INTRODUCTION: Methods of direct measurement of the arm`s propulsive force have several advantages compared with indirect methods, including the possibility of measuring the real action of the athlete, ease of use and lower costs. Limits of the methods using direct measurement used so far, arise however both in the measurement itself and in the validation process. In fact the gauges and supports currently in use, limit hand movements or even change its action, as well as reducing the active surface, thus interfering with the swimmer`s technique. Furthermore, almost all these methods require a swimming flume or gauges connected to the poolside. The method here proposed overcomes most of these downsides. METHODS: Five competitive and four novice swimmers wear two mini-paddles (KZ by APLab), whose size and shape do not interfere with the hand`s movement and sensibility in the water. The paddles measure the pressure field around the hands and store the data in an ECU contained in a little box, that the athletes wear. The box has neutral buoyancy and the whole system does not interfere with the action of the athletes, who can swim freely. The acquired data can be transmitted via a wireless connection. The validation method is based on the correlation between the pressure signal acquired by the paddles and an external measurement by a load cell of the thrust of the swimmer during zero-speed sculling. RESULTS: The maximum force and pressure measured is respectively 95,6+/-12,5N and 5,85+/- 0,65kPa. The data show excellent correspondence between maximum pressure signal at each sculling movement and propulsive force (r=0,92+/- 0,03, p<0,05). The pressure signal shows clearly the different unsteady components of thrust and the different intensity applied by the swimmer. The differences in swimming skills and water sensibility between top level and mediocre swimmers are more than apparent. DISCUSSION: This new measurement tool opens the way to a number of possible research projects. Extensive screening on a large group of high level swimmers has revealed important results concerning swimming technique in different styles, differences between top level and mediocre swimmers, effects of fatigue in technique and attitude towards sprint or long distance competitions. The paddles are therefore a effective, low cost tool for evaluating the effects of training, the efficiency of technique and the amount of muscular strength applied in the stroke.
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