# Biomechanical impact of a passive shoulder exoskeleton through musculoskeletal simulation and indirect interface forces measures: a pilot study

Charles Pontonnier, Olivier Morel, Etienne Ricard, Kévin Desbrosses, Chris Hayot

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Charles Pontonnier, Olivier Morel, Etienne Ricard, Kévin Desbrosses, Chris Hayot. Biomechanical impact of a passive shoulder exoskeleton through musculoskeletal simulation and indirect interface forces measures: a pilot study. PREMUS 2025 - 12th International Scientific Conference on the Prevention of Work-Related Musculoskeletal Disorders, Sep 2025, Tubingen, Germany. pp.1-1. hal-05274033

HAL Id: hal-05274033

https://inria.hal.science/hal-05274033v1

Submitted on 23 Sep 2025

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# Biomechanical impact of a passive shoulder exoskeleton through musculoskeletal simulation and indirect interface forces measures: a pilot study

Charles Pontonnier (1,2), Olivier Morel (3), Etienne Ricard (1,2,3), Kevin Desbrosses (3), Christ Hayot (3)

(1) University of Rennes, France

(2) Inria ComBO Research team, Rennes, France

(3) INRS, Nancy, France

**Introduction:** Evaluating the biomechanical impact of exoskeletons is a key factor in accelerating their use in MSD prevention. Such systems transfer the load from one part of the body to another, inducing beneficial and undesirable effects. To assess these effects, it is necessary to integrate the forces generated at the interface between the operator and the system into a biomechanical analysis of the task, either by modeling the contact or by indirectly measuring this action. We propose a methodology for evaluating the effects of a passive shoulder-assist exoskeleton through indirect measurement of forces and pressure centers at the interfaces between the operator and the system.

**Methods:** We evaluated the Ottobock Shoulder (Ottobock SE & Co. KGaA), a passive exoskeleton of shoulder flexion maximal support torque of 8Nm [1]. A 6-axis force transducer (ATI Industrial Automation, 2040Hz) was integrated into its main dorsal arm. We equipped one subject with the exoskeleton set at 75% of its maximal assistance, reflective markers, to capture his movement (Qualysis, 16 cameras, 120Hz) and 2 pressure maps (Xsensor, 60Hz) on the belt and armband, to measure the pressure centers at the interfaces. The subject performed shoulder sagittal flexion/extension movements at free speed. The data was used to perform inverse kinematics and inverse dynamics in OpenSim 4.5 [2], using a full-body model. The actions measured by the force transducer were applied to the sacrum and arm respectively, at the centers of pressure estimated by the maps. Joint torques at the shoulder and L5/S1 were compared without and with exoskeleton actions.

**Results:** Shoulder joint torques varied from a maximum of 8.7Nm to 4.6Nm in flexion, -7.3Nm to 0Nm in extension, 13.8Nm to 0.7Nm in adduction, -12.9Nm to -2.1Nm in abduction, 0Nm to 2Nm in internal rotation, and -2.4Nm to -1Nm in external rotation, without and with the exoskeleton respectively. L5/S1 joint torques varied from a maximum of 1.5Nm to 0.6Nm in flexion, -1.6 to -0.4Nm in extension, 5.5Nm to 0.5Nm in lateral flexion, 0.6Nm to 0Nm in lateral extension, 0.2Nm to 0Nm in internal rotation and -0.7Nm to -0.1Nm in external rotation, without and with the exoskeleton respectively.

**Discussion:** We observed a decrease in maximal shoulder flexion torque (-47%) and an in maximal shoulder abduction torque (-95%), demonstrating joint compensation for the action of the exoskeleton. This may imply a lesser demand for the deltoid anterior and pectoralis major. We also observed a decrease in most L5/S1 moments. Thus, the presence of the exoskeleton may lead to beneficial effects on both joints. These preliminary results need to be investigated on a larger population with more detailed estimates of muscle forces to investigate the physical changes related to the exoskeleton action.

**Conclusion:** We carried out an initial assessment of the biomechanical impact of a passive shoulder-assist exoskeleton, using indirect measurements of forces at the interfaces. The exoskeleton effectively relieved shoulder flexion. A study on a larger cohort including musculoskeletal analysis is required to qualify these initial results.

**References:**

[1] Ricard, E., Hayot, C., Clerc-Urmès, I., Claudon, L., Desbrosses, K., & Pontonnier, C. (2025). Evaluation of the static and dynamic assistive torque of a passive upper limb occupational exoskeleton. *Wearable Technologies, 6*, e19.

[2] Delp, S. L., Anderson, F. C., Arnold, A. S., Loan, P., Habib, A., John, C. T., ... & Thelen, D. G. (2007). OpenSim: open-source software to create and analyze dynamic simulations of movement. *IEEE transactions on biomedical engineering, 54*(11), 1940-1950.