. If the height of the checkout system was adjustable, a standing position may provide a more appropriate working height also for the shorter cashier. However, neither sitting nor standing by themselves provide the optimal working conditions for an entire working day. Therefore, it is important that the cashier alternates between sitting and standing positions. Job rotation used throughout the supermarket could also be a good alternative.
Improvements A more flexible checkout system, for instance a fast and comfortable way of adjusting seat height, and training of the cashier to use correct working techniques could further improve the work situation. The depth of the cash-box also affects the reach needed by the cashier. A narrower cash-box, which ought to be easy to design for use with the scales beneath the conveyer belt (see Figure 1), would further decrease the reach required. If all articles for weighing were equipped with a barcode identifying the product and the scales beneath the conveyer belt were used, the work of the right hand on the register could be further reduced and this arm could be used for handling the articles more which would reduce the load on the left arm.
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Grandjean, E. (1988) Fitting the ¹ask to the Man, 4th edn, Taylor & Francis, London Harber, P., Pena, L., Bland, G. and Beck, J. (1992) Upper extremity symptoms in supermarket workers. Amer J. Ind. Med. 22, 873—884 Hinnen, U., La¨ ubli, T., Guggenbu¨ hl, U. and Kreuger, H. (1992) Design of checkout systems including laser scanners for sitting work posture Scan. J. ¼ork Environ Health 18, 186—194 Ju¨ rgens, H.W., Aune, I.A. and Pieper, U. (1990) International data on anthropometry, Occupational and Health Series, 65. International Labour Office, Geneva, Switzerland Ja¨ rvholm, U and Palmerud, G. (1990) Arbetsrelaterade skulderbesva¨r— uppkomst och prevention (Work related shoulder disorders—origin and prevention) Arbetsmiljo¨ fondens sammanfattningar 1420, 86—0360 (in Swedish) Karhu, O., Kansi, P. and Kuorinka, I. (1977) Correcting working postures in industry: A practical method for analysis Appl Ergonomics 8, 199—201 Karhu, O., Ha¨ ko¨ nen, R., Sorvali, P. and Vepsa¨ la¨ inen, P. (1981) Observing working postures in industry: Examples of OWAS applications Appl Ergonomics 12, 13—17 Kilbom, As . and Persson, J. (1987) Work technique and its consequences for musculoskeletal disorders Ergonomics 30, 273—279 Kuorinka, I. and Forcier, L. (1995) in Kuorinka, I., Forcier, L., (eds), ¼ork Related Musculoskeletal Disorders ¼MSDs: A Reference Book for Prevention. Taylor and Francis, London Lannersten, L. and Harms-Ringdahl, K. (1990) Neck and shoulder muscle activity during work with different cash register systems Ergonomics 33, 49—65 Lewin, T. (1969) Anthropometric studies on Swedish industrial workers when standing and sitting Ergonomics 12, 883—902 Lundqvist, P. (1990) WOPALAS—a method for ergonomical analysis and practical improvements. Examples from Swedish industry and agriculture, in Das, B., (ed). Advances in Industrial Ergonomics and Safety II, Montreal Taylor & Francis, London, pp. 827—832 Margolis, W. and Kraus, J. F. (1987) The prevalence of carpal tunnel syndrome symptoms in female supermarket checkers J. Occup. Med. 29, 953—956 Morgenstern, H., Kelsh, M., Kraus, J. and Margolis, W. (1991) A cross sectional study of hand/wrist symptoms in female grocery checkers Amer J Ind Med 20, 209—218 Osorio, A. M., Ames, R. G., Jones, J., Castorina, J., Rempel, D., Estrin, W. and Thompson, D. (1994) Carpal tunnel syndrome among grocery store workers. Amer J. Ind. Med. 25, 229—245 Pinzke, S. (1994) A computerised system for analysing working postures in agriculture. Int. J. Ind. Ergonomics 13, 307—315 Ryan, G. A. (1989) The prevalence of musculo-skeletal symptoms in supermarket workers Ergonomics 32, 359—371 Stock, S. R. (1991) Workplace ergonomic factors and the development of musculoskeletal disorders of the neck and upper limbs: a metaanalysis. Amer J. Ind. Med 19, 87—107 Winkel, J. and Westgaard, R. (1992) Occupational and individual risk factors for shoulder-neck complaints: Part II—the Scientific basis (literature review) for the guide Int. J. Ind. Ergonomics 10, 85—104
PII: S0003—6870(97)00016-1
Applied Ergonomics Vol. 29, No. 4, pp. 261—266, 1998 ( 1998 Elsevier Science Ltd All rights reserved. Printed in Great Britain 0003—6870/98 $19.00#0.00
Evaluation of a workplace redesign of a grocery checkout system Anja Johansson1, Gerd Johansson1, *, Peter Lundqvist2, Ingrid As kesson3, Per Odenrick1,4 and Roland Akselsson1,4 1
