## 3 Results and Discussion
### Simulating the Physical Ergonomic Conditions of Assembly Procedures in VR and DHM
#### 3.1.2 Simulating Physical Ergonomics Analysis
The optimal postural condition for joints such as the wrist is neutral, because muscle tension is potentially uncomfortable and can develop carpal tunnel syndrome [24]. While the wrist is flexed (bent toward the palm) or stretched (bent away from the palm), especially when applying force, this condition occurs [24]. The application of torque to the Rear Driveshaft task shows this incorrect posture. The same assembly procedure also analyzed the shoulder (Figure 18) and lower-back posture (Figure 23). Only the moderate condition was identified for these. Figure 16: Hand/wrist-posture simulation (non-immersive). Figure 17: Hand/wrist-posture scale [23]. Figure 18: Shoulder-posture simulation (non-immersive). As a reference, Figure 19 shows the shoulder-posture scale adapted from a general ergonomics industry guideline [23]. The lower-back analysis helps evaluate the spinal forces acting on a virtual human's lower back under any posture and loading condition (Figure 20). Thus, it is possible to determine whether newly defined or existing workplace tasks exceed NIOSH threshold limit values or expose workers to an increased risk of lower-back injury [25]. This analysis could be used to evaluate the risks of lower-back injuries in existing tasks. Figure 21 shows the lower-back-posture scale adapted from a general ergonomics industry guideline [23]. The next simulation was of a radiator assembly procedure, and the DHM shows that the knee flexion is nearly at its extreme limits, with a deviation of 130.4 degrees on a scale ranging from \(-5\) to 160.2 degrees (Figure 22). Figure 19: Shoulder-posture scale [23]. Figure 20: Lower-back-posture simulation (non-immersive). In virtual simulation, the radiator hose-clamp assembly presented a potential critical ergonomics risk. Because the worker must squat to connect the clamp to the radiator hose, it is related to lower-limb posture. It is a high-risk posture for musculoskeletal problems involving joints, most particularly the knee. Analysis of leg stresses allows identifying issues related to the leg. Studies identified three critical areas regarding the leg postures. The position follows the same criteria regarding flexion (neutral, moderate deviation, and extreme deviation) [23]. In this assembly procedure, VR analysis was performed to better understand the worker's postural condition in an immersive assessment (Figure 23). We observed that after the hose is attached to the back of the radiator and no other access is available, this is a blind operation. Finally, a simulated parking-brake assembly was performed. This simulation, like the previous ones, began with DHM. In this assembly procedure, the worker must pick up the portable nutrunners and device to support adjust, access the vehicle, and sit on the vehicle seat while applying torque to the brake lever. The worker's trunk-twist movement was observed in order to see the screw and complete the torque for this task. When the worker rotates the trunk to complete the task, the trunk musculature must work to overcome the body tissues' passive resistance. The passive resistance is low in the neutral position, and the trunk can be twisted in either direction [23]. Even if the worker's lateral rotation deviation is in the middle, flexion of 60 degrees on a scale of \(-52\) to 84 degrees is required to apply the torque in the brake lever (Figure 24). Figure 15.0 Radiator hose-clamp simulation (immersive). Figure 15.1 Leg/knee-posture simulation (non-immersive). Figure 25 shows the trunk twist-posture scale adapted from a general ergonomics industry guideline [23]. Much like the previous assembly procedures, VR was used to analyze how items like the seat and center console could affect the worker's vision during the task (Figure 26). We observed that even with the seat fully adjusted to the rear, it is impossible to view the screw and position the portable nutrunners without lumbar flexion. As a general rule, workers should have a limited exposure to all near-extreme or extreme posture conditions.