Postural Support by a Standing Aid Alleviating Subjective Discomfort among Cooks in a Forward-bent Posture during Food Preparation

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1 J Occup Health 2008; 50: Journal of Occupational Health Postural Support by a Standing Aid Alleviating Subjective Discomfort among Cooks in a Forward-bent Posture during Food Preparation Kazuyuki IWAKIRI 1, Reiko KUNISUE 2, Midori SOTOYAMA 1 and Hiroshi UDO 3 1 National Institute of Occupational Safety and Health, Japan, 2 Saiki-seseragi Nursing Home and 3 Hiroshima Bunkyo Women s University, Japan Abstract: Postural Support by a Standing Aid Alleviating Subjective Discomfort among Cooks in a Forward-bent Posture during Food Preparation: Kazuyuki IWAKIRI, et al. National Institute of Occupational Safety and Health, Japan In this study, we evaluated the effects on subjective discomfort among cooks during food preparation through use of a standing aid that we developed to alleviate the workload on the low back in the forward-bent posture. Twelve female cooks who worked in a kitchen in a nursing home were asked to prepare foods in 2 working postures: (a) supported by the standing aid (Aid) and (b) without the aid (No aid). They were instructed to evaluate discomfort in 13-body regions during food preparation and the degree of fatigue at the day s end and to enter their ratings after the end of the workday. Since a significant correlation was observed between body height and the improvement effect of discomfort through use of the standing aid, cooks were divided into two groups according to the height, and ratings were analyzed in each group. Among the tall cooks, subjective discomfort in the low back and the front and back of thighs was significantly less with the Aid posture than with the No aid posture. However, in short cooks these values tended to increase in the Aid posture compared with the No aid posture. The results suggest that the standing aid was effective in alleviating tall cooks workload on the low back in the forward-bent posture. (J Occup Health 2008; 50: 57 62) Key words: Standing aid, Low back pain, Cook, Forward-bent posture, Food preparation Kitchen work in facilities that provide meals includes Received Mar 16, 2007; Accepted Oct 1, 2007 Correspondence to: K. Iwakiri, National Institute of Occupational Safety and Health, Nagao, Tama-ku, Kawasaki , Japan ( iwakiri@h.jniosh.go.jp) risk factors for musculoskeletal disorders 1 5). During food preparation in which a large deep sink is used, a cook must keep the trunk bent forward for long periods 6). The forward-bent posture places a large workload on the low back 7, 8) and is recognized as a risk factor for low back pain 9, 10). An effective measure for alleviating this workload, however, has not been established. Although a primary measure is height adjustment of the kitchen counter 11), which will change a stooped posture into an upright posture, the kitchen counter cannot be easily adjusted because of the weight of the counter. Also, a chair which alleviates the workload on the low back and legs during work 12, 13) cannot be used because of limited space in facilities that provide meals. In previous studies, we proposed a new measure for alleviating the workload on the low back that adjusts a person s height by using supplemental equipment, which we call a standing aid (Fig. 1) 14, 15). The standing aid supported the shins and the upper edge of the kitchen counter supported the abdomen. With the postural support given by the standing aid, the height of the low back became lower through flexing of the knees and the stooped posture became upright. That is, use of the standing aid has the equivalent effect of an adjustment of the kitchen counter to a suitable height. The cook s height was adjusted to the kitchen counter. In laboratory study, the standing aid was effective in alleviating subjective discomfort and muscle load on the low back and legs 15). In Japanese facilities that provide meals, middle-aged and older cooks perform various tasks for long hours 3, 6, 16). However, the subjects of previous studies were young female college and graduate students, and they only performed plate washing in the laboratory 14, 15). The height of the older cooks is probably shorter than that of young students. Therefore, the effectiveness of the standing aid should be examined in a crossover intervention trial in which both tall and short cooks participate at their workplace.

