Journal of Health and Safety at Work

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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: Computer-based systems have become integral to every aspect of daily life, with the successful performance of such systems heavily reliant on error-free software. Given the significance of these systems, tools are essential for evaluating their usability. One such tool is the Post-Study System Usability Questionnaire (PSSUQ). The present study aimed to localize and psychometrically evaluate the Persian version of the third edition of the PSSUQ and assess the usability of the library website at Mazandaran University of Medical Sciences.
Material and Methods: This descriptive cross-sectional study employed the Backward-Forward method for translating the questionnaire. The study population included 314 participants for cultural adaptation of the scale and 147 postgraduate students for evaluating the library website, all from Mazandaran University of Medical Sciences. Content validity was assessed using the Content Validity Index (CVI) and Content Validity Ratio (CVR). Reliability was determined via Cronbach’s alpha, and exploratory factor analysis was performed. Data analysis was conducted using SPSS version 16, adhering to ethical guidelines at all stages of the study.
Results: The overall content validity index (CVI) of the questionnaire was 0.96, while the overall content validity ratio (CVR) was satisfactory, with clarity and simplicity both scoring 0.91 and necessity at 0.75. Cronbach’s alpha coefficient was 0.95, with correlations between items exceeding 0.30. No significant differences in the usability of the library website were observed based on age, gender, field of study, educational level, or year of admission.
Conclusion: The Persian version of the third edition of the PSSUQ is a valid and reliable tool for evaluating system usability and user satisfaction with digital systems. It holds substantial potential for identifying system weaknesses and areas requiring improvement.