Triathlon Swimming: Faster for Less Effort
Making a Triathlon Swim less of a Drag.
I don’t need to tell the average age group triathlete that water is 1000 times denser than air. This is a result of the billions of hydrogen and oxygen molecules that give water its density. Therefore as a swimmer moves through the water it resists that movement with a force substantially greater than air. This force is known as resistive drag and swimmers must literally move water molecules out of the way to open a hole to allow the body to pass through. This is why drafting in a swim is so beneficial. Therefore a swimmer who reduces the resistive drag they encounter will travel forwards faster and with less effort; and if that swim is the opening component of a triathlon then it is even more beneficial.
Studies (Cappaert, Pease and Troup, 1996) have shown that by reducing resistive drag alone could improve an elite swimmer’s velocity from 1.97m/sec to 2.07 m/sec. This would reduce a 100m time from 50.50s to 48.31s. All of this I concede is a long way from the average age group Ironman triathlete’s swim ability; but before you dismiss this article lets have a closer look at that. Let us stick with the same differential of 0.1m/sec (2.07 – 1.97) between an optimal and sub optimal resistive drag and consider the 3800m of an Ironman swim. The average age grouper will swim the 3.8km in say 1hr and 10 minutes or 4200 seconds. If by making improvements in the drag of 0.1 m/sec then swimmers of equal ability but differing drag coefficients will be 420 metres apart at the end. That is, the triathlete utilising optimal drag will be already on their way to T1 with the sub optimal drag swimmer 420 metres from shore. Who wouldn’t want to be that optimal swimmer?
There are four main ways you create resistive drag namely: the space you take up; the shape you present to the water; sub optimal limb movements and friction.
The former two you may have heard swim coaches refer to as Form Drag. The space that a swimmer takes up imparts on this form drag and has two components, horizontal and lateral. One method of reducing form drag then is to remain as horizontal as possible without any reduction in propulsive force. Swimmers take up less space in the water by keeping the body as horizontal from head to toes. Poor horizontal alignment can result from kicking too deep and / or dropping the hips and legs too deep. Swimmers also take up less space if they keep all the segments within the shoulder width. In other words swimmers should not allow the body to snake down the pool with legs and hips swinging from side to side. One common error in the stroke that coaches often see that will result in this lateral movement is the pulling of the arms too far across the midline during the underwater phase of the arm stroke. Another is when swimmers recover their arms in a wide, lateral manner. A vigorous circular sideward swing of the recovering arm will tend to pull the hips outward and in the direction the arm is moving. This is the reason, if at all possible, we look for a high elbow recovery that minimises the outward movements of the arms during recovery.
As swimmers move forward friction between the skin and the water causes a stream of water molecules to be pulled along with the skin and in turn exert a frictional effect on molecules in adjacent streams. Smooth surfaces cause less friction than rough surfaces and therefore well fitted speed suits and wet suits, and snug fitting tri or swimsuits reduce frictional drag. Wetsuits in general also aid speed by helping with horizontal alignment and reducing form drag. Note this is not an increase in buoyancy overall that reduces form drag but an alignment correction – hence manufacturers will use thicker neoprene on the legs of your wetsuit. There is strong evidence that the swimmers habit of shaving down does reduce frictional drag. Studies showed that average stroke length between shaved and unshaven swimmers increased from 2.07 m/stroke cycle unshaved to 2.31 m/stroke cycle shaved. They also showed that this was due to a reduction of frictional drag and not an increased feel for the water.
In the past, techniques for reducing resistive drag have been overshadowed by methods for improving propulsive force. Recently however there has been a resurgence of interest in the role that reducing drag plays in swimming faster. Many studies now concede, and rightly so, that reducing resistive drag can improve swimming speed even more than skills that increase propulsive forces. Think how you can improve your own drag component by making stroke changes that result in lateral and horizontal alignment improvements, making equipment selections that fit well and reduce frictional drag and aid horizontal alignment and learn how to draft effectively and efficiently during the swim portion of your triathlon.
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