INTRODUCTION The large surface of the single fin (0.5m2) is the main source of generating propulsive forces in fin swimming. The aim of this study was to introduce a diagnostic method based on measuring simultaneously dynamic and kinematic parameters of a single fin movement. METHODS On subject of national level swam 15 m under water at a maximum, average and low speed. Strain gauges were attached on both sides of the fin to record the changes of the fin sag in two points: close to the toes and in the middle of the fin. Dynamic parameters of the fin were recorded and analysed (Rejman 1999). The movement of the swimmer and fin was digitised on video (Colman e.a. 1998). RESULTS Thanks to the combination of the two methods, the evolution of some dynamic and kinematic variables during a stroke cycle could be confronted (Fig.). The forces generated on the 2 points of the fin corresponded well with the respective angles measured by digitising (Fig. a-b). By confronting these curves with the stick figures and with the curve of the corresponding velocity of the centre of mass of the body (Fig. c), interpretations on propulsion principles can be made. DISCUSSION A further kinematic analysis will be required to calculate the horizontal and vertical components of the propulsion. High swimming velocity is expected to be related to high values of horizontal components and small values of vertical components of the forces.
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