Validation of Markerless Motion Capture for Soldier Movement Patterns Assessment Under Varying Body-Borne Loads.

Field performance of modern soldiers is affected by an increase in body-borne load due to technological advancements related to their armour and equipment. In this project, the Theia3D markerless motion capture system was compared to the marker-based gold standard for capturing movement patterns of participants wearing various body-borne loads. The aim was to estimate lower body joint kinematics, gastrocnemius lateralis and medialis muscle activation patterns, and lower body joint reaction forces from the two motion capture systems. Data were collected on 16 participants performing three repetitions of walking and running under four body-borne load conditions by both motion capture systems simultaneously. A complete musculoskeletal analysis was completed in OpenSim. Strong correlations ( $\text{r}>0.8$ ) and acceptable differences were observed between the kinematics of the marker-based and markerless systems. Timing of muscle activations of the gastrocnemius lateralis and medialis, as estimated through OpenSim from both systems, agreed with the ones measured using electromyography. Joint reaction force results showed a very strong correlation ( $\text{r}>0.9$ ) between the systems; however, the markerless model estimated greater joint reaction forces when compared the marker-based model due to differences in muscle recruitment strategy. Overall, this research highlights the potential of markerless motion capture to track participants wearing body-borne loads.