Text

Introduction: Musculoskeletal Disorders of the shoulder have been associated with repetitive overhead work and manual lifting tasks. Upper-limb assistive devices, such as passive exoskeletons, have shown promise for reducing exposure to risk factors associated with shoulder injuries. However, the adoption of passive exoskeletons is adversely affected by fit concerns, particularly among women, who are often at a disadvantage due to a lack of gender-specific design considerations. The purpose of this study was to evaluate the initial static, dynamic, and cognitive fit of various upper-limb exoskeletons for use in manufacturing settings.

Methods: In a repeated-measures laboratory study, 24 participants (sex-balanced) performed a series of exercises, including a range of motion task, simulated manufacturing activities (e.g., overhead wrenching, lifting and lowering a 10 kg box), and test of visual attention, task switching, and speeded set-shifting. Three passive shoulder exoskeletons (Levitate AIRFRAME, Ekso Bionics EVO, and Ottobock Shoulder) and a no-exoskeleton control condition were analyzed. Subjective musculoskeletal discomfort ratings were collected periodically throughout the testing.

Results: The results revealed minimal sex-based differences in discomfort across body parts in the control and exoskeleton conditions. Dynamic fit was associated with higher discomfort in the shoulders and elbows, with 20.8% and 8.3%, respectively, of Levitate wearers experiencing >2-point increase on a 10-point visual analog scale. Differences of <1 unit were found for the Ottobock (shoulder: 95.8%, elbow: 91.6%) and Ekso Bionic (shoulder: 87.5%, elbow: 83.3%). Moderate range of motion restrictions were reported by 70.8% of Levitate wearers and 50% of both Ekso Bionics and Ottobock users.

Discussion: No statistically significant differences for sex were found across all metrics between the control and exoskeleton conditions. The exoskeletons supported the user while performing a specific static range of motion task while hindering others. All exoskeletons significantly increased peak arm elevation for cross-body adduction and external rotation and significantly reduced peak arm elevation for extension and internal rotation, except for the Ottobock in internal rotation. All exoskeletons increased mean arm elevation during pseudo-static, cognitive, and dynamic tasks.

Conclusion: It is important to understand how exoskeletons can affect static, dynamic, and cognitive fit for the successful implementation of exoskeletons in work settings. The insights from this study may result in better exoskeleton design and encourage more research to understand the trade-offs between changes in the range of motion while wearing exoskeletons.