Effects of ergonomic intervention in printing workers on work-related musculoskeletal disorders and visual fatigue

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1 Effects of ergonomic intervention in printing workers on work-related musculoskeletal disorders and visual fatigue Praditpod N a, Mekhora K b,*, Khemthong S c, Klangsin P d Faculty of Physical Therapy and Applied Movement Science, Mahidol University, Phuttamonthon, Nakhonpathom Thailand a nutty_tuyen@hotmail.com, b ptkmk@mahidol.ac.th, c ptskt@mahidol.ac.th, d p_klangsin@hotmail.com *Corresponding author. Tel.: ; Fax.: address: ptmkm@mahidol.ac.th ABSTRACT: Work-related musculoskeletal disorders (WMSDs) are increasingly found in many industrial workers as well as printing workers. The WMSDs, such as clinical symptoms and visual fatigue, are impacting on human and work performance. The literature points a use of ergonomic intervention may be an effective way to improve human and work performance. This study aimed to investigate the effects of ergonomic intervention on clinical symptoms and visual fatigue in printing workers. Physical examinations for the WMSDs, Critical Flicker Frequency (CFF) tests and Reaction Time (RT) tests were performed in 131 printing worker before and after applying the intervention, done by same orthopedic physical therapists. The CFF tests were accomplished for both eyes, while the RT tests were performed for the dominant hand. The ergonomic intervention consisted of a five-minute break (work improvement method) and specific exercises for workers during the break (human improvement method). This intervention was provided for workers over a one-month period. The clinical symptoms of the WMSDs in female workers (e.g. pain and stage of WMSDs) were significantly reduced one month after the completion of the intervention (p < 0.01). Number of the workers reported a reduction of the WMSD severity stages (65.57% in female workers, 42.86% in male workers), of the pain intensity scales (43.24% in female workers, 33.33% in male workers), and of the neural tissue tension (50% in female workers, 57.14% in male workers). Statistically significant differences of the CFF tests and the RT tests were found between baseline, pre-test, and post-test (p < 0.05). In summary, the ergonomic intervention could reduce the clinical symptoms of the WMSDs and visual fatigue in the printing workers. This intervention should be further applied to other workers with similar jobs. Keywords: work-related musculoskeletal disorders, printing workers, visual fatigue, CFF, reaction time 1. INTRODUCTION Work-related musculoskeletal disorders (WMSDs) are increasingly found in many industrial workers as well as printing workers. The WMSDs, such as clinical symptoms and visual fatigue, are impacting on human and work performance [1]. In Thailand, the number of factories has increased from 120,145 factories in 2004 to 126,804 factories in 2007 [2, 3]. This growing is certainly come along with the increased number of industrial workers, who have an opportunity to expose to risk factors for WMSDs with increasing rate of claims and injuries. In the United States, OSHA indicated that musculoskeletal disorders account for onethird of the 1.7 million occupational injuries and illnesses every year. Moreover, the workers who have experience musculoskeletal disorder causing them to be absent from the workplace. More than $45 to $60 billion in workers indirect costs was paid for WMSDs. The workers compensation costs for WMSDs were estimated to be $15 to $20 billion in The average cost per claim for upper extremity and lower back musculoskeletal disorders is approximately twice that of the average non-musculoskeletal disorder workers compensation claim [4, 5]. There are many risk factors that lead to the increase of incidence of WMSDs. Many factors affecting WMSDs were defined as individual, physical ergonomic and psychosocial factors. Individual factors are often beyond the control of workers such as age, gender, and anthropometrics. Physical ergonomic factors are work that results in a biomechanical stress on workers such as force, repetitive movement. Psychosocial factors are included job dissatisfaction, intensified workload, limited job control etc [6, 7]. The impact factors of WMSDs could be prevented and reduced by ergonomic interventions. A three-tier hierarchy of controls is widely accepted as an intervention strategy for controlling WMSDs risk factors. This includes engineering controls, administrative controls, and personal equipment. Engineering controls that preferred approach to prevent and control WMSDs is to design the job including work station design, tool selection 1