2 58 J Occup Health, Vol. 50, 2008 Fig. 1. Primary measure and new proposal for improvement of the forward-bent posture. The primary measure is height adjustment of the kitchen counter. Our new proposal is height adjustment of a person through use of the standing aid. We compared subjective discomfort among cooks with and without the support of the standing aid in a facility that provides meals, and evaluated the effects of the standing aid on the workload on the low back in the forward-bent posture during food preparation. Methods Subjects Twelve female cooks who worked in a kitchen in a nursing home were asked to participate in this study (Table 1). Their ages ranged from 42 yr to 65 yr (mean with standard deviation=52.0 ± 7.6 yr), and their careers as a cook ranged from 10 yr to 35 yr (15.7 ± 7.1 yr); their body heights ranged from cm to cm (152.0 ± 5.5 cm). No cook had a history of cervicobrachial disorder or low back pain, nor had taken time off because of such disorders. The objectives and methods of this study were explained to the participants and informed consent was obtained before the experiment. The protocol for this study was approved by the Institutional Review Board for the Protection of Human Subjects at the National Institute of Occupational Safety and Health. Kitchen work and counter dimensions in the facility Kitchen work in the facility was divided into 5 shifts in the daily work schedule: 5:30 to 14:30, 6:00 to 15:00, 7:30 to 16:30, 9:00 to 18:00 and 10:45 to 19:45. Each Table 1. Characteristics of cooks Cook Age (yr) Career (yr) Height (cm) A B C D E F G H I J K L cook worked a 9-h shift. Tasks within a shift included a staff meeting, food preparation, cooking and cleaning up. Food preparation consisting of washing and peeling of foods was included in two shifts: from 7:30 to 16:30 and from 10:45 to 19:45. The target task in this study was the food preparation in the shifts. A kitchen counter with a large deep sink was used in these tasks (Fig. 2 left). The width, length and height of the kitchen counter were 1,180 mm, 750 mm and 840

3 Kazuyuki IWAKIRI, et al.: Postural Support by a Standing Aid 59 Fig. 2. Standing aid, kitchen counter with a sink (Left) and working posture (Right). Leaning on the standing aid and the upper edge of a kitchen counter, a cook is washing or peeling foods. mm, respectively. This height was commonly observed in the Japanese facilities that we have investigated. The depth of the sink was 280 mm and the thickness of the upper edge of the kitchen counter was 40 mm. Standing aid We developed a standing aid for use at the workplace (Fig. 2 left). The standing aid, 500 mm in width, 600 mm in length and weighing 4.65 kg, consisted of a standing platform, supporting frame and cylindrical cushion. The cylindrical cushion, 120 mm in diameter and 400 mm long, was made by winding a sponge of flexible polyurethane foam around a bar with a diameter of 20 mm and covering it with synthetic leather. The height of the top of cushion could be adjusted from 315 mm to 495 mm. Working postures Cooks were asked to prepare foods in two working postures: (a) supported by the standing aid (Aid) and (b) without the aid (No aid). With the Aid posture, the cooks were instructed to support the shins with the standing aid and to support the abdomen with the upper edge of the kitchen counter (Fig. 2 right). Moreover, they were asked to flex their knees approximately 25 degrees and to stand in the position close to the kitchen counter. With flexion of the knees, the height of the low back is lowered by 4.1 cm to 4.7 cm. In the No aid posture, the cooks supported only the abdomen on the upper edge of the kitchen counter and had to keep the trunk bent forward. Procedure Food preparation for each subject was performed from 30 min to 60 min after the beginning of the daily work schedule. Foods to be prepared consisted of approximately 30 kg of vegetables such as potatoes, carrots and onions. While at food preparation, cooks took food from underneath the sink, washed or peeled it in the sink, and put it back underneath the sink. They were asked to evaluate subjective discomfort in 13 body regions during food preparation and fatigue at the day s end, and enter their ratings at the end of the workday. Each cook was instructed to perform