I wanted to point out the key differences between the long axis and short axis stroke. The axis of rotation, or movement, that a swimmer rotates, or moves around, for Butterfly is the short axis which is the undulation. So, if you look at the little picture over here on the bottom right you can see the long axis is cutting this, kind of holographic person, in half, and then the short axis is kind of chopping them from top to bottom. So, when we’re talking about the Butterfly stroke, We’re talking about undulating around that short axis. In undulation in itself, when we say it as coaches, it’s talking about a smooth wave-like motion that goes up and down. The faster you’re pressing the chest down which pops up, or you press the chest up which pops the hips down, it’s kind of this constant yo-yo that happens as a swimmer goes down the pool. The whole point of undulating and the reason we undulate in all of these strokes is it changes your body position. So, specifically for fly, it can strengthen your pull because it’s putting your body in a better physical position by firing your hips and your lower back more, so a swimmer can engage up top into that catch and be able to grab on to some water. So without undulating, it would be a lot harder to be able to pull down with a lot of power. Because if you think about it, if you don’t raise your chest and get your hands in front of you, if everything was just in line and you tried to pull down, think about a hard resistance band, you could pull some water, but you could pull more if you can engage more with a bit of an arch in the back which is what we see in the Butterfly stroke.