# Squat Lifting Imposes Higher Peak Joint and Muscle Loading Compared to Stoop Lifting
## 4 Discussion  
This study compared whole body loading during two frequently used lifting techniques--squat and stoop lifting--based on joint moments, joint power and muscle activity. In general, squat lifting is the advised method to lift heavy objects because it reduces low back loading. However, it is likely that lifting technique affects joints other than LSS1 and could therefore contribute in the development of WMSDs. Indeed, the present results indicate that lifting technique has no significant effect on the peak moments and power generation in LSS1, but it does significantly increases musculoskeletal demand on the other joints. Furthermore, for the tested weights, the differences between lifting strategies were more pronounced than the effect of the weight lifted. In line with our hypothesis, squat lifting was found to shift musculoskeletal loading merely to the extremities, potentially to safeguard the lower back. However, joint moments and powers in the back were found not to be significantly different between lifting techniques, therefore imposing similar musculoskeletal loading on the back during squat and stoop lifting. Squat lifting was found to be mainly executed by additional active work of the knee extensors compared to stoop lifting. This was further confirmed by the increased muscle activity of the rectus femoris muscle. Furthermore, squat lifting increased musculoskeletal loading in the shoulder and elbow. This could potentially explain the similar prevalence of WMSDs in the shoulder to low back pain in persons exposed to frequent lifting [1]. Previously, squat lifting was advised to be used over stoop lifting to lift heavy objects because lower moments and compressive forces at the back were reported [6; 8; 9; 20; 32]. This is in contrast to the findings of the present study, as similar joint moments were found in the LSS1 joint even when taking the distance between L5 and the object into account. Given the fact that muscle force is the dominant contributor to compressive forces on LSS1 and high muscle force results from high moments around L5S1 [6], we could not conclude that the squat imposes lower compressive forces on L5S1 than the stoop [6]. Based on the assumption that high flexion moments in LSS1 result in high compressive forces, we could assume (as we did not calculate compression and shear forces in this study) that compressive forces are similar between both techniques because both techniques resulted in similar moments around LSS1. Future research should focus on validating biomechanical models in order to calculate compression and shear forces at L5S1. Moreover, based on the LSS1 moment and power, we could not favor squat lifting over stoop lifting in contrast to current literature [6; 9]. On the other hand, [PERSON] et al. 1999 [32] concluded that there is no evidence of advising squat over stoop lifting in their comprehensive review of 27 studies, which is in line with our results. Task characteristics, i.e., initial lifting height and dimensions object lift, influence back loading [33], which makes comparisons with literature delicate. Even small adjustments to the squatting technique such as rotating the knees outwards already reduces back loading [14], which was not controlled in this study. However, the handled weights during this experiment were fairly light, and the box was rather small (width: 21 cm; height: 14 cm; length: 36 cm) compared to other studies [6; 9]. Potentially, the effect of the lifting technique will be more pronounced when heavier weights are handled. On the other hand, [PERSON] et al. 2004 concluded that squat lifting a box of 10.5 kg results in higher net moments and higher compression forces in L5S1 compared to the stoop. Our results, with similar moments in L5S1 during the squat and the stoop, can be explained by the higher upper body acceleration during the squat, as suggested by [PERSON] et al. 2004.