the food preparation in the Aid posture and No aid posture on different days. The order of the working posture, that is, whether the cook began with the Aid posture or No aid posture on the first day of the evaluation, was randomized for each cook. Cooks used the standing aid 7 d or more in order to get used to it before the rating. This study was carried out from July to August in Subjective discomfort Subjective discomfort was rated by a questionnaire with a 100-mm visual analog scale (VAS), ranging from nothing at all (0 mm) at one end of the scale to extreme discomfort (100 mm) at the other end. The 13 body regions were the neck, shoulders, arms, hands, upper back, lower back, front of thighs, back of thighs, knees, shins, calves, tiptoes and heels. They were selected according to the chart used for identification of body parts by Corlett and Bishop17) and Van Dieën et al.18) Fatigue

4 60 J Occup Health, Vol. 50, 2008 Fig. 3. Relationship between body height and improvement effect through use of the standing aids. The improvement effect through use of the standing aid is defined to be total discomfort rating in the No aid posture minus that in the Aid posture. The solid line is the regression line. for the entire day, including that from other work, was also rated. The total discomfort rating which was the sum of 13 regions was utilized to evaluate discomfort of the whole body. Data were calculated according to the distance from nothing at all (0 mm) to a selected rating point on the VAS. Statistical analysis All data for subjective discomfort were subjected to statistical analysis with the paired t-test. Then, to determine the relationship of improvement effect through use of the standing aid to each cook s height, regression analysis was performed. The improvement effect was defined to be the total discomfort rating in the No aid posture minus that in the Aid posture. Since a significant correlation was observed between body height and the improvement effect through use of the standing aid, cooks were divided into a short cook group and a tall cook group at the turning point of the effect, and data were analyzed by the paired t-test for each group. The former group consisted of 6 cooks from cm to cm in height (short cooks: ± 3.9 cm) and the latter group consisted of 6 cooks from cm to cm in height (tall cooks: ± 3.9 cm). SPSS 11.5 for Windows was used for statistical analysis. Statistical significance was set at p<0.05. Results Discomfort rating for all cooks For all cooks, no significant difference between the Aid posture and the No aid posture was found for subjective discomfort in the 13 body regions or the total discomfort rating. Also, no significant difference was found for fatigue at the end of the workday. Relationship between body height and improvement effect The improvement effect through use of the standing aid tended to increase according to the cook s height (r=0.73, p=0.007) (Fig. 3). For tall cooks, who were taller than cm, the total discomfort ratings in the Aid posture were lower than those in the No aid posture. On the other hand, for short cooks, who were shorter than cm, the total discomfort ratings in the Aid posture were higher than those in the No aid posture. Discomfort rating in short cooks and tall cooks All discomfort ratings were examined for the short and tall cook groups. For tall cooks, the discomfort ratings for arms, hands, upper back, lower back, front of thighs, back of thighs, knees, calves, tiptoes, heels and fatigue at the day s end were over fifty (mm) in the No aid posture (Table 2). The discomfort ratings in arms, hands, upper back, lower back, front of thighs, back of thighs, knees, calves, tiptoes, total discomfort rating and fatigue at the day s end were significantly lower with the Aid posture than with the No aid posture, especially for the lower back and the front and back of thighs. For short cooks, the discomfort ratings for all regions were under fifty (mm) in the No aid posture (Table 2). The discomfort ratings in shoulders, front of thighs, back of thighs, total discomfort rating and fatigue at the day s end were significantly higher with the Aid posture than with the No aid posture. Also, ratings for other regions were relatively high with the Aid posture compared with the No aid posture.

