# Development and Biomechanical Evaluation of a Back Exoskeleton to Support Lifting Tasks
## 4 Results
### Kinematic Data  
The mean kinematic trajectories of the hip and knee joints in the sagittal and frontal planes are depicted on the left side of Figures 5-7. The baseline kinematics without the exoskeleton are represented by the blue curve, while the red curve illustrates the kinematics when wearing the exoskeleton. The motion sequence begins in an upright position, followed by grasping the object, and concludes once the object is placed on the platform, returning to an upright posture.  
During the grasping phase, the hip joint flexes up to approximately 100 degrees (Figure 5). As the object was lifted, the flexion angle decreased to around 25\({}^{\circ}\). When bending forward again to place the object onto the platform, the hip joint reaches a more  
Figure 5: (**a**) Mean sagittal hip angle during lifting task with (red) and without (blue) exoskeleton and (**b**) statistical 1D SPM test; * critical t-value.  
Figure 6: (**a**) Mean frontal hip angle during lifting task with (red) and without (blue) exoskeleton and (**b**) statistical 1D SPM test; * critical t-value.  
Figure 7: (**a**) Mean sagittal knee angle during lifting task with (red) and without (blue) exoskeleton and (**b**) statistical 1D SPM test; * critical t-value.  
-flexed position of about 35 degrees. Following this, the participants return to an upright position, completing the movement sequence.  
The corresponding statistical analysis is shown on the right side of Figure 5. The SPM[t] curve (black) is displayed alongside the critical threshold (red, dashed line). If the SPM[t] value exceeds the critical value, statistically significant differences are observed. However, as indicated in the figure, no significant differences were found between the two conditions (with and without exoskeleton) across the entire movement cycle. This suggests that the exoskeleton does not fundamentally alter hip joint kinematics in the sagittal plane during the lifting task.  
Figure 6 illustrates the hip angle in the frontal plane. During the descent to grasp the object, the hip moves into greater abduction, reaching approximately 10 degrees. When using the exoskeleton, the abduction angle is reduced by 2-3 degrees compared to the baseline condition. However, this reduction is not statistically significant. As the participant returns to an upright position and lifts the object onto the platform, the hip angle returns to a neutral posture of approximately 0 degrees. Throughout the entire movement cycle, no statistically significant differences between the conditions were observed, as shown on the right side of the following figure.  
In Figure 7, the knee angle in the sagittal plane is shown. When bending forward to grasp an object, knee flexion increases to approximately 65\({}^{\circ}\). During the lifting phase, as the upper body straightens, the knee angle extends back to around 5\({}^{\circ}\) in an upright position. No significant differences in knee flexion were observed between the conditions with and without the exoskeleton. As shown on the left side of the following figure, the knee follows a similar flexion-extension pattern in both conditions, indicating that the exoskeleton does not impose movement restrictions or alter the knee kinematics during the lifting task.