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Accurate Shoulder Angles Can Be Detected in Single Plane Motions While Body Armor is Worn: A Validation of the
Ayden M Mccarthy1,2,3, Jodie A Wills1,2, Auralea C Fain1,2
1Faculty of Medicine, Health and Human Sciences, Macquarie University, Sydney, NSW 2109, Australia.
Introduction:
Measuring shoulder mobility is essential for assessing function, especially in occupational settings like the military, where movement tasks in the frontal and sagittal planes are involved. Markerless motion capture systems like the HumanTrak may provide an expedient field platform to quantify upper body kinematics in occupational settings because of their portability. Further validation of these systems against established methodologies, such as marker-based motion capture, is required before upscaling their use.
Materials And Methods:
Seventeen participants (7 males and 10 females; age, 25 ± 7 years; stature, 1.70 ± 0.08 m; mass, 72.26 ± 15.09 kg) completed standardized fixed-range shoulder flexion, extension, abduction, and adduction tasks with and without body armor for 3 systems: HumanTrak, 2D video capture, and 3D marker-based motion capture. Joint angles were calculated using planar and Euler algorithms. The HumanTrak's relative and absolute validity was compared against these established methodologies.
Results:
Generally, valid relative and absolute results were found, with Pearson correlations (r) ranging from 0.56 to 0.93 and root mean square errors ranging from 2.51° to 7.35° for shoulder flexion, extension, and abduction with and without body armor. Shoulder adduction measures were generally invalid, as r values ranged from -0.24 to 0.77, and with root mean square errors ranging from 5.27° to 8.42°.
Conclusions:
The HumanTrak's validity is comparable to that of existing field expedient markerless motion capture systems in estimating shoulder joint angles in abduction and the sagittal plane. When movements are standardized to a singular plane of motion and a neutral spine is assumed, valid results can be measured for shoulder flexion, extension, and abduction with and without body armor. Shoulder adduction was generally invalid for both body armor and no body armor conditions, likely because of its multi-planar nature and axial trunk rotation.