5 Kazuyuki IWAKIRI, et al.: Postural Support by a Standing Aid 61 Table 2. Ratio of rating of subjective discomfort in two working postures: with and without the standing aid Item Short cooks: cm (n=6) Tall cooks: cm (n=6) No aid a (mm) Aid b (mm) p c No aid a (mm) Aid b (mm) p c Neck 35.2 ± ± ± ± Shoulder 44.3 ± ± 22.5 < ± ± Arm 41.8 ± ± ± ± 6.1 <0.05 Hand 35.2 ± ± ± ± 15.6 <0.05 Upper back 29.0 ± ± ± ± 13.0 <0.05 Lower back 37.5 ± ± ± ± 9.9 <0.01 Front of thigh 22.8 ± ± 13.7 < ± ± 23.9 <0.05 Back of thigh 23.2 ± ± 13.8 < ± ± 25.1 <0.05 Knee 33.0 ± ± ± ± 15.4 <0.05 Shin 38.7 ± ± ± ± Calf 39.7 ± ± ± ± 21.0 <0.05 Tiptoe 40.7 ± ± ± ± 19.2 <0.05 Heel 45.0 ± ± ± ± Total discomfort rating d ± ± < ± ± <0.01 Fatigue at day s end 58.0 ± ± 19.6 < ± ± 23.8 <0.05 Data were calculated as the distance from nothing at all (0 mm) to a rating point on a 100-mm VAS. Data are means ± SD. a : Posture without the standing aid. b : Posture supported by the standing aid. c : p-value by paired t-test. d : The value is the sum of the discomfort rating of 13 regions. Discussion The results of this intervention study suggest that a standing aid can alleviate subjective discomfort in the low back and legs of tall cooks during food preparation. Moreover, the standing aid could decrease fatigue at the day s end in the facility that provided meals. In the short cooks, the standing aid could not alleviate subjective discomfort in any of the 13 regions. The short cooks discomfort tended to increase with the Aid posture compared with the No aid posture. Previous laboratory studies suggested that the standing aid was effective at alleviating workload on the low back and legs 14, 15). In these two studies, the subjects height was ± 4.0 cm (8 females) and ± 4.7 cm (9 females), and only one subject was cm or less. In these subjects, the height of the low back became low due to flexing of the knees, and the subject s height was adjusted to the kitchen counter. Therefore, it was suggested that the standing aid was an effective measure for alleviating the workload on the low back while the subjects, who were tall, assumed the forward-bent posture in this study. The short cooks discomfort in all regions was slight with the No aid posture. Pekkarinen and Anttonen 19) reported that the rate of disorders in the lumbar region decreased in association with lower height of cooks. This finding indicates that the height of the kitchen counter is more appropriate for short cooks and they did not need to bend the trunk greatly. If this assumption is correct, when the short cooks used the standing aid, the relative height of the kitchen counter would have become too high. It would be hard for short cooks to use the standing aid. Therefore, it is suggested that the standing aid did not have the desired effect of alleviating the short cooks workload on the low back. The improvement effect through use of the standing aid differed between short cooks, who were shorter than cm, and tall cooks, who were taller than cm. Especially, the improvement effect was high among three cooks from cm to cm, whereas it was low in two cm tall cooks. Although this issue needs to be examined further, we consider that the improvement effect may have been affected by other factors, such as cook s arm length and body type, in addition to body height. For the boundary between cm and cm, we speculate that if the kitchen counter height (840 mm) were to change, this boundary would also shift. In this study, since the cooks movement was not measured during food preparation, we were not able to evaluate the duration time of the forward-bent posture and number of forward bending of the upper body. Such movement factors influence the workload on the low back among cooks. However, since cooks performed food preparation in a randomized condition and did similar work every day, we speculate that the movement factors would not have affected the outcome. Whether a cook is tall or not in consideration of the

