Exploring Effects of Shoulder-Assist Exoskeletons on Load-Carrying Stability: A Phase-Specific Approach

Abstract

Manual material handling (MMH), a common task in occupational settings that frequently requires workers to transition immediately from lifting to short-distance load-carrying, is associated with a high risk of musculoskeletal injuries. Although commercial exoskeletons have shown potential to reduce local physical workload during isolated lifting tasks, their effects on walking stability during the workflow-relevant period are not well understood. This study quantified the phase-specific effects of three commercially available shoulder-assist exoskeletons on dynamic stability during the post-lift walking segment of a simulated lift-walk-place task. Participants performed repeated trials under four randomized conditions: no exoskeleton (NE) and three shoulder-assist exoskeleton conditions, denoted as Exoskeleton 1 (EXO1), Exoskeleton 2 (EXO2), and Exoskeleton 3 (EXO3).Whole-body motion capture was used to estimate center-of-mass (CoM) kinematics, and anterior margin of stability (MoS) was calculated from the extrapolated center of mass relative to the anterior base-of-support (BoS) boundary. Step-level minimum anterior MoS was analyzed separately during acceleration, steady walking, and deceleration phases using linear mixed-effects models. No statistically significant exoskeleton effects were observed during acceleration or steady walking. During deceleration, both EXO2 and EXO3 produced statistically significantly more negative minimum anterior MoS values than NE, whereas EXO1 did not differ significantly from NE. These findings suggest a phase-specific pattern in minimum anterior MoS, with the clearest condition-related differences observed during gait deceleration in short post-lift walking.