2 Praditpod N et al./ The 9 th Southeast Asian Ergonomics Society Conference (Page 2) and design, and work task design. Administrative controls strategies include changes in job rules and procedures such as scheduling more breaks to allow for rest and recovery, job rotation, and education workers to recognize WMSDs risk factors and to learn techniques for reducing the stress and strain while performing their work tasks. Lastly, personal equipment is one of the most controversial methods for preventing WMSDs is whether the use of personal equipment worn or used by the workers such as wrist supports or back belt [8]. These interventions have shown some benefits to many industrial workers; for instance, a reduction of WMSDs symptoms leading to both qualitative and quantitative improvement of industrial products [9-12]. An example of ergonomic intervention can be drawn from computer users. An active ergonomic training (AET) in computer users was used as ergonomic intervention by training for six hours at the workplace for all subjects. The results showed that the subjects who had pain at baseline had less upper back pain intensity, pain frequency, and pain duration. Moreover, after receiving AET, the risk factor exposure was reduced and knowledge was increased [13]. There are some studies that used the work improvement in small enterprises (WISE) technique to improve work places and workers in the small industries. Not only can the technique help improve the industries quality and quantity of products, but also reduce the symptoms of WMSDs in the workers [9, 10]. There is a study using a participatory ergonomics process to reduce the risk factors related to musculoskeletal disorders in the newspaper industry. It was found that the participatory ergonomics can be used to implement the ergonomic solution which can reduce the risk factors related to musculoskeletal disorders [14]. In addition, the ergonomic interventions such as using training program to evaluate and adjust own workstation, could individually reduce the compensation costs, paid for the video display terminal (VDT) users with WMSDs, from $15,141 to $1553 in 2001 [15]. These examples of the ergonomic interventions may have positive outcomes to other similar workers such as printing workers. This kind of workers may have increased the physical symptoms of WMSDs and decreased physical, psychomotor, and work performance. However, research involving ergonomic interventions in printing workers is scanty, especially related to visual fatigue. Therefore, this study has an interest in examining effects of an ergonomic intervention on the physical symptoms of WMSDs (i.e. pain scale, stage of disorders, and neural dynamic test) and visual fatigue in printing workers. 2. METHOD 2.1 Subjects One-hundred and thirty one printing workers served as subjects (female = 104, male = 27) working in a proof department and recycling department of printed matter at the printing office more than 6 months. Subjects in the study were workers free from significant neurological problems, eye diseases, and other histories of serious medical conditions. 2.2 Preliminary Fieldwork An observational survey was conducted to understand the nature and process of work task in only 2 of 5 departments of printing office; proof and recycling departments. Fifty-five workers are employed in the proof department to check the quality of the printed matter. More than 8,000 pieces of printed matter are proven per worker per day. The printed matter consists of five types of images (type A, B, C, D, and E) on two sizes of papers (standard and super size). The standard size is cm. whereas the super size is cm. The workstation for this section consists of office desk, raised tray, inclined tray, and adjustable chair. All workers perform their jobs in sitting posture for the whole working period. Work characteristics such as repetitive movement and static posture are common. They work with repetitive movement of hands and visually proven the printed matter for a long period of time. There are different postures of hand movement such as unfolding and lancing the printed matter, which introduce necks, shoulders, backs, and legs being in static posture. At the first step, they turn one piece of the printed matter for making correction in one pattern. Then, they roll over the printed matter for checking that pattern upon every part of the printed matter. If they find any mistake in the printed matter, they have to pull it out from the desk to the inclined tray. Next, they transfer the printed matter after completely checked from their workstation to the storage room.

