# Prevent Workers from Injuries in the Brewing Company via Using Digital Human Modelling Technology
## 4 Discussion  
This study provided one of the first digital ergonomics analyses for brewery workers. The maximum compressive and A/P shear forces were estimated during two common tasks the workers perform daily. Such tasks consist of placing an empty leg on a cleaning platform and lifting a full leg from the ground, and placing it on top of a second leg. The corresponding anatomical joint angles were monitored during the movements. The correlation coefficient between joints and spinal loads determines the key factors affecting the transmission of forces from the hands to the lower back. In Task#1 at Pose#1, the subjects lifted the empty leg from the floor, and the A/P shear force and trunk angular displacement show a strong correlation, which is consistent with the results obtained from previous studies [48, 49] that considered lifting movements. The compressive force was increased with the increase in trunk flexion angle. In [25], a high correlation between compressive force and trunk movement was revealed. Our results reaffirmed this conclusion. The literature shows that a small trunk flexion in parallel with a relatively large hip flexion will result in a less compressive force acting on the lower back than a large trunk flexion with a small hip flexion. However, following this model, as subject#3 flexed his trunk to 13.7\({}^{\circ}\) compared to subject#2 (27.6\({}^{\circ}\)), the latter is supposed to have a larger exerted spinal force than subject#3, but the compressive force estimated on subject#3 was the higher. In this case, we posit that the additional asymmetric hip flexion (right hip: 11.7\({}^{\circ}\), left hip: 46.6\({}^{\circ}\)) is an additional cause for high risk. Furthermore, as the average A/P shear force among the three subjects for this pose was more than 600 N, the  
Figure 8: The analyzed results at Pose#2 in Task#2: (a) the exposed spinal forces with the recommended safety threshold values; (b) the trunk angles; (c) the hip angles; (d) the knee angles. workers should be aware that if there is any beer left in the empty leg, the load on the lower back will easily reach the recommended safety threshold limit of 700 N.  
At Pose#2 in Task#1, as the subjects placed the empty leg on the leg holder, there still is a high correlation between the A/P shear force and trunk flexion. The average A/P shear force exerted on the lower back was greatly reduced at this pose compared with the force at Pose#1 due to the greatly reduced trunk flexion. Additionally, subject#1 extended his trunk to place the empty leg on the holder, while subject#2 flexed his trunk, which directly led to an approximately 1000 N difference in the compressive force acting on their lower back. The result is also consistent with one previous study [25]. However, the difference in compressive force between subject#2 and subject#3 was approximately 500 N, even though the trunk flexion of both subjects was approximately 5\({}^{\circ}\). The hip flexion (20\({}^{\circ}\) vs. 7\({}^{\circ}\)) might play an important role, as it did at Pose#1. For Task#1, if we compare the body height and body weight among these three subjects, subject#2 is the tallest and thinnest, which may cause him to bend the upper body more than the others if the position of the object is constrained, which is consistent with the result in [24]. A previous study [50; 51] emphasized that the proper lifting postures should be with the knees bent, as the upper body is kept straight, inducing the subject to use the strength of the lower body to lift the load. In our population, subject#1 seemed to follow the proper lifting techniques very well. In Task#2, at Pose#1, the subjects lifted the full legs from the floor. The full legs are quite heavy, inducing a force applied on the lower back that is much higher than the recommended safety threshold limits for both compressive and A/P shear forces. This is despite all three subjects having adopted a large knee flexion to avoid more upper-body bending.