When it comes to maximising efficiency through the water in a pool-based triathlon swim, swimming technique is only part of the story.
Why so? Because, after every 25m or 50m, you’ll need to turn, which, whether via a tumble turn or not, will involve a push-off from the wall and a glide back into swimming action.
Of these, it’s the glide that constitutes the lion’s share of the distance covered during a turn, and for that reason gliding efficiently is a crucial part of fast pool swimming.
Some swimmers prefer gliding in a lateral position (side-on with one shoulder pointing down and other up), while others prefer to glide in a prone position (horizontal face-down position with shoulders parallel to the water surface).
So which position is best?
The search for low drag coefficients
Portuguese scientists have been studying the effects of different gliding positions on drag and efficiency in swimming.
These positions were simulated using a technique called computational fluid dynamics (CFD) to determine which resulted in the lowest ‘drag coefficient’ – a measure of the drag forces that impede movement through a medium such as water.
The swimmer was modelled as if he were gliding underwater in a streamlined position, at four different body positions:
– In the prone position
– In a side (lateral) position with an absolute angle between the horizontal plane with the body coronal plane of 45° (in effect, halfway between lateral and prone)
– In a pure side position with 90° of rotation (that is, shoulders perpendicular to the water surface)
– In the dorsal position (on the back)
And the best gliding position is…
The model was specifically designed to represent the geometry and flow conditions of a part of a lane in a swimming pool, while the drag coefficient was computed for velocities of 1.5, 2.0 and 2.5m/s.
The results showed that drag was lowest in the prone position, followed by the side position with 45° of rotation, followed by pure side. The dorsal position produced the highest drag figures.
How low should you go?
Last year another study tried to find out the optimal depth under the water surface for a glide to minimise drag.
It found that, regardless of speed, drag decreased with increasing depth, although after 0.75m, values remained almost constant.
The researchers therefore concluded that gliding at a depth of 0.75m under the surface was a good compromise for swimmers seeking to maximise gliding efficiency.
– When gliding, always use the prone position. You should also ensure that your hands overlap, your head is in between your (extended) arms and your feet are together with toes pointing in line with your legs
– Glide at around 0.75m depth. You will need practice to achieve this (it may help to use a marker on the pool wall at that depth)
– Don’t neglect practising the other still-important aspects of the turn. And make sure your swimwear is as close-fitting and streamlined as possible!