## 4 Discussion  
In a full-body dynamic simulation using JACK Siemens software, the posture of the participant has been evaluated by comparing it to actual human movement captured by the Xsens MVN motion tracking system. Joint angle deviations directly lead to the significant difference in compressive back force and shear force along the L4/L5 spinal segment. As shown in Figure 4, there is no significant difference in spinal forces between the Real_HM and Predicted_HM for the push task. On the other hand, a notable difference in spinal forces was found between males and females in the Real_HM. The correlation of Trunk_F/E and Hip_F/E could be the reason for this dissimilarity in spinal forces between genders. A moderate negative correlation between trunk and hip for females was observed in the Real_HM, where a weak positive correlation for male participants was found. Hence, while pushing, females extended their trunks, whereas males tended to hunch, causing the trunk to flex and bringing the hip into flexion as well. In the most ergonomic pushing technique provided by Mount Nittany Health [20] and the University of Rochester Medical Center [21], the back should be straight, the body should lean toward the object, and the body's weight should be used to move the object forward. The procedure just described will reduce strain on the back. While the procedure was not described during the orientation session, females naturally followed the proper pushing technique more than males. We speculate that this is the result of the load being a larger percentage of body weight for the female group, who are thus forced to use their legs to push rather than rely on the lower back. The different applied pushing techniques between genders may result in the higher spinal forces present in males in comparison to females. In the Predicted_HM, there was also a significant difference in spinal forces between males and females. It is interesting to notice that there was a strong relationship between trunk and hip flexion for males and females. It seems that the trunk and hip flex simultaneously while performing the push task in the Predicted_HM, indicating that the motion algorithm in JACK predicts that both genders would push more by bending their backs. Moreover, for the push task, a high correlation was found in relation to the participant's height and compressive forces. Figure 4 shows how as the height of the participant increased, the spinal forces on the participant increased in both genders and both Real_HM and Predicted_HM. Accordingly, the relatively larger body height in males will result in greater trunk and hip flexion, which will directly result in increased spinal forces for males in the Predicted_HM. Except for the trunk movements we just analyzed, all joint displacements were significantly different between the Real_HM and Predicted_HM. An important difference found was that in the Sh_Abd / Ad, the shoulder performed an abduction in reality, which was estimated as an adduction motion in simulation. As per the aforementioned proper pushing technique provided in [20; 21], the body should lean toward the object. Thus, it stands to reason that a shoulder abduction is more reasonable for pushing an object forward. A statistically significant difference in joint angular displacement between genders only occurs in Sh_F/E, where the female group had a shoulder flexion of over 10\({}^{\circ}\) higher than the male group during the push movement. For the pull task, there was a significant difference between the spinal forces calculated with the Real_HM and Predicted_HM, as well as a statistically significant difference in the spinal forces between males and females (see Figure 4). The difference was not as significant between these genders when comparing the shear forces in the Real_HM. The reason for a notable difference in forces could be caused by the statistical difference between all the joint displacements.