# Squat Lifting Imposes Higher Peak Joint and Muscle Loading Compared to Stoop Lifting
## 4 Discussion
This statement is supported by the fact that higher hip and knee joint powers are combined with lower hip and knee moments during the squat compared to the stoop. However, when accounting for the execution time, i.e., based on the moment impulse on L5S1, squat lifting may still be preferred over stoop lifting. In addition to the slightly longer duration of the stoop lifting task, the longer persistence of the L5S1 extension moment during the stoop than during squat lifting may contribute to this finding (Figure 2). As a result, the cumulative loading during the whole movement is lower during squat lifting. Considering that low back pain is a result of cumulative damage in the lower back [4; 11; 31; 34; 35; 36], the squat should be recommend when lifting frequently to prevent back injury. This finding is also supported by the lower muscle effort in the back muscles during the squat. On the other hand, cumulative loading is higher in the shoulder and elbow during the squat compared to the stoop based on the higher moment impulse in shoulder and elbow. In addition, the higher muscle effort of the m. biceps brachii and trapezius descendens, especially during the lowering phase, support this statement, allowing us to conclude that there is an increased injury risk for the shoulder and elbow during repetitive squat lifting. The handling phase had only a minor effect on musculoskeletal loading in terms of the peak moments, powers and moment impulses, but it had a major effect on muscle activity. In general, muscle activity was higher during lifting than during lowering. This is in line with previous work that has investigated extensor muscle activations during the stoop [9]. The peak EMG of the back extensor muscles were lower during the lowering phase compared to the lifting phase (Figure 7a,c) as back extensor muscles activation peaks twice during the stoop: One small peak during the lowering phase and a larger one during the lifting phase [9]. Our results can be explained by the fact that the muscles have to overcome the moment generated by gravity during the lifting phase, whereas the muscles can cooperate with gravity to perform the required movement during lowering. This can be seen in the higher extensor muscles activity with the squat compared to the stoop while lowering the box, where the moment exerted by gravity can be used advantageous, resulting in higher muscle activation during squat lowering than during stoop lowering. Interestingly, the findings based on the maximal loading (i.e., peak moment and power) differ from those that account for the movement duration (i.e., moment impulse and muscle effort). The most striking example is that the maximal loading in L5S1 did not differ between techniques, whereas moment impulse in L5S1 and muscle effort of the back muscles did differ between lifting techniques. This suggests that future risk assessment tools should also account for the duration of the lifting task instead of only focusing on the peak moments, as is currently typically done in practice. This is in line with a recently formulated fatigue-failure theorem [37] that relates the pathomechanics of WMSDs to both repetition and force magnitude. Combined with our results, this suggests that ergonomic analysis should use a more holistic approach when analyzing the risk for WMSDs in work situations rather than focusing on the musculoskeletal loading of the target region. Moreover, our results indicate that multiple techniques (i.e., moment estimation and electromyography) should be combined when assessing ergonomic risk and evaluating the effectiveness of ergonomic interventions. This is, in particular, illustrated by the difference in elbow moment between the two different lifting techniques, whereas there was no difference in peak EMG or muscle effort for the m. biceps brachii and triceps brachii. Though our results indicate that squat lifting imposes similar peak musculoskeletal loading compared to stoop lifting, our results should be interpreted in the context of some limitations.