Background: Work-related musculoskeletal disorders (WMSDs) are one of the major problems in industrial societies. Awkward postures in theworkplace are considered as a main reasons for these disorders. Therefore, the study and investigation of postures to improve them (in the workplace) have a significant role in appropriate intervention. Objective: This study aimed to design an ergonomic chair for near-ground welding operations and evaluate its impact on the electromyography (EMG) activity of a select group of lower limb muscles. Methods: The EMG activity of lower limb muscles was measured in eight postures consisting of three postures identified via observing welders at work, and five on-chair postures suggested for chair use during welding. The usability of the designed chair was evaluated through the use of the System Usability Scale (SUS). Results: The results showed that the suggested on-chair postures had significantly lower mean muscle activity compared with the identified postures (p < 0.001). Among the identified postures, kneeling posture had the lowest mean muscle activity (p < 0.01), still significantly higher than the mean activity of the on-chair postures (p < 0.001). Applying a 15° slope to the seat pad led to a decrease in muscle activity and an increase in usability score. The usability score of the chair was acceptable in all postures except KCC-90 posture. Conclusions: Using a suitable chair or support for different work postures can prevent detrimental muscle activities during work and the development of musculoskeletal disorders caused by intense muscle activity due to awkward postures.
