THUMB POSITION DOES NOT AFFECT THE HAND'S DRAG FORCE
Marinho, D. A., Reis, V. M., Alves, F. B., Vilas-Boas, J. P., Machado, L., Rouboa, A. I., & Silva, A. J. (2008). The influence of the thumb position in the propulsive force production in swimming. ACSM 55th Annual Meeting Indianapolis, Presentation Number, 725.
This study determined the propulsive force in a swimmer hand 3-D model with the thumb in different positions using computational fluid dynamics. A 3-D domain was created to simulate the fluid flow around three models of a swimmer's hand, with the thumb in different positions: thumb abducted, 50% abducted, and adducted. Models were created by computerized tomography scans of a male swimmer hand, allowing the determination of the boundaries of the hand segments. The whole domain was meshed with a hybrid mesh composed of prisms and pyramids. Numerical simulations for the whole computational steady domain were calculated in 3-D. The governing system of equations considered was the Reynolds averaged Navier-Stokes equations with the standard k-epsilon model. Flow velocities were chosen to be within or near the range of typical hand velocities during the swimming underwater path: from 0.5 m/s to 4 m/s. Angles of attack of the three hand models of 0º, 45º and 90º, with a sweepback angle of 0º (thumb as the leading edge) were used for the calculations. The measured forces on the three hand models were decomposed into drag and lift coefficients.
The position of the thumb had virtually no effect on the coefficient of drag, which was greatest when the hand was at 90º to the line of propulsion. The lift coefficient was greatest at an angle of attack of 45º. However, lift is nowhere near as important as drag because it acts at right angles to the drag force. The hand is only one minor part of the total propulsive surface in swimming. Lift forces off the lower arm and upper arm are negligible. Consequently, drag forces should be maximized in the hand to fall in concert with the other segments of the total propulsive surface.
Implication. The hand should be square to the line of progression to create the best propulsive force. The thumb position only affects the minor lift force off the hand.
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