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The TBN #49-Efficient Swimming: S-Shape Stroke Versus I-Shape Stroke

Read time: 3min.

By Coach Yan Busset

One of the most debated topics among coaches and swimmers alike is the efficiency of different swimming strokes, especially the S-shape versus the I-stroke technique. This discussion, fueled by decades of research and practice, seeks the sweet spot in stroke mechanics for maximizing propulsion while minimizing effort.

The S-Shape Stroke:

Spotted by observations from Coach James "Doc" Counsilman, who studied swimmers underwater extensively, this technique is based on creating a longer path for the hand through water, supposedly allowing for a greater distance per stroke. The S-shape movement aims to generate a vortex that, in theory, enhances propulsion.

However, the S-shape stroke is not without its drawbacks, especially for age groupers. The lateral forces produced by moving the hands too much outward first and then crossing over inward can detract from propulsive efficiency and induce yawing moves from side to side. It might also be more tricky to maintain an early vertical form of the front catch this way.

The I-Stroke: Streamlining Underwater Motion

Enter the I-stroke, a technique that emphasizes a more straightforward, "I"-like path of the arm underwater. This method minimizes lateral movement and introduces a different kind of vortex - the Kármán vortex - named after the Hungarian-American physicist Theodore von Kármán. This vortex is like the whirlpools formed behind a stick in a water stream, in this case, a swimmer's arm. This phenomenon can offer a more arrow/streamlined propulsion, good for speed and efficiency.

Empirical Insights: Bridging Theory and Practice

The debate between the S and I strokes was further enriched by a 2015 study from Takagi, Nakashima, Sato, Matsuuchi, & Sanders, which confirmed that both underwater stroke shapes could effectively generate speed in the water.

Navigating the Waters: Practical Advice for Swimmers

So, what does this mean for swimmers and triathletes? Firstly, it's crucial not to overdo the S-shape, especially an exaggerated one. Instead, focus on a straight, I-stroke-like pull. This doesn't mean your stroke won't naturally have a slight, more skinny S-shape. A narrower S is perfectly acceptable.

The key is to avoid crossing over under your body or applying excessive force outward. Simplify your technique: imagine swimming "on two rails," wide as your shoulders, where your stroke travels online with it. This approach ensures efficiency, especially critical for triathletes who need a repeatable stroke in the open water amidst the chaos of competitors and varying conditions.

Takeaway Related Swim Drill: The Hand in Fist Drill

The hand in fist drill for freestyle swimming is like swimming with small fists instead of open hands. When you swim like this, it feels different because your hands push less water. But, the real magic happens when you open your hands again. Suddenly, your hands feel bigger and can push more water. This change helps you understand better how your hands move underwater. It's like turning on a light in a dark room—you can see and fix what your hands are doing more easily. This drill makes it easier to feel the water, helping you swim better. So alternate for example 50 hands in fist with 50 normal to switch the light bulb.

As you train, focus on refining a stroke that feels natural, effortless, and reduces wasted motion. Always keep in mind your ultimate goal, which is to propel your body forward in the most efficient manner. Share your experiences and thoughts in the comments below, and let's continue to learn from each other in our quest to glide through the water with grace and speed. And as always, stay strong, fast, and furious, my friends!

*Takagi, H., Nakashima, M., Sato, Y., Matsuuchi, K., & Sanders, R. H. (2016). Numerical and experimental investigations of human swimming motions. Journal of Sports Sciences, 34(16), 1564–1580. [](


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