Predicting human gait kinematics and kinetics from a single inertial measurement unit using deep learning and synthetic datasets: A blinded assessment study

A single inertial measurement unit (IMU) can be used with neural networks (NNs) to predict joint kinematics and kinetics. Recent studies, however, often employed virtual IMU data computed from marker-based systems to train NN models, without providing realistic performance assessments on real IMU data. To address this, we present a methodology for developing and blindly evaluating NNs predicting lower-limb joint angles and moments from a sacrum-worn IMU. NN architectures were trained on IMU data simulated from a public marker-based dataset (49 healthy adults), augmented using conditional generative adversarial networks to enhance variability. The developed NNs were blindly tested against a different dataset (seven healthy adults) of real IMU and synchronous marker-based data collected ad hoc after the NN development. The two datasets were collected in different labs using different protocols. These NNs were subsequently fine-tuned (retrained) with this dataset and re-evaluated on another real IMU data (three healthy adults) collected after fine-tuning. The NNs achieved strong predictive performance on virtual IMU data (average root mean squared error (RMSE) of 2.6±1.3° and 0.10±0.05 Nm/kg for joint angles and moments, respectively). However, performance degraded when applied to real IMU data: average RMSE of 4.5±2.0° for joint angles and 0.21±0.14 Nm/kg for moments. Fine-tuning with real IMU data improved model accuracy, recovering RMSEs to 2.6±0.8° and 0.19±0.11 Nm/kg for joint angles and moments, respectively. Overall, our performance metrics were within the reported ranges for systems employing multiple IMU sensors. This work highlights the importance of blinded assessment and fine-tuning for practical biomechanical applications.