When I sat down to write Ring Four: The Book of Butterfly, I knew I was stepping into dangerous territory, not just because butterfly is a brutal stroke, but because it exposes you, and for right or wrong people have strong opinions about it. It might be the most revealing stroke of them all. You can’t fake it. You can’t hide behind endurance, or muscle, or even willpower. If your rhythm is off, if your timing falters, the water tells you immediately.

Often when people think of elite swimmers, they might immediately picture their powerful strokes, and streamlined bodies with a strong kick cutting through the water with picture perfect technique. But behind all these visible elements of swimming success, there's a crucial, often overlooked factor that directly impacts performance: core strength and stability