Vertical stiffness during running using WIMUpro sports tracker in football: validation and correlation analysis with acute:chronic workload ratio

This study explores the correlation vertical stiffness, utilizing trunk-mounted inertial measurement unit (IMU) data and acute:chronic workload ratio. Vertical stiffness estimation accuracy issues are identified in validation using sensorized insoles (loadsol®) as gold standard. During the validation part, results show that the WIMU-proposed algorithm underestimates vertical stiffness compared to loadsol®, but GPS velocity integration and linear regression improve accuracy to a value sufficient for the in-field use. Additionally, the research delves into the link between vertical stiffness and the acute:chronic workload ratio, examining intrinsic parameters like total distance, high-speed running meters, and mechanical work. Statistical analyses unveil significant workload ratio differences. Distinctions arise between the first team and Primavera teams, with higher median vertical stiffness in the first team. In the first team, statistical significance is found for all intrinsic parameters, with over-training groups exhibiting lower vertical stiffness values, possibly due to energetically inefficient gait or fatigue. Primavera teams show fewer differences among workload ratio groups, with limited statistical significance. Limitations include a small sample size and test condition variations. Future research should involve a larger elite player pool, different speed tests, and more controlled conditions. Despite limitations, this study offers valuable insights into vertical stiffness as a sports performance analysis parameter. It highlights its potential for preventing workload-related injuries and improving athlete preparedness. Further investigation of stiffness fluctuations may enhance injury prevention in football and other sports.