The scientists investigated which stroke was more effective in the water; the S-stroke when the arm draws a curve in the water or the I-stroke when it moves straight, and found that the effectiveness of the stroke depended on the distance swum. According to their results the S-stroke is better suited for swimming middle and long distances, when you need propulsive power with less physical exertion, while the I-stroke is better for short distances, which depend on speed over efficiency.

The study explains that this is because “the mechanisms of propulsive power differ between the two strokes. The vortex pairs generated by the S-stroke, with the arm changing orientation in the water, cause unsteady lift force, while the I-stroke’s straight movement causes Kármán vortices that produce drag force.”

However this research doesn’t take into account coping with open-water.

“I-shaped pulls and S-shaped pulls are at extremes of the spectrum. Most people will fit somewhere along that, rather than at either end, depending on height, reach, power, flexibility and feel for the water, a point that will feel most natural to them,” says John Wood, 220 Triathlon swimming coach.

“The way I look at it is that if you have a decent hold on the water with hands and forearms, you  can look to pull relatively straight but your hand/arm will follow a  slight S shape naturally as it tries to find the still water. From there you don’t really need to accentuate the shape. (Actually the more you try and exaggerate the S, the more likely you are to cross under the middle of your body). Rather than worrying too much about the route that the hand takes back under the water, more focus for beginners and experienced swimmers alike should be on ensuring constant pressure on the hand/forearm throughout the pull phase.”

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220 staff writer Jack Sexty says: “There may be truth behind the research claiming that the S-stroke may be the most efficient technique on paper, but it’s important to remember that open-water swimming can throw up a whole host of variables that this research doesn’t account for.

“Many fast open-water swimmers, such as Harry Wiltshire and Jonny Brownlee, employ a faster turnover with a straight-arm pull whilst drafting other swimmers – a faster turnover can help open-water swimmers to keep moving over waves or chops in the water, whilst employing a longer pull could actually work against you if rough water/chop from other swimmers is disturbing your stroke anyway. The research also assumes the swimmer will be employing the technique correctly in the first place – and an incorrect s-stroke is far less efficient than a well executed straight-arm pull!”

What do you think? Which stroke do you use? Let us know in the comments…

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For more tips on improving your swim technique check out our swim section

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