Marinho, D. A., Barbosa, T. M., Mantripragada, N., Vilas-Boas, J. P., Rouard, A. H., Mantha, V., Rouboa, A. I., & Silva, A. J. (2010). The gliding phase in swimming: The effect of water depth. A paper presented at the XIth International Symposium for Biomechanics and Medicine in Swimming, Oslo, June 16–19, 2010.

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This study analyzed the effect of depth on drag during the underwater gliding (double-leg kicking) phase of swimming races. Computational fluid dynamics established a 3-D domain representing a swimming pool of 3.0 m depth, 3.0 m width, and 11.0 m length. Simulations were applied to the flow around a 3-D model of a male adult swimmer in a prone gliding position with the arms extended at the front. During gliding, the swimmer model’s middle line was placed at different water depths: 0.20 m (just under the surface), 0.50 m, 1.0 m, 1.50 m (middle of the pool), 2.0 m, 2.50 m and 2.80 m (bottom of the pool). The coefficient of drag and the hydrodynamic drag force were computed using a steady flow velocity of 1.60 m/s for the different depths run for three seconds in each case.

The drag coefficients at each successive depth were 0.67, 0.62, 0.53, 0.44, 0.36, 0.30, 0.28 and the drag forces were 100.20 N, 92.30 N, 80.50 N, 65.40 N, 53.40 N, 44.70 N and 42.0 N. The swimmer was approximately in the middle of the computational pool. At considerable depth (two meters or more) the retarding drag force is at least reduced by 50%.

Implication. When swimming underwater in races, the deeper a swimmer goes after the dive and turn, the greater is the likelihood of an improved performance because the "slowing effect" of the water is much less that at shallow depths.

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