Royal Dutch Hockey Association 1 article published in JoVE Behavior An Inertial Measurement Unit Based Method to Estimate Hip and Knee Joint Kinematics in Team Sport Athletes on the Field Bram J.C. Bastiaansen*1, Erik Wilmes*2, Michel S. Brink1, Cornelis J. de Ruiter2, Geert J.P. Savelsbergh2, Annemarijn Steijlen3, Kaspar M.B. Jansen3, Frans C.T. van der Helm4, Edwin A. Goedhart5, Doris van der Laan6, Riemer J.K. Vegter1, Koen A.P.M. Lemmink1 1Center for Human Movement Sciences, University Medical Center, University of Groningen, 2Department of Human Movement Sciences, Faculty of Behavioural and Movement Sciences, Vrije Universiteit Amsterdam, 3Emerging Materials, Department of Design Engineering, Delft University of Technology, 4Department of Biomechanical Engineering, Delft University of Technology, 5FIFA Medical Center, Royal Netherlands Football Association, 6Royal Dutch Hockey Association Monitoring athletes is essential for improving performance and reducing injury risk in team sports. Current methods to monitor athletes do not include the lower extremities. Attaching multiple inertial measurement units to the lower extremities could improve monitoring athletes in the field.