6 62 J Occup Health, Vol. 50, 2008 tasks performed can be decided by the relationship between the kitchen counter height and body height. The ratio of the kitchen counter height to body height ranged from 52.0% to 55.1% for the tall cooks and 55.3% to 58.7% for the short cooks in this study. The tall cooks needed to use the standing aid to alleviate subjective discomfort in the forward-bent posture, whereas the short cooks did not. Although the body height at which the standing aid renders a positive effect needs to be examined further, the important thing is that the slight difference in the relative height of the kitchen counter to body height, at a maximum of 6.7%, affected subjective discomfort. Thus, the kitchen counter height should be adjusted according to the height of the cook. However, adjusting the height of a kitchen counter with a large deep sink is not easy. When a counter is too high, cooks can use a footstool but such an effective device or tool is not readily available when the height is too low. We think that the standing aid could be an effective tool for alleviating the workload on the low back when using a low counter. In the future, we would like to introduce the standing aid for prevention of low back pain into facilities that provide meals. Acknowledgments: We would especially like to thank Norikazu Hatanaka and Mikio Kobayashi for their assistance. Our thanks are also due to the cooks who participated. References 1) Nagira T, Suzuki J, Oze Y, Ohara H and Aoyama H: Cervicobrachial and low-back disorders among school lunch workers and nursery-school teachers in comparison with cash-register operators. J Human Ergol 10, (1981) 2) Huang J, Ono Y, Shibata E, Takeuchi Y and Hisanaga N: Occupational musculoskeletal disorders in lunch centre workers. Ergonomics 31, (1988) 3) Ono Y, Shimaoka M, Hiruta S and Takeuchi Y: Low back pain among cooks in nursery schools. Ind Health 35, (1997) 4) Udo H, Kobayashi M, Udo A and Branlund B: Participatory ergonomic improvenment in nursing home. Ind Health 44, (2006) 5) Haukka E, Leino-Arjas P, Solovieva S, Ranta R, Viikari-Juntura E and Riihimaki H: Co-occurrence of musculoskeletal pain among female kitchen workers. Int Arch Occup Environ Health 11, (2006) 6) Sakai K, Watanabe A, Onishi N, Shindo H and Temmyo Y: Features and workload in hospital food service operation. J Science of Labour 69, (1993) (in Japanese with English abstract) 7) International Organization for Standardization (ISO). Ergonomics Evaluation of static working postures. ISO Geneva: ISO, ) Keyserling WM, Sudarsan SP, Martin BJ, Haig AJ and Armstrong TJ: Effects of low back disability status on lower back discomfort during sustained and cyclical trunk flexion. Ergonomics 48, (2005) 9) Burdorf A: Exposure assessment of risk factors for disorders of the back in occupational epidemiology. Scand J Work Environ Health 18, 1 9 (1992) 10) Ministry of Labor in Japan: Guidelines on worksite prevention of low back pain. Labor standards bureau notification No.547. Ind Health 35, (1997) 11) Stephenson J: Determining optimal work surface height for Surrey Memorial Hospital food service workers. J Can Diet Assoc 55, (1994) 12) Kirvesoja H, Vayrynen S and Haikio A: Three evaluations of task-surface heights in elderly people s homes. Appl Ergon 31, (2000) 13) Occupational Safety and Health Administration (OSHA), U.S. Department of Labor: Guidelines for retail grocery stores Ergonomics for the prevention of musculoskeletal disorders. OSHA, (online), < (accessed ). 14) Iwakiri K, Yamauchi S and Yasukouchi A: Effects of a standing aid on loads on low back and legs during dishwashing. Ind Health 40, (2002) 15) Iwakiri K, Sotoyama M, Mori I, Jonai H and Saito S: Shape and thickness of cushion in a standing aid to support a forward bending posture: effects on posture, muscle activities and subjective discomfort. Ind Health 42, (2004) 16) Oze Y: Studies on health hazards among cooks providing school lunch service, Repot 2. An analysis of factors associated with the development of health hazards. Jpn J Ind Health 26, (1984) (in Japanese with English abstract) 17) Corlett EN and Bishop RP: A technique for assessing postural discomfort. Ergonomics 19, (1976) 18) Van Dieën JH, Jansen SMA and Housheer AF: Differences in low back load between kneeling and seated working at ground level. Appl Ergon 28, (1997) 19) Pekkarinen A and Anttonen H: The effect of working height on the loading of the muscular and skeletal systems in the kitchens of workplace canteens. Appl Ergon 19, (1988)