Department of ¸und Institute of ¹echnology, P.O. Box 118, SE-221 00 ¸und, Sweden Department of Agricultural Biosystems and ¹echnology, Swedish ºniversity of Agricultural Sciences, P.O. Box 88, 945, SE-230 53 Alnarp, Sweden 3 Department of Occupational and Environmental Medicine, ¸und ºniversity Hospital, SE-221 85 ¸und, Sweden 4 Change@¼ork, P.O. Box 118, ¸und ºniversity, ¸und, Sweden 2
(Received 5 June 1996; in revised form 6 March 1997)
The aim of this study was to evaluate the effects on the working postures and movements of a cashier when two different locations of the scales (one to the left of the cashier, the other under the conveyer belt in front of the cashier) were used in a grocery checkout system. Two cashiers (of average stature and short stature) were videotaped while working, in both sitting and standing working positions. Analysis of the video tapes was performed using the WOPALAS method and video observations. The results of the study show that the design of the checkout system with the scales under the conveyer belt provides a more favourable working position for both the taller and the shorter cashier. Additionally, the results indicate that a standing position is more favourable than a sitting one for the taller cashier while for the shorter cashier the sitting position is better. ( 1998 Elsevier Science Ltd. All rights reserved. Keywords: checkout system, scales, evaluation, working postures, movements
Introduction
gdahl, 1990; Hinnen et al, 1992). An increased risk of developing carpal tunnel syndrome has also been reported (Margolis and Kraus, 1987; Morgenstern et al, 1991; Osorio et al, 1994). The work of a supermarket cashier includes manual handling of large quantities of articles during each working day, often combined with a stressful workplace which may cause exposure to some of the above-mentioned risk factors for the development of musculoskeletal disorders. In a study of the neck and shoulder muscle activity, Lannersten and Harms-Ringdahl (1990) found that work with scanners and pen readers caused higher loads than conventional keyboard operation in the trapezius, infraspinatus and thoracic erector spinae muscles. Standing positions showed lower muscle activity at all load levels than did sitting positions. However, the main problems identified were the repetitive handling and the constant static load. To decrease the musculoskeletal load, several authors have suggested that the cashier alternates between sitting and standing positions (Lannersten and HarmsRingdahl, 1990; Ryan, 1989). A further improvement can be achieved by combining the checkout work with other kinds of work in the shop (Hinnen et al, 1992). Alternatively, Baron and Habes (1992) have suggested placing the weigh scales under the conveyer belt.
Work-related musculoskeletal disorders are recognised as a major occupational problem. An association between stressful working postures and movements and the development of musculoskeletal disorders in the neck and upper extremities is now widely acknowledged in the literature (Kuorinka and Forcier, 1995). Some risk factors have been suggested to be of special interest, for example joint positions such as constrained postures, positions close to extremes, and steep forward bending of the head. Furthermore, high repetitiveness, high force, high static muscle and joint load can compound the problems (Stock, 1991; Winkel and Westgaard, 1992). In recent years, musculoskeletal disorders among supermarket cashiers have been reported in several studies (Ryan, 1989; Baron and Habes, 1992; Harber et al, 1992). The symptoms are commonly found in the neck and the upper extremities, especially the left arm (Baron and Habes, 1992; Harber et al, 1992). The introduction of laser scanners for price registration seems to have further increased the problems (Lannersten and Harms-Rin-
*Author to whom correspondence should be addressed 261
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262
The aim of this study was to evaluate the effects on the working postures and movements of a cashier when two different locations of weigh scales were used in the same checkout system as that investigated by Lannersten and Harms-Ringdahl (1990). A location of the scales to the left of the cashier was compared with a location under the conveyer belt, in front of the cashier. The effects of sitting and standing working positions and of different body sizes of the cashiers were also studied.
