DRAG FORCES PREDOMINATE OVER LIFT FORCES IN EFFECTIVE PROPULSION
Sanders, R. H. (1997a). Extending the 'Schleihauf' model for estimating forces produced by a swimmer's hand. In B. O. Eriksson & L. Gullstrand, (Eds), Proceedings of the XII FINA World Congress on Sports Medicine (pp. 421-428). Goteborg, Sweden: Chalmers Reproservice.
Sanders, R. H. (1997b). Hydrodynamic characteristics of a swimmer's hand with adducted thumb: Implications for technique. In B. O. Eriksson & L. Gullstrand, (Eds), Proceedings of the XII FINA World Congress on Sports Medicine (pp. 429-434). Goteborg, Sweden: Chalmers Reproservice.
Hand lift and drag coefficients for crawl stroke were measured in a testing tank. The coefficients were determined for the entire range of possible pitch and sweepback angles, defined in accordance with the convention established by Schleihauf in 1979.
The greatest forces were obtained when the pitch angle was close to 90 degrees to the flow. At that orientation the force was due almost entirely to drag. Lift made its greatest contribution to resultant force at pitch angles near 45 degrees. However, even at 45 degrees, the contribution due to drag was as great as that of lift at most sweepback angles. When considered in three dimensions it was found that drag made a larger contribution to propulsive force than lift in all parts of the pull.
During the most propulsive phase of the stroke the pitch was 50-60 degrees. That pitch took advantage of drag forces with a smaller contribution from lift. The fluid flow at this time was from the wrist to the fingers, a direction contrary to that depicted in most swimming texts (a foil generating lift forces from lateral movements which produce a flow across the hand).
Implication. In crawl stroke, the hand is not used like a foil. The major proportion of propulsive force comes from drag force although lift force does make some contribution.
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