Iranian Journal of Ergonomics

Introduction: Advances in technology and the use of complex systems at work have imposed high mental workloads to operators; so, continuous monitoring of mental workload can help to prevent mental problems and maintain mental health. Therefore, this study aimed to investigate the impact of mental workload on physiological and subjective responses.

Methods: This cross-sectional descriptive-analytical study was performed on 16 healthy university students in 2014 at a laboratory setting. Physiological parameters of surface electromyography and electrocardiography in six blocks (resting, high mental work, moderate, low, very low and recovery) were measured using NeXus-4. After performing each block, the NASA-TLX questionnaire was completed. Statistical analysis was conducted using SPSS software version 21.0. A 5% significance level was adopted in all the tests.

Results: The results showed significant differences for the average score of NASA-TLX between the different levels of mental work load (P < 0.05). Also, the analysis of repeated measures variance showed significant differences for heart rate and heart rate variability parameters in the six blocks (P < 0.05), but no significant difference was observed for the shoulder muscles activity.

Conclusions: Different levels of mental work load can impact on people's subjective responses and some of their physiological responses. Thus, in such workplaces, it will be necessary to conduct an ergonomic program to manage mental health.

Background: The aim of this study was to investigate the effect of the heel wedges on the electromyography activities of the selected left and right lower back muscles during load lifting.
Methods: A total of 17 male subjects voluntarily participated in this quasi-experimental study. The selected subjects lifted a box, weighing 10% of their body weight, above the height of their hip joint, descending as far as the thigh, parallel to the ground, and then ascending to the starting position. The above task was performed nine times in two conditions, including with and without the heel wedges. Using the ME6000 electromyography system, the activity level variables were normalized and the median frequencies of the erector spinae (ES) and the multifidus (MU) muscles were recorded. The subjects also held the box for 30 s in the standing position with stretched hands. The paired t-test was used for the data analysis.
Results: The results showed that during static load lifting using the heel wedge, the median frequency of the right ES muscle changed significantly (P<0.05). Also during dynamic load lifting using the heel wedge, the activities of the left and the right ES muscles as well as the left MU muscle decreased significantly (P<0.05). However, no significant differences between the two conditions were observed for the other variables (P>0.05).
Conclusion: During such occupational tasks, a decrease in the activities of the selected lower back muscles with the heel wedge might result in a delay in the onset of muscle fatigue. The above findings might be used in the design of shoes, suitable for the work environments. However, further investigations are needed in this area in order to provide more accurate results.
 

Background and Objectives: In recent years, due to the rapid growth of metropolitan cities and the shortage of urban public transport means, including urban bus transportation, many people are forced to travel in a standing position when using these vehicles. This situation may cause pain and discomfort and non-collision injuries for passengers. The purpose of this study was ergonomic assessment of the sit-standing seat in passengers standing on urban buses.
Methods: To do this study, 8 young people with a mean age of 25.25±2.12 years were enrolled. For evaluation and assessing the effect of sit-standing seat two methods of surface Electromyography (sEMG) and Borg scale scores were applied in Fall 2018. The data was analyzed using SPSS 24.
Results: In all body parts, except for the hip, the mean scoring of Borg’s scale for perceived discomfort in sit-standing position was less than standing position. Also, the amount of contractile activity of the leg muscles in sit-standing position was significantly lower than the standing position (P<0.05).
Conclusion: Considering the results obtained from the Borg scale scores and the contraction activity of the leg muscles as a result of the use of the mentioned seat, which led to a reduction in the level of discomfort and the leg muscles contraction, it is recommended to apply the sit-stand seat instead of being in a standing position.