Tehran University of Medical Sciences International Journal of Occupational Hygiene 2008-5109 17 3 2026 06 08 162 169 Shahram Vosoughi Occupational Health Research Center, Department of Occupational Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran Mohammad Samadi Gol Gholab Department of Occupational Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran Jamileh Abolghasemi Department of Biostatistics, School of Public Health, Iran University of Medical Sciences, Tehran, Iran Ardalan Vosoughi Department of Environmental Health Engineering, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Zahra Sadat Mousavi Fard Occupational Health Research Center, Department of Occupational Health Engineering, School of Public Health, Iran University of Medical Sciences, Tehran, Iran 2025 02 20 2025 08 31 Background: Work related musculoskeletal disorders and exposure to thermal stress are considered as some of the most significant challenges for workers in the tire manufacturing industry, which can lead to decreased human performance and work capacity, as well as increased physical and psychological burden during the execution of tasks. Therefore, the aim of this study is to determine the simultaneous effects of thermal stress and postural stress on the occupational strain index of workers employed in a tire manufacturing company. Methods: In this descriptive-analytical (cross-sectional) study, 147 individuals with at least one year of work experience were selected as the sample based on the inclusion criteria. Participants in the study were divided into three groups: the postural stress exposure group (n = 49), the group exposed simultaneously to thermal and postural stress (n = 49), and the control group (n = 49). For data collection, the Nordic questionnaire and a demographic questionnaire were used. Additionally, the REBA (Rapid Entire Body Assessment) observational method was utilized to determine the postural stress score, while the WBGT (Wet Bulb Globe Temperature) index was employed to assess the thermal stress of the workers. The occupational strain index was determined using JSI 2001 software, and statistical analyses were conducted using SPSS version 16. Results: More than 60% of the production line workers at the tire company reported suffering from one or more musculoskeletal disorders in the past nine months. The average strain index in the first exposure group (postural stress exposure) was 32.80 ± 4.212, while in the second exposure group (simultaneous exposure to postural and thermal stress), it was 33.50 ± 2.801. According to the strain index standard, all individuals in the second exposure group and 90% of those in the first exposure group were classified as being at a dangerous level of risk. Additionally, a significant positive correlation was found between the strain index score and the REBA (Rapid Entire Body Assessment) score (r = 0.646), whereas no significant correlation was observed between the strain index and the WBGT (Wet Bulb Globe Temperature) index (p > 0.05). Conclusion: In the tire manufacturing workers studied, the strain index level ranged from “moderate” to “high-risk strain levels”, with most reporting musculoskeletal disorders in the lower back and spine. There was a significant relationship between the strain index and the final REBA score, while no significant relationship was found between the strain index and the WBGT index. https://ijoh.tums.ac.ir/index.php/ijoh/article/view/676 https://ijoh.tums.ac.ir/index.php/ijoh/article/download/676/879