Experimental design The experiments were performed in a laboratory using a commercially available supermarket checkout system (UK 90, manufactured by ABO METALL AB Jo¨nko¨ping, Sweden). The checkout system, with a non-adjustable working height of 90 cm, is designed for both sitting and standing working positions. It was equipped with a flexible chair which each cashier was able to adjust to a comfortable height and sitting position.
Figure 1 The two arrangements of the checkout system, with the scales to the left (a) and under the conveyer belt (b). Articles are supplied from the right. Only the middle part of the checkout system is shown. (A"scanner, B"scales, C"cash-box, D"cash register and E"cashier)
The checkout system had a vertical scanner and an adjustable cash-register keyboard. The scales of the original version of the system were located to the left of the cashier and the cash-box between the cashier and the conveyer belt. In the modified checkout system, the scales were removed and relocated under the conveyer belt just in front of the cashier. When an article is not registered by the scanner, the conveyer belt automatically stops, the cashier registers the article code and the article is weighed; then the belt automatically starts again. As the scales to the left were removed, the original cash-box, 18]49 cm, could be replaced by another with a depth of 15 cm and a width of 52 cm. The layouts of the two checkout system designs are shown in Figure 1. Two female cashiers with several months of daily experience ('6 months) using the checkout system in question (vertical laser scanner and the scales to the left) but with different anthropometric data were selected to participate in the study. No attempt was made to standardise their working technique. Both were righthanded and had no history of musculoskeletal disorders. One cashier (no. 1) was of medium stature (height 170 cm, weight 60 kg, age 21 yr) while the other (no. 2) was shorter (height 153 cm, weight 60 kg, age 25 yr). Ju¨rgens et al (1990) estimated the stature for a female North-European population; the values were 158.5, 169.0 and 179.5 cm for the 5-, 50- and 95-percentile, respectively. Twenty-five different grocery items (average weight 0.8 kg) with a total weight of 19.7 kg were used during the study. The prices of 17 articles were registered by the scanner while the other eight (average weight 1.1 kg) required weighing. The proportion of articles needing to be weighed was chosen to be higher than normally expected in order to detect better, any differences due to the location of the scales. The positions and orientations of of each article were marked on the conveyer belt to allow the experiment to be repeated with the same initial positions. For each cashier, both standing and sitting positions were studied and analysed for the two locations of the scales. Each experimental situation was repeated five times. When the working cycle started, all the articles were placed in the same initial positions on the conveyer belt and the cashier registered these. A working cycle lasted about 90 s. In Table 1, the properties of the experimental sequence are shown. During each experiment the cashier was videotaped from behind, from the left side and from above.
