Effects of take-off angle on take-off velocity, flight distance and block time during swim-start

The starting technique is one of the most important factors for sprint performance in competitive swimming. Take-off velocity and take-off angle determine the horizontal take-off velocity and flight distance in the aerial phase. The most appropriate take-off angle for start performance has not been investigated, although the importance of take-off velocity is well known. The purpose of this study was to clarify the effects of take-off angle on take-off velocity, flight distance and block time during swim-start. Twelve elite competitive swimmers performed three different types of start trial. In the experimental starting trials, swimmers were instructed to take off from the starting block higher (High) and lower (Low) than the usual grab start trial (Normal). The starting motions of subjects were recorded by a high-speed camera (Photron FAST-CAM PCI, 250 fps) and the 2D-DLT method was used for calculating the kinematic variables. The starting movement was modeled by a pendulum model, and the take-off velocity was resolved to the rotational component and the extensional component. A decrement of the take-off angle resulted in an increment of rotational component, extensional component of take-off velocity. Therefore, the decrement of flight distance with decrement of the take-off angle resulted in fewer disadvantages for start performance. In addition, there was no correlation between take-off angle and the block time in Normal trials. Considering the importance of horizontal take-off velocity, which is in the direction of swimming, take-off angle should be approximately 0 degree in the aerial phase.