Inertial Measurement Unit Use for Elite Women’s Water Polo Upper Limb External Training Monitoring: An Observational Study

ABSTRACT – Introduction – Water polo external training load monitoring using technology remains an open research topic. Measuring upper limb movement volume in water polo is important because it may affect injury risk and performance. Other sports, such as football and cricket, use inertial measurement units (IMUs) to measure high training load demands. IMUs and machine learning have demonstrated accuracy in measuring water polo upper limb movements under standardized conditions. It remains unknown if this method can be applied longitudinally over an entire water polo season in multiple contexts and how this method relates to current internal training monitoring, namely, sessional rate of perceived exertion (sRPE). To address this, longitudinal IMU upper limb monitoring was used over a water polo season to classify upper limb movements, and its relationship with sRPE was observed. Methods – Eleven elite athletes wore two IMUs on the upper back and distal forearm over 860 athlete-sessions and performed overhead movements in practice sessions, swimming fitness sessions, and official games. IMU features were computed then classified using random forest modeling. sRPE and IMU movement class relationships were explored using Spearman’s rank correlation and linear mixed-effects models, with the athlete as the random effect and IMU movement class as the fixed effect. Results – Over 415 athlete-sessions, 913, 481 movements were recorded. Movements were classified as swimming, high-intensity throwing, low-intensity throwing, blocking with ball contact, and blocking without ball contact. There were no correlations between sRPE and the IMU classes. Individual athlete variability had a significant effect on linear mixed-effects model variance. Conclusion – IMUs can be used longitudinally over a water polo season and are a distinct monitoring metric to sRPE. This method could be used by coaches and sports science/medicine staff for monitoring upper limb movement volumes to assist with training planning and progression.