The Science of Underwater Swimming: How Staying Submerged Gives Olympians the Winning Edge
upstart writes:
The science of underwater swimming: How staying submerged gives Olympians the winning edge:
The energy required to generate waves comes from the swimmer themselves, so a lot of the power generated by the swimmer's muscles is used in wave generation rather than moving the swimmer forwards.
But waves aren't formed when we (or fish, dolphins or whales) swim under the water, because waves only form when an object (like us) moves at the boundary between two fluids of different densities, such as water and air during swimming. And this fact hints at an intriguing solution to the drag issue.
[...] First, swimmers who stay underwater for the full 15 [allowed] meters will have faster starts, turns and overall race times. This effect is particularly strong in backstroke events, and when swimmers make the most of the final turn in a race (when swimmers usually surface quicker because they are growing tired).
Second, staying deeper underwater is important. Wave drag is slightly reduced by swimming just below the surface, but swimming 40-60 centimeters underwater can reduce drag by 10-20%. And there are further benefits when swimming a meter or more under the water, especially when start and turn push-off speeds are fast (as in most shorter races).
Additional improvements come from kicking faster and from keeping feet as horizontal as possible during the dolphin kick.
More details in the source story and on Wikipedia's coverage of underwater and undulating swimming.
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