Validity and reliability of inertial measurement units in obtaining a lower limb stiffness running measure in high-level track and field athletes

Introduction: Recent developments in inertial sensor technology mean real time monitoring and tracking of athletes in the daily training environment is now a possibility. Such developments have the potential for injury prevention and performance maximisation. Stiffness of the lower limb has known links to performance and injury risk; however, these measures have so far been limited to laboratory-based settings. Application of current sensor technology has the potential for ongoing stiffness assessment not only in the laboratory but also in the daily training environment. Actual training monitoring and changes to the way an athlete deals with loading (leg stiffness) on a regular basis could provide vital feedback to athletes, coaches, medical and support staff allowing for effective systems to be put in place to ensure athletes reach their potential. Study 1: The first aim of this thesis was to review existing literature surrounding the longitudinal assessment of lower limb stiffness in adult athletic populations. A systematic review was conducted which initially produced 630 results before being reduced to 6 for final analysis, highlighting the lack of research in this area. Data extracted focused on the population, methodologies and key findings of each study. The results concluded that the longitudinal assessment of lower limb stiffness had so far been isolated to laboratory-based settings and predominately measured through simple vertical hopping and jump tasks in the specific sporting population of Australian Rules Football players. From the results, the need for a field-based measure of lower limb stiffness was identified in order for stiffness to be assessed at more regular intervals to better understand the prospective links between lower limb stiffness, performance and injury. Study 2: Based on the findings from study 1, the primary aim of this study was to develop a valid and reliable field-based measure of lower limb stiffness in high-level track and field athletes during running (a task reflective of training and competition) using inertial measurement units. Nineteen high-level track and field athletes completed six running gait trials at a pace reflective of their event during competition. Data was captured using a fourteen-camera motion analysis system (250Hz), a force plate (1000Hz) and three inertial measurement units (500Hz). The gold standard stiffness measures from the motion analysis system were than compared with the stiffness measures derived from the inertial measurement units. Poor validity was found between the gold standard stiffness measures and the measures derived from the inertial measurement units. In addition, the results demonstrated that the data output from the inertial measurement units were not reliable when substituted into the existing measures of stiffness, warranting the need for further research. Conclusion: This thesis makes a novel contribution to the assessment of lower limb stiffness in athletic populations. Although a valid and reliable measure of lower limb stiffness using inertial measurement units still needs to be established, it is hoped that this research is the first step in developing a daily monitoring tool which may provide a proactive approach in managing an athlete’s response to load. However, further refinements to the algorithm and developments in inertial sensor technology are required before this technology can be considered for use outside the traditional laboratory setting