Abstract des Autors

The precision of the point of impact on the racket determines the amount of rotations of the racket. These have to be managed by the hitting arm and can mean high stress for the wrist, the elbow and the shoulder at the moment of impact depending on the velocity of the racket and the firmness of the grip. We used 2 NAC High Speed Video Cameras (200-400 frames per second) in order to analyse wrist and racket actions of world class and spare time players. Using this method it is possible to get quantitative data about technical aspects and stress of the hitting arm as well. Approx. 150 ms before impact there is a quick stretching of the muscles of the forearm - e.g. in the form of a dorsal flexion of the wrist - that obviously leads to the storage of elastic energy and induces the stretch reflex. This mechanism contributes considerably to high velocities of the racket at impact esp. in world class tennis (over 30 m/s for the groundstrokes and the 1st service). Advanced players reach significantly lower values in these situations (approx. 25 m/s), combined with great deviations of the impacts on the racket. The comparable low racket velocities at the return on 1st serve (approx. 19 m/s) can be attributed to an increased stiffness of the wrist. In contrast to the world class players advanced players often show (approx. 50%) eccentric points of impact on the racket head which lead to rotations and mean stress for the striking arm. Verf.-Referat