The Effect of Arm Support Exoskeletons in Realistic Work Activities: A Review Study

The use of arm-support exoskeletons could be a strategy to unload the shoulder in elevated arm work. In this paper the effects of these type of exoskeletons on objective parameters of shoulder load, subjective measures and performance measures were reviewed. The review resulted in eleven papers addressing ten arm-support exoskeletons. Seven of these exoskeletons were passive (spring-based) exoskeletons, one was an active exoskeleton mounted to the wall and two exoskeletons were equipped with a supernumerary limb (snl) attached to the waist. For the exoskeletons with a snl, the concept of transferring loads from the shoulder to the waist did not result in the expected reductions in shoulder muscle activity. The passive exoskeletons did show reduced levels of activity in the agonistic muscles (those involved in arm elevation), ranging from 16% to 130%, both in quasi-static tasks like overhead drilling and overhead assembly, but also in lifting and stacking tasks that involved elevation of the arms. However, the activity in antagonistic muscles was found to increase by up to 107%. The adoption of arm support exoskeletons in practice depends on whether the positive effects of lowered muscle activity would outweigh negative effects like increased antagonistic muscle activity and other potentially adverse effects regarding discomfort or usability. With regards to subjective experiences and performance related measures, mixed results were reported. The effectivity and subjective experience seem to be task-dependent. Therefore, it is important to consider the specific working environment and envisioned results, to select the exoskeleton that best suits the specific working conditions.