Table 1 Description of the experimental design. The cycle time is shown as mean value (SD) Experimental situation
Cashier number
Number of cycles
Position
Position of the scales
Average cycle time [s]
Scanning failures per cycle
1 2 3 4 5 6 7 8
2 1 2 1 2 1 1 2
5 5 5 5 5 5 5 5
Sitting Sitting Standing Standing Sitting Sitting Standing Standing
Left Left Left Left Conveyer belt Conveyer belt Conveyer belt Conveyer belt
93.1 87.6 81.9 83.2 87.1 99.6 76.3 73.0
0—2 4—7 2—4 1—14 1—4 3—14 1—5 0—3
(8.3) (5.7) (2.8) (5.0) (11.0) (14.4) (3.0) (2.0)
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Methods used for evaluation For ergonomic studies of the postures and movements of the whole body, the WOPALAS method (Lundqvist, 1990) developed from the OWAS method (Karhu et al, 1977; Karhu et al, 1981) was used. The WOPALAS method differs from the OWAS method in that it separates registrations for left and right arms and legs. It also has a more detailed registration of the arm positions and finally it uses more levels of weight and force registration. The WOPALAS method is based on work sampling techniques which provide both the frequency of each posture and the time spent in each. The method includes registration of the postures of the back, the arms, the legs and the head. The angles registered for the arms are the deviations from the body—that is, a combination of flexion and abduction. It is also possible to register the weights and forces handled. These forces come from, for example lifting or dragging grocery items. In this study, the body posture was registered every 3 s. The WOPALAS analysis was carried out by a researcher experienced with this method. For the evaluation of the different designs of the checkout system, it was important to study further, the postures and movements of the head and the left arm, and this was done using the VIRA method (Kilbom and Persson, 1987). As opposed to the WOPALAS method, VIRA uses continuous registrations for one body part at the time. A VIRA analysis was carried out for the flexion and the abduction of the left upper arm, and an analysis using the same principles as the VIRA method was carried out for the rotation of the head. A computer program developed for this purpose was used (Pinzke, 1994). The chosen angle intervals for the classification of the flexion and abduction of the left upper arm were in this case: neutral position (the arm is at 0°), (0°, 0—30°, 30—60°, and '60°. These angles refer to the angle between the projection in the sagittal (flexion) or frontal (abduction) plane of the upper arm studied and the line of gravity. The chosen angle intervals for the rotation of the head were: '45° left, 15—45° left, 15° left—15° right, 15—45° right, and '45° right. The VIRA analysis was carried out from video tapes played in slow motion (1/5 of normal speed) by manually registering the occurrence of a body part in a certain angle segment. A further refinement of the ergonomic evaluation of the work situation of the cashier was to use additional video observations to record the time spent in particular working positions as a percentage ofthe total time of a work cycle. The particular positions are: 1. The left lower arm is supported. 2. The left elbow angle is less than 30°, combined with a flexion angle for the left upper arm of more than 30° (Figure 2a). The choice of a flexion angle of 30° is based on the results from the work of Ja¨rvholm and Palmerud (1990). Such positions are hereafter abbreviated as ‘stretching’. 3. The left upper arm is close to the body and the left forearm is in external rotation of more than 30° (Figure 2b). This position is henceforth abbreviated as ‘external rotation’. All five working cycles of each experimental situation were analysed with all three methods. The duration of the
Figure 2 (a) Definition of elbow extension and arm flexion. (b) Definition of external rotation
working cycles varied between 71 and 121 s. The number of failures when the price was not registered by the scanner varied between 0 and 14 per working cycle. A failure required the cashier to re-scan the bar-code of the article until the price was registered.
Results All the results from the WOPALAS-analysis are summarised in Table 2. In Table 3, the results from the other video observations are presented. All the differences between the designs of the checkout system, the working positions (sitting, standing) and the cashiers are significant at at least the 5% level (p(0.05). For the statistical analysis unpaired t-tests combined with Mann—Whitney º-tests were used. Medium stature cashier (person no. 1) in a sitting position When the scales are placed under the conveyer belt, the WOPALAS-analysis shows f decreased occurrence of postures in the larger angle segments both for the left ('30°) and the right arm ('10°); f the cashier spends less time handling heavy (1.5—5.0 kg) articles during a working cycle; f a reduction in occurrence of the head in a twisted ('45°) position. The VIRA-method shows improvements for the left arm with the scales placed under the conveyer belt. The external rotation of the left arm is eliminated and the arm is in neutral position (0°), supported position or both for a substantial part (about 30%) of the working cycle. The results in Table 3 also show that the head is rotated more towards the left and less time is spent in the extreme angle intervals ('45°) when the scales are under the conveyer belt. Medium stature cashier in a standing position When the cashier is standing with the scales situated under the conveyer belt, the same kind of improvements as for sitting are found for both the arms and the head. Also the time of handling of articles weighing 0.5—1.5 kg is decreased in this case.
Evaluation of a workplace redesign. A. Johansson et al.
