Effects of a Passive Back-Support Exoskeleton on Muscle Activity and Perceived Discomfort Across Lifting and Lowering Tasks of Varying Heights and Weights

Manual material handling tasks are a major source of physical workload and work-related musculoskeletal disorders in industrial environments. This study evaluated the effects of a passive back-support exoskeleton (BSE) on muscle activity and perceived discomfort during lifting and lowering tasks performed under varying working height and weight conditions. Ten healthy male participants completed lifting and lowering tasks across seven height levels, seven weight levels (3–15 kg), and two exoskeleton conditions (with and without BSE). Surface electromyography was recorded from 12 muscles, and perceived discomfort was assessed using a visual analog scale. The BSE significantly reduced muscle activity in the middle trapezius, erector spinae longissimus, biceps femoris, and gastrocnemius lateralis, while a slight increase was observed in the flexor digitorum superficialis. Among all muscles, the middle trapezius exhibited the greatest reduction with the BSE. The reduction in muscle activity was more pronounced during lowering tasks and at extreme working heights, indicating that the exoskeleton provided greater biomechanical assistance under excessive postural conditions. Perceived discomfort was also significantly reduced, particularly at extreme height levels and heavier loads (13–15 kg). These findings suggest that passive BSEs can effectively reduce physical demands and improve user comfort during material handling tasks, although potential load redistribution to distal muscles should be considered when implementing exoskeleton systems in occupational settings.