Accuracy and Reliability of Markerless Human Pose Estimation for Upper Limb Kinematic Analysis Across Full and Partial Range of Motion Tasks

Markerless human pose estimation is increasingly used for kinematic assessment, but evidence of its applicability to upper limb movements across different ranges of motion (ROM) remains limited. This study examined the accuracy and reliability of a markerless pose estimation system for shoulder, elbow and wrist flexion-extension analysis under full and partial ROM tasks. Ten healthy participants performed standardized movements which were synchronously recorded, with an optoelectronic motion capture system used as a reference. Joint angles were compared using RMSE, percentage RMSE (%RMSE), accuracy (Acc), intraclass correlation coefficients (ICC), and Pearson correlation of ROM values. The markerless system reproduced the temporal morphology of the movement with high coherence, showing ICC values above 0.91 for the elbow and 0.94 for the shoulder in full ROM trials. Wrist tracking presented the lowest RMSE values and low inter-subject variability. The main critical aspect was a systematic underestimation of maximum flexion, especially at the shoulder, indicating a magnitude bias likely influenced by occlusion and joint geometry rather than by temporal fluctuations. Despite this limitation, the system adapted consistently to different ROM amplitudes, maintaining proportional variations in joint excursion across tasks. Overall, the findings outline the conditions in which markerless pose estimation provides reliable upper limb kinematics and where methodological improvements are still required, particularly in movements involving extreme flexion and occlusion.