Available online at www.sciencedirect.com ScienceDirect Procedia Manufacturing 2 (2015 ) 296 300 2nd International Materials, Industrial, and Manufacturing Engineering Conference, MIMEC2015, 4-6 February 2015, Bali Indonesia Effect of Working Posture on Back Pain Occurrence among Electronic Workers in Malaysia Roseni Abdul Aziz a *, Ademola James Adeyemi b,c, Aini Zuhra Abdul Kadir b, Jafri Mohd Rohani b, Mat Rebi Abdul Rani b a The Ergonomics Excellence Centre, National Institute of Occupational Safety and Health, Johor, Malaysia. b Department of Materials, Manufacturing and Industrial Engineering, Universiti Teknologi Malaysia, Johor, Malaysia. c Department of Mechanical Engineering, Waziri Umaru Federal Polytechnic, Birnin Kebbi, Nigeria Abstract Back pain remains a major work-related musculoskeletal disorder (WMSD) and has caused loss in individuals workdays and organisations productivity. Hence, this study compares muscular activities of the trapezius and erector spinae muscles of the back, in order to identify the onset of fatigue among standing and sitting electronics workers in Malaysia. Surface electromyography was used to evaluate the muscular activities in 11 electronics assembly workers, made up of six males and five females, continuously for one hour. Two measures, mean power frequency and average electromyography were used to identify the difference. Both measures indicated significant difference between the upper back muscles of standing and sitting workers, and more muscular activities were observed among sitting workers than the standing workers. However, the reduction in frequency was not significant enough to show fatigue among both standing and sitting workers. Hence, organisations should provide short breaks after every hour to reduce WMSD, and improve general wellbeing of the workers. 2015 The Authors. Published by by Elsevier B.V. B.V. This is an open access article under the CC BY-NC-ND license Selection (http://creativecommons.org/licenses/by-nc-nd/4.0/). and Peer-review under responsibility of the Scientific Committee of MIMEC2015. Selection and Peer-review under responsibility of the Scientific Committee of MIMEC2015 Keywords:Work-related musculoskeletal disorders; fatigue; electromyography; erector spinae; trapezius; Malaysia. * Corresponding author. Tel.: +60176287924 E-mail address: roseni@niosh.com.my; roseni.niosh@gmail.com 2351-9789 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Selection and Peer-review under responsibility of the Scientific Committee of MIMEC2015 doi:10.1016/j.promfg.2015.07.052
Roseni Abdul Aziz et al. / Procedia Manufacturing 2 ( 2015 ) 296 300 297 1. Introduction Musculoskeletal disorders (MSDs) remain a major occupational problem affecting the general well-being of working adults all over the world [1]. It has been identified as a major cause of insurance and health costs associated with national productivity [2]. These work-related musculoskeletal disorders (WMSDs) occur in different body regions and the level of prevalence or intensity at the regions differ by task, profession/occupation and other physical or psychosocial factors [3]. The high prevalence of MSDs in different body regions with little evidence of successful intervention must be responsible for previous conclusion about its ubiquitous nature [3]. Some studies have identified back pain as the most severe and one of the most costly, because it accounted for a fourth of all claims and one-third of all costs of compensation [2,4 6]. This may be because the back region shows major link between various risk factors and MSDs [1]. Hence, this study aims at evaluating muscular activities of the erector spinae and trapezius muscles in order to determine their effect on individual fatigue. 2. Methods 2.1. Participants Eleven assembly workers made up of six males and five females from two electronics assembly plants in Johor Bahru Malaysia took part in the study. They are made of five workers who carried out their job activities sitting, and another six workers, whose tasks required that they stand while working. Only workers that gave their consent and have not taken medical leave or show any reaction during the study were included in the final analysis. The participants age vary between 20 and 35 years. The protocols were approved by the Research committee of the Faculty of Mechanical Engineering of the Universiti Teknologi Malaysia and National Institute of Occupational Safety and Health, Malaysia. 