264
Table 2 Percentage distribution of working postures according to the WOPALAS-analysis for the different locations of the scales (xN "mean value, s"standard deviation). Furthermore, the percentage distribution of the weights handled are shown Person no. 1 Sitting Left Conveyer x6 s x6 s Back Straight 100 Left arm 0—10° 15.5 10—30° 28.9* 30—90° 55.7* Right arm 0—10° 72.7* 10—30° 23.9* 30—90° 3.3 Head T wisted ('45°) 16.0* Weights handled (kg) 0—0.5 45.1 0.5--1.5 47.6 1.5--5.0 7.3*
0
100
Person no. 1 Standing Left Conveyer x6 s x6 s
0
100
0
3.4 7.0 5.2
17.3 37.9* 44.7*
5.8 4.3 3.0
18.4* 44.0 37.7*
5.7 3.7 7.5
1.6 4.6 3.5
96.0* 4.0* 0
2.7 2.7 0
91.5* 8.5* 0
6.1 6.1 0
0
2.2
0*
6.4 5.3 4.3
0
46.4 51.8 1.8*
0
8.8 7.8 2.8
51.9* 41.8* 6.3*
100
0
37.1* 47.8 15.1*
8.6 7.8 2.8
Person no. 2 Sitting Left Conveyer x6 s x6 s
Person no. 2 Standing Left Conveyer x6 s x6 s
100
100
0
100
5.3 4.1 6.7
25.0 38.6 36.4
2.1 4.0 3.4
28.0 39.3 32.6
100* 0* 0
0 0 0
81.3* 18.1* 0.6
2.1 2.7 1.3
100* 0* 0
0
0
11.6*
3.7
3.9 3.9 0
58.0 35.5 6.5*
11.8 12.0 2.4
71.7* 28.3* 0*
0.8* 61.2 38.8 0*
0
0
100
0
5.7 4.9 3.9
14.3* 43.4 42.3*
2.7 4.1 4.3
24.0* 44.2 31.8*
3.0 4.1 5.1
0 0 0
92.9* 7.1* 0
4.1 4.1 0
99.2* 0.8* 0
1.7 1.7 0
1.7
2.8*
1.6
2.4 2.4 0
48.1* 41.9* 9.9*
7.5 6.5 2.5
0* 64.3* 34.9* 0.8*
0 6.7 6.6 1.7
*indicates significant differences between the mean values for different locations of the scales (p(0.05)
Table 3 Percentage distribution of the time spent in a working position according to the video observations for the different locations of the scales (xN "mean value, s"standard deviation)
Upper left arm Flexed (0° +0° (neutral) 0—30° 30—60° '60° Abducted (0° +0° (neutral) 0—30° 30—60° '60° Head Rotated '45°left 15—45° left 15° left—15°right 15—45° right '45° right Left arm Supported Stretched External rotated
Person no. 1 Sitting Left Conveyer x6 s x6 s
Person no. 1 Standing Left Conveyer x6 s x6 s
Person no. 2 Sitting Left Conveyer x6 s x6 s
Person no. 2 Standing Left Conveyer x6 s x6 s
34.6* 2.1* 32.3 28.2 2.8*
2.1 2.3 4.3 4.6 1.4
1.8* 37.0* 35.7 25.0 0.5*
2.3 4.7 5.8 4.8 0.2
37.5* 7.5* 44.0 11.0 0
3.4 3.3 4.1 3.1 0
6.6* 38.1* 43.2 11.3 0.7
5.2 11.8 16.1 8.6 1.6
20.8* 20.0 34.1 23.0 2.0
2.7 4.2 5.4 3.8 1.5
0* 31.6 39.2 27.1 2.1
0 10.6 7.0 8.7 1.7
26.0* 6.2 44.0 23.2* 0.5*
10.0 4.2 6.0 9.8 0.6
9.4* 2.3* 76.5* 11.1 0.6
3.0 2.6 5.3 4.6 0.3
15.4* 32.5* 44.7* 6.2 1.2
3.1 4.0 7.5 3.2 1.3
15.6* 38.0 44.2* 2.3* 0
3.4 5.6 3.0 1.9 0
29.0* 44.7 26.3* 0* 0
2.4 8.9 8.3 0 0
25.7 19.0* 44.6 10.2 0.6
4.2 3.7 5.1 3.9 0.6
21.7 29.1* 42.3 6.6 0.3
6.7 8.7 7.8 3.2 0.4
28.3 7.5* 46.0 18.2* 0
3.4 4.3 6.6 2.2 0
17.6 12.1 32.6* 8.6 39.4 7.8 10.4* 4.8 0 0
0.5* 23.2* 39.8 25.8 10.6*
0.3 3.3 4.9 5.0 2.3
4.2* 35.4* 36.9 23.1 0.4*
1.5 4.8 2.4 4.2 0.3
1.1 15.0* 49.1* 22.0* 12.9*
0.9 3.3 6.6 4.2 2.4
3.7 47.7* 37.6* 10.6* 0.3*
3.1 2.2 5.0 6.6 0.6
1.4* 20.1* 42.9* 28.3 7.3*
0.6 9.6 11.1 8.1 4.0
5.5* 41.2* 23.0* 29.2 1.1*
2.2 4.0 3.0 6.0 0.8
2.6 12.1* 48.5* 29.4 7.4*
1.4 4.3 6.4 4.3 2.2
2.3 40.8* 26.3* 28.6 1.9*
3.5 7.3 6.5 2.9 1.3
1.8* 7.2 35.5*
3.7 1.4 3.2
32.4* 5.5 0*
5.1 2.0 0
0.6* 4.2 31.5*
1.3 2.3 3.6
7.5* 2.8 6.6*
1.2 1.4 3.4
15.1* 18.1* 17.3*
4.4 2.1 2.3
30.2* 22.4* 0*
10.7 1.8 0
4.4 27.6 20.3*
2.6 6.5 2.9
6.8 31.0 2.6*
2.8 4.7 2.5
0.2* 8.8 43.0 45.6* 2.3*
0.2 4.3 6.3 4.9 1.6
*Indicates significant differences between the mean values for the different locations of the scales (p(0.05)
The results further show that, for this cashier, the standing position is more favourable when evaluating the angle distributions of both the left and right arm. The left arm is in more of a neutral position when standing and the stretching movements are decreased.
In the standing position, the cashier is, however, only supporting the arm 8% of the time compared to 32% when sitting. The WOPALAS-analysis further shows more twisted positions for the head when sitting with the scales to the left and less handling of articles
Evaluation of a workplace redesign. A. Johansson et al.
