The effects of hand configuration on propulsive forces in swimming

During front crawl swimming, water is driven backwards with the limbs. Drag forces generated by the limbs are consequently used for forward propulsion. The hands are responsible for approximately 60% of the generated propulsive forces. Reaching a podium place in competitive swimming is dependent on differences in finishing times smaller than 0.5%. For this reason, investigating the effects of hand configuration on swimming performance is of interest. Configurable properties of the hand are the finger spreading and hand palm cupping. It is argued that a small finger spreading leads to a larger obstruction in the fluid flow compared to closed fingers, resulting in larger generated drag forces. Similarly, a small hand cupping is expected to increase the drag forces in analogy to the drag increase experienced by cupped disks. In this thesis, an experimental investigation is carried out to look into the effects of both finger spreading and hand cupping. Furthermore, CFD simulations are used for the abstract modelling of hands with finger spreading by use of slotted disks. Towing tank experiments in water are performed to investigate the effects of finger spreading for five full-scale arm models. The research showed that a small finger spreading of 5° can increase the drag coefficient of the hand with 1.7%, in comparison to closed fingers. Larger spreadings were found to influence the drag coefficient disadvantageously, where a 20° finger spreading reduced the drag with 1.5%. The found effects indicate that finishing times can be reduced with 0.3% by using 5° finger spreading instead of 20° spreading.Wind tunnel experiments are used to look into the effects of hand cupping. Dynamic scaling based on the Reynolds number is used to account for the used air flow. Effects for five full-scale arm models with different hand cuppings were investigated, these have a 5° finger spreading which was found optimal from previous research. It appeared that small rotations around the longitudinal axis of the arm have large influences on the drag coefficient, where a maximum in drag was never found for the hand palm perpendicular to the flow, but with an abducted thumb opposing the flow. The research showed that 6% more drag is generated for a flat hand in comparison to the largest investigated hand cupping. This indicates that finishing times can be reduced with 0.8% by using a flat hand instead of a large hand cupping. In conclusion, the research found a hand configuration with 5° finger spreading and a flat hand palm optimal for maximizing drag forces. The found effects on finishing times indicate that using this hand configuration can play an important role in reaching podium places during front crawl swimming.<br/

The effect of hand posture on swimming efficiency

Abstract: Our quest is for the thumb and finger positions that maximize drag in front crawl swimming and thus maximize propulsion efficiency. We focus on drag in a stationary flow. Swimming is in water, but using Reynolds similarity the drag experiments are done in a wind tunnel. We measure the forces on real-life models of a forearm with hands, flexing the thumb and fingers in various positions. We study the influence on drag of cupping the hand and flexing the thumb. We find that cupping the hand is detrimental for drag. Swimming is most efficient with a flat hand. Flexing the thumb has a small effect on the drag, such that the drag is largest for the opened (abducted) thumb. Flow structures around the hand are visualized using robotic volumetric particle image velocimetry. From the time-averaged velocity fields we reconstruct the pressure distribution on the hand. These pressures are compared to the result of a direct measurement. The reached accuracy of ≈ 10% does not yet suffice to reproduce the small drag differences between the hand postures. Graphical Abstract: [Figure not available: see fulltext.].AerodynamicsFluid Mechanic