Journal of Health and Safety at Work

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Introduction: Carpet-weaving is one of the hard and harmful jobs, which affect the health of the workforce. Based on the previously conducted research, musculoskeletal disorders in the neck, shoulder, and lower back regions are common among carpet weavers. This study conducted to investigate the muscle activity of the shoulder and lower back regions in carpet weavers during work on traditional and ergonomic workstations by surface electromyography.
Material and Methods: 18 experienced male weavers with a mean age of 38 and mean weaving experience of 11.1 years participated in this study. Each weaver took part in two trails of 120 min. Surface EMG signal recordings were done during weaving for four muscles (bilaterally in trapezius and erector spine). The RMS and MPF values were extracted from the raw EMG signal to estimate muscle activity and fatigue.
Results: The results obtained from the 5-time intervals indicated the lowered MPF in the ergonomic workstation compared to the traditional one. The result of the mean RMS in most of the recorded times was lower in the ergonomic workstation than that in the traditional one.
Conclusion: According to the results of the study, the modified workstation was well-suited for trapezius muscles, and the traditional one had an advantage for the erector spine muscles.

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Introduction: Low back pain is one of the most common musculoskeletal disorders leading to disability around the world. Several studies have suggested that prolonged computer/ laptop work contributes to the development of low back pain and discomfort. The results of the studies conducted on the association of back discomfort and muscle activity are contradictory. Thus, the present study aims to evaluate the relationship between the activity level and relative rest time of the trunk muscles with back discomfort while working with a laptop in a sitting position.
Material and Methods: First, 20 young healthy males performed laptop work including mouse work and typing in conventional and ergonomic setups. In the ergonomic setup, the screen height and keyboard placement were specifically adjusted for each individual. In addition, the electromyographic activity of the lumbar erector spinae, right and left multifidus and transversus abdominis, rectus abdominis, external oblique muscles, and the posture of the lumbar spine were recorded in the first and last two minutes of an 8-min task. After the end of each task, the participants scored their back discomfort.
Results: The results showed a positive correlation (r=0.57 and p=0.009) between back discomfort and the EMG amplitude of the lumbar erector spinae muscle. In addition, back discomfort was negatively correlated to the relative rest time of the multifidus muscle (r=0.50 and p=0.023), and a positive correlation was reported with the relative rest time of the transversus and rectus abdominis (r=0.47, p=0.039, and r=0.45, p=0.049, respectively).
Conclusion: The relative rest time of the trunk muscles may be a better index than that of the EMG amplitude to highlight the risk factors for back discomfort. However, a causative link between muscle activity and discomfort cannot be implied from this study. The current results do not undermine the role of other factors associated with the increased level of discomfort during sitting.

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Introduction: Given the high prevalence of low back pain in manual handling activities, its known relationship with spinal loads, and the role of muscular fatigue and the body’s adaptive mechanisms to counteract fatigue, this study investigated the effect of repetitive lifting tasks on trunk muscular fatigue and the kinematics of the spine and load-in-hand.
Material and Methods: Eighteen male volunteers lifted a box from the floor to their waist height at a pace of ten lifts per minute until they could no longer continue the task and reported the highest level of exhaustion. Kinematic data and muscle electromyographic activity were simultaneously recorded using a motion capture system and an electromyography device. In this study, average trunk flexion angle and trunk angular velocity were calculated as trunk kinematic variables, while average box vertical travel distance, average box horizontal displacement from L5-S1, and average box vertical displacement velocity were considered as box kinematic variables. The median frequency of electromyographic signals from selected muscles was quantified as a muscle fatigue indicator. Since subjects performed different lifting cycles, the total number of cycles was divided into five distinct blocks for data analysis.
Results: The results showed significant effects of lifting trial blocks on trunk angle (p=0.004) and vertical box displacement (p<0.001). Median frequency was significantly affected by lifting blocks for right (p=0.016) and left erector spinae (p=0.014), right (p=0.021) and left multifidus (p<0.001), right latissimus dorsi (p=0.001), and left rectus abdominis (p=0.039).
Conclusion: Overall, the results highlight variations in most kinematic parameters and a reduction in the frequency content of EMG signal spectra. These changes serve as indices of the central nervous system’s control over lifting behavior under dynamic conditions. A better understanding of these central nervous system adaptations could have practical applications in interventions such as workstation design, exoskeleton development, and worker training to manage musculoskeletal disorders.