2.2. Procedure The workers were invited to a private room where they were assured of the safety of the exercise and informed of the purposed of the study. Only workers who gave their consent were included in the procedure. In other to reduce the accumulated effect on the muscles, measurements were only initiated at the participants resumption of duty or after break. The targeted parts of the participants skin were shaved and cleaned with methylated spirit to minimise skin impedance. The surface disposable electrodes were thereafter fixed to the targeted muscles before connecting to the electromyography device. The participants thereafter returned to their duty post and the EMG device monitored the muscular activities continuously for one hour without interruption. 2.3. Instrumentation and data processing Two muscles were monitored bilaterally on each of the participants while carrying out their duties. They are the middle fibres of the trapezius muscles at the thoracic area of the upper back and the erector spinae muscles at the L4-L5 lumbar vertebra area of the lower back. Disposable electrodes (Ambu Blue Sensor) were connected to the targeted muscles at an inter electrode distance (IED) of 25mm. The bi-polar electrodes were connected parallel to the direction of the muscle fibres while the earth electrodes were connected 20-30mm away from the bipolar electrodes. The electrodes were all connected to a 16 channelled Megawin ME6000 surface electromyography device. The data were processed using MEGAWIN 3.0 windows software. The EMG signals were band passed filtered at 20-450Hz with a sampling frequency of 1000Hz. Fatigue which is an indication of the change in Mean Power Frequency (MPF) and Average integrated EMG (AEMG) were analysed using the software. The values were normalised with the Maximum Voluntary Contraction of each muscles expressed in Hz for the MPF and μv for AEMG. All the MPF and AEMG values for each participant were exported to SPSS version 18. The signals were plotted using 10 minutes interval to identify any significant trends. A non-parametric test (Mann-Whitney Test) was
298 Roseni Abdul Aziz et al. / Procedia Manufacturing 2 ( 2015 ) 296 300 carried out on the data to determine whether there are significant difference in the workers postures and their gender. All tests were conducted at the 0.05 significant levels. 3. Results Fig. 1 and Fig. 2 show the rate of fatigue based on the working postures. No significant difference was observed between the left and right side muscles except in the AEMG of the lower back. The AEMG graphs of the lower back also revealed similarity in the left muscles of standing and sitting workers with the activities showing no sign of fatigue. At the upper back region, the decrease in frequency (2.3Hz) can only be observed among sitting men. However, at the lower back, the MPF revealed gradual decrease in the EMG frequencies in both standing (2.6 Hz) and sitting (4.10 Hz) workers, although the activities were more stable in men than women. Reduction in MPF can be observed after 30 minutes in legs of both standing and sitting workers while the workers did not show any sign of fatigue in the hands. Fig. 1: Mean power frequency and Average electromyography of trapezius muscles of the workers
Roseni Abdul Aziz et al. / Procedia Manufacturing 2 ( 2015 ) 296 300 299 Fig. 2: Mean power frequency and Average electromyography of erector spinae muscles of the workers Table 1 shows significant difference in muscular activities between standing and sitting workers at the left (p=0.011) and right (p=0.009) upper back muscles, while there was also significant difference in muscular frequencies at the left (p=0.02) and right (p=0.015) lower back. Thus, there exists no region where both AEMG and MPF revealed significant difference in EMG activities between standing and sitting workers. Table 1: Mann-Whitney Non-parametric test to identify significant differences in working Posture Body region Side Mean rank sitting Mean rank standing p-value Left upper back MPF 32.05 34.71 0.571 AEMG 40.08 28.01 0.011 Right upper back MPF 33.23 33.72 0.916 AEMG 40.23 27.89 0.009 Left lower back MPF 27.5 38.5 0.02 AEMG 35.58 31.76 0.419 Right lower back MPF 27.22 38.74 0.015 AEMG 33.78 33.26 0.912