3 Praditpod N et al./ The 9 th Southeast Asian Ergonomics Society Conference (Page 3) In recycling department, ninety-six workers are employed in this section to check the quality of used printed matter to be reused and circulated in markets. The workstation for this section consists of two office desks, adjustable chair and selective machine. Three workers work in each workstation. They perform in both standing and sitting posture without back support and arm rest. Many work characteristics are observed and found that repetitive movement of hands and visual to prove the print matter for a long period of time are common. At the first step, they carry a pack of the printed matter, weight, and move to the first office desk, and cut its plastic strap. Then, they twist and unfold the printed matter. Next, a worker reduce the humidity of the printed matter using a hot air douche and the other put the printed matter into a machine to be automatically selected. After that the printed matter comes out from the machine, the last worker pick up the reusable printed matter. At the last step, the reusable printed matter is arranged in series and sent back to be reused. From an observational survey, it was found that proof and recycling departments had work characteristics in the same way. The work characteristics were included static posture, repetitive movement of hands and fixated eye a long period of time. 2.3 Procedure There are 3 steps of the study details. The procedure of this study was shown in figure 1. Baseline Measurement working for 2 hours Pre-test Measurement 1 month period working for 2 hours Post-test Measurement Figure 1: Procedure of the study The first step is physical examination and visual fatigue evaluation. Physical examinations for the WMSDs, Critical Flicker Frequency (CFF) tests and Reaction Time (RT) tests were performed in the participants by orthopedic physical therapists. Physical examinations were performed to find out the WMSD severity stages, pain scale and neural dynamic tests. The WMSD severity stages could progress in stages from mild, moderate and severe. In the mild stage, the symptoms are defined as aching and tiredness of the affected limb occur during the work shift but disappear at night and during days off work. There is no reduction of work performance. In the moderate stage, the symptoms are defined as aching and tiredness occur early in the work shift and persist at night. There is a reduction of capacity in repetitive work. In the severe stage, the symptoms were defined as aching, fatigue, weakness persist at rest, and inability to sleep and to perform light duties. The numerical rating scale was used to measure pain. On the 0-10 pain rating scale, 0 means no pain and 10 means the worst pain possible. Neural dynamic tests included the Upper Limb Neurodynamic Test (ULNT), straight leg raising (SLR), and slump test. A positive test is indicated by resistant and symptoms during test; therefore, the neural tissues are involved. Visual fatigue was measured using CFF tests and RT tests. The CFF tests were accomplished for both eyes whereas the RT tests were only performed for the dominant hand. Both tests were conducted twice. The first time was measured before starting working in the morning (baseline measurement) and the second time was measured after working for 2 hours (pre-test measurement). 3

4 Praditpod N et al./ The 9 th Southeast Asian Ergonomics Society Conference (Page 4) Second step was implementation of ergonomic intervention. After knowing information from the first step, brainstorming was conducted between workers, ergonomic physical therapist and health and safety officer for finding solutions. The ergonomic intervention consisted of additional five-minute break (work improvement method) and specific exercises for worker during the break (human improvement method). Ergonomic intervention was performed 5-10 minutes twice a day. This intervention was provided for the workers over a one-month period. Third step was re-evaluation of physical examination and visual fatigue. After the workers performed the intervention over a one-month period, the physical examinations, CFF tests, and RT tests were reevaluated as post-test measurement by the same orthopedic physical therapists. 3. RESULTS 3.1 Physical examination The WMSD severity stages, pain scale, and neural dynamic tests were used to measure severity of symptoms. In addition to the data analysis, Wilcoxon Signed Ranks test was used to determine the difference between groups (pre-test, and post-test). The level of significance was set up at p-value less than Table 1: The WMSD severity stages, pain scale, and neural dynamic tests between groups WMSD severity stages Female workers Pain scale Neural dynamic test WMSD severity stages Male workers Pain scale Neural dynamic test Post < Pre 75 (67.57%) 48 (43.24%) 13 (50%) 9 (42.86%) 7 (33.33%) 4 (57.14%) Post > Pre 27 (24.32%) 27 (24.32%) 6 (23.08%) 5 (23.81%) 6 (28.57%) 2 (28.57%) Post = Pre 9 (8.11%) 36 (32.43%) 2 (26.92%) 7 (33.33%) 8 (38.10%) 1 (14.29%) p-value <0.001* 0.003* * Wilcoxon Signed Ranks test with significant level at the 0.05 The results of the WMSD severity stages, pain scale, and neural dynamic tests were shown in Table 1. In female workers, the total number of area of the WMSD severity stages and pain scale were 111 