This paper investigates a comparative analysis of hand muscle behavior during fastening operations, contrasting manual execution with power tool assistance. Through the deployment of electromyography (EMG), the study examines the distinct muscular responses associated with these two operational modes. The research’s significance lies in its relation to worker efficiency and productivity, intricately linked to ergonomic considerations. Enhancing ergonomic design can improve safety while overall efficiency can be maximized. The research method involves EMG measurements during screw tightening using a spanner and a power tool, facilitating a nuanced assessment of muscle behavior. The study’s implications can extend to the redesign of power tools with improved ergonomics, informed by the comparative insights garnered from manual and power tool operations. By leveraging the findings on muscular behavior, power tools can be revamped to enhance productivity. Additionally, the research contributes to the broader understanding of skeletal muscle activity and its intricate interaction with the nervous system. In summary, this investigation sheds light on hand muscle dynamics during fastening, offering valuable insights for ergonomic enhancements and improved productivity in manual and power tool applications.