Propulsive fractions of joint work during maximal sprint running

Purpose: The purpose of the study was to determine which of the ankle, knee or hip joint is the most important contributor to horizontal velocity during maximal sprint running. Furthermore, it was undertaken to quantify the fraction of propulsive power and work produced at each of the three joints. Methods: Seven athletes of national class served as subjects for the study. One running cycle of each subject was recorded by four video cameras (240 f/s) and a recessed force platform. Inverse dynamics in 3D was calculated as well as an angle between joint moment and angular velocity to express propulsive power and propulsive joint work. Results: Previous studies indicating the hip joint being the most important joint could not be confirmed by the present results due to large inter-individual differences for the hip joint. Averaged across all subjects, 64% of the normalized positive ankle joint work and 71% of the knee joint work were propulsive, while for the hip joint, four athletes showed 0%, one athlete 8%, and two athletes 96% and 97% propulsive work, respectively. For the whole leg, the propulsive fraction was 70% of the total positive work (range 40–87%). Normalized propulsive work was significantly correlated with maximal running velocity. Conclusion: The whole leg should be considered as one functional unit in which one or more of the joints may dominate generation of propulsive joint work.