Effects of drafting on the hydrodynamic and metabolic responses of the drafter behind and at the side of a passive and an active lead swimmer were related to the influence of a lead swimmer on the flow field of the draftee.
Passive drag of the draft swimmer was compared for the nondrafting condition, in the drafting conditions behind a passive and an active lead swimmer, and at the side of a passive and an active lead swimmer. The effect was also evaluated with oxygen uptake measurements. Fluid pressure measurements were made behind and at the side of a passive and an active lead swimmer to examine the flow field.
Behind a passive lead swimmer, passive drag was significantly reduced by 20%, and behind an active lead swimmer, it was reduced by 9%. At the side of a passive lead swimmer, passive drag was significantly increased by 9%, and at the side of an active lead swimmer, it increased by 8%. Oxygen uptake was significantly reduced by 25% behind a passive lead swimmer, by 11% behind an active lead swimmer, and only marginally changed at the side of a lead swimmer. The pressure measurements indicated a 33% decrease in mean flow velocity behind an active lead swimmer but an increase in peak flow velocities due to the kick of the lead swimmer. These increases could explain the lesser decrease in passive drag behind an active versus a passive lead swimmer.
The best position for a draft swimmer was found to be directly behind an active lead swimmer at a distance of 0.50 m between the toes of lead swimmer and the hands of drafter, with significant reductions in both passive drag and oxygen uptake when drafting.
1Faculty of Human Movement Sciences, Research Institute MOVE, VU University Amsterdam, Amsterdam, THE NETHERLANDS; 2Academy for Physical Education, Technical University of Applied Sciences of Amsterdam, Amsterdam, THE NETHERLANDS; and 3University of Otago, Dunedin, NEW ZEALAND
Address for correspondence: Huub M. Toussaint, Ph.D., Research Institute MOVE, VU University Amsterdam, Vrije Universiteit, van der Boechorststraat 9, 1081 BT Amsterdam, The Netherlands; E-mail: H_M_Toussaint@fbw.vu.nl.
Submitted for publication April 2008.
Accepted for publication September 2008.