heavier than 0.5 kg when standing using the scales beneath the conveyer belt. However, the same tendency for the head rotation cannot be observed from the video observations.
265
f exhibited more forward ‘stretching’ movements with the left arm, the difference was greater in standing positions.
Discussion Short stature cashier (person no. 2) in a sitting position For the shorter cashier, when the scales are under the conveyer belt the WOPALAS-analysis shows a reduction of the time the upper right arm is found in a position '10° out from the body, a reduction of the time the head is twisted and the time heavier articles are handled. The time the left arm is supported or in a neutral position is increased and the rotation of the left arm is reduced. A slight increase from 18 to 22% of the stretching of the left arm is registered using the scales beneath the conveyer belt. Moreover, for this cashier the head (see Table 3) is more rotated towards left when using the new scale location. Short stature cashier in a standing position The WOPALAS-analysis shows more obvious improvements for this work situation when using the scales beneath the conveyer belt. The time spent in the larger angle segment is reduced for both arms as the time spent handling articles heavier than 0.5 kg. The VIRA-analysis gives a decrease for the time the left arm is in the angle segment '30° for abduction but an increase for flexion. No significant change is found in ‘stretching’ the left arm when the scales beneath the conveyer belt are used. The external rotation movements of the left arm are also reduced and the head is more often rotated towards the left. Comparing sitting and standing position for the shorter cashier shows that the sitting position is superior for the left arm. There are more support and neutral positions for this arm, as well as less stretching and less time spent in several angle intervals '30°. However, the WOPALAS-analysis shows more twisted positions for the head for a sitting position when the scales are set to the left. Comparison of the two cashiers The average cycle times presented in Table 1 show that the work rates of the two cashiers are almost the same and that no significant change is found for the two different locations of the scales. When the working position is changed from sitting to standing the average work rate, however, seems to increase (the difference is statistically significant in three out of four working situations). Upon comparing the two cashiers we found that person no. 2. (shorter stature) f spent substantially less time in external rotation when the scales were located to the left, f supported her left arm more and had this arm in a more neutral position when sitting with the scales located to the left; in a standing position, the taller cashier (no. 1) had the arm in a neutral position more frequently; f had the upper left arm in the angle segment '30° more when standing and less when sitting;
The two cashiers were selected to represent, a person of medium stature in the distribution of North-European females and a very short stature. Both cashiers were very experienced working with the checkout system in question with the scales to the left, but neither had used the system with the scales under the conveyer belt. The observed differences between the cashiers are probably due to both different body constitutions and different working techniques. The shorter cashier worked using more flexed or stretched movements of the left arm, probably due to a shorter reach. She had less failures when using the scanner. Her working technique also differed from that of the taller cashier when weighing the articles. The taller cashier lifted the articles more and kept her left arm in a externally rotated position while weighing. The shorter cashier rested her left arm more when using the checkout system with the scales to the left. Whether these increased periods of resting the arm are due to a better working technique or to a greater need for rest caused by a higher work load is difficult to determine. The results of this study show that the design of the checkout