Measurement and application of wearable inertial measurement unit systems in athlete kinematics and load monitoring

Abstract The proliferation of microelectromechanical systems (MEMS) has catalyzed a paradigm shift in sports science, enabling the transition of biomechanical analysis from controlled laboratory environments to ecologically valid field settings. Wearable Inertial Measurement Units (IMUs), comprising accelerometers and gyroscopes, have emerged as a cornerstone of this revolution. They offer unprecedented opportunities to quantify athlete kinematics and monitor training loads continuously and unobtrusively. This review paper provides a comprehensive and critical analysis of the current state of IMU technology in sports science. It delves into the technical underpinnings of IMU-based kinematic measurement, scrutinizing the validation methodologies and inherent sources of error when compared against gold standard optical motion capture systems. Furthermore, the paper examines the application of IMUs for athlete load monitoring, critically evaluating popular metrics such as PlayerLoad™ and discussing the challenges in establishing their direct relationship with physiological and biomechanical stress. We discuss the major controversies pervading the field, including the profound lack of standardization in methodology, the ongoing debate regarding ecological validity, and the ethical dilemmas posed by continuous athlete surveillance. Finally, we explore future directions, focusing on the transformative potential of machine learning, advanced sensor fusion, and the development of benchmark datasets to overcome current limitations. This review synthesizes existing literature to provide a nuanced perspective on the capabilities and caveats of IMU systems, aiming to guide future research and practice towards more robust and meaningful applications in enhancing athletic performance and mitigating injury risk.