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Introduction: Commercial fishing often requires repetitive and sustained torso bending, which is a well-known risk factor associated with low back injuries. While back-support exoskeletons (BSEs) have been identified as an effective intervention to reduce low back stress, their effectiveness can vary depending on the supporting torque provided by BSEs. Therefore, this study aimed to determine how different supporting torques of a passive BSE affected biomechanical load in the low back during crab sorting, an essential task in commercial crab fishing.

Methods: Twenty male participants (aged 18 years or older) were recruited for this repeated-measures laboratory study. While sorting mock-up crabs by color at a self-selected speed, their full-body kinematics data were collected using a three-dimensional motion capture system. The collected kinematic data were used to perform biomechanical simulations in the AnyBody Modeling System. A combined human-exoskeleton model was applied with five different supporting torque levels ranging from 22 to 52 Nm. Outcome measures included erector spinae (ES) muscle activity, lumbosacral (L5/S1) compression and shear forces, and contact forces in the chest and thigh areas. A mixed model was used to evaluate the impact of BSE torque levels (fixed effect) on each outcome measure, with ‘participant’ included as a random effect.

Results: The results showed that as the supporting torque increased, the peak ES muscle activity, compression and shear force decreased (p<0.001). Specifically, ES muscle activity decreased from 6% (lowest torque) to 25% (highest torque). A similar trend was observed for the peak L5/S1 compression and shear forces, with reductions of up to 26% and 23%, respectively (p<0.001). Lastly, the chest contact force increased from 47 (lowest torque) to 118 N (highest torque); the thigh contact force increased from 37 (lowest torque) to 89 N (highest torque).

Discussion: Findings suggest that BSEs can effectively reduce low back loads in commercial crab fishing, with supporting torque playing a crucial role. While higher torque levels provide greater spinal load reduction, they also increase contact forces in the chest and thigh areas, potentially leading to discomfort – a common BSE side effect. Balancing spinal load reduction and user comfort is essential when determining optimal BSE torque.

Conclusion: The supporting torque level of passive BSEs is a key design factor influencing their ability to reduce musculoskeletal load in the low back. Given the trade-off between spinal load reduction and increased contact forces, further studies are needed to optimize BSE torque for both effectiveness and comfort.