Validação do protocolo força x velocidade para avaliar o chute de jogadores de futebol

Abstract

Given that kicking is one of the main components of soccer, breaking down the variable for better evaluation is of great value to sports science. The force-velocity profile (F.v) is an approach that allows a performance parameter to be viewed through various parameters of interest and has not yet been applied to kicking. The aim was to test the validity and reproducibility of the test that measures the F.v ratio in soccer players' kicks. Fifteen healthy volunteers aged 18 ± 1 years, male soccer players, with a body mass of 69.8 ± 13.1 kg and a height of 176 ± 8 cm and who participate in systematic training, were invited to take part in this study. Of these fifteen volunteers, eight returned for a second test session to analyze the test's reproducibility. To measure the force of the kick, we applied a new methodology, using a load cell, which sends an electrical signal to a signal acquisition system and stores it in a computer to be analyzed using specific software. To carry out the test, the test subject had their ankle tied to a low-resistance elastic rope. Four different resistances were used, and for each one, three attempts were made to kick the ball, applying as much force as possible with a 0.15 second interval between them, totaling 12 kicks per athlete. Ankle projection speed was assessed using videogrammetry, i.e. the kicks were filmed by 2 4k UHD cameras that were calibrated using points with known distances on the field, marked for this purpose. The movement was tracked from a point on the ankle using the DvideoW software and the position of this point was reconstructed using the DLT (Direct Linear Transformation) method to units of meters on the three axes of the Cartesian plane. Finally, a function was built in Matlab to analyze the trajectory of the ankle. The function then returned the athlete's resulting velocity using the vector composition method using the Pythagorean theorem, to check which would best fit the F.v. relationship model. Based on the force values obtained by the load cell and the foot velocity obtained by videogrammetry, it was possible to generate relationships between force and velocity and between force and power individually for each athlete. Analysis of the data shows that the model confirms the hypothesis in question. The kicking speeds were significantly lower and the maximum forces higher as the resistance increased. It was possible to apply the F.v relationship model to soccer players using the kicking motion against different resistances. The fit of the line was not ideal in all cases and differed greatly in the reproducibility analysis. It was possible to apply the model of the force x velocity relationship to soccer players using the kicking motion against different resistances. The force exerted was indeed lower against lower resistance, and the speeds were higher against lower resistance. The straight line fit was not ideal in all cases and differed greatly in the reproducibility analysis.