300 Roseni Abdul Aziz et al. / Procedia Manufacturing 2 ( 2015 ) 296 300 4. Discussion Prolonged sitting has been identified as a risk factor for low back pain, and yet, task design based on prolonged sitting has been increasing [6]. Other studies has also identified prolonged standing as the most significant predictor of MSD [4,7]. In this study, sitting workers revealed higher level of muscular activities at the upper back while there were higher activities among standing workers at the lower back. However, while most studies has identified significant activity leading to fatigue at the lower back of both standing and sitting workers, there was no fatigue identified in this study within the one hour duration, because the decrease in MPF is less than 12-23 frequency band [8]. This is contrary to what was observed among those who worked for two hours or more. Low back pain was reported among sitting workers who work for two hours [9]. Low back pain was also reported among standing workers who work continuously for two hours [10]. Hence, the less presence of fatigue after an hour for both standing and sitting posture may serve as suggestive intervention that can reduce the occurrence of musculoskeletal disorder in different body regions. Since repetitive tasks and prolonged tasks duration at static posture has been identified as major risk factors, the introduction of regular break of short duration after an hour will introduce flexibility into operations and alter working postures, thereby reducing the possibility of musculoskeletal disorders or injuries occurring. Although this interruption might reduce active time, the reduction in fatigue occurrence will lead to increase productivity and save cost associated with treatment of MSDs and loss man-hour. 5. Conclusion The study shows that there is no significant sign of fatigue at the back of both standing and sitting workers after executing their tasks for an hour. However, evidence of reduction in the muscular frequencies can be observed within the hour, especially among sitting workers. Therefore, it is suggested that organisations may introduce 3-5 minutes posture manoeuvre or exercise after every hour, to allow workers flex to their muscles and alternate their work posture, so as to accommodate variation in work posture. This is likely to relax the muscles and reduce the possibilities of fatigue setting while working. Acknowledgements This work was supported by the National Institute of Occupational Safety and Health, Malaysia under Grant no 01/NIOSH/11-01/NG0015). The researchers expressed their appreciation to the staff of the Ergonomics Excellence Centre, NIOSH and the management of the companies that participated in the research. Special thanks to Nuryana Umar, Afifi Mat Rebi and Noorul Azreen Aziz for assisting in data collection. References [1] Lanfranchi J-B, Duveau a. Explicative models of musculoskeletal disorders (MSD): From biomechanical and psychosocial factors to clinical analysis of ergonomics. Rev Eur Psychol Appliquée/European Rev Appl Psychol 2008;58:201 13. [2] Guo HR, Tanaka S, Halperin WE, Cameron LL. Back pain prevalence in US industry and estimates of lost workdays. Am J Public Health 1999;89:1029 35. [3] Andersen JH, Haahr JP, Frost P. Risk factors for more severe regional musculoskeletal symptoms: a two-year prospective study of a general working population. Arthritis Rheum 2007;56:1355 64. [4] Marshall PWM, Patel H, Callaghan JP. Gluteus medius strength, endurance, and co-activation in the development of low back pain during prolonged standing. Hum Mov Sci 2011;30:63 73. [5] Daynard D, Yassi a, Cooper JE, Tate R, Norman R, Wells R. Biomechanical analysis of peak and cumulative spinal loads during simulated patient-handling activities: a substudy of a randomized controlled trial to prevent lift and transfer injury of health care workers. Appl Ergon 2001;32:199 214. [6] Schinkel-Ivy A, Nairn BC, Drake JDM. Investigation of trunk muscle co-contraction and its association with low back pain development during prolonged sitting. J Electromyogr Kinesiol 2013;23:778 86. [7] Tissot F, Messing K, Stock S. Studying the relationship between low back pain and working postures among those who stand and those who sit most of the working day. Ergonomics 2009;52:1402 18. [8] Nimbarte AD, Chowdhury SK, David Cartwright E. Empirical evaluation of neck muscle fatigue generated by healthcare related exertions. Saf Sci 2013;57:100 7. [9] Mörl F, Bradl I. Lumbar posture and muscular activity while sitting during office work. J Electromyogr Kinesiol 2013;23:362 8. [10] Gregory DE, Callaghan JP. Prolonged standing as a precursor for the development of low back discomfort: An investigation of possible mechanisms. Gait Posture 2008;28:86 92.