system with the scales under the conveyer belt provides a more favourable working position for both the taller and the shorter cashier. The external rotation of the left arm decreased substantially, the time spent handling articles was reduced and the possibilities for resting the left arm or keeping it in a neutral position were greatly improved. The twisting of the head was also decreased when the scales were placed under the conveyer belt. The reduction in the handling of the articles is more pronounced for a standing working position. More daily work with the scales beneath the conveyer belt may further improve the cashiers’ work technique, which may decrease the musculoskeletal load but may increase the work rate. However, the improvements due to the placement of the scales are more evident for the taller cashier than for the shorter. The reason for a more twisted position of the head towards the left side when using the scales under the conveyer belt is that the cashiers position themselves closer to the register found to their right. Hence, when observing the articles on the belt, they twist their heads more towards the left. The most common working position for cashiers is sitting. In our case, the cashiers can partly adjust their sitting position by adjusting the chair. When standing they have, however, a fixed working height (conveyer belt 90 cm). The elbow height is an average 103 cm for a person of mean height 169 cm (Ju¨rgens et al, 1990; Lewin, 1969) and 95 cm for a person of 158.5 cm stature. A suitable working height for light manipulative tasks is 5—10 cm below elbow level (Grandjean, 1988). The extension of the articles means that the working height of the cashiers is approximately 5 cm above the conveyer belt. Therefore the height of the checkout system (90 cm) is suitable for the taller cashier but to obtain a more suitable working height for the shorter cashier the height of the checkout system should be about 10 cm lower.
266
Evaluation of a workplace redesign. A. Johansson et al.
Several authors (Lannersten and Harms-Ringdahl, 1990; Ryan, 1989) suggest alternating between sitting and standing positions during checkout work. Lannersten and Harms-Ringdahl (1990) showed for this check-out system, with the scales to the left, that the muscle activity in the neck and shoulders at all levels of load was lower when standing. In our study, the work rate increased slightly in the standing position, which may or may not cause a work situation with more stress depending on the organisation of the work. Additionally, the possibility of resting the left arm by supporting it is decreased. However, the results indicate that a standing position is more favourable than sitting for the taller cashier. For the shorter cashier, the sitting position is better. If the height of the checkout system was adjustable, a standing position may provide a more appropriate working height also for the shorter cashier. However, neither sitting nor standing by themselves provide the optimal working conditions for an entire working day. Therefore, it is important that the cashier alternates between sitting and standing positions. Job rotation used throughout the supermarket could also be a good alternative.
Improvements A more flexible checkout system, for instance a fast and comfortable way of adjusting seat height, and training of the cashier to use correct working techniques could further improve the work situation. The depth of the cash-box also affects the reach needed by the cashier. A narrower cash-box, which ought to be easy to design for use with the scales beneath the conveyer belt (see Figure 1), would further decrease the reach required. If all articles for weighing were equipped with a barcode identifying the product and the scales beneath the conveyer belt were used, the work of the right hand on the register could be further reduced and this arm could be used for handling the articles more which would reduce the load on the left arm.
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