Investigation of the Impact of a Passive Shoulder Exoskeleton on the Shoulder Range of Motion: A Preliminary Study

This study presents a pilot experiment to systematically explore the influence of exoskeleton supportive force, exoskeleton physical design, and external loads on the user’s shoulder range of motion (ROM). A within-subjects two-factor factorial design was applied to assess ROM changes under nine experimental conditions (3 exoskeleton settings × 3 loads). The exoskeleton settings were varied among three levels: without exoskeleton as the baseline (NoExo), with a force-on exoskeleton (the supportive force of the exoskeleton was turned on; ExoWithForce), and with a force-off exoskeleton (the supportive force of the exoskeleton was turned off; ExoNoForce). Three different loads (0, 3, and 6 kg) were tested under each exoskeleton setting. Nine healthy young male subjects voluntarily participated and their ROMs in shoulder flexion/extension (FLEX), vertical abduction/adduction (VABD), and horizontal abduction/adduction (HABD) were recorded via a motion capture system. The results showed that the exoskeleton setting significantly influenced the shoulder ROM in the VABD but not that in the HABD and FLEX. Meanwhile, load significantly limited the shoulder ROMs of FLEX, VABD, and HABD. No statistical significance was observed for the interaction effect between load and exoskeleton setting on the ROMs of the shoulder. Notably, compared to the No Exo condition, the mean ROM of VABD of the ExoNoForce and ExoWithForce conditions was lower. There was no significant difference between the ExoNoForce and ExoWithForce conditions of VABD. These findings suggest that while the physical design of the exoskeleton and external load can limit shoulder ROM, the supportive force could partially offset this effect.