Q: why elite swimmers use spaced fingers during the power stroke? Since the overall area of the hand surface is independent on finger spacing, is that strategy pointing towards a more comfortable stroke or is it meant to increase the hand drag (thus the thrust)?

A: we used a 3D mesh manipulation software (Poser) to model hands with differently spaced fingers. Successively, the obtained meshes were ‘virtually’ immersed in a water flow at different speed, to assess the drag caused by the different spacings. A CFD (Computational Fluid Dynamics) program (Fluent and CFX) simulated all the eddies and vortices for each water speed and spacing, as by using a real flum. Results focussed on a given spacing, very close to the passive finger posture, which maximizes the hand drag, thus the thrust.

The fluid-dynamics explaining such results are discussed below.

REF Minetti A.E., G. Machtziras & J. Masters, J. Biomech. 42: 2188-2190, 2009.