areas. The total number of workers who had neural tissue tension was 26 workers. The WMSD severity stages, pain scale, and neural dynamic tests were better in 67.57%, 43.24%, and 50% respectively. There was 24.32%, 24.32%, and 23.08% of the WMSD severity stages, pain scale, and neural dynamic tests that had got worse. There was 8.11%, 32.43%, and 26.92% of workers reported the WMSD severity stages, pain scale, and neural dynamic tests were remained. In male workers, the total number of area of the WMSD severity stages and pain scale were 21 areas. The total number of workers who had neural tissue tension was 7 workers. The WMSD severity stages, pain scale, and neural dynamic tests were better in 42.86%, 33.33%, and 57.14% respectively. There was 23.81%, 28.57%, and 28.57% of the WMSD severity stages, pain scale, and neural dynamic tests that had got worse. There was 33.33%, 38.10%, and 14.29% of workers reported the WMSD severity stages, pain scale, and neural dynamic tests were remained. Finally, there was only the WMSD severity stages (p<0.001) and pain scale (p=0.003) in female workers that had significant difference between post-test and pre-test. 3.2 Critical Flicker Frequency (CFF) The CFF tests were run lighting from high to low frequency values. The higher value indicates the tolerance of visual fatigability. In other words, the workers who had visual fatigue could not detect the change of flash light at higher frequency. In addition to the data analysis, Wilcoxon Signed Ranks test was used to determine the difference between groups (baseline, pre-test, and post-test). The level of significance was set up at p-value less than The results of CFF tests were shown in Figure 2. The mean CFF in female workers was 9.53, 9.38, and 9.53 Hz at baseline, pre-test, and post-test respectively. There was significant difference between pre-test and baseline (p<0.001) and post-test and pre-test (p<0.001). From the results, the mean of CFF at baseline was higher than the mean of pre-test. This could explain the possible impact of the WMSD on CFF in female 4

5 Praditpod N et al./ The 9 th Southeast Asian Ergonomics Society Conference (Page 5) workers. After applying intervention, the mean of CFF could return to baseline indicating the reduced visual fatigue. * p=0.036 * p=0.009 * p<0.001 * p< Critical Flicker Frequency (Hz) baseline pre-test post-test female male Figure 2: The CFF values between groups It was found that in male workers the mean of CFF was 9.42, 9.41, and 9.53 Hz at baseline, pre-test, and post-test respectively. There was significant difference between post-test and baseline (p=0.036) and posttest and pre-test (p=0.009).the results revealed that the mean of CFF at pre-test was near at baseline, whereas the mean of CFF at post-test was higher than baseline and pre-test. The analysis of the results could explain the effects of intervention on CFF in male workers. After applying intervention, the mean of CFF not only could return to baseline but also better than the baseline. So, the visual fatigue was significantly reduced. 3.3 Reaction Time (RT) The RT tests for each subject were included ten response times (msec). The faster the averaged RT, the higher the tolerance of visual fatigability. In other words, the workers who had visual fatigue could not response to the stimulus rapidly. The repeated measurement was used to determine the difference between groups in male workers whereas Wilcoxon Signed Ranks test was used to determine the difference between groups in female workers. The level of significance was set up at p-value less than * p=0.03 * p<0.001 * p< Reaction Time (msec) female male 0.23 baseline pre-test post-test Figure 3: The RT values between groups 5

6 Praditpod N et al./ The 9 th Southeast Asian Ergonomics Society Conference (Page 6) The results of RT tests were shown in Figure 3. It was found that in female workers, the means of RT were 0.261, 0.284, and msec at baseline, pre-test, and post-test respectively. The mean of RT at baseline was lower than the mean of pre-test. It could indicate the impact of the WMSD on RT in female workers. After applying intervention, the mean of RT could return near to baseline which could explain that the visual fatigue was reduced. Moreover, there was significant difference between pre-test and baseline (p<0.001) and post-test and pre-test (p<0.001). It was found that in male workers, the mean of RT was 0.249, 0.265, and msec at baseline, pretest, and post-test respectively. The results of male workers were in the same way of the results of female workers. After applying intervention, the mean of RT could return near to baseline which could explain that the visual fatigue was reduced. Whereas, there was only significant difference between pre-test and baseline (p=0.03). 