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Introduction: In many occupations, users must sit for prolonged periods during their job activities. Prolonged sitting is associated with fatigue, leading to postural changes that can increase spinal loads. Despite the importance of this topic in terms of the extent of prolonged sitting and its subsequent adverse consequences, little attention has been given to this occupational activity. Hence, this study investigates changes in neck, trunk, and muscle activities and fatigue levels in prolonged sitting computer tasks.
Material and Methods: Twenty healthy subjects (gender-balanced) from the student community with at least five years of experience in computer work aged between 20-30 years were asked to randomly perform three types of computer tasks for 90 minutes (each task for 30 minutes). Electromyographic (EMG) activities of right and left cervical (ESCR and ESCL), thoracic (ESTR and ESTL), and lumbar (ESLR and ESLL) erector spine and upper trapezius (UTR and UTL) muscles were continuously recorded. Root mean square (RMS) and median frequency were extracted as EMG metrics. Subjects also rated their perceived discomfort using a Visual Analogue Scale (VAS). The effect of time, gender, and their interaction on muscle EMG activities, fatigue, and discomfort were explored.
Results: Time had a statistically significant effect on UTR, ESCR, and ESTR muscle activities. UTL and ESCR muscle activities significantly differed between male and female subjects. Further, the findings confirmed the interactive effect of time and gender on ESTR muscle activity. UTR, ESCR, ESCL, ESTL, and ESLL muscles’ fatigue index changed statistically over time.
Conclusion: The findings confirmed neck and trunk muscles’ fatigue by increasing muscular activity and reducing frequency contents over time, per the subjective rating of discomfort.

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Introduction: Prolonged sitting postures are among the risk factors for musculoskeletal disorders in occupational settings, leading to increased musculoskeletal discomfort in various body regions. This discomfort can negatively impact individuals’ health and impose high costs on society in terms of work absences, early disabilities, and reduced productivity. The purpose of this study is to investigate the effect of stretching exercises on the level of discomfort, muscle activity, and muscle fatigue in the neck and trunk region during prolonged sitting tasks.
Material and Methods: This experimental study was conducted among 20 healthy male and female participants under two test conditions: control and intervention. In the control condition, participants performed cognitive tasks (watching videos, typing, text editing, and nback cognitive test) without any intervention. In the intervention condition, participants performed stretching exercises before each task. The Visual Analogue Scale was used to assess perceived discomfort. Also, muscle fatigue was evaluated using an electromyography (EMG) device and RMS and MPF measures.
Results: Discomfort in hands and arms (p-value=0.04) and lower back (p-value=0.03) during video-watching was higher in the control condition than in the intervention. Regarding muscle activity, the activity of the right cervical erector spinae during the video-watching task was lower in the control condition than in the intervention. In the n-back cognitive test and text editing, the right lumbar erector spinae muscle activity was significantly higher in the control condition than in the stretching exercises intervention. Regarding the left cervical erector spinae, a significant difference was observed between fatigue in control and intervention conditions during the video-watching task. Also, right thoracic erector spinae fatigue in text editing was higher in the control condition than in the exercise intervention; however, for the n-back test, the level of fatigue was lower in the control condition compared to the intervention.
Conclusion: The perceived discomfort in seated computer tasks is generally lower in the exercise intervention compared to the control condition. The stretching exercises used in this study improved muscle activity and reduced fatigue in some of the trunk muscles, although the effects of the exercises depend on the type of task. Overall, muscle fatigue in two cognitive tasks, text editing and n-back, was more affected by stretching exercises than other tasks.