Metrological Characterization of MediaPipe for Knee Joint Angle Estimation During Squat Execution

Markerless pose estimation is increasingly used for human motion analysis due to its low cost and ease of deployment. However, the measurement uncertainty and sensitivity under operating conditions remain incompletely explored. This study aims to evaluate the metrological performance of MediaPipe for knee flexion angle estimation during squat execution, with particular attention to the effects of acquisition geometry and clothing configuration. MediaPipebased estimates were compared against the BioVal (Biorescue, RM Ingenierie, France), an inertial measurement unit (IMU) used as reference. A preliminary static analysis was performed to identify the optimal camera-subject distance, which was then used for the dynamic protocol. Dynamic acquisitions were performed at viewing angles ranging from 45° to 90° and under three clothing conditions (shorts, long trousers, and tight-fitting trousers). Results show a systematic underestimation of the knee flexion angle by MediaPipe, with a residual of (-13.9 pm 15.1)° (reported as mean ± standard deviation) and 95% limits of agreement of [-43.5°, 15.5°]. From our tests it results that the estimation performance is influenced by the acquisition geometry, with lateral views yielding the mean deviation and variance ((-2.3 pm 6.4)°. at .90°). Clothing configuration also contributes to measurement uncertainty, with tight-fitting trousers yielding more stable estimates (i.e., (1.6 pm 3.5)° at 9 0°) compared to shorts.