Determinaçâo da força de resistência passiva na natação: nado peito

Abstract

Swimming is a sport practiced in water, able to improve health and assist in physical rehabilitation processes of people with and without disabilities. The modalities crawl, butterfly, breaststroke and backstroke are differentiated through specific motor gestures of legs and arms. In all these styles, to reduce resistance in order to improve human displacement, it is important to adapt an extended position of the trunk, an embedded hip, good alignment of the body and keep lower members tight. The propulsive force must be applied to break the state of inertia promoting body advancement in water. For this purpose, the propulsive force is to be promoted, at a minimum, greater than the hydrodynamic drag force imposed by the water, against the swimmer's moving direction. Therefore, the reduction of these resistance forces is crucial for increasing performance, it also depends on the improvement of the cardiorespiratory system. Associated with these aspects, there are not many swimming equipment dedicated for evaluation of fitness which respects the swimmer's motor gesture in the pool. The objective of this study is to contribute to the development of new technologies in swimming, studying and evaluating the swimmer passive drag. This study aims to develop a swimming power equipment for passive drag associated with an instrumentation for acquisition of force levels and methodology for the estimation of the cross-sectional area in the breaststroke. Four positions were selected from the breaststroke, being evaluated in a stretch of 12 m in 5-different speed levels. The biomechanical behavior was evaluated by measuring the passive resistance force in water and drag coefficients according to shape and contact. With the results, we observed a difference in passive resistance forces among the positions adopted, especially for 1st position (fully extended body) which was the most hydrodynamics. Polynomial equations have been proposed in order to estimate passive resistance values at different speeds in order to rapidly assess different positions on the breaststroke. The methodology used to obtain the cross sections areas of the swimmer's trunk via ImageJ software was effective and compatible with real values. Evaluation of forces in swimming was a first step for the future development of the prototype of an ergometer for swimming.