Determinação da força das linhas do kite sobre um praticante em terra, utilizando o trapézio e a cadeirinha do kitesurfing / Ascertainment of the kite’s lines forces on an athlete in land, using trapeze harness and seat harness of Kitesurfing

No Kitesurfing, o indivíduo utiliza o vento para deslizar com uma prancha sobre a água por meio de um kite, que pode ser preso ao praticante pelos equipamentos: trapézio (posicionado em volta da cintura) ou cadeirinha (posicionada em volta do quadril). A diferença entre eles consiste no ponto em que o kite exerce força sobre o indivíduo. O objetivo do presente estudo foi medir a força das linhas do kite (FLK) exercida sobre um praticante em terra, utilizando o trapézio e a cadeirinha em diferentes posições angulares entre o tronco do indivíduo e as linhas do kite. Um praticante foi preso às cordas de um kite, que foram fixadas à parede e ao teto de uma sala. Ele foi solicitado a manter por 8 s o corpo com certa inclinação em relação ao solo de modo a formar ângulos próximos de 35, 45, 60 e 90° entre a linha de ação da FLK e o seu corpo (medidos com um goniômetro manual), utilizando a cadeirinha e o trapézio. Com uma célula de carga foi registrado a FLK exercida sobre o indivíduo (normalizada pelo seu peso) e com uma câmera de vídeo foram verificadas a sua posição angular. Com o trapézio, a força avaliada foi 43,4±0,2%, 48,5±0,5%, 57,1±0,3% e 25,4±0,11% para os ângulos avaliados em ordem crescente; com a cadeirinha, a força foi 51,9±0,2%, 62,1±1,5%, 57,9±0,2% e 28,3±0,1% para os mesmos ângulos. A FLK sobre o praticante variou de 25 a 60% do peso corporal.

During kitesurfing, the athlete propels himself and his board across the water by transferring the energy of the wind into speed by a large controllable kite, which can be attached to the athlete by 2 equipment: the trapeze harness (placed around the waist) or the seat harness (placed around the hip). The difference between them consist on the point where the kite apply force on the athlete, changing the sailing conditions. However, measuring this force is not easy, due to the environment in which the sport is practiced, therefore to evaluate this force on earth is the first step towards the development of a methodology. To measure the Kite’s lines forces (KLF), applied on the athlete in land, using a trapeze harness and a seat harness in different angular positions between his trunk and the kite’s lines. One practitioner (22years old; 76kg; 1,79m) was attached to the kite’s lines, which were linked to the wall and to the ceiling of a room. The practitioner was asked to keep during 8 s the body with determined inclination in relation to the ground to form angles close to 35, 45, 60 and 90 ° between the line of action of KLF and his body (measured by a manual goniometer and similar to the angles that occur in the sport) using a trapeze harness and a seat harness. The KLF was recorded with a dinamometer. Later this force was normalized by the practitioner weight. And with a video camera the body position and angles desired were checked. With the trapeze harness, the forces evaluated were 43,4±0,2%, 48,5±0,5%, 57,1±0,3% e 25,4±0,11% for the angles measured in ascending range; with the seat harness the forces were 51,9±0,2%, 62,1±1,5%, 57,9±0,2% e 28,3±0,1% for the same angles. The KLF on the practitioner ranged from 25 to 60% of the practitioners weight. The next step will be evaluate the forces and practitioner’s the body position in land with the kite, to later perform measurements in terms of the sport.