Costa, L., Ribeiro, J., Figueiredo, P., Fernandes, R. J., Marinho, D., Silva, A. J., Rouboa, A., Vilas-Boas, J. P., & Machado, L. (2010). Hydrodynamic characterization of the first and second glide positions of the underwater stroke technique in breaststroke. A paper presented at the XIth International Symposium for Biomechanics and Medicine in Swimming, Oslo, June 16–19, 2010.

This study analyzed the first and second gliding positions of the breaststroke underwater stroke used after starts and turns at several gliding velocities by characterizing: gliding velocity, body cross-sectional area, drag coefficient, and passive drag. National level male swimmers (N = 6) participated. A methodology similar to that described in Vilas-Boas et al. (in press) was used, namely determining cross-sectional area using planimetry while passive drag and drag coefficient were assessed through inverse dynamics based upon the velocity to time curve of each glide, monitored through a swim-meter.

The first glide presented higher mean values of velocity while the higher values of acceleration were verified by comparing them to the second glide. Passive drag increased with velocity while the drag coefficient decreased. Swimmers showed a smaller cross-sectional area in the first glide position than in the second.

Implication. The first glide in the breaststroke underwater stroke obtains higher velocity values, because it results from the impulse force generated off the wall and employs a better hydrodynamic swimmer position. For both glides, passive drag increases with velocity, while the drag coefficient decreases. The first glide is characterized by lower passive drag and drag coefficient values for all velocities, probably due to a parallel and concurrent effect of cross-sectional area and drag coefficient caused by the increased body length and slenderness associated with the flexed shoulders and extended arms. Therefore, swimmers and coaches should stress the need for body position control during both glides, and the need for technical evaluation, control, and advice to foster drag reductions during the underwater stroke performance in breaststroke. The common emphasis only on increasing propulsion in the underwater stroke will not produce the maximum possible benefits that could accrue from the combination of drag reduction and propulsion emphases.

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