finger spread

The effect of finger spreading on drag of the hand in human swimming.

admin Biomechanics, Blog, Research Abstract 2 Comments

The effect of finger spread on overall drag on a swimmer’s hand is relatively small, but could be relevant for elite swimmers. There are many sensitivities in measuring this effect. A comparison between numerical simulations, experiments and theory is urgently required to observe whether the effect is significant. In this study, the beneficial effect of a small finger spread in swimming is confirmed using three different but complementary methods. For the first time numerical simulations and laboratory experiments are conducted on the exact same 3D model of the hand with attached forearm. The virtual version of the hand with forearm was implemented in a numerical code by means of an immersed boundary method and the 3D printed physical version was studied in a wind tunnel experiment. An enhancement of the drag coefficient of 2% and 5% compared to the case with closed fingers was found for the numerical simulation and experiment, respectively. A 5% and 8% favorable effect on the (dimensionless) force moment at an optimal finger spreading of 10° was found, which indicates that the difference is more outspoken in the force moment. Moreover, an analytical model is proposed, using scaling arguments similar to the Betz actuator disk model, to explain the drag coefficient as a function of finger spacing.

Practical Implication: Swimmers should use slight finger spread while swimming for a theoretical propulsion improvement. More research on actual, non-3D models would confirm findings. Also, research on the finger spread in various strokes would be beneficial.

Reference:

  1. van Houwelingen J, Willemsen DHJ, Kunnen RPJ, van Heijst GF, Grift EJ, Breugem WP, Delfos R, Westerweel J, Clercx HJH, van de Water W. The effect of finger spreading on drag of the hand in humanswimming. J Biomech. 2017 Aug 10. pii: S0021-9290(17)30408-6. doi: 10.1016/j.jbiomech.2017.08.002. [Epub ahead of print]

Comments 2

  1. To produce results, do you get a swimmer that swims with their fingers together to focus on swimming with their fingers apart?
    Conversely, do you get a swimmer that swims with their fingers apart to focus on their fingers together when swimming?
    The results can only be formed by using an individual swimmer in one of these scenarios as you can’t compare swimmers to each other to get a meaningful result. You would also have to know how the swimmers minds work. To get any sort of results you would virtually have to do hundreds of repeats to change a swimmer’s habits to get the outcomes. And only then, once that swimmer’s habits have been changed can a result be analyzed. And, depending on the results, a swimmer who was doing it “wrong” has to go through the whole process again to change new habits learn back.
    An experiment such as this must take many, many months to complete and the results are perhaps too small to measure. Maybe other areas of measurable technique would be better to test and leave what is basically natural to remain.
    Evidence of actually changing to a different hand position can only be done after a habit has been changed.
    So any results over a short period of time would be questionable.

    1. Conducting the research in the way you described is probably impossible. The method used by van Houwelingen et al. is presumably Computational Fluid Dynamics (CFD) – in this kind of research there is just virtual model (no swimmer). There are also many simplifications in this method that may affect the results (I do not know about this research). For example, the fact of modeling the flow around the hand, the accuracy of the model or the possibility of introducing changes in the speed of the liquid as well as the angle of the “virtual” hand.
      CFD is a very expensive method and therefore it is used in case studies. Of course you are right that it may not be appropriate to apply these results to any swimmer (male, female, short, tall, child, youth, etc.). Nevertheless, the goal of this website (swimmingscience.net) is to popularize the scientific approach to swimming. In my opinion, this article serves this purpose.
      This article simply shows what swimmers feel intuitively – that little fingers spreading is better than keeping the fingers together.

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