Error distribution and post hoc disturbance features in IMU-based hip joint angle estimation during complex movements

Existing evaluations of IMU-based joint angle estimation mainly rely on global accuracy metrics, which may obscure local error exposure during complex functional movements. This study analyzed data from 16 healthy male participants in the Hip-ROM-Y dataset. Using leave-one-subject-out outputs from a unified left hip joint predictor, we characterized left hip angle estimation errors by movement category, normalized movement phase, and high-error segment. The relationship between error distribution and post hoc disturbance features was further examined. The results showed that, under the current model and data conditions, complex movements (CMs) generally produced higher errors than basic movements. However, the increase in error was not uniformly distributed, but was mainly concentrated in local mid-phase periods of several CMs and was accompanied by greater deviations in the relative relationship between the pelvis and thigh segment. These findings suggest that evaluations of hip angle estimation under similar wearable configurations should pay attention to local error distributions during CMs and to the stability of the pelvis-thigh segment relationship.