Design and evaluation of an ergonomic chair for near-ground welding based on muscle activity and usability.

BACKGROUND: Work-related musculoskeletal disorders (WMSDs) are one of the major problems in industrial societies. An awkward posture in the workplace is considered as one main reason 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.