Background The swimmer's body position after immersion determines the success of the start rather than his/her starting body position in the block or during the fly.1 There are swimmers gliding in a lateral position whereas others prefer a prone one. Moreover, during this phase, swimmers may alter their body posture and, as far as some techniques are concerned, swimmers must change the position of the limbs.2 The purpose of this study was to analyze the effects of body positions in drag coefficient during the glide in swimming using computational fluid dynamics.
Methods In order to create the three-dimensional digital model computer tomography scans of a human body of a male swimmer were applied3. The swimmer was modelled as if he were gliding underwater in a streamlined position, at four different body positions: (i) in the prone position, (ii) in a side position with an absolute angle between the horizontal plane with the body coronal plane of 45°, (iii) in a side position with 90° of rotation and, (iv) in the dorsal position. The boundary conditions of the model were designed to represent the geometry and flow conditions of a part of a lane in a swimming pool. Steady-state computational fluid dynamics analyses were performed using the Fluent® code and the drag coefficient was computed for velocities of 1.5, 2.0 and 2.5 m/s.
Results Drag coefficient reaches its lowest value in the prone position, followed by the side position with 45° of rotation (0.29%, 0.15%, 0.01% drag increment for 1.5, 2.0, and 2.5 m/s, respectively), the side position with 90° of rotation (1.03%, 0.94%, 0.64% increment), and the dorsal position (2.21%, 1.42%, 0.96% increment), in which the highest value of drag coefficient is obtained.
Discussion/Conclusions Main data shows that the prone position presented the lowest drag coefficient values, whereas dorsal position presented the highest values during the underwater gliding. The prone position seems to be the one that should be adopted after the starts and turns phases of a competitive swimming event, especially during freestyle events and after pushing-off from the wall during the turn where swimmers can freely choose the best body position.
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