Musculoskeletal effectiveness of exoskeletons in lifting tasks in the logistics sector

Purpose: Physically demanding work increases the risk of developing musculoskeletal disorders, especially low back pain. Economic and social consequences may be severe: While sickness levels rise in an organization, individual quality of life can be impacted for years or even permanently, placing a significant burden on the national healthcare systems. To ad-dress this challenge, passive exoskeletons are used worldwide at increasing rates in the logistics sector, trying to reduce the daily physical load of workers in storehouses, assembly lines and ship-ping. While previous research suggests that passive exoskeletons may alter the load onto the musculoskeletal system, details of their effect often remain unknown. Reasons are the broad variety of passive and active exoskeletons available on the global market, being subject to different working mechanisms and technical realisations, and individual physical prerequisites and conditions that further contribute as (practically often uncontroll able) cofactors. To compare the effectiveness of two passive exoskeletons for the lower body commonly used in the German logistics branch, we examined their impact on the musculoskel-etal load experienced during typical lifting tasks in package warehousing and shipping. Methods: Muscular load during self-controlled lifting task execution is compared via surface electromyography between passive exoskeletons of two leading manufacturers (Hunic, Laevo) and to the unassisted case. Lifting tasks comprise a lower-limb driven movement pattern (“proper lifting”) and a back-and- hipdriven pattern (“incorrect lifting”), each for a weight of 0 and 10 kg. Each participant (4 m, 2 f, all healthy) performed 12 repetitions of every lifting task. Myoelectrical activity was assessed during lifting tasks in 7 relevant muscles (trapezius - ascending part, latissimus dorsi, gluteus maximus, biceps femoris, rectus femoris, vastus medialis and gastrocnemius lateralis). Results: As expected, an increase in weight from 0 to 10 kg leads to an elevated mean muscle activity in all muscles studied. While, on the individual level some, muscle groups experience a clear unloading when wearing an exoskeleton, the general situation is more complex for the whole cohort: Only a few muscle groups seem to be generally supported, whereas others exhibit an even higher load when wearing a passive exoskeleton. Conclusions: Passive exoskeletons may reduce muscular load in various muscle groups of the lower and upper body for common lifting tasks. However, the amount of unloading seems to depend decisively on lifting movement pattern and the weight to be lifted, and may even turn into an unintended increase of muscular load instead of a reduction. Further research is strongly indicated.