Of all the swimming strokes humans have invented, none is faster or more efficient than the front-crawl. That’s why all competitors use it in freestyle events, and why it’s the only stroke that appears in races longer than 200 meters. But elite swimmers don’t perform the front-crawl the same way in a sprint as they do in a longer race. Instead, researchers found that swimmers use three different regimes of arm coordination.
For long-distance races, elite swimmers adopt a stroke that has only one arm in the water at a time. Each stroke is followed by a glide phase with one arm stretched in front of them. Researchers compared this to the burst-and-coast method that fish use to minimize the energy they use. As a swimmer’s speed increases, they shorten the glide phase and begin to maximize the force produced with each propulsive stroke.
In the third regime — the fastest one used by elite sprinters — the strokes of a swimmer’s arms are superposed, with both arms engaged in propulsion at the same time during parts of the cycle. This mode maximizes propulsive force but requires a lot of energy, so swimmers can only sustain it for a short while.
Since researchers built their observations into a physical model that explains how and why elite swimmers do this, the model can actually be used to advise individual swimmers on how they can adapt their stroke based on their size, desired speed, and other physical characteristics. (Image credit: J. Chng; research credit: R. Carmigniani et al.)
Related topics: More on swimming physics including why swimmers are faster underwater and how to design faster pools.
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