## 2 Materials and Methods  
### Research Methods  
The pressure distribution between the human-chair interface is recognized as a crucial objective indicator of seat comfort [31; 32; 33]. By attaching sensors to the surface of a sit-stand chair, researchers can monitor real-time pressure distribution during the sitting-to-standing transition, thereby assessing the chair's comfort. Analyzing these pressure distribution maps enables researchers to evaluate the design rationality of sit-stand chairs and refine their structure and materials for enhanced comfort. However, it is worth noting that pressure sensors only provide data related to pressure and do not capture information on muscle activity or attention allocation.  
Surface electromyography (sEMG) signals are a noninvasive technique used to measure muscle activity by placing electrodes on the surface of muscles to capture electrical activity. In studies related to the comfort of sit-stand chairs, researchers can employ sEMG technology to evaluate the influence of different sitting postures and standing durations on muscle activity. By analyzing muscle activity patterns and intensity, researchers can determine whether sit-stand chair designs meet ergonomic standards and provide insights for improving these chairs. Notably, the process of collecting sEMG signals is noninvasive and safe for users, as it does not require skin penetration. Furthermore, sEMG signals can delineate the intensity, pattern, and fatigue level of muscle activity, providing comprehensive information.  
Based on a review of existing research on seating and human posture comfort, our chosen methodology involves synchronously testing body pressure distribution and sEMG. This approach enables us to extrapolate comfort levels across various tasks at seat tilt angles of 0\({}^{\circ}\), 20\({}^{\circ}\), and 40\({}^{\circ}\). By incorporating sEMG alongside body pressure distribution, we address the limitations of pressure sensors, which only provide pressure-related data and do not capture muscle activity or attention allocation. The integration of sEMG signals enhances the reliability of our experimental data. The research methodology process is illustrated in Figure 1.  
In the surface electromyography (sEMG) experiment, the selected muscle groups are the bilateral erector spinae, bilateral vastus lateralis, and bilateral gastrocnemius. These muscle groups play important roles in maintaining trunk stability, posture control, and dynamic balance. The erector spinae primarily stabilize the spine and control posture, the vastus lateralis supports the thigh and stabilizes the knee joint, and the gastrocnemius is crucial for foot and lower limb stability. These three muscle groups provide muscle activity data from different body regions, covering the lower back, thighs, and calves, thereby offering a comprehensive reflection of the impact of standing chairs on various body parts. This ensures the comprehensiveness and representativeness of the study results. Additionally, many related studies have selected these key muscles as subjects. For example, [PERSON] et al. (2018) [8] compared the muscle activity of the erector spinae, vastus lateralis, and gastrocnemius in standard chairs and standing chairs with different tilt angles. Our study aligns with these previous studies to facilitate comparison and validation of the results.  
Figure 1: Research method flow chart.