4. DISCUSSION This study mainly emphasized on the effect of ergonomic intervention by using micro-break and specific exercise on physical symptoms and visual fatigue. Interventions in the present study were work and human improvements. Work improvement was schedule more rest breaks [10, 16]. Human improvement were giving education about basic knowledge to recognize ergonomic risk factors and awareness during work and training workers in exercise for reducing WMSD [17-19]. Evaluation and follow up of the results were physical examination, the CFF, and the RT tests. Evaluation was applied within 1 month period. The results of this study found that the WMSD severity stages, pain scale, and neural dynamic tests were significant difference between pre-test and post-test. Besides, in some areas of symptoms, the WMSD severity stages, pain scale, and neural tension tissue got better, but some got worse and the rest were remained. Moreover, these interventions were a good remedy for a reduction of the WMSD severity stages, pain scale, and neural tension tissue in female workers more than male workers. Since there were many factors associated with WMSD which could not be controlled and there was variation in subjects such as demographic characteristics, activity daily living, and having other jobs or exercises. The result of physical examination in this study was similar to other researches [9, 20-23]. Klangsin found that the WISE technique could reduce the severity of WMSD [9]. In addition, McLean et al examined the benefit of micro breaks. The study revealed that micro breaks had a positive effect to reduce discomfort [20]. Moreover, Mekhora et al found that the adjustment of their own workstations according to ergonomic recommendations could reduce the discomfort level of subjects with tension neck syndrome [21]. Pillastrini et al revealed the efficacy of a preventive ergonomic intervention. The group which received the ergonomic intervention an informative brochure had a lower Rapid Entire Body Assessment (REBA) score and reduced lower back, neck, and shoulder symptoms compared with group which received only the brochure [22]. Cole DC. et al assessed the ergonomic program, included employee Repetitive Strain Injury (RSI) training, proactive assessment of workstations and workstation modifications, and encouragement of early treatment through on-site physiotherapy, could reduce in frequent and severe pain [23]. On the other hand, Gerr et al studied the effect of two workstation and postural interventions on the incidence of musculoskeletal symptoms among computer users. They found that there was no significant difference in the incidence of musculoskeletal symptoms among the intervention groups. Their results provided evidence that postural interventions were unlikely to reduce the risk of upper extremity musculoskeletal symptoms among computer users [24]. The results of CFF test in this study found that there was significant difference between baseline, pretest, and post-test. After applying ergonomic intervention, the CFF were improved to the CFF measured at baseline. The results in present study supported a study of Balci and Aghazadeh. They evaluated the workrest schedules for VDT operators considering data entry and mental arithmetic tasks. They found that 30- minute work/5-minute rest resulted in the lowest eyestrain and blurred vision which followed by 15-minute work/micro breaks respectively. The 15-minute work/micro breaks could reduce discomfort in the neck, lower back, and chest than other schedules for data entry task. Moreover, a 15-minute work/micro break was the most schedules that could reduce discomfort in the elbow and arm for the arithmetic task [25]. The results of RT test in this study found that there was significant difference between baseline, pre-test, and post-test. After applying ergonomic intervention, the RT was improved to the RT measured at baseline. This study highlights an improvement of RT from the method of specific exercises and micro-breaks. To 6

7 Praditpod N et al./ The 9 th Southeast Asian Ergonomics Society Conference (Page 7) support this positive outcome, Davranche et al [26] and Collardeau et al. [27] concluded as a positive effect of exercise on reaction time. On the other hand, a few arguments showed no effect of exercise on reaction time if vigorous exercise [28] and sport skills [29, 30] are included in the intervention. In conclusion, this current study showed significant reduction of WMSD symptoms and visual fatigue. This reduction can be expalined by that subject had pause break. This break might stop process of WMSD development from being working for a long period of time. Furthermore, exercises specific to the symptoms could help improve the conditions over period of time as physical fitness and performance might be better and the body might be able to tolerate to the exposure. 5. CONCLUSION This study was a guideline of ergonomic intervention by using micro-break and specific exercise which were applied in a printing factory. These interventions could reduce the symptoms of WMSD and visual fatigue. Workers should be provided basic knowledge of prevention and self treatment to solve their problems by themselves. This study revealed the effect of interventions, but the fact that there were many ergonomic interventions to be further investigated in various factories. Moreover, longitudinal study might be of interest to find out solutions for industrials. REFERENCES [1] National Institute for Occupational Safety and Health (NIOSH). Work-Related Musculoskeletal Disorders. Available from: [2] Industrial Statistics. Total number of factory in Available from: านวนโรงงานสะสม 47.xls [3] Industrial Statistics. Total number of factory in Available from: [4] Federal Occupational Health (FOH). Investment Benefits of an Ergonomics Porgram. 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