Shoulder exoskeletons in assembly processes: mismatch between reduced muscle load and increased discomfort

Exoskeletons represent a promising technological solution for reducing musculoskeletal strain in workers performing physically demanding tasks. The aim of this study is to examine deltoid muscle activity, perceived exertion, and discomfort during shoulder exoskeleton use under real industrial conditions. The first testing phase involved 24 operators, the second phase involved 10 operators, and the main test involved 5 operators. In the main test, deltoid muscle activity was measured using electromyography in five operators performing three specific assembly processes with and without the exoskeleton. Perceived exertion and perceived discomfort were also assessed using the Rating of Perceived Exertion and Rating of Perceived Discomfort scales. Across the three processes, measured deltoid muscle activity was lower with the exoskeleton, with a mean reduction of 25.1%. Mean perceived exertion was approximately 5.1% higher, whereas mean perceived discomfort was approximately 110.5% higher when using the exoskeleton than without it. In this small field sample, lower measured deltoid muscle activity coincided with greater perceived discomfort.